TOWN COUNCIL WORKSHOP AGENDA DOCUMENTATION

PREPARATION DATE: March 10, 2009 SUBMITTING DEPARTMENT : Emergency Management MEETING DATE: March 16, 2009 DEPARTMENT DIRECTOR: Jason Biermann PRESENTERS: Jason Biermann and Barb Beck

SUBJECT: Teton County/Town of Jackson Multi-Hazard Mitigation Plan (MHMP) Update

PURPOSE OF WORKSHOP ITEM 1. Provide the Town Council information regarding the status of the quintennial update to the MHMP, its identified goals and projects; specifically, those pertaining directly to the Town Council and/or TOJ departments. 2. Receive input from the Town Council regarding the identified goals and projects, including additions or deletions.

DESIRED OUTCOMES 1. A comprehensive, acceptable document. Ultimately, following approval by both the Wyoming Office of Homeland Security and FEMA, this document will need to be approved and adopted by the Town and County. In order to streamline the entire process, staff would like to implement any changes prior to submitting the plan to WOHS, etc. 2. An understanding of the proposed projects and the provision of preliminary guidance to staff regarding prioritization of the agreed upon tasks, so that implementation can begin as funding becomes available.

BACKGROUND/ALTERNATIVES Background: FEMA requires all jurisdictions wishing to participate in its pre-disaster mitigation (PDM) grant program to approve and adopt a multi-hazard mitigation plan, and update the adopted plan every five years. In 2004, the Teton County Board of County Commissioners and the Jackson Town Council adopted the Teton County Hazards Mitigation Plan , a plan that was created internally. In 2008, TCEM contracted Beck Consulting to complete an objective update to the existing plan in accordance with current FEMA guidance with a scheduled adoption date of 2009. Alternatives: Failure to adopt the update within the five-year window can result in the loss of grant funding; however, the jurisdiction could decide to forgo the update and any potential associated revenue.

ALIGNMENT WITH COUNCIL’S STRATEGIC INTENT This item directly supports the Council’s stated objective of “Governmental Consolidation”, especially definitions #3 and 4. Locally, our approach to addressing all phases of emergency management has been, and will continue to be, from the perspective that any large incident occurring in Town will affect the County and vice versa, and that in a time of disaster, we will certainly become a “single community”. Therefore, the MHMP, its goals and projects, are both multi-agency and multi-jurisdictional, and will require buy-in and participation from not only the Town and County, but our State and Federal partners as well.

STAKEHOLDER ANALYSIS An advisory committee provided input to the consultant. This committee consisted of representatives from emergency management, Fire/EMS, law enforcement (Sheriff and PD), public works, transportation, and the Red Cross, in collaboration with State and Federal entities including the National Park Service and WYDOT. Finally, public participation was encouraged through three public meetings, as well as a seven-week comment period during which the draft MHMP was made available in both hardcopy and on-line. With the exception of a letter from the Geologists of Jackson Hole, public input was very limited.

FISCAL IMPACT All projects listed were assigned a priority and cost (High, Medium, or Low) based upon definitions found on page 16.3. The fiscal impact to the Town and County will be subject to the elected officials’ discretion, i.e. which projects staff are directed to pursue.

STAFF IMPACT Similar to the fiscal impact, staff impact will be directly related to the projects identified for completion.

LEGAL ISSUES N/A

ATTACHMENTS 1. Two (2) copies of draft MHMP made available to public dated December 2008. 2. Eight (8) copies of amended goals and projects dated February 27, 2009. TETON COUNTY TOWN OF JACKSON, WYOMING MULTI-HAZARD MITIGATION PLAN UPDATE

Prepared by: Teton County with assistance from Beck Consulting, Red Lodge, Montana Draft--December 2008

Teton County Multi-Hazard Mitigation Plan Table of Contents

Executive Summary I...... Introduction ...... 1.1 II...... Hazards Identification and Risk Analysis ...... 2.1 III...... Dam Failure ...... 3.1 IV...... Drought ...... 4.1 V...... Earthquake ...... 5.1 VI...... Flood ...... 6.1 VII. .... Hail...... 7..1 VIII. ... Hazardous Materials and Waste ...... 8.1 IX...... Landslides ...... 9.1 X...... Lightning ...... 10.1 XI...... Snow Avalanches ...... 11.1 XII. .... Tornadoes ...... 12.1 XIII. ... Wildland Fire ...... 13.1 XIV. ... Winter Storms and Blizzards ...... 14.1 XV. .... Terrorism ...... 15.1 XVI. ... Goals and Mitigation Actions ...... 16.1 XVII. .. Monitoring ...... 17.1

Appendices

A. 2004 Multi-Hazard Mitigation Projects and Status ...... 1 B. Vulnerability by Jurisdiction ...... 3 C. Briefing Papers ...... 4 D. Meeting Documentation ...... 7 E. Critical Municipal and County Public Assets ...... 35 F. Acronyms Used in the Plan ...... 38 G. Vulnerable Populations ...... 39 H. Resolution of Adoption ...... 41

Figures

1.1 Teton County Map ...... 1.6 2.1 Areas Covered by Airborne Ash Flows, Tuff and Pumices ...... 2.4 2.2 Volumes of Eruptive Materials ...... 2.5 3.1 Dams Inspected by the State Engineer’s Office and USBR ...... 3.2 4.1 Wyoming Annual Precipitation (1895-2003) ...... 4.2 5.1 Historic Earthquakes in Wyoming ...... 5.1 5.2 500-Year Probabilistic Acceleration Map ...... 5.26 5.3 1000-Year Probabilistic Acceleration Map ...... 5.27 5.4 2500- Year Probabilistic Acceleration Map ...... 5.28 6.1 Wyoming FIRM Coverage ...... 6.4 6.2 Wyoming FIRM Exposure ...... 6.5 7.1 Hail Damage by County ...... 7.4

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9.1 Mapped Landslides in Wyoming ...... 9.1 9.2 Wyoming Landslide Classification ...... 9.2 9.3 Mapped Landslides in Teton County ...... 9.10 9.4 Wyoming Landslide Exposure by County ...... 9.11 9.5 Teton County Landslide Building Exposure Values ...... 9.12 10.1 Average Flash Density ...... 10.5 11.1 Wyoming Relative Risk for Avalanche Fatalities ...... 11.2 11.2 Wyoming Avalanche Fatalities by Activity ...... 11.3 11.3 Wyoming Avalanche Fatalities by Location ...... 11.3 12.1 Wyoming Tornado Data ...... 12.5 13.1 Wildland Fire Hazard Map ...... 13.7 13.2 Wildland Fire Critical Hazard Area Building Exposure ...... 13.8

Tables

4.1 Wyoming’s Recent Worst Multi-Year, Statewide Droughts ...... 4.2 4.2 Peak Commodity Production Changes (1994-1998) ...... 4.3 4.3 1999 Production and Inventory Value Impact ...... 4.4 4.4 2000 Production and Inventory Value Impact ...... 4.4 4.5 2001 Production and Inventory Value Impact ...... 4.4 4.6 2002 Production and Inventory Value Impact ...... 4.4 4.7 2003 Production and Inventory Value Impact ...... 4.5 4.8 Production and Inv. Values Impact, Worst Year of Drought ...... 4.5 5.1 Modified Mercalli Intensity ...... 5.24 5.2 Earthquake Potential Losses ...... 5.32 5.3 County Impact Rated by Loss Ratio ...... 5.33 5.4 County Impacts Rated by Dollar Loss ...... 5.33 6.1 NFIP Status ...... 6.1 6.2 Teton County Flood Data ...... 6.2 6.3 FIRM Building Exposure ...... 6.3 7.1 Damaging Hail Storms ...... 7.2 7.2 Hail Damage (2004 Dollars) ...... 7.4 9.1 Building Exposure Values for Landslides ...... 9.13 10.1 Teton County Lightning History ...... 10.2 11.1 ...... Teton County Avalanche Fatalities…………………………………………11.4 12.1 ...... Fujita Scale for Intensity……………………………………………………..12.1 12.2 ...... Wyoming Tornado Data Totals (1907-2003)………………………………12.2 12.3 ...... Teton County Damaging Tornado Events……………………...... 12.3 12.4 ...... Tornado Damage by County…………………………………………………12.4 13.1 ...... Wildfire Events in Teton County……………………………………………..13.3 14.1 ...... Teton County Winter Storms…………………………………………………14.2 16.1 ...... Goal One……………………………………………………………………….16.4 16.2 ...... Goal Two……………………………………………………………………….16.5 16.3 ...... Goal Three……………………………………………………………………..16.8 16.4 ...... Goal Four………………………………………………………………………16.9 16.5 ...... Goal Five……………………………………………………………………….16.9 16.6 ...... Goal Six……………………………………………………………………….16.10 16.7 ...... Goal Seven……………………………………………………………………16.10 16.8 ...... Goal Eight……………………………………………………………………..16.11

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EXECUTIVE SUMMARY

Teton County and the town of Jackson developed and adopted a Multi-Hazard Mitigation Plan in 2004. This plan revises and updates that original plan.

This revision was prepared by Teton County with the assistance of contractor Beck Consulting. The content of the plan relies heavily on the advice and guidance of a local advisory committee formed for this purpose. The committee met to review accomplishments from the 2004 plan and to develop goals and projects for this revision. A variety of interests were invited to participate on the advisory committee. Those interests that were most active on the committee represented emergency management, fire, emergency medical services, law enforcement, public works/transportation, and the American Red Cross.

Public involvement was limited, not by the opportunity to participate, but by citizens’ choice. Competing events such as the national election, local issues, and holidays together with difficulty getting press coverage produced poor showings at the three public meetings. Information was readily available about the project throughout the process on the county’s website and two briefing papers were produced. The draft plan was made available at town and county offices, the public library, and online, for a seven-week period.

The Emergency Management Program in Teton County serves both the county and the single incorporated community, the town of Jackson. Town and county Fire and Emergency Management Services are consolidated and discussions are underway regarding the possibility of consolidating law enforcement services following the retirement of the county sheriff. The two local governments, the county and the town, enjoy a close working relationship. This relationship has produced good coordination in the area of emergency services as evidenced in part by accomplishments since the adoption of the 2004 hazard mitigation plan. Both local governments regularly budget for and pursue identified mitigation projects regardless of outside funding and have also been successful in obtaining outside funds. The fire program is the prime example of this.

Teton County is predominantly made up of publicly-owned lands containing portions of Yellowstone and Grand Teton National Parks, and the Bridger-Teton National Forest. The county does not have jurisdiction over the federal lands, however the National Park Service did participate in the plan revision process.

Lands available for private development outside of Jackson are limited. A portion of those lands that are available present some significant hazards. A total of 13 hazards, 11 natural and 2 manmade, were identified and profiled for the county. These hazards included; dam failure, drought, earthquakes, floods, hail, hazardous materials, landslides, lightning, snow avalanches, terrorism, tornadoes, wildland fire, and winter storms and blizzards.

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The goals and action items in this MHMP revision were developed after consideration of:

the projects identified in the 2004 MHMP, the history of disasters in the county, the vulnerability of key systems and facilities, available resources and capacities, and several disaster scenarios.

Hazard Mitigation Goals

Eight goals with a total of 54 projects were developed for this revision. Projects that had not been accomplished from the 2004 plan, that were still appropriate, and that were specific enough to understand were incorporated into the revision.

Goal One: Increase the disaster resistance of the transportation infrastructure and prepare to respond effectively when transportation routes are compromised.

Goal Two: Be prepared for isolation of and within the valley.

Goal Three: Increase levels of general preparedness and awareness for a variety of potential hazard situations.

Goal Four: Be ready to respond to the inevitable winter storms.

Goal Five: Reduce potential damage, injury, and loss of life from earthquake hazard.

Goal Six: Be prepared to respond to a Hazmat incident.

Goal Seven: Minimize potential losses from flooding and wind events.

Goal Eight: Reduce vulnerability to terrorism.

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Chapter I. Introduction

Specific Jurisdictions Represented in the Plan

The jurisdictions represented in this plan are Teton County, and the town of Jackson, Wyoming. Jackson is the only incorporated community in the county. These are the same two jurisdictions that participated in and adopted the original MHMP in 2004. There are no new or non-participating jurisdictions for the plan.

How the Jurisdictions Participated in the Plan Update

The two local jurisdictions participated in the planning process. Participation occurred in the following ways: By providing key staff to participate in the Advisory Committee meetings, By identifying actions taken on projects from the 2004 plan, By providing information on critical infrastructure and facilities, By providing existing plans and documents, By meeting with the contractor one-on-one as requested, By providing feedback on draft goals, By providing specific project ideas for the town and the county, By reviewing and commenting on the draft plan, and By adopting the plan--pending.

Opportunity for Involvement by Other Interests

The Wyoming Office of Homeland Security, neighboring Wyoming counties of Lincoln, Sublette, Fremont, and Park Counties were all notified that Teton County was undertaking a revision to the MHMP and invited to provide input, comments, and review the draft plan. In addition Bonneville, Fremont, and Teton Counties, Idaho, and the Idaho State Office of Emergency Management were notified about the project and invited to participate as they wished. Notification was done by phone and/or e-mail and included the current status of the update, where to find more information on the project, and contact information for questions and input.

The Local Emergency Planning Committee (LEPC) was briefed on December 18. The consolidated town/county fire chief (LEPC Chair) and the Jackson Public Works Director (Vice-chair) were both on the Advisory Committee.

There is no higher education facility located in the county. The Teton Science School and the public school districts were made aware of the process through local media. The National Park Service (Grand Teton National Park) was notified about the project and attended the Advisory Committee meetings. Local non- profits, businesses, and other organizations had opportunity to learn about and become involved in the process through legal ads and community calendar postings in the Jackson Hole News and Guide and coverage by the local radio stations.

Teton County MHMP 1.1

Process Followed to Update the Plan

The process followed to update the plan had several steps. Teton County retained a hazard mitigation planner, Beck Consulting of Red Lodge, Montana. To kick-off the project, the contractor met with the Deputy County Emergency Management Coordinator to receive an orientation to the county and the emergency management program. Relevant plans were obtained. Key individuals were identified to serve on an advisory committee (AC) and the revision and meetings’ schedule was finalized. Channels of communication were established for the project and the contractor was introduced to several key individuals.

The contractor then reviewed and updated the hazard profiles provided by the Wyoming Office of Homeland Security from their recently approved MHMP update. The state’s information was current through 2005. This update was done by researching the local newspapers and using standard information sources such as the National Climate Data Center. The updated hazard profiles and histories were then posted on the emergency management page of the county’s website.

One month later, the AC convened. Because many on the committee were new to the hazard mitigation planning process, the contractor provided an explanation of the reasons for and benefits of updating the plan, outlined the schedule and process, covered the roles of all involved, gave a summary of past disasters in the county, and gave an overview of the goals and projects in the 2004 plan. The process followed to update the plan relied on the use of this AC. Membership of the committee is provided below. The AC met and performed the following functions; provided relevant plans, reviewed the 2004 Multi-Hazard Mitigation Plan, determined the status of projects listed in the 2004 plan, contributed information on natural hazards, developed scenarios and potential impacts from the scenarios, identified new project ideas, reviewed and commented on draft goals and project ideas, and shared information about the process with other staff on their units. Following each of the committee meetings, the contractor documented the meetings and re-drafted products such as goals and projects as per the committee’s guidance.

Public meetings were scheduled In between the AC meetings to inform the public about the planning process, report on progress made by the committee, and gather input specifically on hazards, goals, and projects.

Once the goals and projects were drafted, the contractor and Deputy Emergency Management Coordinator attended the LEPC meeting to brief members of that key committee. Following this meeting, the goals and projects were finalized as were the other sections of the plan.

Teton County MHMP 1.2

The entire draft plan was posted on the county’s website and its availability announced in the Jackson Hole News and Guide. Hard copies of the draft plan were made available at the town hall, county courthouse, emergency management, and public library in Jackson. The public comment period was open from January 1 through February 20, 2009. Comments received on the draft were reviewed by the Deputy County Emergency Management Coordinator and forwarded to the contractor who incorporated them into the plan.

How the Plan Advisory Committee Reviewed and Analyzed the Existing Plan

The list of mitigation actions (projects) in the 2004 MHMP was deemed the most important section of the plan for close scrutiny by the advisory committee (AC.) The AC spent much of their first meeting on October 21, 2008, reviewing those projects and determining their status as ongoing, completed, partially completed, still needed, and/or no longer necessary. The updated hazard assessment was posted on the county’s website and the AC and members of the public were invited to review and comment upon those assessments. AC members also pointed out that they have been using the Incident Command System to manage large local special events, exposing additional individuals to the system and successfully managing complex multi-jurisdictional, multi-functional incidents.

December 18 briefing at the Local Emergency Planning Committee meeting. (Left to right, Police Chief Zivkovich, County Commissioner Christensen, FD Staff Smith, and Fire Chief Palmer)

Teton County MHMP 1.3

Individuals/Groups Involved in the Plan Update Process

The following individuals and organizations were involved in the plan update.

Advisory Committee

Fire/EMS Law enforcement (town and county) Emergency Management (town and county) Planning (county) Public Health (county) Public Works (town) Road and Levy (county) Red Cross Chamber of Commerce National Park Service (Grand Teton National Park) Wyoming Department of Transportation (maintenance and trooper)

The contractor briefed the Local Emergency Planning Committee in December. In addition to advisory committee involvement, two County Commissioners, representatives from the airport and local press, and additional town and county staff attended the briefing. The county commission-appointed liaison for Emergency Management attended the LEPC briefing. The elected officials of the town of Jackson and the county commissioners were provided with a written briefing in December (see appendices.) Emergency Management Coordinators from adjacent counties were invited to participate. And, the Wyoming Office of Homeland Security was kept abreast of progress and invited to review products throughout the process.

How the Public Was Involved in the Update Process

Three public meetings were held in Jackson, the only incorporated community in the county. The first meeting was held on October 22. There were no attendees. The second meeting was held on November 19 to brief the public about the project and to present the preliminary goals and mitigation projects. The final meeting was held on December 18, 2008. At the final meeting, the contractor presented the draft goals and projects. Meeting sign-in sheets can be found in Appendix D. In addition to the public meetings, the local radio station broadcast interviews with the Emergency Management Coordinator about the plan update.

Products of the planning process were posted on the Emergency Management page of the county’s website as they became available. These products included the one-page project briefing paper, the elected official briefing paper, chapters containing the hazard assessments, and the goals and mitigation actions. The public meetings were also posted on the website. The entire draft plan was posted once it was completed.

Teton County MHMP 1.4

Meeting attendance at the public meetings was poor. There was difficulty in getting the local newspapers to print press releases or attend meetings early on, so legal ads were purchased in the Jackson Hole News and Guide announcing the second and third public meetings. Both Planet Jackson and the Jackson Hole News and Guide did print articles prior to the third public meeting and both included the meetings in their community calendar sections. The local radio stations made announcements of the meetings as well.

Unfortunately, the hazard mitigation planning process and public meetings coincided with national elections, the preparation of a new comprehensive land use plan, and discussions about town and county consolidation of services. As a result, there were inevitable conflicts with the public meetings for the hazard mitigation project and these other activities. One final reason for poor attendance at the public meetings appears to be the fact that citizens have a high level of trust in and feel well served by their emergency services providers.

County Profile

Teton County encompasses approximately 4,008 square miles and is located in northwestern Wyoming. Approximately 97% of the county is publicly-owned. The county shares its western border with Idaho and in order to reach the unincorporated area of Alta, which lies in Teton County, one must travel through Idaho.

The population of the county in 2000 was 18,251 which is an increase of 7,709 persons (63.3% change) compared to the 1990 census (11,172). Within its boundaries lie the incorporated town of Jackson, Grand Teton National Park, and roughly half of Yellowstone National Park. The topography is primarily mountainous and includes the dramatic Teton Range, portions of the Gros Ventre and Absaroka Ranges, and the Yellowstone Plateau. The county is the headwaters of the Snake River and contains Yellowstone and Jackson Lakes. Tourism and recreation is the main financial stay of the county.

Teton County MHMP 1.5

Figure 1.1 Teton County Map

Teton County MHMP 1.6

The following county profile information was compiled by Headwaters Economics based upon data from the U.S. Census and Bureau of Labor Statistics and is contained in the SocioEconomic Profile. (www.headwaterseconomics.org) Compared to other U.S. counties, Teton County has the following characteristics:

Population growth (annualized rater, 1970-2005) was very fast. Employment growth (annualized rate, 1970-2005) was extremely fast. Personal Income growth (adjusted for inflation, annualized rate, 1970- 2005) was extremely fast. Non-labor income share of total in 2005 was high. Median age was somewhat young. Per capita income was extremely high. Average earnings per job was high. Education rate (% of population 25 and over with a college degree) was extremely high. Education rate (% of population 25 and over who have less than a high school diploma) was low. Employment was specialized. Rich-poor ratio (for each household that made over $100K, how many households made less than $30K) was somewhat low. Housing affordability was less affordable. Government share of total employment was somewhat low. Unemployment rate in 2006 was low.

Residences on East Gros Ventre Butte, northwest edge of Jackson

Teton County MHMP 1.7

Development Trends

Land use change and residential and commercial development are limited by both geography and land ownership. Because such a large percentage of the county is publicly-owned, development is precluded over most of the county-- other than that of the natural resources. According to Teton County Planner, Jeff Daugherty, development has already occurred on all of the “easy ground” for development. Development proposals coming in now typically have a list of complex concerns related to natural hazards that could include floodplain, faults, wildland fire, steep slopes, landslides, and/or rockslides. Developers are required to provide soils and geotechnical information with their applications in situations where there is a full review, such as a new subdivision. State law, however, exempts 35-acre and smaller parcels from full review so the county currently lacks the full breadth of authority in these situations. New construction and development is largely occurring with proper mitigation for natural hazards where known, but this is not true for all previous development.

The volume of development applications has been down in 2008 for Teton County. In a typical year, 300 applications would be received by the county. From January through October 2008 those numbers are off by approximately one-third.

The unincorporated area of Alta is located over Teton Pass from Jackson Hole. Future development associated with Grand Targhee Resort has been proposed.

Commercial development that had previously been permitted is being completed. Much of the proposed development that had not yet been approved is currently stalled due to the difficulty of obtaining financing. One example of this is the master plan for expansion of Grand Targhee Ski Resort. Preliminary approval of the master plan was given in the spring of 2008 and the developer is now working on satisfying the conditions in that preliminary approval, but the project does not appear to be moving towards construction in the near term. This project will include approximately 400-450 lodging units and some commercial space located in the unincorporated Alta area—an area already problematic to access for emergency services.

Teton County MHMP 1.8

A second major project, the Snake River Sporting Club, has master plan approval, but not development approval, and has gone into bankruptcy. This project as originally proposed included new structures located in the Snake River setback and a 40-unit lodge utilizing geothermal tubes.

Smaller-scale residential and commercial projects—not detailed here--are being proposed continuously within the incorporated limits of Jackson.

The town and Wyoming Department of Transportation recently announced agreement on the conceptual plan for a major road project at the five-way intersection of West Broadway, Pearl Streets, and Flat Creek Drive. The project will provide five 11-foot driving lanes for cars, a center turn lane and bicycle lanes on both sides of the highway. This project will likely be positive from a hazard mitigation standpoint because it should provide for better traffic flow should there be a need for evacuations or movement of apparatus and equipment.

An additional road project, a second bridge over the Snake River north of Jackson is being discussed as a result of increasing traffic volumes. The traffic analysis projects that if built, this bridge would decrease traffic on the Moose- Wilson Road and increase traffic on the main north-south valley highway, Highway 191. Both of these roads could be used in the event of a natural disaster. If constructed at some future date, this bridge could provide an additional route for crossing the Snake River if the bridge at Moose were to fail.

The comprehensive land use plan for the town and county is being updated simultaneously with this Hazard Mitigation Plan. Planners have developed maps depicting future land use for this planning process. According to the county planner, the land use plan projects a substantial amount of new construction along the high school road south of town over the next ten years. From ten to twenty years out, additional lot development with a higher density of mixed uses is anticipated in South Park—also south of town. Flat Creek flows through these areas. And, in South Park, the creek is controlled by non-certified levies. If development occurs as anticipated, this issue should be revisited when the Hazard Mitigation Plan is updated in another five years.

To ensure that hazard mitigation is incorporated into the land use plan, the Deputy County Emergency Manager and the hazard mitigation consultant have been invited to review and comment on the chapters relevant to natural hazards.

Teton County MHMP 1.9

Chapter 2. Hazards Identification and Risk Analysis

The Teton County Emergency Management Agency along with the Wyoming State Geological Survey identified 18 potential hazards that could affect Teton County, 12 of which were considered to be significant and potentially life threatening. The local advisory committee asked that terrorism be added as a potential hazard to be planned for, during the 2008-09 revision and update of the plan. Definitions and explanations of all potential hazards are below with those analyzed in depth for Teton County identified by an asterisk.

*Dam Failure: Dam failure is the uncontrolled release of impounded water resulting in downstream flooding, which can affect life and property. Flooding, earthquakes, blockages, landslides, lack of maintenance, improper operation, poor construction, vandalism, or terrorism can cause dam failures.

*Drought: Drought is described as a protracted period of deficient precipitation resulting in extensive damage to vegetation.

*Earthquake: A sudden motion or trembling that is caused by a release of strain accumulated within or along the edge of the earth’s tectonic plates.

Expansive Soils: Expansive soils contain clays that have the potential to swell and shrink when they become wetted or dried. Expansive soils can have significant impact on roads, bridges and other transportation facilities, as well as on buildings. According to the Wyoming Multi-Hazard Mitigation Plan Teton County has over $13 million in buildings built on or over expansive soils. However, there is little actual damage reported in Teton County from expansive soils. It is suspected that most problem areas are being dealt with during construction.

*Flood / Flash Flood: A general and temporary condition of partial or complete inundation of normally dry land areas from (1) the overflow of inland or tidal waters, (2) the unusual and rapid accumulation or runoff of surface waters from any source, or (3) mudflows or the sudden collapse of shoreline land. Flash flood: a flood event occurring with little or no warning where water levels rise at an extremely fast rate.

*Hail: Hail is ice that forms, grows and ultimately falls from thunderclouds. Severe storms can drop enough hail to blanket the ground, flatten crops or clog storm sewers.

Teton County MHMP 2.1

*Hazardous Materials: As defined by the U.S. Department of Transportation (DOT), is one that poses an unreasonable risk to health and safety of operating or emergency personnel, the public, and/or the environment if not properly controlled during handling, storage, manufacture, processing, packaging, use, disposal, or transportation.

*Landslide: A downward movement of a slope and materials under the force of gravity.

Land Subsidence: Land subsidence is a gradual settling or sudden sinking of the Earth's surface owing to subsurface movement of earth materials. In Wyoming this is often associated with roof collapse of mined-out areas. There are a few abandoned underground hard rock and coal mines and prospects in Teton County, but no documented subsidence problems. Although some may have been reclaimed, no development should be allowed at the sites until it can be shown that reclamation has occurred and that the reclamation has been successful.

*Lightning: Lightning is a sudden electrical discharge released from the atmosphere that follows a course from cloud to ground, cloud to cloud, or cloud to surrounding air, with light illuminating its path. Lightning’s unpredictable nature causes it to be one of the most feared and deadly weather elements.

Liquefaction: Liquefaction is the temporary transformation of near surface (within 30 feet), water-saturated sands and silts into a “quicksand”- like state during severe ground motions. It is usually triggered by earthquakes, but can be caused by explosives as well. Loss of soil bearing strength during liquefaction can severely damage anything built on or buried within liquefiable soils. According to the Wyoming Multi-Hazard Mitigation Plan Teton County has over $1.8 billion in buildings built on or over liquefiable soils, primarily in the Snake River Valley and portions of Yellowstone National Park. However, there is no damage documented in the county from liquefaction from past seismic events.

*Winter Storms and Blizzards: A winter storm can range from a moderate snow over a few hours to blizzard conditions with blinding wind-driven snow that lasts several days.

*Terrorism: A willful act committed by a person (domestic--U.S. citizen or non-U.S. citizen) intended to cause disruption, fear and panic, damage and/or loss of life.

Teton County MHMP 2.2

*Tornadoes: Tornadoes are violently rotating column of air extending from a thunderstorm to the ground.

Urban Fire: Urban fire is described as fire usually in manmade structures within a developed city / town that has the ability to spread from one structure to another.

Windstorms: Windstorms are the violent movement of air across the surf of the earth causing damage to assets. Damaging windstorms are not common in Teton County, but they have occurred.

Windblown deposits: Windblown deposits include areas of shifting silts and sands that can encroach on development, roads, and agricultural areas. Some areas of windblown deposits are located in southeastern and southwestern Teton County, but are not known to have caused problems. If these deposits are disturbed, they could potentially destabilize.

*Wildland Fire: An uncontrolled fire spreading through vegetation fuels, exposing and possibly consuming structures.

Volcanism and Yellowstone Volcanic Explosion: Very large-scale explosive volcanic activity has occurred in the Yellowstone area within the past 2.5 million years, which, in geologic time, is very recent. Because of this, the Yellowstone volcanic area is considered a substantial threat across Wyoming and well beyond. As can be gathered from Figures 2.1 and 2.2, the volume and extent of volcanic materials produced from past eruptions at Yellowstone were immense. It is possible that another eruption of similar magnitude will occur, but probably not within the next 20,000 or more years. In the event that another large-scale eruption did occur, thickness of the volcanic material produced would once again be immense. For example, it is predicted that ash in Southeastern Wyoming would be over three feet deep. And, as stated in Smith and Siegel in Windows Into the Earth, 2000: “Devastation would be complete and incomprehensible at the caldera. Imagine Yellowstone National Park and everything in it destroyed. Nearby towns like West Yellowstone, Gardiner, and Cooke City, Montana, likely would be wiped out by ash, mudflows or pyroclastic flows. A Yellowstone caldera explosion today would dump ash over hundreds of thousands of square miles…”

Teton County MHMP 2.3

Figure 2.1. Map showing areas covered by airborne ash flows, tuffs, and pumices of four large Cenozoic volcanic eruptions of the western U. S. Note the 0.62 Ma (~620,000 years before present) Yellowstone eruption and the 2.0 Ma (~620,000 years before present) Yellowstone eruption. From Smith and Braile, 1993. Ages of Yellowstone tuffs based on most recently determined age dates may differ from ages of ashes shown on this diagram.

The large-scale explosive events at Yellowstone occurred 640,000 years before present, 1,300,000 years before present, and 2,100,000 years before present. The recurrence intervals of these events range from 660,000 years (1,300,000 – 640,000) to 800,000 years (2,100,000 – 1,300,000). Only 640,000 years has elapsed since the last event, so 20,000 – 160,000 years may be left before a large event is expected. There are smaller events that occur more frequently. These include several lava flows that were emplaced

Teton County MHMP 2.4

Figure 2.2. Volumes of eruptive materials from volcanic explosions. From Smith and Braile, 1993. Ages of Yellowstone tuffs based on most recently determined age dates may differ from ages of ashes shown on this diagram (see Christiansen, 2001)

at approximately 150,000 years before present, 110,000 years before present, and 70,000 years before present. These events were localized within the Yellowstone area, not having the widespread effect of the previously described explosive events.

Because of the overly long expected occurrence of frequency (greater than 10,000 years) for explosive volcanism at Yellowstone, and the fact that a good response or mitigation plan is not possible for an event of this magnitude, it was not analyzed in this document.

Hazards Risk Analysis

Based on the histories and potential future occurrences of hazards that may cause significant impacts in Teton County, the following hazards are addressed in more detail in the hazard-specific chapters of this plan: dam failures, droughts, earthquakes, floods, hail, hazardous materials, landslides, lightning, snow avalanche, terrorism, tornadoes, wildfire, and winter storms and blizzards. Hazards that were not addressed further were those that were not likely to occur in the next 100 years or those that have not had a historical impact on property or life safety.

Teton County MHMP 2.5

At the end of each of the following hazard-specific chapters there is a summary of the risk to people and property for each hazard. The probability of the hazard occurring is assessed as well. The Teton County Emergency Management Agency generated a ranking of hazards to determine the most significant potential threats posed by natural and man-made hazards. The attached hazard analysis is based on a high, medium and low level of risk, as defined below, based on past history and the potential for future occurrence.

High: This ranking carries the highest threat. The potential of this hazard occurring in the assessment area is considered a matter of “when” it will occur, as opposed to “if” it will occur. The potential for damage is widespread. Hazards in this category may have already occurred in the past.

Medium: This ranking carries a moderate threat level to the general population. The potential of occurrence may be the same as the “high” ranking but the potential damage is more isolated and less costly than a more widespread disaster.

Low: The lowest ranking in the survey, the occurrence and potential cost of damage to life and property is minimal.

Jurisdiction(s) Affected: This indicates how widespread the hazard is within the county, and where the risk varies across the planning area.

Vulnerability to Repetitive Loss

Flooding is the primary hazard of concern with respect to repetitive losses. No history of repetitive loss has been established for any hazard in the county, including flooding. Upstream dams provide flood control on the Snake River.

Other hazards, for example hail, winds, and winter storms are broad ranging geographically and it is not possible to predict an exact location. Seismic activity which in some cases might be predictable along active fault lines, has also occurred across the entire county over recorded history with small, but no repetitive damages reported for any specific location.

The potential risk of loss to wildland fire is more geographically based than most of the other hazards, but catastrophic fire in heavy fuel types occurs less frequently than 100-year intervals and as such also does not have any historical record of repetitive losses. There are no privately owned structures in Teton County situated directly in the heaviest fuel types, these lands are under management of the National Parks and National Forest system. Areas with flashy fuels such as grasses are primarily undeveloped or utilized for grazing.

Teton County MHMP 2.6

Chapter 3. Dam Failures

Dams and reservoirs serve a very important role for Wyoming residents and industry. Rarely, however, the dams fail, either completely or partially, and become a significant hazard for those downstream.

Dam failures can be classified into four classifications: overtopping, foundation failure, structural failure, and other unforeseen failures. Overtopping failures result from the uncontrolled flow of water over, around, and adjacent to the dam. Earthen dams are most susceptible to this type of failure. Hydraulic failures account for approximately 28% of all dam failures. Foundation and structural failures are usually tied to seepage through the foundation of the main structure of the dam. Deformation of the foundation or settling of the embankment can also result in dam failure. Structural failures account for approximately 28% of all dam failures, and foundation problems account for another 25%. Earthquakes or sabotage account for 12% of all dam failures, while inadequate design and construction account for the remaining 7% of failures.

In 1981, the U.S. Army Corps of Engineers completed an inspection program for nonfederal dams under the National Dam Inspection Act (P.L. 92-367). This was a four-year work effort and included compiling an inventory of about 50,000 dams and conducting a review of each state’s capabilities, practices, and regulations regarding design, construction, operation, and maintenance of dams. Part of the inspection included evaluating the dams and assigning a hazard potential based on the effects downstream should one of the dams fail. The dams were rated (1) high, (2) significant, and (3) low hazard. The Corps of Engineers based the hazard potential designation on such items as acre-feet capacity of the dam, distance from nearest community downstream, population density of the community, and age of the dam. High hazard dam failures would involve property losses over $1 million and have probable loss of life. Significant hazard dam failures would cause over $1 million in property damage and involve possible loss of life. There were 1,458 dams in Wyoming that were reviewed by the Corps of Engineers.

Teton County has 12 dams that are inspected by the Wyoming State Engineer’s Office. Of the 12, four are considered high hazard, the rest are low hazard dams. These high hazard dams are the Jackson Lake, Jackson Lake North Dike, Jackson Lake South Dike, and Grassy Lake dams.

History

Teton County has one documented dam failure. On May 18, 1927, a dam that was formed by the lower Gros Ventre landslide, north of Jackson, in 1925, partially failed during a spring with heavy runoff. A 40-foot wall of water came down the valley. The town of Kelly was severely impacted and partially destroyed, and six lives were lost. The town of Wilson was damaged, ranger

Teton County MHMP 3.1

buildings were destroyed, irrigation head gates were washed away, and a bridge was washed out ($75,000 to $150,000 damage). The American Red Cross had expenditures of $12,201.20. Total damages have been estimated at $500,000. There was also a heavy livestock loss. The American Red Cross, Wyoming State Government, Wyoming Governor Emerson, and the Highway Department responded.

Figure 3.1 Dams Inspected by the Wyoming State Engineers Office and the U.S. Bureau of Reclamation.

Impacts

The impact from this one dam failure in Teton County was significant, equivalent to $5.2 million in 2005 dollars. Lives lost in 1927 were partly due to attempts to save belongings or not heeding warnings.

Future Impacts

With four high hazard dams in the county there is a possibility of dam failure in the future, with the potential for $1 million or more in flood damages and probable loss of life. Development or future development along the Snake River could be at risk to dam failure flooding.

Teton County MHMP 3.2

Summary

PROPERTY AFFECTED: Medium POPULATION AFFECTED: Medium PROBABILITY: Low JURISDICTION AFFECTED: Portions of unincorporated county including the community of Wilson

Teton County MHMP 3.3

Chapter 4. Drought

Of all the natural weather-related disasters, drought is by far the most costly to our society. It indirectly kills more people and animals than the combined effects of hurricanes, floods, tornadoes, blizzards, and wildfires. And, unlike other disasters that quickly come and go, drought's long-term unrelenting destruction has been responsible in the past for mass migrations and lost civilizations. The 1980 and 1988 droughts in the US resulted in approximately 17,500 heat-related deaths and an economic cost of over $100 billion. Drought occurs in four stages and is defined as a function of its magnitude (dryness), duration, and regional extent. Severity, the most commonly used term for measuring drought, is a combination of magnitude and duration.

The first stage of drought is known as a meteorological drought. The conditions at this stage include any precipitation shortfall of 75% of normal for three months or longer. The second stage is known as agricultural drought. Soil moisture is deficient to the point where plants are stressed and biomass (yield) is reduced. The third stage is the hydrological drought. Reduced stream flow (inflow) to reservoirs and lakes is the most obvious sign that a serious drought is in progress. The fourth stage is the socioeconomic drought. This final stage refers to the situation that occurs when physical water shortage begins to affect people.

As these stages evolve over time, the impacts to the economy, society, and environment converge into an emergency situation. Without reservoir water to irrigate farms, food supplies are in jeopardy. Without spring rains for the prairie grasslands, open range grazing is compromised. Without groundwater for municipalities, the hardships to communities result in increases in mental and physical stress as well as conflicts over the use of whatever limited water is available. Without water, wetlands disappear. The quality of any remaining water decreases due to its higher salinity concentration. There is also an increased risk of fires, and air quality degrades as a result of increased soil erosion in strong winds (blowing dust).

History

Long periods of sustained dryness are part of Wyoming’s climate. The most recent statewide drought started in 1999, but began in earnest in the spring of 2000. It is considered by many to be the most severe in collective memory. However, some old timers have indicated that they remember streams drying up in the 1930s and 1950s. According to instrument records, since 1895 there have been only seven multi-year (three years or longer) statewide droughts. Based on deficit precipitation totals (negative departures from the long term average), they are ranked statewide. Refer to Table 4.1 on the following page.

Teton County MHMP 4.1

Table 4.1 Wyoming’s Recent Worst Multi-Year, Statewide Droughts Period Drought Deficit (departure from annual precipitation) 1952-1956 94% 1999-200x (thru 2003) 82% 1958-1964 77% 1900-1903 72% 1931-1936 61% 1987-1990 61% 1974-1977 41%

Widespread droughts in Wyoming, as determined from stream flow records, were most notable during three periods: 1929-1942, 1948-1962, and 1976-1982. Teton County– specific data are not available at this time.

Instrumentation Record

As a whole, Wyoming's precipitation record from 1895-2003 reveals that, for the first half of the 20th century (except for the Dust Bowl years of the 1930s), there was generally a surplus of moisture. During the second half of the century there was an increasing trend of increased periods of drought (Figure 4.1).

Figure 4.1 Wyoming Annual Precipitation (1895-2003)

Teton County MHMP 4.2

Impacts

Based upon Table 4.1 and Figure 4.1, the drought of 1999-2003 is as significant, if not more significant than any other droughts in the last 100 years for the entire state. The Jackson Hole News and Guide reported in August of 2007, that warm water temperatures caused by drought were affecting fish and causing mortality. The data have not been analyzed for Teton County. Data from the Wyoming Climate Atlas, indicates that the most significant droughts in the last century, in terms of precipitation deficit, were in 1952-1956 and 1999-2007.

Table 4.2 Peak Commodity Production Changes from Pre-Drought (1994-1998) to Drought (1999-2003) 5-Year Lowest Year Pre-Drought Production of Percent Commodity Production Units During Lowest Change Average Drought Production (1994-1998) (1999-2003)

Alfalfa Hay 1581 1,000 tons 1150 2002 -27% Other Hay 817 1,000 tons 450 2002 -45% Cattle/ Calves 1552 1,000 head 1320 2002 -15% Inventory

Drought impacts to the Wyoming agricultural community were greater in the 1999-2003 drought than in the 1952-1956 drought. With the exception of dry beans, all commodities in the worst years of the 1999-2002 drought showed a greater percentage decline in production than in the 1952-1956 drought. As a result, the 1999-2002 drought will be used as the drought of historic record to calculate dollar impacts.

Dollar Impacts

Dollar impacts of drought are derived from “Wyoming Agricultural Statistics 2003” that is compiled by the Wyoming Agricultural Statistics Service of the U.S. Department of Agriculture. Supplemental data through 2003 were provided by the Cheyenne, Wyoming office of the agency.

Drought impacts to agriculture in Teton County would be found primarily in hay and livestock production. The data below represent changes in production value for crops and changes in inventory value for cattle and calves. The data should be considered impact value versus loss value. For example, with cattle and calves (Tables 4.3 through 4.8) the inventory has decreased during the drought. Therefore the value of inventory on hand has decreased. The inventory decreased, however, because of the sale of the cattle and calves. The sales resulted in an increase in cash receipts to the farming and ranching community. The net result, however, is a decrease in inventory value, which is a negative drought impact.

Teton County MHMP 4.3

Table 4.3 1999 Production and Inventory Value Impact 5-Year Pre- Drought Production and 1999 Commodity Production Units Value (USD) Inventory Value Production Average Impact (USD) (1994-1998) Alfalfa Hay 1581 1,000 tons 1782 67.00/ton + 13,467,000 Other Hay 817 1,000 tons 1008 60.00/ton + 11,436,000 Cattle/Calves 1536 1,000 head 1580 770.00/head + 33,880,000 Inventory TOTAL + $58,783,000

Table 4.4 2000 Production and Inventory Value Impact 5-Year Pre- Drought Production and 2000 Commodity Production Units Value (USD) Inventory Value Production Average Impact (USD) (1994-1998) Alfalfa Hay 1581 1,000 tons 1449 85.00/ton - 11,220,000 Other Hay 817 1,000 tons 650 80.00/ton - 13,392,000 Cattle/Calves 1536 1,000 head 1550 780.00/head +$10,920,000 Inventory TOTAL - $35,532,000

Table 4.5 2001 Production and Inventory Value Impact 5-Year Pre- Drought Production and 2001 Commodity Production Units Value (USD) Inventory Value Production Average Impact (USD) (1994-1998) Alfalfa Hay 1581 1,000 tons 1276 110.00/ton - 33,550,000 Other Hay 817 1,000 tons 605 105.00/ton - 22,302,000 Cattle/Calves 1536 1,000 head 1470 780.00/head - 51,480,000 Inventory TOTAL - $107,332,000

Table 4.6 2002 Production and Inventory Value Impact 5-Year Pre- Drought Production and 2002 Commodity Production Units Value Inventory Value Production Average Impact (1994-1998) Alfalfa Hay 1581 1,000 tons 1150 $111.00/ton - $ 47,841,000 Other Hay 817 1,000 tons 450 $106.00/ton - $ 38,944,400 Cattle/Calves 1536 1,000 head 1320 $760.00/head - $164,160,000 Inventory TOTAL - $250,945,400

Teton County MHMP 4.4

Table 4.7 2003 Production and Inventory Value Impact 5-Year Pre- Drought Production and 2003 Commodity Production Units Value (USD) Inventory Value Production Average Impact (1994-1998) Alfalfa Hay 1581 1,000 tons 1560 82.00/ton - 1,722,000 Other Hay 817 1,000 tons 770 75.00/ton - 3,555,000 Cattle/Calves 1536 1,000 head 1400 890.00/head - 121,040,000 Inventory TOTAL - $126,317,000

Table 4.8 Production and Inventory Value Impact for Worst Year of Drought 5-Year Pre- Drought Worst Yearly Production and Commodity Production Units Production Year Value (USD) Inventory Value Average Of Drought Impact (USD) (1994-1998) Alfalfa Hay 1581 1,000 tons 1560 2002 111.00/ton - 47,841,000 Other Hay 817 1,000 tons 770 2002 106.00/ton - 38,944,400 Cattle/Calves 1536 1,000 head 1400 2003 760.00/head - 164,160,000 Inventory TOTAL - $250,945,400

Future Potential Impacts

The 1999-2007 drought can be shown to be the drought of historic record. There have been significant impacts on the agricultural industry from this drought. The worst-case year was 2002, with a negative dollar impact of $308,171,390 statewide. As a general measure, using the land base of Teton County at 4.1% of the State of Wyoming, the potential drought impact in Teton County for 2002 would have been approximately $12.9 million. The total impact statewide for the 1999-2003 drought (for which figures are available) is $565,489,036. If it is assumed that the drought impact is equally distributed across the state the potential drought impact in Teton County for the years 1999-2003, has been approximately $23.7 million.

This estimation does not take into account economic losses to the tourism industry upon which Teton County’s economy is largely based. Drought could have significant impacts to the skiing, rafting, fishing and hunting industries within the county. Wildfire concerns may lead to fire bans and public land area closures, with an additional resulting loss in tourism and recreation revenue.

Summary

PROPERTY AFFECTED: High POPULATION AFFECTED: High PROBABILITY: High JURISDICTION AFFECTED: All

Teton County MHMP 4.5

Chapter 5. Earthquakes

An earthquake is generally defined as a sudden motion or trembling in the Earth caused by the abrupt release of slowly accumulated strain. The most common types of earthquakes are caused by movements along faults and by volcanic forces, although they can also result from explosions, cavern collapse, and other minor causes not related to slowly accumulated strains.

Historically, earthquakes have occurred in every county in Wyoming (Figure 5.1). The first was reported in Yellowstone National Park in 1871. Yellowstone National Park is one of the more seismically active areas in the United States.

Figure 5.1 Historic Earthquakes in Wyoming

Teton County MHMP 5.1

Historic Seismicity in Teton County

Hundreds of magnitude 2.0 and greater earthquakes have been recorded in Teton County. The most significant earthquakes are discussed below.

1900s Earthquakes: The first earthquake that was reported in Teton County occurred on October 6, 1906, approximately 2.5 miles northwest of Jackson (U.S.G.S. National Earthquake Information Center). No damage was reported from this intensity IV event.

1920s Earthquakes: On March 24, 1923, an intensity V earthquake occurred approximately 13 miles northeast of Jackson. This earthquake was felt as far south as the Green River Basin. The Jackson Hole Courier (March 29, 1923) reported that several shocks were felt, with the largest rocking buildings all over the county. The paper reported that ―Rocks weighing tons were shaken loose along the Tetons and in the hills about Grovont, and rolled into the valley. Many of the snow slides which run about this time of year or a little later were started on their way by the Quake‖. A local resident reported that it felt like his home had been lifted up and shaken violently, and set down with a thump. No significant damage was reported.

On June 23, 1925, the lower Gros Ventre landslide north of Jackson activated, damming the Gros Ventre River. Nearby seismic activity on June 21 was reported by the Jackson Hole Courier (June 25, 1925) as being ―quite severe.‖ Voight (1978) described a report of local seismic activity on June 22, 1925, the night before the Gros Ventre River was dammed by the landslide. An intensity IV earthquake was also reported near Jackson on September 3, 1925. Most town residents felt the earthquake, which was centered approximately 3 miles northwest of Jackson. Objects were rattled, but no damage occurred (Blackwelder, 1926).

On March 31, 1928, an intensity IV earthquake occurred approximately 18 miles north of Jackson. Reports indicated that many residents in the area felt a trembling sensation. This was the strongest earthquake to date along the Gros Ventre River above Kelly. The earthquake was not felt at Moran (Heck and Bodle, 1930).

1930s Earthquakes: Several earthquakes were recorded in Teton County in the 1930s. An intensity VI earthquake occurred on March 26, 1932, approximately 4 miles northeast of Jackson. The earthquake cracked plaster walls and foundations in several Jackson homes and businesses. The main shock was preceded by a few events along the Upper Gros Ventre River, and was followed by a number of intensity III

Teton County MHMP 5.2

and IV aftershocks. Because the event occurred at night, several residents ran from their homes without grabbing any clothing, and a few were thrown from their beds. The earthquakes were felt in Jackson, Kelly, Grovont, Wilson, Teton Pass, and the Snake River Canyon, but were not felt at Moran (Jackson Hole Courier, January 28, 1932).

On January 14, 1936, and intensity VI, magnitude 5.0 (estimated) earthquake occurred approximately 19 miles southwest of the south entrance to Yellowstone National Park. The earthquake, which was not felt in Jackson, cracked two brick chimneys and moved small objects. Residents of Moran reported beds rocking (Neumann, 1938).

In 1939, two earthquakes occurred approximately 3 miles northwest of Jackson. The first, an intensity III event, took place on October 22, 1939. The second, an intensity IV event, occurred on November 2, 1939. Neither caused damage.

1940s Earthquakes: Four earthquakes occurred in the county in the 1940s. Two intensity III earthquakes were detected on October 22, 1940 and on November 2, 1940 (U.S.G.S. National Earthquake Information Center). Both were located approximately 3 miles northwest of Jackson, but neither caused damage.

The next earthquake in the county occurred on January 8, 1947. This intensity IV earthquake was located approximately 3.5 miles southeast of the south entrance to Yellowstone National Park. No damage was associated..

On February 23, 1948, an intensity VI, magnitude 5.0 (estimated) earthquake was recorded approximately 13 miles west of Jackson. Some residents in the area reported that their houses rocked and swayed in an east-to-west direction. People also reported that dishes and windows rattled and pictures fell from walls. Some buildings in Jackson sustained cracked and twisted logs (Jackson Hole Courier, February 26, 1948).

1950s Earthquakes: Only one earthquake was reported in Teton County in the 1950s. An intensity IV earthquake occurred on March 15, 1953, approximately 2 miles northeast of Alta. Many area residents reported that buildings creaked and loose objects rattled. In addition, thunderous sounds were heard before and during the earthquake (Murphy and Cloud, 1955).

1960s Earthquakes: Teton County experienced several earthquakes in the 1960s. On October 6, 1962, an intensity IV earthquake occurred approximately 11 miles north of Jackson. The event lasted a few seconds and rattled dishes and windows (Casper Tribune-Herald and Star, October 7, 1962).

Teton County MHMP 5.3

On October 12, 1963, a magnitude 3.9-4.0 earthquake occurred near the south border of the county, approximately 9 miles west-southwest of Hoback Junction. No damage was reported from this event. Two earthquakes were detected in December of 1963. The first magnitude 4.0 event occurred on December 8, 1963, approximately 26 miles southeast of Moran Junction. A few days later, on December 14, 1963, a magnitude 4.1 earthquake was reported approximately 19 miles southeast of Moran Junction. Neither of the December 1963 earthquakes caused damage or was felt.

A magnitude 3.8 earthquake occurred in Teton County on February 27, 1964. This event was centered approximately 23 miles southeast of Moran Junction. Again, this earthquake caused no damage and no one felt it. On May 1, 1964, a magnitude 4.0 earthquake was recorded approximately 17.5 miles south- southeast of Moran Junction. This event was followed by another earthquake on May 7, 1964. No specific magnitude or intensity has been associated with the May 7 earthquake, which was centered approximately 16.5 miles east-southeast of Hoback Junction. On June 24, 1964, another earthquake of no specific magnitude or intensity occurred approximately 4 miles southwest of Hoback Junction. None of the May or June 1964 earthquakes caused damage or were felt.

No other earthquakes were recorded in Teton County until December 20, 1967, when an earthquake of no specific magnitude or intensity occurred approximately 6 miles southeast of Moran Junction. It was not felt and did not cause damage.

The last earthquake to occur in Teton County in the 1960s took place on November 15, 1968. This magnitude 3.9 earthquake was recorded approximately 19 miles southeast of Moran Junction. No one reported feeling the earthquake.

1970s Earthquakes: Twenty-one earthquakes were recorded in Teton County in the 1970s. Most of the earthquakes that occurred during this decade were not felt and did not cause any damage. On November 12, 1970, a magnitude 3.9 earthquake was detected in the northern portion of the county. This event was centered approximately 14 miles southeast of the south entrance to Yellowstone National Park. No one felt this earthquake.

An earthquake of no specific magnitude or intensity occurred in the same area on June 23, 1971. Again, no one reported feeling this event.

Three more earthquakes of no specific magnitude or intensity were recorded on March 24, 25, and 29, 1973. These March 1973 events were centered approximately 17, 20, and 23 miles northeast of Moran Junction, respectively. None of these earthquakes were felt.

Teton County MHMP 5.4

On September 23, 1974, an earthquake was detected by the U.S.G.S. in western Teton County. No one reported feeling this magnitude 3.0 event, although it was centered approximately 0.5 mile northeast of Alta. On October 18, 1974, a magnitude 3.6, intensity IV earthquake was recorded approximately 4 miles southeast of the south entrance to Yellowstone National Park. No damage was associated with this event. Another non-damaging earthquake occurred on December 22, 1974. This magnitude 3.3 event was located approximately 10.5 miles southeast of the south entrance to Yellowstone National Park.

Four earthquakes occurred in Teton County in 1975. The first was recorded on January 23, 1975, approximately 12.5 miles east of the Yellowstone National Park south entrance. This magnitude 2.5 event was not felt and did not cause any damage. Magnitude 3.3 earthquakes occurred in the county on June 17, 1975, and on July 17, 1975. The June 17 event was located approximately 12 miles southwest of Jackson, while the July 17 event was centered approximately 9 miles east-southeast of Moran Junction. Neither of these earthquakes was felt. The last earthquake to occur in the county in 1975 took place on August 14, 1975. The epicenter of this non-damaging, magnitude 3.0 earthquake was approximately 11.5 miles east-southeast of Moran Junction.

In March of 1976, a series of earthquakes occurred in southern Teton County. The University of Utah Seismograph Stations detected a magnitude 2.0 earthquake on March 11, 1976. No one reported feeling this earthquake that was centered approximately 12.5 miles west-northwest of Hoback Junction. On March 14, 1976, a magnitude 3.7 earthquake was recorded approximately 5 miles south-southeast of Hoback Junction. This event was followed by a magnitude 3.9 earthquake on March 17, 1976. This earthquake was centered approximately 6 miles south-southeast of Hoback Junction. On March 21, 1976, a magnitude 2.9 earthquake and a magnitude 2.8 earthquake occurred approximately 5 miles southeast of Hoback Junction. These events were followed by a magnitude 2.7 earthquake on March 27, 1976. This earthquake was centered approximately 10 miles east-southeast of the south entrance to Yellowstone National Park. No one reported feeling any of the March 1976 earthquakes, and no damage was associated with them. A magnitude 3.1 earthquake was detected in Teton County on May 8, 1976, approximately 17.5 miles east of Kelly. Again, no one reported feeling this earthquake.

On July 22, 1977, a magnitude 3.0 earthquake occurred approximately 16 miles east-northeast of Jackson. No one reported feeling this earthquake.

Teton County did not experience another earthquake until March 10, 1978. On this date, a magnitude 3.2 earthquake occurred approximately 17 miles east- southeast of Moran Junction. No one reported feeling this event.

On July 3, 1979, a magnitude 3.2, intensity IV earthquake occurred approximately 5 miles southeast of Jackson. Jackson residents reported that

Teton County MHMP 5.5

dishes rattled and that pictures on walls moved. Horses at the Teton County Fairgrounds were also noticeably disturbed (Casper Star-Tribune, July 4, 1979).

1980s Earthquakes: A number of earthquakes occurred in Teton County in the 1980s, but few caused any significant damage. The first earthquake in this decade was recorded on January 5, 1980. This non-damaging, magnitude 2.8 event was centered in the east-central portion of the county, approximately 22 miles east of Moran Junction. On May 31, 1980, a magnitude 2.5 earthquake occurred approximately 10.5 miles southeast of the south entrance to Yellowstone National Park. No one reported feeling this event.

The first earthquake that was felt in the 1980s occurred on May 6, 1981. The epicenter of the magnitude 3.7, intensity IV earthquake was located approximately 7 miles southeast of Jackson. A local disc jockey reported that ―window frames changed position briefly, and the turntable and the seat of my pants came up and down at the same time‖. A local secretary said her desk moved during the event (Casper Star-Tribune, May 7, 1981). A magnitude 3.0 earthquake occurred a few days later on May 12, 1981, centered approximately 10 miles southeast of Moran Junction, but no one reported feeling it.

On November 2, 1983, a magnitude 3.5, intensity IV earthquake was recorded approximately 10 miles west-southwest of Jackson. Although the event was felt, no damage occurred. Another non-damaging earthquake occurred a week later on November 9, 1983. This magnitude 3.6, intensity III earthquake was centered approximately 17.5 miles east-southeast of Moran Junction. The U.S.G.S. National Earthquake Information Center reported that this event was felt. The next earthquake to occur in Teton County took place on December 20, 1983, approximately 10 miles south of Jackson. This magnitude 4.5, intensity IV earthquake was felt from Jackson to the Palisades Reservoir in Idaho. In Jackson, there were reports of Christmas trees falling over and dishes breaking (Laramie Daily Boomerang, December 21, 1983). A number of aftershocks followed the December 20, 1983 event. The largest aftershock was a magnitude 3.4 earthquake that occurred on December 22, 1983.

On January 5, 1984, a magnitude 3.0 aftershock occurred in the same area. A magnitude 2.6 earthquake was detected on January 17, 1984, approximately 11 miles east of the south entrance to Yellowstone National Park. No one reported feeling this event. A magnitude 2.8 earthquake was detected on March 23, 1984, approximately 3 miles northwest of Hoback Junction. Area residents reported feeling it as an intensity II event. An earthquake was detected on November 2, 1984, approximately 6 miles northwest of Jackson. People did report feeling the earthquake, which was a magnitude 3.1, intensity III event.

Teton County MHMP 5.6

On May 25, 1985, a magnitude 2.6-2.8 earthquake was recorded approximately 4 miles northwest of Moran Junction. This event was not felt.

Beginning in June of 1986, the U.S. Bureau of Reclamation began operation of the Jackson Hole Seismic Network. Hundreds to thousands of earthquakes have been detected since 1986. Only the earthquakes that were jointly detected by the U.S. Geological Survey and the University of Utah Seismograph Stations are described in detail in this report. A yearly summary of the number of earthquakes detected by the U.S. Bureau of Reclamation will be noted.

In 1986, no earthquakes of magnitude 3.0 or greater were recorded in Teton County. The U.S. Bureau of Reclamation did detect approximately 14 additional earthquakes ranging in magnitude between 2.0 and 2.8 in or in the near vicinity of Teton County.

On February 20, 1987, two earthquakes occurred in Teton County, approximately 11 miles southeast of Moran Junction. No damage was reported from these magnitude 3.1 and 3.2 events (U.S. Bureau of Reclamation). Another magnitude 3.1 earthquake was recorded by the U.S. Bureau of Reclamation on June 4, 1987. It was centered approximately 9 miles southwest of the south entrance to Yellowstone National Park. No one reported any damage from this earthquake. The U.S. Bureau of Reclamation detected approximately 396 additional earthquakes ranging in magnitude from 0.2 to 2.8 in or in the near vicinity of Teton County in 1987.

Teton County did not experience another earthquake until August 24, 1988, when two earthquakes occurred approximately 3.5 miles northeast of Jackson. Area residents reported feeling the first earthquake, which was a magnitude 2.8 event, but no one reported feeling the second, magnitude 2.4 earthquake. The U.S.G.S. National Earthquake Information Center detected two earthquakes in southern Teton County on October 21, 1988. The first, a magnitude 3.6 earthquake, was centered approximately 16.5 miles east-southeast of Hoback Junction. The second earthquake was a magnitude 3.5 event, located approximately 19 miles east-northeast of Hoback Junction. Neither earthquake was felt. A magnitude 3.6 earthquake on December 4, 1988, was centered approximately 22 miles east of Jackson. No one felt this earthquake. In 1988, the U.S. Bureau of Reclamation detected approximately 41 additional earthquakes ranging in magnitude between 2.0 and 2.9 in or in the near vicinity of Teton County.

On May 12, 1989, a magnitude 2.6 earthquake occurred approximately 1.5 miles east-northeast of Jackson. No one reported feeling this earthquake. It was followed closely by a magnitude 3.1 earthquake approximately 5 miles southeast of Jackson. The U.S.G.S. National Earthquake Information Center reported that the earthquake was felt as an intensity III event in Jackson, but no damage occurred. On June 24, 1989, two earthquakes were felt strongly at Jackson.

Teton County MHMP 5.7

They both were centered approximately 2 miles north of Jackson. The first earthquake, which occurred at 3:25 a.m., had a magnitude of 3.8. The second earthquake, which occurred one hour later, had a magnitude of 3.7. People reported windows rattling, but no damage was associated with these earthquakes (Casper Star-Tribune, June 25, 1989). Two more earthquakes were detected by the U.S.G.S. National Earthquake Information Center later that same day. Both were magnitude 3.0, but neither was felt. On July 26, 1989, the U.S. Bureau of Reclamation recorded a magnitude 3.1 earthquake approximately 22 miles southeast of Kelly. No damage was reported from this event. In 1989, the U.S. Bureau of Reclamation detected approximately 49 additional earthquakes ranging in magnitude between 2.0 and 2.9 in or in the near vicinity of Teton County.

1990s Earthquakes: The first earthquake to be detected in Teton County in the 1990s occurred on March 4, 1990. This magnitude 4.1 earthquake was centered approximately 6 miles south of Jackson. Jackson area residents felt the earthquake as an intensity IV event, but no damage was reported (Casper Star-Tribune, March 6, 1990). On March 14, 1990, a magnitude 3.4 earthquake was detected by the U.S. Bureau of Reclamation near the Teton County-Sublette County border. No damage was reported from this event that was centered approximately 10 miles southeast of Hoback Junction. Two earthquakes occurred in the county in October of 1990. The first took place on October 2, 1990, when a magnitude 3.6 earthquake was recorded approximately 16 miles east-northeast of Jackson. The second event was a magnitude 3.0 earthquake that occurred on October 26, 1990. Its epicenter was located approximately 17 miles east-southeast of Moran Junction. No one reported feeling either of these October 1990 earthquakes. In 1990, the U.S. Bureau of Reclamation detected approximately 17 additional earthquakes ranging in magnitude between 2.0 and 2.5 in or in the near vicinity of Teton County.

On August 14, 1991, a magnitude 3.0 earthquake was recorded approximately 4.5 miles northeast of Hoback Junction. This earthquake was not felt. A magnitude 3.2 earthquake that occurred on September 29, 1991, approximately 26 miles east of Jackson, was also not felt. The U.S. Bureau of Reclamation recorded a magnitude 3.1 earthquake in Teton County on December 19, 1991. No damage was reported from this event, which was located approximately 9 miles southeast of Kelly. In 1991, the U.S. Bureau of Reclamation detected approximately 41 additional earthquakes ranging in magnitude between 2.0 and 2.7 in or in the near vicinity of Teton County.

The area near Mount Leidy experienced a magnitude 3.7 earthquake on September 24, 1992. No one felt this earthquake that was located approximately 25 miles northeast of Jackson. In 1992, the U.S. Bureau of Reclamation detected approximately 35 additional earthquakes ranging in magnitude between 2.0 and 2.9 in or in the near vicinity of Teton County.

Teton County MHMP 5.8

The first earthquake to occur in Teton County in 1993 took place on February 27, 1993. The epicenter of this magnitude 3.0 earthquake was located approximately 5 miles northeast of Hoback Junction (U.S. Bureau of Reclamation). No damage was associated with this earthquake. On April 1, 1993, a magnitude 3.1 event was centered approximately 21.5 miles southeast of Moran Junction. No one felt this earthquake. The U.S. Bureau of Reclamation recorded a magnitude 3.0 earthquake on May 15, 1993, in western Teton County, approximately 4 miles south-southeast of Alta. No damage occurred from this event. On November 26, 1993, a magnitude 3.8 earthquake occurred approximately 29 miles east-northeast of Jackson. Again, this event was not felt. A magnitude 4.7 earthquake, intensity V earthquake occurred on December 28, 1993, approximately 34 miles east of Jackson. The earthquake was felt in Jackson, Dubois, Hudson, Lander, and Rock Springs. Most reports indicated that the earthquake felt like a heavy truck passing by. A ranch near the epicenter reported swinging lights, but no damage. In 1993, the U.S. Bureau of Reclamation detected approximately 44 additional earthquakes ranging in magnitude between 2.0 and 2.8 in or in the near vicinity of Teton County.

On February 3, 1994, a magnitude 2.7 and magnitude 2.6 earthquakes were detected in southwestern Teton County, approximately 15 miles southwest of Jackson. No one reported feeling these earthquakes. The U.S.G.S. National Earthquake Information Center detected a magnitude 2.9 earthquake on July 31, 1994, approximately 6 miles south of the south entrance to Yellowstone National Park. According to the U.S.G.S., people did report feeling the earthquake as an intensity III event. Four other earthquakes occurred in the county in 1994, but none were felt and no damage was reported. These include a magnitude 3.0 earthquake on May 19, 1994, that was located approximately 10 miles southeast of Moran Junction, a magnitude 3.0 earthquake on September 7, 1994, that was centered approximately 20 miles southeast of Moran Junction and magnitude 2.2 and 3.1 earthquakes on December 4, 1994, approximately 5 miles southwest of the south entrance to Yellowstone National Park. In 1994, the U.S. Bureau of Reclamation detected approximately 82 additional earthquakes ranging in magnitude between 2.0 and 2.9 in or in the near vicinity of Teton County.

On January 27, 1995, an earthquake was recorded approximately 20 miles east- northeast of Jackson. No one reported feeling this magnitude 3.5 event. On August 27, 1995, three earthquakes occurred in the vicinity of Joy Park and Enos Lake in northeastern Teton County. The first event had a magnitude of 4.5, and was felt at Flagg Ranch, south of Yellowstone National Park, as well as at Fishing Bridge and Grant Village within the Park. At Flagg Ranch, there were reports of buildings vibrating and dishes rattling. At Grant Village, the event was felt for 10-15 seconds, and a few items fell off the shelves at the Hamilton Store. The magnitude 4.5 earthquake was quickly followed by a magnitude 2.6 earthquake that caused no damage. Within two hours, another non-damaging, magnitude 3.8 earthquake also occurred. In 1995, the U.S. Bureau of

Teton County MHMP 5.9

Reclamation detected approximately 64 additional earthquakes ranging in magnitude between 2.0 and 2.9 in or in the near vicinity of Teton County.

On January 29, 1996, a magnitude 3.2-3.7 earthquake occurred in the vicinity of Lower Slide Lake, approximately 16 miles northeast of Jackson. No damage was associated with the earthquake. As mentioned previously, there were reports of seismic activity in the same area in 1925. On May 10, 1996, a magnitude 3.1 earthquake occurred approximately 3 miles southeast of Jackson (U.S. Bureau of Reclamation). No damage was associated with this earthquake. A magnitude 3.7 earthquake was recorded on June 22, 1996, approximately 29 miles southeast of Moran Junction. No one felt this event. On July 5, 1996, a magnitude 3.1 earthquake occurred approximately 23 miles east-northeast of Jackson. A magnitude 3.2 earthquake was also detected 12 miles east- northeast of Jackson on July 5, 1996. Again, no one felt these earthquakes. The U.S. Bureau of Reclamation recorded a magnitude 3.0 earthquake on September 23, 1996. No damage was reported from this event, which was centered approximately 25 miles southeast of Kelly. In 1996, the U.S. Bureau of Reclamation detected approximately 65 additional earthquakes ranging in magnitude between 2.0 and 2.8 in or in the near vicinity of Teton County.

The largest earthquake to occur in Teton County in 1997 took place on September 13, 1997. This magnitude 2.8 event was centered approximately 5 miles east-southeast of Jackson, but no one reported feeling it. In 1997, the U.S. Bureau of Reclamation detected approximately 46 additional earthquakes ranging in magnitude between 2.0 and 2.5 in or in the near vicinity of Teton County.

A series of earthquakes occurred in the county during the spring of 1998. On June 14, 1998, a swarm of earthquakes with magnitudes greater than 2.0 began to occur approximately 3.5 miles southeast of Hoback Junction near Camp Davis. Approximately 14 earthquakes with magnitudes ranging from 2.0 to 3.3 preceded a magnitude 4.7 earthquake that occurred in this area on June 20, 1998. No damage was reported from the magnitude 4.7 event, but it was distinctly felt at Hoback Junction and was felt by many residents of Jackson. Through June 22, 1998, approximately 14 aftershocks with magnitudes greater than 2.0 occurred in the area. On July 11, 1998, a magnitude 3.0 earthquake was detected approximately 6.5 miles east of Jenny Lake. Again, this event was not felt. Two earthquakes occurred on August 23, 1998, approximately 5 miles north-northeast of Alta. No one felt the first earthquake, which was a magnitude 3.2 event. People in this area did, however, feel the magnitude 4.2 earthquake that quickly followed. This same area experienced several more earthquakes in 1998, including magnitude 3.8 earthquakes on August 26, 1998 and September 17, 1998; a magnitude 3.3 earthquake on September 26, 1998; and magnitude 3.2 events on October 18, 1998 and November 1, 1998. None of these earthquakes were felt and no damage was associated with any of them. In 1998, the U.S. Bureau of Reclamation detected approximately 123 additional

Teton County MHMP 5.10

earthquakes ranging in magnitude between 2.0 and 2.9 in or in the near vicinity of Teton County.

On January 15, 1999, a magnitude 3.4 earthquake was recorded approximately 3 miles northeast of Alta. A few days later, on January 20, 1999, a magnitude 3.2 earthquake occurred in the same area. No one reported feeling either of these earthquakes. Another earthquake occurred in the Alta area on April 10, 1999. Area residents did report feeling this magnitude 3.8 event. Three more earthquakes were recorded in Teton County in 1999, but none of them were felt and no damage was reported from any of them. On April 19, 1999, a magnitude 2.8 earthquake occurred approximately 3 miles southeast of Hoback Junction. A magnitude 3.6 event was detected on June 29, 1999, approximately 4 miles northeast of Alta. The last earthquake to occur in the county in 1999 took place on November 16, 1999. This magnitude 3.1 event was centered approximately 19 miles east-northeast of Hoback Junction. In 1999, the U.S. Bureau of Reclamation detected approximately 75 additional earthquakes ranging in magnitude between 2.0 and 2.9 in or in the near vicinity of Teton County.

2000s Earthquakes: Five earthquakes occurred in Teton County in 2000. On February 3, 2000, a magnitude 3.0 earthquake was detected approximately 18 miles east-northeast of Moran Junction. No one reported feeling this event. Another magnitude 3.0 earthquake occurred on April 9, 2000. Area residents did report feeling this earthquake, which was centered approximately 6 miles west-southwest of Jackson. On April 20, 2000, a magnitude 2.7 earthquake and a magnitude 2.3 earthquake were detected in far southern Teton County. No one reported feeling these earthquakes, which were centered approximately 6 miles south-southeast of Hoback Junction. A magnitude 3.9 earthquake occurred on October 3, 2000, approximately 18 miles southeast of Moran Junction. No one felt this event. In 2000, the U.S. Bureau of Reclamation detected approximately 30 additional earthquakes ranging in magnitude between 2.0 and 2.6 in or in the near vicinity of Teton County.

Several earthquakes occurred in Teton County in 2001. On February 3, 2001, a magnitude 2.5 earthquake was detected approximately 8 miles southeast of the south entrance to Yellowstone National Park. No one felt the earthquake. The U.S. Bureau of Reclamation recorded a magnitude 3.1 earthquake on February 19, 2001, in the southeastern portion of the county. No damage resulted from this event, which was centered approximately 30 miles southeast of Kelly. A magnitude 3.3 earthquake occurred approximately 5 miles southwest of Hoback Junction on June 14, 2001. No damage was reported. The U.S. Bureau of Reclamation detected another earthquake on August 22, 2001, approximately 20.5 miles east of Jackson. No damage was associated with this magnitude 3.1 event. On September 27, 2001, an earthquake was recorded near the Fremont County-Teton County-Sublette County borders, approximately 36 miles east of Jackson. Area residents reported feeling this magnitude 4.3 event. On

Teton County MHMP 5.11

November 15, 2001, a magnitude 2.9 earthquake and a magnitude 2.8 earthquake were recorded approximately 11 miles south of Moran Junction. Neither event was felt. In 2001, the U.S. Bureau of Reclamation detected approximately 69 additional earthquakes ranging in magnitude between 2.0 and 2.9 in or in the near vicinity of Teton County.

Several earthquakes were also recorded in Teton County in 2002. An increase in seismic activity was noted in the Kelly, Wyoming area in 2002. From January 1, 2002 to April 15, 2002, 31 small earthquakes occurred approximately 1.5-3 miles south of Kelly. These events can be classified as a small swarm. Earthquake swarms are common in northwestern and western Wyoming. Most have not been precursors to larger events. On January 2, 2002, a magnitude 3.1 earthquake occurred approximately 26 miles east of Jackson. No one reported feeling this event. On January 29, 2002, an earthquake was detected approximately 11 miles northeast of Jackson. According to the U.S.G.S. National Earthquake Information Center, residents in this area did report feeling this magnitude 3.7 earthquake. A magnitude 2.9 earthquake occurred 11 miles northeast of Jackson on March 5, 2002. This event was not felt. A magnitude 2.8 earthquake occurred in eastern Teton County on April 24, 2002. No one reported feeling this earthquake, which was centered approximately 14.5 miles east-northeast of Moran Junction. The U.S. Bureau of Reclamation recorded a magnitude 3.1 earthquake in Teton County on May 12, 2002. No damage resulted from this earthquake, which was centered approximately 4 miles southeast of Kelly. On June 30, 2002, the U.S. Bureau of Reclamation recorded a magnitude 3.0 earthquake approximately 13.5 miles east-northeast of Jackson. No damage was reported. Another magnitude 3.1 earthquake was detected by the U.S. Bureau of Reclamation on July 25, 2002. No damage was associated with this event, which was centered approximately 3 miles southeast of Kelly. On November 8 and 9, 2002, two earthquakes occurred approximately 17.5 miles southeast of Kelly. No damage resulted from these magnitude 3.1 earthquakes. A magnitude 3.2 earthquake was recorded in northern Teton County on November 20, 2002. This non-damaging event was centered approximately 7 miles southeast of the south entrance to Yellowstone National Park. This same area experienced two more earthquakes in November 2002. The U.S. Bureau of Reclamation recorded a magnitude 3.1 earthquake on November 22, 2002, and most recently, a magnitude 3.2 earthquake on November 24, 2002. No damage was associated with any of the November 2002 earthquakes. In 2002, the U.S. Bureau of Reclamation detected approximately 156 earthquakes ranging in magnitude between 1.5 and 2.9 in or in the near vicinity of Teton County.

The mid-March 2007, minor earthquakes shook at both ends of Jackson Hole— one in the Teton Wilderness and one east of Alpine. The quakes were 2.3 and 2.9 respectively. No damages were reported in Teton County from these quakes. A swarm of 16 small earthquakes measuring up to 2.7 shook Yellowstone Park in May 2007. There were no reports of damage in Teton County from this event.

Teton County MHMP 5.12

Regional Historic Seismicity

Teton County is in close proximity to Yellowstone National Park, one of the most volcanically and seismically active regions in the United States. Many known active faults are exposed in the Yellowstone area and thousands of earthquakes have been recorded inside the Park boundaries since the late 1800s. The largest earthquake recorded in this region occurred on August 17, 1959. This magnitude 7.5, intensity X event occurred just outside of Yellowstone National Park, near Hebgen Lake in Montana. The event triggered a landslide that dammed the Madison River and created Earthquake Lake. Twenty-eight people lost their lives; most of them were buried in the campground located directly beneath the landslide. Numerous aftershocks, some as large as magnitude 6.5, occurred within or near Yellowstone National Park. This earthquake is a model for what can occur along the Teton fault in Teton County. The largest earthquake that occurred inside Yellowstone National Park boundaries was on June 30, 1975. This magnitude 6.4, intensity VII event caused landslides and large cracks in the ground.

Several earthquakes have also occurred in the counties near Teton County, beginning in the 1960s. On June 25, 1963, a magnitude 4.2 earthquake occurred in western Park County, approximately 27.5 miles northeast of Moran Junction. No one felt this earthquake. A magnitude 4.3 earthquake was recorded in eastern Idaho on October 11, 1963. No one reported feeling this event, which was located approximately 18 miles southwest of Jackson. A magnitude 4.4 earthquake occurred on October 8, 1966, in northern Lincoln County. This non- damaging earthquake was centered approximately 16 miles southwest of Hoback Junction. This same area experienced a magnitude 3.7 earthquake on October 27, 1966. No one reported feeling the October 1966 earthquakes. The last earthquake to occur in the region in the 1960s took place on February 25, 1969. This non-damaging, magnitude 3.6 event was centered in eastern Idaho, approximately 6 miles north-northwest of Alta.

Four earthquakes were recorded near Teton County in the 1970s. The first occurred on September 21, 1970, in northern Lincoln County near the Elbow Campground, approximately 9 miles south-southwest of Hoback Junction. The Jackson Hole Guide (September 24, 1970) reported that residents from Jackson through the Hoback Canyon to Bondurant felt this magnitude 4.4 earthquake. Some residents from Jackson thought that the event was a sonic boom. At Camp Davis, a resident reported a figurine knocked off a television set and a ―vibrating‖ staircase. Eleven miles south of Jackson, a resident reported rattling windows and a shaking bed. Near Bondurant, in Sublette County, a resident reported that windows rattled and her whole house shook. A magnitude 3.6 earthquake was recorded in southern Yellowstone National Park on April 24, 1974, approximately 9 miles east-northeast of the south entrance to the Park. No one reported feeling this earthquake and no damage was reported. On December 27, 1975, a magnitude 3.1 earthquake occurred in northern Lincoln

Teton County MHMP 5.13

County. Its epicenter was located approximately 12 miles south-southwest of Hoback Junction. No damage was reported from this earthquake.

On January 28, 1980, a magnitude 2.8 earthquake occurred in western Fremont County. No one felt this event, which was centered approximately 25 miles east of Moran Junction. Local residents did feel the earthquake that occurred on February 8, 1983. This magnitude 4.4, intensity V earthquake was located in eastern Idaho, approximately 24 miles southwest of Jackson. No damage was reported. On November 2, 1983, a magnitude 3.5 earthquake was recorded in northern Sublette County, approximately 41 miles east-northeast of Hoback Junction. This event was not felt. In August and September of 1985, four earthquakes occurred in northern Lincoln County, three of which were felt in Jackson. The first, a magnitude 4.8, intensity V event on August 21, 1985, was lightly felt in Jackson. A local business reported that ―it felt like something hit the side of the building‖ (Casper Star-Tribune, August 22, 1985). The second earthquake, a magnitude 4.3, intensity IV event, occurred on August 22, 1985, but was not felt in Jackson. The third, a magnitude 4.3, intensity V event on August 30, 1985, was felt in Jackson, but caused no damage (Laramie Daily Boomerang, August 31, 1985). The last earthquake occurred on September 6, 1985. This magnitude 4.6, intensity V event was felt as an intensity IV earthquake in Wilson. An earthquake-induced landslide temporarily closed a portion of U.S. Highway 89 in the Snake River Canyon (Casper Star-Tribune, September 8, 1985). Two earthquakes occurred in Lincoln County on November 17, 1986, approximately 12 miles south-southwest of Hoback Junction. The first was a magnitude 3.9 event, which was felt by residents in the area. The second, a magnitude 3.7 earthquake, was not felt.

Several earthquakes occurred near Teton County in the 1990s. A magnitude 3.5 event was detected in northern Lincoln County on April 9, 1990. The earthquake, which was located approximately 13 miles south-southeast of Hoback Junction, did not cause any damage. On April 19, 1990, a magnitude 3.3 earthquake was recorded in eastern Idaho, approximately 22 miles west-southwest of Hoback Junction. Residents in the area reported feeling this earthquake as an intensity IV event. The next earthquake that caused any concern occurred on April 3, 1992. The magnitude 4.0, intensity IV earthquake was located in eastern Idaho, approximately 4 miles north-northwest of Alta. Although it was felt as an intensity III event at Moose and Wilson, it did not cause any damage (Casper Star- Tribune, April 4, 1992). On August 22, 1993, approximately 34 miles southeast of Moran Junction, a magnitude 3.1 earthquake occurred in eastern Fremont County. No one reported feeling this event. Another 3.1 earthquake was detected in northern Lincoln County on October 10, 1993. No one felt this earthquake, which was centered approximately 12 miles west-southwest of Hoback Junction. On November 7, 1996, a magnitude 3.8 earthquake was detected in eastern Lincoln County, approximately 4 miles southwest of Alta. Residents in the area reported feeling this earthquake. A magnitude 2.8

Teton County MHMP 5.14

earthquake was detected in eastern Idaho on June 28, 1999. No one reported feeling this event, centered approximately 7.5 miles north-northwest of Alta.

On April 21, 2001, a magnitude 5.4 earthquake occurred in eastern Idaho, approximately 42 miles southwest of Hoback Junction. It was felt as far away as Logan, Ogden, and Salt Lake City, Utah. In Wyoming, it was felt as an intensity V earthquake at Etna, an intensity IV earthquake at Thayne, and an intensity III earthquake at Afton, Jackson, and Wilson. On October 21, 2002, a magnitude 3.2 earthquake was detected approximately 3 miles northeast of Alpine or 16.5 miles southwest of Hoback Junction (U.S. Bureau of Reclamation). This event was followed closely by a magnitude 4.4 earthquake and a magnitude 4.2 earthquake (U.S. Bureau of Reclamation) centered in approximately the same area. Residents in the area reported feeling both of these earthquakes. No damage was reported from either event. On October 23, 2002, a magnitude 3.4 earthquake was reported approximately 4.5 miles north-northeast of Alpine. No one reported feeling this most recent earthquake.

Deterministic Analysis of Regional Active Faults with a Surficial Expression

Several active fault systems are present in Teton County. The Teton fault system is a series of northeast-southwest-trending normal faults located on the eastern edge of the Teton Range near Jackson, Wyoming. While Quaternary/Holocene-aged fault scarps have been identified along the entire length of the fault (Smith et al., 1990a, Wong et al., 2000), much is still unresolved about the Teton fault system. Previous investigations have divided it into northern, central, and southern segments (Smith et al., 1990a; Susong et al., 1987). Other researchers prefer an unsegmented model of the Teton fault (Ostenaa et al., 1988, Byrd et al., 1994). In addition, questions still exist as to whether or not the Beula-Hering Lakes faults in Yellowstone National Park are a northern extension of the Teton fault (Wong et al., 2000). Based upon unsegmented surface rupture lengths (48 miles/77 km including Beula-Hering Lakes faults; 40miles/64km not including Beula-Hering Lakes faults), Wong and others (2000) estimate that the Teton fault is capable of generating a magnitude 6.9 to 7.5 earthquake. This agrees with other analyses, in which a maximum credible earthquake of magnitude 7.5 and a recurrence interval of 800-3600 years were suggested for the Teton fault (Doser and Smith, 1983; Gilbert et al., 1983). A trench on the Teton fault indicated that the fault most recently activated between 4800-7000 years ago (Smith et al., 1993). As a result, Case (1997a) suggests that the Teton fault may be overdue for a magnitude 7.5 earthquake. If a magnitude 7.5 earthquake did occur on the Teton fault, it could potentially generate peak horizontal accelerations of approximately 20%g -21%g at Alta, approximately 20%g at Hoback Junction, approximately 39%g at Jackson, approximately 80%g at Jackson Lake Dam and Jenny Lake, approximately 36%g at Kelly, approximately 62%g at Moose, approximately 23%g at Moran Junction, and greater than 80%g at Wilson (Campbell, 1987). These accelerations are roughly equivalent to intensity IX earthquakes at Jackson Lake Dam, Jenny Lake

Teton County MHMP 5.15

and Wilson, intensity VIII earthquakes at Jackson, Kelly, and Moose, intensity VII earthquakes at Alta, Hoback Junction, and Moran Junction. Jackson Lake Dam, Jenny Lake and Wilson could sustain heavy damage. Heavy to moderate damage could occur at Jackson, Kelly, and Moose, and moderate to heavy damage could occur at Alta, Hoback Junction, and Moran Junction.

The Baldy Mountain fault system is a series of short faults located approximately 21 miles (33 km) east of the Teton fault. Investigators at the U.S.G.S. identified areas where the faults offset Quaternary-aged glacial moraines. No maximum magnitude earthquake has been specifically postulated for the Baldy Mountain fault system. It is generally accepted that a magnitude 6.5 earthquake is required to produce ground surface rupture. While evidence of ground surface rupturing has been identified on the Baldy Mountain fault system, the ground surface rupture length is not consistent with a magnitude 6.5 event. In the interest of public safety, however, this report will model the Baldy Mountain fault system as being capable of generating a magnitude 6.5 earthquake with a recurrence interval of approximately 13,000-25,000 years (Machette et al., 2001; Pierce and Morgan, 1992). A magnitude 6.5 earthquake on this fault system could, in turn, generate peak horizontal accelerations of approximately 3.6%g at Alta, approximately 3.3%g at Hoback Junction, approximately 4.5%g at Jackson, approximately 13%g at Jackson Lake Dam, approximately 8.2%g at Jenny Lake, approximately 7.4%g at Kelly, approximately 7.0%g at Moose, approximately 20%g at Moran Junction, and approximately 3.8 %g at Wilson (Campbell, 1987). These accelerations are roughly equivalent to an intensity VII earthquake at Moran Junction, an intensity VI earthquake at Jackson Lake Dam, intensity V earthquakes at Jackson, Jenny Lake, Kelly, and Moose, and intensity IV earthquakes at Alta, Hoback Junction, and Wilson. Moderate damage could occur at Moran Junction, light damage could occur at Jackson Lake Dam, and very light damage could occur at Jackson, Jenny Lake, Kelly, and Moose. No damage should occur at Alta, Hoback Junction, or Wilson.

The last active fault system in Teton County is the Togwotee Lodge fault system. This series of faults lie in the eastern part of the county, approximately 9 miles (15 km) west of Togwotee Pass. The U.S.G.S. found evidence that Quaternary- aged glacial deposits have been offset along the fault traces, with a recurrence interval of approximately 16,000-23,000 years (Marchette et al, 2001). As with the Baldy Mountain fault system, the Togwotee Lodge faults have a shorter ground surface rupture length than would be produced by a magnitude 6.5 earthquake. The presence of any ruptured ground surface along these faults, however, suggests that they may be capable of producing at least a magnitude 6.5 earthquake. A magnitude 6.5 earthquake on the Togwotee Lodge fault system could generate peak horizontal accelerations of approximately 2.8%g at Alta and Hoback Junction, approximately 3.5%g at Jackson, approximately 8.4%g at Jackson Lake Dam, approximately 5.4%g at Jenny Lake, approximately 6.2%g at Kelly, approximately 5.2%g at Moose, approximately 10.1%g at Moran Junction, and approximately 3.1%g at Wilson (Campbell, 1987). These

Teton County MHMP 5.16

accelerations are roughly equivalent to an intensity VI earthquake at Moran Junction, intensity V earthquakes at Jackson Lake Dam, Jenny Lake, Kelly, and Moose, and intensity IV earthquakes at Alta, Hoback Junction, Jackson, and Wilson. Light damage could occur at Moran Junction, and very light damage could occur at Jackson Lake Dam, Jenny Lake, Kelly, and Moose. No damage should occur at Alta, Hoback Junction, Jackson, or Wilson.

Active fault systems present in the southern portion of Yellowstone National Park may also affect Teton County. Love and Christiansen (1985) describe the Buffalo Fork fault as beginning on the western side of the South Arm of Yellowstone Lake and continuing south to Gravel Mountain in Teton National Forest. This normal fault that reactivated a reverse fault surface offsets the Quaternary Lava Creek Tuff near Channel Mountain (U.S.G.S., 1972). Based upon a maximum surface rupture length of 32 miles (51 km), a maximum credible earthquake of magnitude 7.1 has been postulated for this fault (Wong et al., 2000). No definite recurrence interval has been determined for the Buffalo Fork fault. The U.S.G.S. suggests a long recurrence interval of approximately 10,000 to 100,000 years (Marchette et al., 2001), since at least one event has occurred on the fault since the glaciers receded from the area. A magnitude 7.1 earthquake on the Buffalo Fork fault could potentially generate peak horizontal accelerations of approximately 4.7%g at Alta, approximately 3.6%g at Hoback Junction, approximately 4.8%g at Jackson, approximately 13.5%g at Jackson Lake Dam, approximately 8.4%g at Jenny Lake, approximately 7.8%g at Kelly, approximately 7.2%g at Moose, approximately 17%g at Moran Junction, and approximately 4.3%g at Wilson (Campbell, 1987). These accelerations are roughly equivalent to intensity VI earthquakes at Jackson Lake Dam and Moran Junction, intensity V earthquakes at Alta, Jackson, Jenny Lake, Kelly, Moose, and Wilson, and intensity IV earthquakes at Hoback Junction. Light damage could occur at Jackson Lake Dam and Moran Junction, and Alta, Jackson, Jenny Lake, Kelly, Moose, and Wilson could sustain very light damage. No damage should occur at Hoback Junction.

The Beula-Hering Lakes faults are present east of Hering Lake and extend south into Teton County. They may even be an extension of the Teton fault system (Case, 1997a; Love, 1961; Love et al., 1992; Wong et al., 2000). For this analysis, however, they will be considered as a separate fault system. (See the first paragraph of this section for information related to including the Beula-Hering Lakes faults as part of the Teton fault) The Quaternary-aged Huckleberry Ridge Tuff and Lewis Canyon Rhyolite are displaced by the Beula-Hering Lakes faults. Based upon a maximum surface rupture length of 8 miles (13 km), Wong and others (2000) estimated that a maximum magnitude 6.7 earthquake could result from this fault system. A long recurrence interval is probable, as the most recent event is dated to less than 630,000 years before present (offset of the Lava Creek Tuff), but the 70,000 year old Pitchstone Plateau rhyolite flow is not disturbed by these faults (U.S.G.S., 1972; Marchette et al., 2001). A magnitude 6.7 earthquake on the Beula-Hering Lakes faults could generate peak horizontal

Teton County MHMP 5.17

accelerations of approximately 6%g at Alta, approximately 2.3%g at Hoback Junction, approximately 3.2%g at Jackson, approximately 11%g at Jackson Lake Dam, approximately 7.5%g at Jenny Lake, approximately 4.8%g at Kelly, approximately 5.2%g at Moose, approximately 9%g at Moran Junction, and approximately 3.3%g at Wilson (Campbell, 1987). These accelerations are roughly equivalent to an intensity VI earthquake at Jackson Lake Dam, intensity V earthquakes at Alta, Jenny Lake, Kelly, Moose, and Moran Junction, and intensity IV earthquakes at Hoback Junction, Jackson, and Wilson. Light damage could occur at Jackson Lake Dam. Alta, Jenny Lake, Kelly, Moose, and Moran Junction could sustain very light damage, but no damage should occur at Hoback Junction, Jackson, and Wilson.

The Mount Sheridan-Heart River fault system extends from the Heart Lake Geyer Basin southwest of Yellowstone Lake to near Bobcat Ridge in the Bridger-Teton National Forest. Quaternary-aged movement has been identified along these north-south-trending faults, as they offset the Huckleberry Ridge Tuff in several locations. Based upon a maximum surface rupture length of nearly 26 miles (41 km), a maximum magnitude 7.0 earthquake has been suggested for this fault system (Wong et al., 2000). The U.S.G.S. estimated that because this fault system has a high slip rate (1-5mm/yr), the recurrence interval for the Mount Sheridan-Heart River fault is less than 5,000 years. The age of the most recent events are not known, as no dating has been done on this fault system. A magnitude 7.0 earthquake on the Mount Sheridan-Heart River fault could generate peak horizontal accelerations of approximately 6%g at Alta, approximately 3.2%g at Hoback Junction, approximately 4.4%g at Jackson, approximately 19%g at Jackson Lake Dam, approximately 10%g at Jenny Lake, approximately 7.2%g at Kelly, approximately 7.4%g at Moose, approximately 16.5%g at Moran Junction, and approximately 4.3%g at Wilson (Campbell, 1987). These accelerations are roughly equivalent to an intensity VII earthquake at Jackson Lake Dam, intensity VI earthquakes at Jenny Lake and Moran Junction, intensity V earthquakes at Alta, Jackson, Kelly, Moose, and Wilson, and an intensity IV earthquake at Hoback Junction. Jackson Lake Dam could sustain moderate damage, while Jenny Lake and Moran Junction could sustain light damage. Very light damage could occur at Alta, Jackson, Kelly, Moose, and Wilson. No damage should occur at Hoback Junction.

The Yellowstone River Valley in the southeastern portion of Yellowstone National Park is bounded by several active normal faults. These faults displace Quaternary/Holocene deposits and alluvium along their trace. Based upon a maximum surface rupture length of 14 miles (22 km), these faults could generate a maximum magnitude 6.6 earthquake (Wong et al., 2000). No specific recurrence interval has been determined for these faults. A magnitude 6.6 earthquake on these faults could in turn generate peak horizontal accelerations of approximately 2.1%g at Alta, approximately 1.9%g at Jackson, approximately 4.7%g at Jackson Lake Dam, approximately 3.1%g at Jenny Lake, approximately 2.8%g at Kelly, approximately 2.7%g at Moose, approximately 5.2%g at Moran

Teton County MHMP 5.18

Junction, and approximately 1.9%g at Wilson (Campbell, 1987). These accelerations are roughly equivalent to intensity V earthquakes at Jackson Lake Dam and Moran Junction, and intensity IV earthquakes at Alta, Jackson, Jenny Lake, Kelly, Moose, and Wilson. Very light damage could occur at Jackson Lake Dam and Moran Junction. Alta, Jackson, Jenny Lake, Kelly, Moose, and Wilson should sustain no damage. Hoback Junction would be subjected to ground accelerations of less than 1.5%g, which should not cause any damage.

The Yellowstone Lake fault extends from Dot Island in Yellowstone Lake south to Overlook Mountain. The U.S.G.S. (1972) found evidence that this fault has disturbed Quaternary Lava Creek Tuff and Mount Jackson Rhyolite deposits, as well as lacustrine deposits from Yellowstone Lake. Based upon a maximum surface rupture length of 17.5 miles (28 km), Wong and others (2000) estimated that a maximum magnitude 6.8 earthquake could be generated by this fault. Preliminary investigations of the Yellowstone Lake fault suggest a recurrence interval of approximately 7,000 years for the middle section of the fault (Marchette et al., 2001; Locke et al., 1992). A magnitude 6.8 earthquake could produce peak horizontal accelerations of approximately 3%g at Alta, approximately 2.2%g at Jackson, approximately 6%g at Jackson Lake Dam, approximately 3.9%g at Jenny Lake, approximately 3.2%g at Kelly, approximately 3.3%g at Moose, approximately 5.9%g at Moose, and approximately 2.2%g at Wilson (Campbell, 1987). These accelerations are roughly equivalent to intensity V earthquakes at Jackson Lake Dam, Jenny Lake and Moran Junction, and intensity IV earthquakes at Alta, Jackson, Kelly, Moose, and Wilson. Jackson Lake Dam, Jenny Lake, and Moran Junction could sustain very light damage, but no damage should occur at Alta, Jackson, Kelly, Moose, and Wilson. Hoback Junction would be subjected to ground accelerations of less than 1.5%g, which should not cause any damage.

Two active fault systems are also present near Teton County in northern Lincoln County. The Grey’s River fault system is located in northern Lincoln County on the western side of the Wyoming Range. Evidence of late-Holocene movement has been identified on this north-south-trending normal fault (Jones and McCalpin, 1992; McCalpin, 1993). Based upon an estimated surface rupture length of 54 km, the Grey’s River fault system could potentially generate a magnitude 7.1 earthquake with a recurrence interval of approximately 2970 – 3400 years (Jones, 1995; Jones and McCalpin, 1992). However, because no movement occurred on the Grey’s River fault system between approximately 5000 and 15,000 years before present, this recurrence interval may be variable (Jones and McCalpin, 1992). A magnitude 7.1 earthquake could generate peak horizontal accelerations of approximately 2.8%g at Alta, approximately 9.2%g at Hoback Junction, approximately 5.8%g at Jackson, approximately 2.5%g at Jackson Lake Dam, approximately 3.2%g at Jenny Lake, approximately 4.0%g at Kelly, approximately 3.8%g at Moose, approximately 2.6%g at Moran Junction, and approximately 5.4%g at Wilson (Campbell, 1987). These accelerations are roughly equivalent to an intensity V-VI earthquake at Hoback Junction, intensity

Teton County MHMP 5.19

V earthquakes at Jackson, Kelly, and Wilson, and intensity IV earthquakes at Alta, Jackson Lake Dam, Jenny Lake, Moose, and Moran Junction. Hoback Junction could sustain some light damage, while very light damage could occur at Jackson, Kelly, and Wilson. No damage should occur at Alta, Jackson Lake Dam, Jenny Lake, Moose, or Moran Junction.

The Star Valley fault system is the other active fault system in northern Lincoln County. This fault system, which has been subdivided into north and south segments, bounds the eastern edge of the Star Valley. Investigations of the Star Valley fault system determined that Holocene and late-Pleistocene offsets exist along the south fault segment (Piety et al., 1990; McCalpin et al., 1990; McCalpin, 1990). Several maximum magnitude earthquakes have been suggested for the Star Valley fault system. Piety and others (1986) proposed that the Star Valley fault system is capable of generating a maximum credible earthquake of magnitude 7.5 with a recurrence interval of 5,000 to 7,000 years. Based upon a surface rupture length of 27 miles, McCalpin and others (1990) determined that the Star Valley fault system could produce a maximum magnitude 7.2 earthquake. When McCalpin (1990) trenched a portion of the Star Valley fault near Afton, he determined that a magnitude 7.3 earthquake with a recurrence interval of 2550-6000 years is possible on this system. Because of the extensive seismic activity associated with the area surrounding the Star Valley fault, and because of the close proximity of towns to this fault system, a maximum magnitude of 7.5 will be used for this analysis. It should also be noted that it has been approximately 5500 years since the last confirmed event on the Star Valley fault at Afton. This fault system is therefore nearing its recurrence interval limit. A magnitude 7.5 earthquake could generate peak horizontal accelerations of approximately 7.5%g at Alta, approximately 17%g at Hoback Junction, approximately 14%g at Jackson, approximately 4.8%g at Jackson Lake Dam, approximately 6.7%g at Jenny Lake, approximately 7.8%g at Kelly, approximately 8.2%g at Moose, approximately 4.7%g at Moran Junction, and approximately 15%g at Wilson (Campbell, 1987). These accelerations are roughly equivalent to intensity VI earthquakes at Hoback Junction, Jackson, and Wilson, and intensity V earthquakes at Alta, Jackson Lake Dam, Jenny Lake, Kelly, Moose, and Moran Junction. Hoback Junction, Jackson, and Wilson could sustain light damage, but only very light damage should occur at Alta, Jackson Lake Dam, Jenny Lake, Kelly, Moose, and Moran Junction.

Teton County MHMP 5.20

Floating or Random Earthquake Sources

Federal regulations require analysis of the earthquake potential where active faults are not exposed, and earthquakes are tied to buried faults without surface expression. Regions with a uniform potential for the occurrence of such earthquakes are called tectonic provinces. Within a tectonic province, earthquakes associated with buried faults are assumed to occur randomly, and can theoretically occur anywhere within that area of uniform earthquake potential. In reality, that random distribution may not be the case, as all earthquakes are associated with specific faults. If all buried faults have not been identified, however, the distribution has to be considered random. ―Floating earthquakes‖ are earthquakes that are considered to occur randomly in a tectonic province. It is difficult to accurately define tectonic provinces when there is a limited historic earthquake record. When there are no nearby seismic stations that can detect small-magnitude earthquakes, which occur more frequently than larger events, the problem is compounded. Under these conditions, it is common to delineate larger, rather than smaller, tectonic provinces.

The U.S. Geological Survey identified tectonic provinces in a report titled ―Probabilistic Estimates of Maximum Acceleration and Velocity in Rock in the Contiguous United States‖ (Algermissen and others, 1982). In that report, Teton County was classified as being in a tectonic province with a ―floating earthquake‖ maximum magnitude of 6.1. Geomatrix (1988b) suggested using a more extensive regional tectonic province, called the ―Wyoming Foreland Structural Province‖, which is approximately defined by the Idaho-Wyoming Thrust Belt on the west, 104 West longitude on the east, 40 North latitude on the south, and 45 North latitude on the north. Geomatrix (1988b) estimated that the largest ―floating‖ earthquake in the ―Wyoming Foreland Structural Province‖ would have a magnitude in the 6.0 – 6.5 range.

Federal or state regulations usually specify if a ―floating earthquake‖ or tectonic province analysis is required for a facility. Usually, those regulations also specify at what distance a floating earthquake is to be placed from a facility. For example, for uranium mill tailings sites, the Nuclear Regulatory Commission requires that a floating earthquake be placed 15 kilometers from the site. That earthquake is then used to determine what horizontal accelerations may occur at the site. A magnitude 6.5 ―floating‖ earthquake, placed 15 kilometers from any structure in Teton County, would generate horizontal accelerations of approximately 17%g at the site. That acceleration would be adequate for designing a uranium mill tailings site, but may be too large for less critical sites, such as a landfill. Critical facilities, such as dams, usually require a more detailed probabilistic analysis of random earthquakes. Based upon probabilistic analyses of random earthquakes in an area distant from exposed active faults (Geomatrix, 1988b), however, placing a magnitude 6.5 earthquake at 15 kilometers from a site will significantly underestimate the ground acceleration that may actually occur in Teton County.

Teton County MHMP 5.21

Probabilistic Seismic Hazard Analyses

The U.S. Geological Survey (USGS) publishes probabilistic acceleration maps for 500-, 1000-, and 2,500-year time frames. The maps show what accelerations may be met or exceeded in those time frames by expressing the probability that the accelerations will be met or exceeded in a shorter time frame. For example, a 10% probability that acceleration may be met or exceeded in 50 years is roughly equivalent to a 100% probability of exceedance in 500 years.

The USGS has recently generated new probabilistic acceleration maps for Wyoming (Case, 2000). Copies of the 500-year (10% probability of exceedance in 50 years), 1000-year (5% probability of exceedance in 50 years), and 2,500- year (2% probability of exceedance in 50 years) maps are attached. Until recently, the 500-year map was often used for planning purposes for average structures, and was the basis of the most current Uniform Building Code. The new International Building Code, however, uses a 2,500-year map as the basis for building design. The maps reflect current perceptions on seismicity in Wyoming. In many areas of Wyoming, ground accelerations shown on the USGS maps can be increased due to local soil conditions. For example, if fairly soft, saturated sediments are present at the surface, and seismic waves are passed through them, surface ground accelerations will usually be greater than would be experienced if only bedrock was present. In this case, the ground accelerations shown on the USGS maps would underestimate the local hazard, as they are based upon accelerations that would be expected if firm soil or rock were present at the surface. Intensity values can be found in Table 1.

Although 2,500-year probabilistic acceleration maps are adequate for designing most structures, a more conservative estimate of ground acceleration is usually necessary for dams and associated reservoirs. Wong and others (2000) developed 10,000-year (0.5% probability of exceedance in 50 years) and 50,000- year (0.1% probability of exceedance in 50 years) acceleration models for eastern Idaho and western Wyoming. Because of Jackson Lake Dam’s close proximity to the Teton fault, these more conservative 10,000-year and 50,000- year acceleration models will be used to determine peak horizontal ground accelerations that could occur at Jackson Lake Dam.

Based on the 500-year map (10% probability of exceedance in 50 years), the estimated peak horizontal acceleration in Teton County ranges from approximately 12%g in the southeast to greater than 25%g in the southwest, north-central, and northeast areas. These accelerations are roughly comparable to intensity VI earthquakes (9.2%g – 18%g) and intensity VII earthquakes (18%g – 34%g). Intensity VI earthquakes can result in fallen plaster and damaged chimneys. Intensity VII earthquakes can result in slight to moderate damage in well-built ordinary structures, and considerable damage in poorly built or badly designed structures, such as unreinforced masonry. Chimneys may be broken. Jackson would be subjected to accelerations of over 25%g or intensity VII.

Teton County MHMP 5.22

Based upon the 1000-year map (5% probability of exceedance in 50 years) (Figure 3), the estimated peak horizontal acceleration in Teton County ranges from approximately 17%g in the southeastern portion of the county to over 40%g in the southwestern, south-central, and central portions of the county. These accelerations are roughly comparable to intensity VI earthquakes (9.2%g – 18%g), intensity VII earthquakes (18%g – 34%g), and intensity VIII earthquakes (34%g – 65%g). Intensity VI earthquakes can result in fallen plaster and damaged chimneys. Intensity VII earthquakes can result in slight to moderate damage in well-built ordinary structures, and considerable damage in poorly built or badly designed structures, such as unreinforced masonry. Chimneys may be broken. Intensity VIII earthquakes can result in considerable damage in ordinary buildings and great damage in poorly built structures. Panel walls may be thrown out of frames. Chimneys, walls, columns, factory stacks may fall. Heavy furniture may be overturned. Jackson would be subjected to accelerations of approximately 40%g or intensity VIII.

Based upon the 2500-year map (2% probability of exceedance in 50 years) (Figure 4), the estimated peak horizontal acceleration in Teton County ranges from nearly 30%g in the southeastern corner of the county to over 60%g in the central portions of the county. These accelerations are roughly comparable to intensity VII earthquakes (18%g – 34%g), intensity VIII earthquakes (34%g – 65%g), and possibly intensity IX earthquakes (65%g-124%g). Intensity VI earthquakes can result in fallen plaster and damaged chimneys. Intensity VII earthquakes can result in slight to moderate damage in well-built ordinary structures, and considerable damage in poorly built or badly designed structures, such as unreinforced masonry. Chimneys may be broken. Intensity VIII earthquakes can result in considerable damage in ordinary buildings and great damage in poorly built structures. Panel walls may be thrown out of frames. Chimneys, walls, columns, factory stacks may fall. Heavy furniture may be overturned. Intensity IX earthquakes can cause considerable damage in specially designed structures and great damage and partial collapse in substantial buildings. Well-designed frame structures could be thrown out of plumb. Buildings can be shifted off their foundations. The ground can crack and underground pipes could be broken. Jackson would be subjected to accelerations of approximately 60%g, or intensity VIII, with local accelerations perhaps justifying an intensity IX designation.

Based upon the 10,000-year probabilistic peak horizontal acceleration model (Wong et al., 2000), Jackson Lake Dam would be subjected to accelerations of approximately 89%g, or intensity IX. Intensity IX earthquakes can cause considerable damage in specially designed structures and great damage and partial collapse in substantial buildings. Well-designed frame structures could be thrown out of plumb. Buildings can be shifted off their foundations. The ground can crack and underground pipes could be broken.

Teton County MHMP 5.23

Based upon the 50,000-year probabilistic peak horizontal acceleration model (Wong et al., 2000), Jackson Lake Dam would be subjected to accelerations of approximately 119%g, or intensity IX to X. Intensity IX earthquakes can cause considerable damage in specially designed structures and great damage and partial collapse in substantial buildings. Well-designed frame structures could be thrown out of plumb. Buildings can be shifted off their foundations. The ground can crack and underground pipes could be broken. Intensity X earthquakes can destroy some well-built wooden structures and most masonry and frame structures with foundations. Railroad rails can be bent. Considerable landslides on riverbanks and steep slopes may occur. Sand and mud can shift, and water may splash out over riverbanks.

As the historic record is limited, it is nearly impossible to determine when a 2,500-year, a 10,000-year, or a 50,000-year event last occurred in the county. Because of the uncertainty involved, and based upon the fact that the new International Building Code utilizes 2,500-year events for building design, it is suggested that the 2,500-year probabilistic maps be used for most Teton County analyses. The 10,000-year and 50,000-year probabilistic models should be use for an analysis of Jackson Lake Dam and Reservoir. This conservative approach is in the interest of public safety.

Table 5.1. Modified Mercalli Intensity

Modified Acceleration Perceived Potential Damage Mercalli (%g) Shaking Intensity (PGA) I <0.17 Not felt None II 0.17 – 1.4 Weak None III 0.17 – 1.4 Weak None IV 1.4 – 3.9 Light None V 3.9 – 9.2 Moderate Very Light VI 9.2 – 18 Strong Light VII 18 – 34 Very Strong Moderate VIII 34 – 65 Severe Moderate to Heavy IX 65 – 124 Violent Heavy X >124 Extreme Very Heavy XI >124 Extreme Very Heavy XII >124 Extreme Very Heavy Modified Mercalli Intensity and peak ground acceleration (PGA) (Wald, et al 1999).

Teton County MHMP 5.24

Abridged Modified Mercalli Intensity Scale

Intensity value and description: I Not felt except by a very few under especially favorable circumstances.

II Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing.

III Felt quite noticeably indoors, especially on upper floors of buildings, but many people do not recognize it as an earthquake. Standing automobiles may rock slightly. Vibration like passing of truck. Duration estimated.

IV During the day felt indoors by many, outdoors by few. At night some awakened. Dishes, windows, doors disturbed; walls make creaking sound. Sensation like heavy truck striking building. Standing automobiles rocked noticeably.

V Felt by nearly everyone, many awakened. Some dishes, windows, and so on broken; cracked plaster in a few places; unstable objects overturned. Disturbances of trees, poles, and other tall objects sometimes noticed. Pendulum clocks may stop.

VI Felt by all, many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster and damaged chimneys. Damage slight.

VII Everybody runs outdoors. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable in poorly built or badly designed structures; some chimneys broken. Noticed by persons driving cars.

VIII Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse; great in poorly built structures. Panel walls thrown out of frame structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Sand and mud ejected in small amounts. Changes in well water. Persons driving cars disturbed.

IX Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb; great in substantial buildings, with partial collapse. Buildings shifted off foundations. Ground cracked conspicuously. Underground pipes broken.

X Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations; ground badly cracked. Rails bent. Landslides considerable from river banks and steep slopes. Shifted sand and mud. Water splashed, slopped over banks.

XI Few, if any, (masonry) structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipelines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly. XII Damage total. Waves seen on ground surface. Lines of sight and level distorted. Objects thrown into the air.

Teton County MHMP 5.25

Figure 5.2 500-year probabilistic acceleration map (10% probability of exceedance in 50 years).

Teton County MHMP 5.26

Figure 5.3 1,000-year probabilistic acceleration map (5% probability of exceedance in 50 years).

Teton County MHMP 5.27

Figure 5.4 2,500-year probabilistic acceleration map (2% probability of exceedance in 50 years).

Teton County MHMP 5.28

Impacts

There have been numerous historic earthquakes with a magnitude greater than 2.0 recorded in and near Teton County. Because of the limited historic record, it is possible to underestimate the seismic hazard in Teton County if historic earthquakes are used as the sole basis for analysis. Earthquake and ground motion probability maps and specific fault analyses give a more reasonable estimate of damage potential in Teton County.

Current earthquake probability maps that are used in the newest building codes suggest a scenario that would result in moderate to heavy damage to buildings and their contents, with damage increasing from the southeast to the west and north-central. More specifically, the probability-based or fault activation-based worst-case scenario could result in the following damage at points throughout the county:

Intensity X Earthquake Areas

Jackson Lake Dam

Intensity X earthquakes can destroy most masonry and frame structures with foundations and some well-built wooden structures. Railroad rails can be bent. Considerable landslides on riverbanks and steep slopes may occur. Sand and mud can shift, and water may splash out over riverbanks.

Intensity IX Earthquake Areas

Hoback Junction Jackson (in certain areas) Jenny Lake Moose Teton Village Wilson

Intensity IX earthquakes can cause considerable damage in specially designed structures and great damage and partial collapse in substantial buildings. Well- designed frame structures could be thrown out of plumb. Buildings can be shifted off their foundations. The ground can crack and underground pipes could be broken.

Intensity VIII Earthquake Areas

Kelly Jackson Moran Junction

Teton County MHMP 5.29

Intensity VIII earthquakes can result in considerable damage in ordinary buildings and great damage in poorly built structures. Panel walls may be thrown out of frames. Chimneys, walls, columns, factory stacks may fall. Heavy furniture may be overturned.

Potential Future Damage Impacts

HAZUS (Hazards U.S.) is a nationally standardized, GIS-based, risk assessment and loss estimation computer program that was originally designed in 1997 to provide the user with an estimate of the type, extent, and cost of damages and losses that may occur during and following an earthquake. It was developed for the FEMA by the National Institute of Building Sciences (NIBS). There have been a number of versions of HAZUS generated by FEMA, with HAZUS-MH (HAZUS – Multi-Hazard) being the most recent release. HAZUS-MH incorporates a flood and wind module with the previously existing earthquake module. Hazus-99 (1999 version) was previously used by the Wyoming State Geological Survey (WSGS).

HAZUS was originally designed to generate damage assessments and associated ground motions based largely upon analysis at the census-tract level. Census tracts average 4,000 inhabitants, with the tract boundaries usually representing visible features. HAZUS-99 calculated a ground motion value for the centroid of a census tract, and applied that value to the entire tract. The calculations are based on United States Geological Survey National Seismic Hazard Maps. In many of the western states, census tracts are very large, and parts of the tracts may be subjected to ground shaking that is considerably different than the value at the centroid. FEMA Region VIII and their subcontractor on HAZUS, PBS&J from Atlanta, have worked closely with the Wyoming State Geological Survey (WSGS) to develop a census-block-based analysis for HAZUS-MH in Wyoming. In fact, Wyoming is the national pilot project for the census-block-based analysis. The block-level analysis is a significant improvement. Census blocks are a subdivision of census tracts. Many blocks correspond to individual city blocks bounded by streets, but blocks – especially in rural areas – may include many square miles and may have some boundaries that are not streets. Ground motion values for Wyoming are now calculated at the centroid of census blocks.

Teton County MHMP 5.30

As part of the development of the State of Wyoming Multi-Hazard Mitigation Plan a HAZUS probabilistic scenario was run for every Wyoming County. The scenario used a 2,500 year return period, and uses the USGS ground shaking data represented in figure 5.4. The probability of such an event is 2% in 50 years. Lincoln County used a driving Magnitude of 7.5 associated with the scenario. The results are presented in Tables 5.2 through 5.4

There are two methods to rank the counties to determine where earthquake impacts may be the greatest. Either the loss ratios (Table 5.3) or total damage (Table 5.4) figures can be used. The loss ratio is determined by dividing the sum of the structural and non-structural damage by the total building value for the county. The loss ratio is a better measure of impact for a county as it gives an indication of the percent of damage to buildings. The total damage figure by itself does not reflect the percentage of building damage. If a county has a number of valuable buildings, such as Laramie County, small damage to a number of valuable buildings may result in a higher total damage figure that may be found in a county with fewer, less expensive buildings, with a higher percentage of damage.

Teton County MHMP 5.31

Table 5.2. Earthquake Potential Losses Loss Total Loss Capital Stock Losses Income Losses County Ratio (Thousands (Thousands of Dollars) (Thousands of Dollars) (%) of Dollars) Non- Capital- Structural Contents Inventory Relocation Wages Rental Loss structural Related Albany 9,714 36,865 13,946 151 2.32 276 2,717 3,198 4,210 71,078 Big Horn 3,470 12,203 4,647 65 2.43 84 533 694 963 22,660 Campbell 5,116 20,093 9,419 282 1.37 144 1,484 2,013 1,592 40,144 Carbon 7,140 26,320 10,480 170 3.08 190 2,120 2,700 1,810 50,920 Converse 6,054 24,172 9,787 185 4.15 152 984 1,303 1,845 44,482 Crook 836 2,640 896 17 1.04 21 107 139 211 4,867 Fremont 14,890 61,030 24,640 460 3.75 380 2,920 3,940 3,190 111,450 Goshen 2,168 6,982 2,543 69 1.13 57 392 528 623 13,364 Hot Springs 3,038 10,871 4,176 52 4.20 82 799 1,149 969 21,136 Johnson 3,293 13,062 5,514 94 3.40 86 557 648 1,066 24,320 Laramie 13,605 47,839 17,577 233 1.25 406 3,926 4,402 4,976 92,963 Lincoln 65,670 225,594 64,429 2,538 31.08 1,211 8,579 10,359 15,347 391,727 Natrona 36,764 137,379 57,269 1,149 3.99 981 9,890 13,033 12,245 268,911 Niobrara 423 1,585 617 12 1.20 12 72 83 132 2,935 Park 11,430 42,694 15,289 429 2.98 285 5,173 6,217 4,487 86,004 Platte 1,875 6,894 2,697 36 1.60 51 326 418 554 12,850 Sheridan 7,830 29,154 12,057 233 2.09 213 1,898 2,402 2,636 56,423 Sublette 9,654 30,667 9,436 222 8.24 206 2,438 3,052 2,665 58,340 Sweetwater 12,782 50,213 20,753 542 2.84 313 2,180 2,514 3,719 93,017 Teton 92,477 359,169 110,323 2,402 24.72 1,821 37,784 43,975 34,030 681,981 Uinta 39,912 135,111 38,841 1,007 15.84 782 5,888 8,741 11,004 241,284 Washakie 4,115 13,761 5,656 134 3.54 99 904 1,019 1,236 26,925 Weston 897 3,016 1,085 21 0.96 26 147 266 302 5,760

Teton County MHMP 5.32

Table 5.3 County Impact Rated by Loss Ratio Total Loss Loss County (Thousands of Ratio Dollars) 1. Lincoln 31.08 391,727 2. Teton 24.72 681,981 3. Sublette 8.24 58,340

Table 5.4 County Impacts Rated by Dollar Loss Total Loss Loss County (Thousands of Dollars) Ratio 1. Teton 681,981 24.72

In summary, Teton County is one of the, if not the most at-risk county in Wyoming when it comes to earthquakes. It is estimated that if a worst-case event occurred in Teton County, $681 million in building related damage could occur. HAZUS estimates that 3,222 buildings (64% of the total in the county), would be at least moderately damaged. An estimated 379 buildings would be completely destroyed. The probability of such an event is 2% in 50 years.

Summary

PROPERTY AFFECTED: High POPULATION AFFECTED: High PROBABILITY: Medium JURISDICTION AFFECTED: All

Teton County MHMP 5.33

Chapter 6. Floods

A flood, as defined by the National Flood Insurance Program, is a general and temporary condition of partial or complete inundation of two or more acres of normally dry land area or of two or more properties from: overflow of waters; unusual and rapid accumulation or runoff of surface waters from any source; or, a mudflow. Floods can be slow or fast rising, but generally develop over a period of many hours or days.

Floods can also occur with little or no warning and can reach full peak in only a few minutes. Such floods are called flash floods. A flash flood usually results from intense storms dropping large amounts of rain within a brief period. Floods can occur for reasons other than precipitation or rapidly melting snow. They can also occur because of ice jams.

According to the National Flood Insurance Program Community Status Book Teton County joined the NFIP in 1989. Details on NFIP participation and flood map status are provided in the table below.

Table 6.1. NFIP Status Community Date of entry into Current effective map date program Teton County 5/4/89 5/4/89 unicorp. areas Jackson 5/4/89 5/4/89

Sources of flooding in Teton County include the Snake River, Gros Ventre River, Hoback River, Cache Creek, Flat Creek, and other small creeks and drainages.

History

The documented flood history for Teton County is limited and extends back to 1981. The abbreviated flood history in Table 6.2 below was in large part derived from the monthly Storm Data reports generated and released by the National Oceanic and Atmospheric Administration’s National Climate Center. Other sources are unpublished reports from the Wyoming Office of Homeland Security, newspaper accounts, and periodicals from public libraries. The table represents floods that have caused damage, injuries, or loss of life. There is not enough flood data for the county to calculate how often damaging floods occur.

6..1

Table 6.2 Teton County Flood Data County Location Start Date Deaths Injuries Prprty Dmg Crop Dmg Total Dmg Information

18-Aug Teton Jackson 0 0 Unknown 0 Unknown Flash flood three miles S-SW of Jackson flooded one basement. 2007 Heavy rain (1-1.5 inches/hour) caused at least nine mud and rock slides. Closed Hoback 17-Aug Teton 0 0 Unknown 0 Unknown US191 around Sublette-Teton County line. Guard rail destroyed. Mud 3-5 feet Junction 2007 deep. Flash flood from heavy rain in Jensen Canyon closed Fish Creek Road and left at least one man stranded in his house. Road closed to traffic and an Incident Jensen 26-July Teton 0 0 unknown 0 unknown Command Center was set up. Earth and debris including trees, boulders, and mud Canyon 2007 were transported enveloping one house. Private road to the house was washed out and two cars tipped over. Flooding caused by 2-3 inches of rain in three hours. Countywide, One bridge and part of road damaged; levee erosion; dam estimated at $290,000; Teton upper Snake 1-Jun-1981 0 0 $290,000 $0 $290,000 total damages prevented by local flood protection projects River

Teton County MHMP 6.2

Impacts

The flood history above shows that damaging floods have occurred occasionally in Teton County, and that flood mitigation has helped reduce losses. Dams on the Snake River have largely addressed downstream flooding of the Snake in the valley bottom. Flash floods with associated debris flows remain the primary concern in the county. Fortunately, there has been no loss of life or any significant injury caused by floods in the county, with the exception of the Gros Ventre Slide dam failure incident discussed in the Dam Failure section.

Flood of Record for Future Impacts

The June 1, 1981 flood, as the most damaging event recorded, can be considered the flood of record for Teton County. As a result of adjusting the dollar losses to a 2004 equivalent, the damage sum is $631,000, which can be used as an estimate of the expected damages for future major flood events in Teton County. There is potential for larger floods to occur in the region.

Building Values within Floodplains

There is another method that can be used to rank counties for their flood impact potential. The Wyoming State Geological Survey has estimated the building exposure value for buildings that may occur within a floodplain. All Flood Insurance Rate Maps (FIRMs) for Wyoming have been digitized. The flood boundaries on the maps have then been digitally crossed with Census block building values. In some cases, a floodplain boundary will dissect a census block. In that case the proportional value of buildings in the census block will be assigned to the floodplain.

If a census block is within a floodplain, then the values of all the buildings in the census block is assigned. Figure 6.1 shows the floodplains that have been mapped on Flood Insurance Rate Maps. Figure 6.2 and Table 6.3 show the building exposure values estimated for those floodplain areas.

Table 6.3 FIRM Building County Exposure Value (USD) 1. Teton 597,409,650

Teton County MHMP 6.3

Figure 6.1 Wyoming FIRM Coverage

Teton County MHMP 6.4

Figure 6.2 Wyoming FIRM Exposure

Teton County MHMP 6.5

Small floods are likely to occur in Teton County, mostly in the unincorporated areas. The result of the exposure analysis summarizes the values at risk in the floodplain. Based on this GIS analysis, Teton County has roughly $597 million in building value that could be exposed to flooding, the highest in the State of Wyoming. When a flood occurs seldom does the event cause total destruction. Potential losses from flooding are related to a variety of factors including flood depth, flood velocity, building type and construction. Based on Flood Insurance Administration (FIA) flood Dept-Damage curves the percent of damage is directly related to the flood depth. FEMA’s flood benefit/cost module uses this simplified approach to model flood damage based on building type and flood depth. A damage estimation of 20 percent of the total value was used based on FEMA FIA Depth-Damage curves based assumption of damage of at least 22 percent of the value of the structure and 20 percent of the contents value to a one-story structure with no basement flooded to two feet. While there are several limitations to this model, it does present a methodology to estimate potential damages. By multiplying the building exposure value by 20%, based on this assumption, expected 100 year flood damages would be roughly $119 million for the County. There is a 1% chance of these damages occurring in any given year.

Summary

PROPERTY AFFECTED: High POPULATION AFFECTED: Low PROBABILITY: Low JURISDICTION AFFECTED: Jackson, unincorporated areas of the county

Teton County MHMP 6.6

Chapter 7. Hail

Hail causes more than a billion dollars of property damage nationally each year, mostly to crops. The southeast corner of Wyoming lies within the nations “Hail Alley”. While Teton County is not in “Hail Alley”, damaging hail storms have still occurred.

History

There have been three damaging hail storms in Teton since 1959, which equates to a damaging hail storm about every 15 years. Table 7.1 presents a history of documented, damaging hail storms. The data were derived from the monthly Storm Data reports generated and released by the National Oceanic and Atmospheric Administration’s National Climate Center. Other sources are unpublished reports from the Wyoming Office of Homeland Security, newspaper accounts, and periodicals from public libraries. The table represents hail storms that have caused damage, injuries, or loss of life plus two recent storms without documented damage. Fortunately there have been no documented injuries or loss of life from hail in Teton County.

Teton County MHMP 7.1

Table 7.1 Damaging Hail Storms Estimated Estimated Character of County Location Start Date Deaths Injured Damage- Damage- Information Storm Property Crops Teton Jackson 15-Aug-1960 $27,500 $27,500 Hail Park and Yellowstone Hail up to 1.25 inches diameter and up to 4 inches deep in the Hayden 20-Jun-1977 0 0 $275,000 $0 Hail Teton Park Valley area caused damage to campers, trailers, tents, etc. Some unusually severe thunderstorms swarmed over northwest Wyoming during the afternoon. One of the first indications of these severe thunderstorms was the 60 MPH wind gusts reported by a radio station in Jackson at 1300 MST. As these severe thunderstorms moved northeast additional reports of hail between 1 and 2.25 inches in diameter were observed along with winds gusting above 58 MPH. Also, torrential rains were noted from Jackson northeast to Cody. When these severe thunderstorms moved northeast of Jackson over the Teton Wilderness Area it spawned the highest elevation F4 tornado ever documented. The devastating winds from the tornado produced a massive blow down of 15,000 acres of mostly mature lodge pole pines Teton Teton Village 21-Jul-1987 0 0 $27,500 $0 Hail (2.25) which ranged from 80 to 100 feet tall. The massive blow down stretched slightly over 24 miles from Box Creek Trailhead, 10 miles east-northeast of Moran Junction, on the south to beyond the Yellowstone River on the north and was about 1 to 2 miles wide, 2.5 miles at the widest. An eyewitness to the blow down stated, "You could look up a hillside where there had been a dense forest and count the trees left standing." Later, as these severe thunderstorms moved over the East Entrance of Yellowstone National Park, torrential rains produced mudslides which closed highways for a few hours. The Park County sheriff reported that some of these mudslides buried about 50 yards of highway to a depth of 2 feet. Golf-ball size hail fell on Jackson. Damaged numerous cars, ripped Teton Jackson 14-Jun-2006 0 0 Unknown 0 Hail tree limbs and leaves. Blocked storm drains causing minor flooding. Thunder- Thunderstorm produced 1-inch diameter hail in Jackson. No reported Teton Jackson 5-Aug-2007 0 0 0 0 storm with damages. hail Teton Jackson 18-Aug-2007 0 0 0 0 Hail Hail fell on South Park area for 10 minutes. No damages reported.

Teton County MHMP 7.2

Impacts

Hail storms have occurred in every county in Wyoming, although hail damage has only occurred in twenty-two counties. Sublette and Uinta counties have no recorded hail damage. Figure 7.1 below shows the distribution of the number of hail storms, number of deaths and injuries, and amount of crop and property damage in reported dollars. The total documented hail damage for Teton County is $82,500 in year of damage dollars and $393,350 in 2004 dollars.

Figure 7.1 Hail Damages by County

Teton County MHMP 7.3

Table 7.2 Hail Damage (2004 Dollars)

Hail Dollar Damage: County 2004 Dollars 19. Teton 393,350 State total $556,400,914

Future Impacts

Teton County, based on past events, will continue to occasionally experience damaging events, based on a recurrence interval of every 15 years. Based on the past documented storm damage (August 15, 1960 - $55,000) converted to 2004 dollars it is suggested that $340,000, at a minimum, be used as the potential cost of the worst-case future hail storm in Teton County. Future hail storms could impact private and public property such as cars, roofs, equipment, buildings, hay crops, and livestock.

Summary

PROPERTY AFFECTED: Medium POPULATION AFFECTED: Medium PROBABILITY: Low JURISDICTION AFFECTED: All

Teton County MHMP 7.4

Chapter 8. Hazardous Materials

A general definition of hazardous material is: A substance or combination of substances which because of its quantity, concentration, or physical, chemical or infectious characteristics, may either (1) cause, or significantly contribute to, an increase in mortality or an increase in serious, irreversible, or incapacitating reversible, illness; or (2) pose a substantial present or potential hazard to human health or environment when improperly treated, stored, transported, disposed of or otherwise managed.

The US Department of Transportation, U.S. Environmental Protection Agency, and the Occupational Health and Safety Administration all have responsibilities in regards to hazardous materials and waste. Presented below are the various definitions and general responsibilities of each of the agencies.

The U.S. Department of Transportation, which has control over transported hazardous materials, uses the following definition: Hazardous material means a substance or material that the Secretary of Transportation has determined is capable of posing an unreasonable risk to health, safety, and property when transported in commerce, and has designated as hazardous under section 5103 of Federal hazardous materials transportation law (49 U.S.C. 5103). The term includes hazardous substances, hazardous wastes, marine pollutants, elevated temperature materials, materials designated as hazardous in the Hazardous Materials Table (see 49 CFR 172.101), and materials that meet the defining criteria for hazard classes and divisions in part 173 of subchapter C of this chapter. The U.S. DOT has nine classes of hazardous material:

Explosives Compressed Gasses: Flammable Gasses; Non-Flammable Compressed Gasses; Poisonous Gasses Flammable Liquids: Flammable (Flash Point Below 141 degrees); Combustible (Flash Point 141 degrees – 200 degrees) Flammable Solids Flammable Solids; Spontaneously Combustible; Dangerous When Wet Oxidizers and Organic Peroxides: Oxidizer; Organic Peroxide Toxic Materials: Material that is Poisonous; Infectious Agents Radioactive Material Corrosive Material: Destruction of Human Skin; Corrode Steel at a Rate of 0.25 Inches Per Year Miscellaneous

Teton County MHMP 8.1

The U.S. Environmental Protection Agency also has responsibility for hazardous materials, chemicals, and wastes that have the potential to be released into the environment through stationary facilities. The Environmental Protection Agency (EPA) addresses through the Resource Conservation and Recovery Act (RCRA), the need for facilities with hazardous waste substances to store containers in some kind of containment system. Stationary containers, such as tanks, as well as portable storage containers, such as 55-gallon drums, are required to have a system that will protect the environment from this waste if a leak were to occur. Hazardous waste regulations appear in Title 40 of the Code of Federal Regulations. Portable container containment is addressed under Subpart I, Use and Management of Containers (EPA 40 CFR 264.175). Facilities dealing with the storage of hazardous materials may also be required to have containment if they are to meet the Uniform Fire Code (UFC) standards. Within the UFC standards, Section 80, Division III refers to Hazardous Materials Storage Requirements pertaining to containers and tanks and Division IV refers to Spill Containment with regard to hazardous materials.

The Emergency Planning and Community Right-to-Know Act (EPCRA) requires certain regulated entities to report information about hazardous chemicals and substances at their facilities to federal, state, and local authorities. The objective is to improve the facilities, or government agency's ability to plan for and respond to chemical emergencies, and to give citizens information about chemicals present in their communities. The President has issued Executive Orders to federal agencies that mandate their compliance with certain EPCRA requirements. Part of EPA's mission is to ensure that Federal facilities comply with these requirements. Sections 301 and 303 of EPCRA mandate the creation of two organizations; The State Emergency Response Commission (SERC) and the Local Emergency Planning Committee (LEPC). Sections 311-312 of EPCRA require facilities to submit material safety data sheets or Tier II forms (lists of hazardous chemicals on-site (above threshold quantities)) to SERC’s, LEPC’s, and local fire departments.

In addition to EPCRA, there is a Risk Management Program. When Congress passed the Clean Air Act Amendments of 1990, it required EPA to publish regulations and guidance for chemical accident prevention at facilities using extremely hazardous substances. The Risk Management Program Rule (RMP Rule) was written to implement Section 112(r) of these amendments. The rule, which built upon existing industry codes and standards, requires companies of all sizes that use certain flammable and toxic substances to develop a Risk Management Program, which includes a(n):

Hazard assessment that details the potential effects of an accidental release, an accident history of the last five years, and an evaluation of worst-case and alternative accidental releases; Prevention program that includes safety precautions and maintenance, monitoring, and employee training measures; and Teton County MHMP 8.2

Emergency response program that spells out emergency health care, employee training measures and procedures for informing the public and response agencies (e.g the fire department) should an accident occur.

By June 21, 1999, a summary of the facility's risk management program (known as a "Risk Management Plan" or "RMP") was to be submitted to EPA, which will make the information publicly available. The plans must be revised and resubmitted every five years.

The Risk Management Program is about reducing chemical risk at the local level. This information helps local fire, police, and emergency response personnel (who must prepare for and respond to chemical accidents), and is useful to citizens in understanding the chemical hazards in communities. EPA anticipates that making the RMPs available to the public stimulates communication between industry and the public to improve accident prevention and emergency response practices at the local level.

The Occupational Safety and Health Administration (OSHA), established under the Department of Labor by the OSHA Act of 1970, regulates the storage and use of toxic and hazardous substances as they relate to worker health and safety. OSHA regulations are found in Title 29 of the Code of Federal Regulations (CFR), Part 1910, Subpart H.

History

Three 50-gallon drums full of diesel fuel spilled and hit oncoming traffic on October 29, 2006, on Togwotee Pass. No one was injured, but one lane of traffic was closed for about an hour while hazardous material crews cleaned up the spill.

According to the ―Wyoming State Emergency Response Commission 2003 Annual Report‖, there were a total of 4 hazardous material spills reported in Teton County in 2003. There were 3 reported spills in 2004. The majority of the spills statewide in both years were related to petroleum production.

Impacts

Hazardous material spills occur every year in the state and almost every year in Teton County. To date, there has not been a large-scale spill or release documented in Teton County. There are not readily available data on response and cleanup costs. It is estimated that the costs of cleaning up a serious spill could be many tens of thousands of dollars.

Teton County MHMP 8.3

Future Impacts

Hazardous material spills will continue in Wyoming and the rest of the nation. There are some facilities, however, that contain extremely hazardous substances. There are no Risk Management Plan facilities present in Teton County and no extremely hazardous materials generated in the county. It is not known how many trucks carrying hazardous materials and what type of materials are passing through Teton County at this time. In the event of a hazardous material incident, the closest response team would be deployed from Rock Springs—requiring several hours to arrive depending on travel conditions and mode or travel. No additional information is available for this report because of Homeland Security concerns.

Summary

PROPERTY AFFECTED: Low POPULATION AFFECTED: Medium PROBABILITY: Medium JURISDICTION AFFECTED: Jackson and county

Teton County MHMP 8.4

Chapter 9. Landslides

Landslides are one of the most common geologic hazards in Wyoming, with some of the highest landslide densities in the country found in the State. The figure below shows mapped landslides in Wyoming.

Figure 9.1. Mapped Landslides in Wyoming

There are many types of landslides present in Wyoming. In order to properly describe landslide type, the Geologic Hazards Section developed a landslide classification modified from Varnes (1978) and Campbell (1985). As can be seen in Figure 9.2 there are five basic types of landslides that occur in three types of material. Falls, topples, slides, lateral spreads, and flows can occur in bedrock, debris, or earth. While individual landslide types can occur in nature, most landslides are complex, or composed of combinations of basic types of landslides.

Teton County MHMP 9.1

Figure 9.2 Wyoming Landslide Classification

Landslide History and Distribution

Numerous landslides are present in Teton County. Specifically, landslides are present on the following quadrangles:

Angle Mountain Darwin Peak Bailey Lake Davis Hill Blue Miner Lake Doubletop Peak Bull Creek Driggs Burnt Mountain Grand Teton Cache Creek Granite Basin Camp Davis Granite Falls Cave Falls Gravel Mountain Clause Peak Green Mountain Colter Bay Grizzly Lake Crater Lake Gros Ventre Junction Crystal Peak Hominy Peak

Teton County MHMP 9.2

Huckleberry Mountain (15’) Rammel Mountain Jackson Ranger Peak Jenny Lake Rendezvous Peak Joy Peak Rosies Ridge Lava Mountain Shadow Mountain Mc Renolds Reservoir Sheridan Pass Moose Survey Peak Moran Teton Pass Mosquito Lake Teton Village Mount Baird Togwotee Pass Mount Bannon Tripod Peak Mount Hancock (15’) Turquoise Lake Mount Leidy Two Ocean Lake Mount Moran Two Ocean Pass (15’) Munger Mountain Upper Slide Lake Observation Peak Victor Ouzel Falls Warm River Butte (15’) Palisades Peak Whetstone Mountain Pine Creek

The Wyoming State Geological Survey and Teton County Emergency Management examined all quadrangles, and the following areas were determined to pose a potential hazard to homes, roads, or other facilities.

Impacts

Angle Mountain Quadrangle: U.S. Highway 26/287 passes by or through several landslides, including blockslide/rockslide/flow, alluvial fan/debris flow, debris flow/flow, and slump/flow complexes. If these landslides destabilize, damage could occur to the highway. Secondary roads off the highway are also at risk of being damaged if the nearby slump/flow, rockslide/flow, flow, and blockslide/flow complexes destabilize. Buffalo Fork River, South Buffalo Fork River, Black Rock Creek, and the North Fork Spread Creek could be dammed by the, slump/flow, blockslide/flow, blockslide/ rockslide/flow, rockslide/flow, blockslide/rockslide/ flow/debris flow, or debris flow/Quaternary alluvium complexes that are present on the south side of the rivers. Heavy periods of precipitation or significant development could have an effect on slope stability.

Blue Miner Lake Quadrangle: Flat Creek could potentially be dammed by the debris flow/alluvial fan, debris flow/talus flow, rockslide/flow, debris flow/flow, blockslide/rockslide/flow/Quaternary terrace, and talus flow/flow/debris flow complexes that are present along the creek. In addition, Flat Creek Ranch is located on a talus flow/flow/debris flow complex. If this landslide destabilizes, damage could occur to ranch structures. Heavy periods of precipitation or significant development could have an effect on slope stability.

Teton County MHMP 9.3

Bull Creek Quadrangle: U.S. Highway 187/189 passes through several landslides in the southwestern portion of the quadrangle. If these landslides (which include rockslide/Quaternary terrace, Quaternary terrace/rockslide/debris flow, rockslide/flow, rockslide/debris flow, blockslide/slump/flow, rockslide/debris flow/alluvial fan, and rockslide/flow/debris flow complexes) destabilize, damage could occur to the highway, either directly or by flooding if the landslides dam the Hoback River. Although the southeast corner of the quadrangle is in Sublette County, landslide dams or a damaged/destroyed highway in that area would have a significant impact on Teton County. Hoback Campground structures could also be damaged if the landslides in this area destabilize. In addition, the secondary road in the east-central portion of the quadrangle could be damaged if the nearby debris flow/surface wash, debris flow/Quaternary alluvium, rockslide/flow, or debris flow/alluvial fan complexes reactivate. Finally, Bull Creek, Granite Creek, and Little Granite Creek could be dammed if any of the landslides along the creeks destabilize. This could damage structures near Little Granite Creek in T39N R114W Section 27. Heavy periods of precipitation or significant development could have an effect on slope stability.

Cache Creek Quadrangle: Flow, slump/flow, and colluvium/rockslide/flow complexes are present in the northwestern corner of the quadrangle near the town of Jackson (T41N R116W Sections 34 and 35). If these landslides destabilize, damage could occur to structures and roads in Jackson, some of which have been built on top of these landslides. Cache Creek could also be dammed if the colluvium`/rockslide/flow, rockslide/slump/flow, blockslide/rockslide/flow, rockslide/flow, or debris flow/alluvial fan landslide complexes located along the creek reactivate. A rupture of a landslide dam could, in turn, cause flooding in Jackson. Several landslides, including slump/flows, flow, and blockslides are present in the southwestern corner of the quadrangle (T40N R116W Section 34; T39N R116W Section 3). If these landslides reactivate, damage could occur to U.S. Highway 26/89 or the secondary road, either directly or by flooding if the landslides dam the Snake River. Heavy periods of precipitation or significant development could have an effect on slope stability.

Camp Davis Quadrangle: Numerous landslides are present on this quadrangle. If any of the landslides along U.S. Highway 26/89 or U.S. Highway 187/189 destabilize, damage could occur to the highways, secondary roads, and structures along the highways, either directly or by flooding if the landslides dam the Hoback or Snake Rivers. A large blockslide/slump/flow complex is located in the southeastern corner of the quadrangle. If this landslide destabilizes, damage could occur to Camp Davis (T38N R115W Section 5), nearby structures, and nearby secondary roads. Heavy periods of precipitation or significant development could have an effect on slope stability.

Colter Bay Quadrangle: A slump/flow complex is present in the northern portion of the quadrangle. U.S. Highway 89/287 passes through this landslide. If the landslide were to reactivate, damage could occur to the highway. Heavy periods of precipitation or significant development could have an effect on slope stability.

9.4

Crystal Peak Quadrangle: Numerous rockslide/flow, rockslide/flow/debris flow, debris flow/alluvial fan, and rockslide/alluvium complexes are present along Granite Creek. If any of the landslides destabilize, they could dam the creek. Heavy periods of precipitation or significant development could have an effect on slope stability.

Darwin Peak Quadrangle: A rockslide/flow complex is present along the Gros Ventre River near Chateau Lake. If it destabilizes, it could dam the Gros Ventre River. Heavy periods of precipitation or significant development could have an effect on slope stability.

Davis Hill Quadrangle: A slump/flow complex is located in T45N R114W Section 25. If this landslide destabilizes, damage could occur to U.S. Highway 26/287. Damage could also occur to the Buffalo Valley road in T45N R113W Sections 22 and 23 if the blockslide/terrace or rockslide/flow complexes in these sections destabilizes. In addition, if the large blockslide/rockslide/slump/flow, rockslide/flow, flow, and slump/flow complexes in the southern portion of the quadrangle destabilize, they could dam Spread Creek. Heavy periods of precipitation or significant development could have an effect on slope stability.

Granite Basin Quadrangle: Several landslides, including debris flow/alluvial cone and blockslide/rockslide/flow/debris flow complexes are present along Teton Creek in the southern portion of the quadrangle. If these landslides activate, damage could occur to the nearby road. Campgrounds in this area may also be at risk of being damaged. Heavy periods of precipitation or significant development could have an effect on slope stability.

Granite Falls Quadrangle: Numerous slump/flow, debris flow/alluvial fan, debris flow/flow/alluvial fan, flow/alluvial fan, slump, debris flow, debris flow/alluvial cone, slump/flow/debris flow/alluvial cone, and rockslide/talus flow/flow complexes are present along Granite Creek. If any of these landslides destabilize, damage could occur to the road that parallels Granite Creek, and which crosses through several of the landslides. The Granite Creek campground could also sustain damage if the debris flow/alluvial fan complex on which it is built destabilizes. In addition to being directly damaged, the road and campground could be flooded if the landslides dam Granite Creek. Heavy periods of precipitation or significant development could have an effect on slope stability.

Grizzly Lake Quadrangle: Several landslides, including slump/flow, slump, rockslide/flow, debris flow/alluvial fan/surface wash, blockslide/rockslide/flow, rockslide/flow, and flow complexes are present in the northern portion of the quadrangle. If any of these landslides activate, damage could occur to the road and/or campgrounds near the Gros Ventre River. If any of the landslides dam the Gros Ventre River, the road and campground structures could also be flooded. Heavy periods of precipitation or significant development could have an effect on slope stability.

9.5

Gros Ventre Junction Quadrangle: A blockslide and a blockslide/flow complex are present in T41N R116W Sections 10 and 15. If these landslides destabilize, damage could occur to U.S. Highway 26/89/187. In addition, a road passes through the debris flow/alluvial fan/Quaternary alluvium complex in T41N R116W Section 23 and 24. If this landslide destabilizes, damage could occur to the road. Heavy periods of precipitation or significant development could have an effect on slope stability.

Huckleberry Mountain 15’ Quadrangle: Blockslide/flow, blockslide/slump/flow, and slump/flow complexes are present along U.S. Highway 89/287. If these landslides destabilize, damage could occur to the highway and/or structures at Flagg Ranch. If the landslides near the south entrance to Yellowstone National Park dam the Snake River, flooding could also affect the highway and/or Flagg Ranch. If the flows, rockslide/flow, and slump/flow complexes around Jackson Lake activate, they could pose a hazard to tourists, fishermen, or boaters. Heavy periods of precipitation or significant development could have an effect on slope stability.

Jackson Quadrangle: Several landslides are present near the town of Jackson. If the alluvial fan/debris flow complex in T41N R116W Section 33 destabilizes, damage could occur to U.S. Highway 26/89/187 and nearby structures. If the landslide dams Flat Creek, flooding could affect the highway and structures in Jackson. Structures in Jackson could also be damaged if the rockslide/flow, slump/flow, and loess/slump/flow complexes in T41N R116W Sections 33 and 34 activate. In addition, if the debris flows in T40N R116W Section 8 and the Quaternary alluvium/debris flow complex in T40N R116W Sections 21 and 28 activate, U.S. Highway 26/89/187 could again be damaged. Heavy periods of precipitation or significant development could have an effect on slope stability.

Jenny Lake Quadrangle: Debris flow/Quaternary alluvium, rock fall/Quaternary terrace, and rockslide/Quaternary terrace complexes are present on the west side of Jenny Lake. If these landslides activate, damage could occur to tourist-frequented trails in the area. Heavy periods of precipitation or significant development could have an effect on slope stability.

Lava Mountain Quadrangle: A large blockslide/slump/flow complex is present in the northern part of the quadrangle on the Teton County-Fremont County border. If this landslide destabilizes, damage could occur to U.S. Highway 26/287, a secondary road, and a picnic area, all of which are located within the landslide complex. Heavy periods of precipitation or significant development could have an effect on slope stability.

Moran Quadrangle: Blockslide/slump, blockslide, and blockslide/slump/flow complexes are present in T44N R114W Sections 16, 17, and 20. If these landslides activate, damage could occur to U.S. Highway 26/89/187 and/or a secondary road in Section 20. Heavy periods of precipitation or significant development could have an effect on slope stability.

9.6

Mount Hancock Quadrangle: If the blockslide/rockslide/flow complex in the south- central portion of the quadrangle destabilizes, damage could occur to the Gravel Creek Patrol Cabin. Heavy periods of precipitation or significant development could have an effect on slope stability.

Mount Leidy Quadrangle: Several landslides, including debris flow/Quaternary alluvium, flow, slump, and slump/flow complexes, are present in the southwestern corner of the quadrangle. If these landslides destabilize, damage could occur to the nearby road or the Gros Ventre River could be dammed. There are also a number of flow/debris flow, blockslide, rockslide/flow, and rockslide/slump/flow complexes along Slate Creek. If any of the landslides destabilize, they could dam the creek. Heavy periods of precipitation or significant development could have an effect on slope stability.

Munger Mountain Quadrangle: Blockslide/rockslide/flow, rockslide/flow, flow, blockslide/slump, alluvial fan/debris flow, debris flow/alluvial fan, and debris flow/Quaternary alluvium complexes are present near the Snake River in the east- central portion of the quadrangle. If these landslides activate, damage could occur to U.S. Highway 26/89 or to the road on the south side of the Snake River. U.S. Highway 26/89 could also be damaged if the slump/flow/debris flow complex through which it passes in the south-central portion of the quadrangle destabilizes. Heavy periods of precipitation or significant development could have an effect on slope stability.

Ouzel Falls Quadrangle: Large blockslide/rockslide/flow, rockslide/flow, and slump/flow complexes are present along the Gros Ventre River. If these landslides destabilize, the Gros Ventre River could be dammed. Heavy periods of precipitation or significant development could have an effect on slope stability.

Rendezvous Peak Quadrangle: State Highway 22 passes through several landslides in the southern portion of the quadrangle. If any of these rockslide/debris flow/alluvial fan, blockslide/rockslide/slump, Quaternary alluvium/rockslide/debris flow, avalanche/rockslide, rockslide, and debris flow/alluvial fan complexes destabilize, damage could occur to the highway. A transmission line in the southwestern corner of the quadrangle could also be damaged if the landslides in this area destabilize. Heavy periods of precipitation or significant development could have an effect on slope stability.

Rosies Ridge Quadrangle: Slump/flow, flow, and debris flow/alluvial fan complexes are present in the northern portion of the quadrangle. If these landslides destabilize, damage could occur to the road that passes through the flow. Several landslides, including debris flow/flow, rockslide/flow, flow, blockslide, talus flow/debris flow/flow, slump/flow, and blockslide/slump/flow complexes, are also present along U.S. Highway 26/287 and Black Rock Creek. If these landslides activate, Black Rock Creek could be dammed, and damage could occur to the highway, a ranger station, and/or a secondary road in T45N R113W Section 36. In addition, flow, flow/surface wash, rockslide/flow, slump/flow, and rockslide/slump/flow complexes are present along Flagstaff Creek in the southeastern portion of the quadrangle. If these landslides destabilize, damage

9.7

could occur to the nearby road. Numerous lockslide/slump, rockslide/flow, flow, and rockslide complexes are present along Spread Creek and the North and South Forks of Spread Creek in the southern part of the quadrangle. If any of these landslides activate, the creeks could be dammed. Heavy periods of precipitation or significant development could have an effect on slope stability.

Shadow Mountain Quadrangle: The southern portion of this quadrangle is well known for the Gros Ventre Slide that occurred on June 23, 1925. A large blockslide/rockslide/rock fragment flow/flow complex activated and dammed the Gros Ventre River, creating Lower Slide Lake. Local seismic activity may have contributed to the landslide. This area contains numerous other landslides, including debris flow/flow/Quaternary alluvium, debris flow/alluvial cone, blockslide/rockslide/flow, rockslide/flow, blockslide/flow, slump/flow, slump/rockslide/flow, slump/blockslide/flow, and flow complexes. If any of these landslides were to activate, the Gros Ventre River could again be dammed. In addition to flooding problems, the Gros Ventre Road, the Atherton Creek campground, and other local structures could be damaged directly by a landslide. Rockslide/flow and slump/flow complexes are also present in T43N R115W Sections 24 and 25. If these landslides destabilize, damage could occur to the nearby road. Finally, structures at the Lost Creek Ranch (T44N R114W Section 30; T44N R115W Section 36) could be damaged if the nearby rockslide/flow and rockslide/blockslide/flow complexes destabilize. Heavy periods of precipitation or significant development could have an effect on slope stability.

Teton Pass Quadrangle: Slump/rockslide/flow, avalanche/rockslide, slump/flow, and debris flow/alluvial fan complexes are present in the northern portion of the quadrangle. If these landslides destabilize, damage could occur to State Highway 22, which passes through several of the landslides, and/or to structures at Trail Creek Ranch. Also, the road paralleling Mosquito Creek in the center of the quadrangle could be damaged if any of the nearby slump/flow, rockslide/flow, or blockslide/flow complexes activate. Heavy periods of precipitation or significant development could have an effect on slope stability.

Teton Village Quadrangle: Rockslide/debris flow/alluvial fan and debris flow/alluvial fan complexes are present in the western portion of the quadrangle in T42N R117W Section 35 and T41N R117W Section 2. If these landslides activate, damage could occur to the nearby road. Heavy periods of precipitation or significant development could have an effect on slope stability. Togwotee Pass Quadrangle: Large blockslide/rockslide/flow, slump/flow, and blockslide/slump/flow complexes are present in the southwestern portion of the quadrangle. If these landslides destabilize, damage could occur to U.S. Highway 26/287. A remote chance also exists that the rockslide/flow complex in the northern portion of the quadrangle could deflect South Buffalo Fork. Heavy periods of precipitation or significant development could have an effect on slope stability.

Two Ocean Lake Quadrangle: Landslides are present along the edges of Two Ocean Lake and Emma Matilda Lake. If these landslides activate, they may pose a risk to

9.8

tourists, fishermen, or boaters. Heavy periods of precipitation or significant development could have an effect on slope stability.

Upper Slide Lake Quadrangle: Upper Slide Lake in this quadrangle was formed when a large blockslide/rockslide/flow complex activated and dammed the Gros Ventre River. Other large blockslide/rockslide/flow, rockslide/flow, alluvial fan/debris flow, and slump/flow complexes are present along the Gros Ventre River. If these landslides activate, the Gros Ventre River could be dammed again. The road that parallels the river could also be damaged, either directly or by flooding. Heavy periods of precipitation or significant development could have an effect on slope stability.

Whetstone Mountain Quadrangle: Several landslides, including slump/flow, rockslide/blockslide/slump/flow, and rockslide/flow complexes are present on the west and northwest side of Pacific Creek. If these landslides destabilize, damage could occur to Pacific Creek Road, which passes through some of the landslides. Activated landslides could also damage the Wilderness Ranch. Blockslide/slump/flow, rockslide/slump/flow, and blockslide/flow complexes are present near the confluence of pacific Creek and Whetstone Creek. If any of the landslides destabilize, they could dam either of the creeks. Heavy periods of precipitation or significant development could have an effect on slope stability.

9.9

Mapped landslides for Teton County are shown on the figure below.

Figure 9.3 Mapped Landslides in Teton County

Teton County MHMP 9.10

Future Impacts

There are three measures of future landslide impacts – historic dollar damages, estimated yearly damages, and building exposure values. There are not enough current data to estimate historic or yearly dollar damages.

The WSGS has calculated the building exposure value for buildings that may occur within or within 100 feet of a landslide. All landslides mapped in Wyoming have been digitized. The landslides then had a 100-foot buffer digitally added to the outside of the landslides. The modified landslides were then digitally crossed with Census block building values. In some cases, a landslide boundary will dissect a census block. In that case the proportional value of buildings in the census block will be assigned to the landslide. If a census block is within a landslide, then the values of all the buildings in the census block is assigned. The values derived by county are shown in Figure 9.4 below. Table 9.1 shows the ranking of counties based upon landslide building exposure values.

Figure 9.4 Wyoming Landslide Exposure by County

As can be seen above, there is approximately $42 Million in building value that is built on or near landslides. More detail for the county is provided in Figure 9.5

Teton County MHMP 9.11

Figure 9.5 Wyoming Landslide Exposure in Teton County

Teton County MHMP 9.12

Table 9.1 Building Exposure Values for Landslides Landslide Building Exposure County Value (USD) 1. Teton 130,857,545

The probability of a landslide causing damage in Teton County is difficult to determine because of the poor historic data. According to GIS modeling, Teton County is one of the most at-risk Wyoming counties to landslides. Based on the geologic studies, future impacts are likely to affect transportation corridors (major roads), reservoirs, transmission lines, campgrounds, pipelines, and occasional structures. There is also a possibility that many smaller creeks within the county could be dammed by landslide activity. This could create a flash flood hazard downstream if the landslide dam fails or is overtopped (see discussion of Gros Ventre Slide in Dam Failure Section). Heavy periods of precipitation or significant development could have an effect on slope stability in the mapped hazard areas. Both the town of Jackson and Teton County have adopted land development restrictions based on slope percentages as a tool to reduce future landslide damage potential.

Summary

PROPERTY AFFECTED: High POPULATION AFFECTED: Low PROBABILITY: Medium JURISDICTION AFFECTED: Jackson, unincorporated areas of the county

Teton County MHMP 9.13

Chapter 10. Lightning

Lightning is a sudden electrical discharge released from the atmosphere that follows a course from cloud to ground, cloud to cloud, or cloud to surrounding air, with light illuminating its path. Lightning’s unpredictable nature causes it to be one of the most feared weather elements.

Anyone that is caught in an exposed area during a thunderstorm could be at risk to a lightning strike. In Wyoming, outdoor enthusiasts venturing to high and exposed areas such as the Teton Range should be especially cautious because rapid thunderstorm development with associated lightning can place even the most experienced climbers in jeopardy without warning. Hikers and climbers above the timberline (including areas of Grand Teton and Yellowstone National Parks and the Bridger-Teton National Forest) should be off exposed mountain tops and ridges by 1400 MST during the summer months to avoid being struck by lightning unless proper shelter is available (Wyoming Climate Atlas).

History

U.S. statistics show that one in 345,000 lightning flashes results in a death and one in 114,000 results in an injury. According to meteorologists at Vaisala, Inc., the odds for an American being hit by lightning sometime in the course of an 80-year lifespan is about 1 in 3,000. Wyoming ranks 36th in number of lightning fatalities, 33rd in injuries, and 40th in property damage from 1959 to 1994 according to the National Oceanic and Atmospheric Administration, National Severe Storms Laboratory (NOAA, NSSL). From 1959 to 2003 lightning has been responsible for 26 deaths, 103 injuries, over $3.2 million in property damage, and $22,750 in crop damage in Wyoming. Dollar damage estimates may include damage from associated severe weather, including precipitation and wildland fire. Table 10.1 includes Wyoming lightning events that have caused deaths, injuries, and damage in Teton County. Lightning has caused death, injuries, and sparked numerous wildfires within the county. According to the data in the table, a damaging lightning event occurs about every 1.6 years in the county.

Teton County MHMP 10.1

Table 10.1. Teton County Lightning History Total Estimated Number Number estimated County Location Date property Information killed injured damage damage (2004 USD) Jackson 10 September 11, Lightning struck two road construction workers causing minor Teton 0 2 $0 S 1967 injuries. Yellowstone August 07, Man struck by lightning while canoeing on Lewis Lake, thrown Teton 1 0 $0 Park 1975 into water and either killed by lightning or drowned. A boy, 8 years old, was killed and a young lady, 26, injured while August 07, Teton 1 1 $0 on a hiking trip 15 miles northeast of Jackson on the Gros 1977 Ventre River drainage. A blaze sparked by a lightning strike burned 1080 acres in August 30, Teton 0 0 $140,000 $243,056 Grand Teton National Park, destroying 10 cabins and inflicting 1985 an estimated $140,000 worth of damage. Jackson Lightning strikes near the Gros Ventre River destroyed a Teton June 09, 1987 0 0 $350,000 $575,658 (27NE) $350,000 home. Some unusually severe thunderstorms swarmed over northwest Wyoming during the afternoon. One of the first indications of these severe thunderstorms was the 60 mph wind gusts reported by a radio station in Jackson at 1300 MST. As these severe thunderstorms moved northeast additional reports of hail between 1 inch and 2.25 inches in diameter were observed along with winds gusting above 58 mph. Also, torrential rains were noted from Jackson northeast to Cody. When these severe thunderstorms moved northeast of Jackson over the Teton Wilderness Area it spawned the highest elevation F4 tornado ever documented. The devastating winds from the tornado produced a massive blowdown of 15,000 acres of mostly mature Teton Jackson 8S July 21, 1987 0 0 $2,750 $4,523 lodgepole pines which ranged from 80 to 100 feet tall. The massive blowdown stretched slightly over 24 miles from Box Creek Trailhead, 10 miles east-northeast of Moran Junction, on the south to beyond the Yellowstone River on the north and was about 1 to 2 miles wide, 2.5 miles at the widest. An eyewitness to the blowdown stated, "You could look up a hillside where there had been a dense forest and count the trees left standing." Later, as these severe thunderstorms moved over the East Entrance of Yellowstone National Park, torrential rains produced mudslides which closed highways for a few hours. The Park County sheriff reported that some of these mudslides buried about 50 yards of highway to a depth of 2 feet. During the month of July, at least 59 fires were started by lightning from mostly high-based thunderstorms that produced Park, Teton, Carbon, July 01, 1988 0 0 $364,430 $575,719 little rainfall. These included very large forest fires such as the Sweetwater, and Natrona Clover Mist Blaze in Yellowstone National Park and the Lost Fire over the Big Horn Mountains of northern Wyoming. On a week-

Teton County MHMP 10.2

Total Estimated Number Number estimated County Location Date property Information killed injured damage damage (2004 USD) by-week basis, the breakdown of lightning fire is as follows. Before and including the 2nd, fourteen lightning fires were started. During the 10th through the 16th, 18 such fires were reported. From the 17th through the 23rd, there were eight fires. Between the 24th and 30th, ten lightning blazes occurred. Finally, on the 31st, there were four fires. According to the BLM for Wyoming, 3,644.3 acres were torched with an estimated lost resource value of $364,430. This does not include the fires started by lightning in Yellowstone National Park because this information is not yet available. Park, Teton, Sweetwater, Same as Sheridan, Natrona, July 03, 1988 0 0 1 July See 1 July 1988 description Fremont, Albany, Laramie, 1988 Crook, and Johnson Park, Teton, Sweetwater, Fremont, Johnson, July 10, 1988 0 0 See 1 July 1988 description Laramie, Washakie, Converse and counties Park, Teton, Fremont, Same as Sweetwater, Washakie and July 17, 1988 0 0 1 July See 1 July 1988 description Natrona 1988 Same as Park, Teton, Uinta, July 24, 1988 0 0 1 July See 1 July 1988 description Johnson, and Sublette 1988 Same as Park and Teton July 31, 1988 0 0 1 July See 1 July 1988 description 1988 Park, Teton, Campbell, August 01, Crook, Natrona, 0 0 $415,900 $657,030 See 1 July 1988 description 1988 Sweetwater and Weston Park, Teton, Converse, Same as August 07, Sweetwater, Lincoln and 0 0 1 August See 1 July 1988 description 1988 Carbon 1988 Teton, Park, Sweetwater, Same as August 14, Lincoln, Fremont, 0 0 1 August See 1 July 1988 description 1988 Washakie and Hot Springs 1988 Same as Teton, Park and August 21, 0 0 1 August See 1 July 1988 description Sweetwater 1988 1988 Lightning started the Mormon Row fire in the Antelope Flats area August 28, Teton Moose $60,000 $75,662 on the 28th and the fire grew quickly to 3200 acres by the end of 1994 the month. 19 NNW Teton July 20, 1999 0 1 Person struck by lightning on Table Mountain. Jackson

Teton County MHMP 10.3

Total Estimated Number Number estimated County Location Date property Information killed injured damage damage (2004 USD) 10 NNW August 05, Teton Jackson 0 2 Two people struck by lightning on the Grand Teton. 1999 Airport A boat was hit by lightning. The lightning blasted a hole in the Teton 3 W Moran June 22, 2002 0 5 boat floor. 20 N One person died and five were seriously injured when they were Teton July 26, 2003 1 5 Jackson struck by lightning while climbing Grand Teton. F25OU The Blacktail Wildfire was started by lightning on August 10. On August 11, Gros Ventre Campground had to be evacuated as August 10, Teton 3 S Moose 0 0 the fire approached. Smoke impacted air traffic at Jackson 2003 Airport and Highway 26/89/91 was temporarily closed on August 12. The fire burned 2,650 acres. The East Wildfire, located near the East Entrance of Yellowstone National Park, was started on August 11 by lightning. Thirty-one residences and 43 commercial buildings need protection as 10 E gusty winds caused rapid fire growth. The wildfire burned four August 11, Teton Fishing 0 0 private vehicles. On August 15, the East Entrance of 2003 Bridge Yellowstone National Park was closed, only to be opened temporarily, 3 hours in the morning and 3 hours in the afternoon, from August 29-31. The fire burned 23,500 acres. The estimated cost of fighting the fire was $6.6 million. Fishing Lightning struck 15 yards from boardwalk at Old Faithful. 11 by- Teton 21-Jun-2005 0 11 0 0 Bridge standers injured. Lightning struck a climber on Grand Teton. Climber was able to Teton Moose 24-Jul-2007 0 1 0 0 get down.

Teton County MHMP 10.4

Impacts

Based on the lightning data for Teton County, lightning has killed 3 and injured 25 persons and been associated with $2,131,648 in property damage (2004 dollars) since 1967. Nationwide lightning strikes are routinely monitored by Vaisala, Inc. with accuracies to within a 0.625-mile (1 kilometer) resolution. For the period of 1998 through 2000, the Wyoming annual lightning strike frequency is depicted in Figure 10.2. Clearly the eastern plains have more than three times the cloud to ground lightning strikes as does the western half of the state. Despite annual variation, the locations of maximum and minimum strikes do not change much from year to year. In 1998 the state's precipitation average was well above normal, in 1999 near normal, and in 2000 was below normal (Wyoming Climate Atlas).

Figure 10.1—Average annual lightning flash density for 1998-2000 over Wyoming. Each pixel represents 5 km2. Illustration courtesy of Vaisala Inc.

Teton County MHMP 10.5

Future Impacts

Future impacts from lightning are difficult to determine because of the erratic nature of storms. Because of Teton County’s location in western Wyoming and mountainous terrain it will remain susceptible to lightning strikes. A damaging lightning event occurs every 1.6 years on average in the county. Impacts to persons and property have been significant in Teton County. Outdoor workers and outdoor enthusiasts and livestock will remain susceptible to lightning strikes. Lightning caused wildland fires may result in more extensive damage.

Summary

PROPERTY AFFECTED: Medium POPULATION AFFECTED: Medium PROBABILITY: High JURISDICTION AFFECTED: All

Teton County MHMP 10.6

Chapter 11. Snow Avalanches

Wyoming is one of the top-ranking states for avalanche hazard because of its rural character, terrain, and mountain recreation. Skiers, snowboarders, and snowmobile operators are most commonly associated with avalanche hazards. However, motorists and others not engaging in recreation are also at risk of being caught in an avalanche. An avalanche is defined as a large mass of snow, ice, earth, rock, or other material in swift motion down a mountainside or over a precipice (Merriam-Webster). In the case of this evaluation, avalanche medium refers to snow.

An avalanche is a mass of snow sliding down a mountainside. An avalanche occurs when the stress (from gravity) trying to pull the snow downhill exceeds the strength (from bonds between snow grains) of the snow cover. There are four ingredients of an avalanche: a steep slope, a snow cover, a weak layer in the snow cover, and a trigger. About 90% of all avalanches start on slopes of 30-45 degrees; about 98% of all avalanches occur on slopes of 25-50 degrees. Avalanches release most often on slopes above timberline that face away from prevailing winds (leeward slopes collect snow blowing from the windward sides of ridges.) Avalanches can run, however, on small slopes well below timberline, such as gullies, road cuts, and small openings in the trees. Very dense trees can anchor the snow to steep slopes and prevent avalanches from starting; however, avalanches can release and travel through a moderately dense forest.

The Teton and Gros Ventre Mountain ranges in Teton County, due to their steep terrain, high elevations, and winter snows, experience avalanches every winter. Generally the avalanches occur in remote areas and have little impact, except when unwary backcountry travelers get caught and buried. Highway 22 over Teton Pass traverses the run-out zones of several avalanche paths, and is often closed in winter for avalanche control work.

History

Avalanche fatalities provide the best indicator for locations of where events occur that can impact humans and thus what populations are most threatened. According to the U.S. Forest Service, Utah Avalanche Center, Wyoming ranks fifth among the eight states with the most avalanche fatalities. Wyoming comprised 8% of avalanche deaths in the U.S. from 1996 through 2002 (Figure 11.1).

Teton County MHMP 11.1

US Avalanche Fatalities by State (1996-2002)

California, 3% Idaho, 5% Alaska, 24% Washington, 7% Wyoming, 8%

Utah, 12% Colorado, 22% Montana, 19%

Figure 11.1—Wyoming relative risk for avalanche fatalities Figure adapted from the USDA Forest Service, Utah Avalanche Center.

Since 1911, there have been over 50 fatalities from avalanches with the majority resulting from individuals partaking in mountain recreation, most predominantly backcountry skiers. Although deaths occur primarily in the backcountry, motorists, residents, and workers in high angle, avalanche-prone terrain must be aware of the danger; at least five individuals have perished this way. The majority of fatalities in the State occurred in western Wyoming, in particular the Teton area. This area presents a population of outdoor enthusiasts; a population engaging in extreme winter sports, heavy snowfalls; and high angle, avalanche-prone terrain.

Teton County MHMP 11.2

Wyoming Avalanche Fatalities by Activity (1911 – 2003)

Figure 11.2—Wyoming avalanche fatalities by activity. (Bridger-Teton National Forest Avalanche Center)

Wyoming Avalanche Fatalities by Location (1911 – 2003)

Figure 11.3—Wyoming avalanche fatalities by location (Bridger-Teton National Forest Avalanche Center)

Teton County MHMP 11.3

Western Wyoming and Teton County in particular have achieved notoriety nationwide for their avalanche hazard susceptibility. Teton County has had 36 deaths since 1911.

Table 11.1 Teton County Avalanche Fatalities

County Location Date Age Activity/travel Teton Mail Trail, Teton Pass 1911 Mail Carrier Teton Freight Trail, Teton Pass 1914 Freighter Teton Crater Lake, Teton Pass February 11, 1932 15 Resident Teton Crater Lake, Teton Pass December 15, 1945 15 Skier in Vehicle Teton Horse Creek Ranch February 13, 1949 32 Rancher Teton Leeks Canyon, Snow King Mountain March 05, 1956 57 Lift Skier Out of Area Teton Snow King Mountain March 12, 1964 30 Patroller Teton Glacier Gulch, Teton Range January 16, 1974 20 Backcountry Skier Teton Glacier Gulch, Teton Range January 16, 1974 18 Backcountry Skier Teton Glacier Gulch, Teton Range January 16, 1974 20 Backcountry Skier Teton South Leigh Canyon, Teton Range March 20, 1976 20 Backcountry Skier Teton Grand Teton, Teton Range April 26, 1979 24 Climber Teton Grand Teton, Teton Range April 26, 1979 22 Climber Teton Ferrin's Slide, Snow King Mt February 16, 1984 27 Lift Skier Out of Area Teton Mt Wister, Teton Range February 03, 1985 29 Climber Teton Rendezvous Mountain, Teton Range December 02, 1985 48 Patroller Teton Rendezvous Mountain, Teton Range February 17, 1986 37 Patroller Teton Dry Ridge, Teton Range February 28, 1992 21 Snowmobiler Teton Simpson Peak, Togwotee Pass December 28, 1992 41 Backcountry Skier Teton Taylor Mountain, Teton Range April 19, 1995 22 Backcountry Skier Teton Factory Hill, Yellowstone March 03, 1997 49 Backcountry Skier Teton Factory Hill, Yellowstone March 03, 1997 37 Backcountry Skier Teton Dry Lake Creek, Togwotee Pass January 04, 1999 35 Snowmobiler Teton Rendezvous Mountain, Teton Range January 19, 1999 17 Lift Skier Teton Glory Bowl, Teton Range December 01, 2000 28 Backcountry Snowboarder Teton Titmouse Ridge, Teton Pass December 09, 2000 29 Backcountry Skier Teton South Badger Creek, Teton Range December 25, 2000 26 Backcountry Skier Teton Rock Springs, Teton Range February 06, 2001 43 Lift Skier Out of Area Teton Granite Canyon, Teton Range February 23, 2001 24 Lift Skier Out of Area Teton Grove Creek, Big Hole Range March 12, 2002 16 Snowmobiler Teton Near Ski Lake, Teton Range January 04, 2003 19 Backcountry Snowboarder Teton Kettle Creek, Togwotee Pass January 25, 2003 44 Snowmobiler Teton Avalanche Bowl, Teton Pass January 27, 2003 27 Backcountry Snowboarder Teton Hourglass Couloir, Teton Range February 10, 2003 41 Lift Skier Closed Area Teton S Fork of Darby Canyon March 11, 2007 24 Backcountry skier Teton Rock Springs Bowl January 5, 2007 25 Backcountry Skier

Reference: Bridger Teton National Forest Avalanche Center

Teton County MHMP 11.4

Impacts

Avalanches cause two primary hazards—road blocks and death. Fatalities are the most-documented impact related to avalanches. Time is of the essence when a person is buried in an avalanche. Victims buried more than 30 minutes rarely survive. Most that do survive are dug out within 15-30 minutes, and these survivors are often aided by personal locator beacons and prepared backcountry partners that are also equipped with shovels and beacons. Furthermore, there are costs and risks associated with “search and rescue” and removal of the injured or deceased.

Road blockages are another major concern where roads intersect an avalanche path. The major costs associated with road blocks are snow removal and traffic diversion, which both necessitate personnel and equipment. Another less frequent issue is the costs associated with rescuing motorists if they were involved in the avalanche. History and costs for avalanche road blocks are currently unavailable.

Future Impacts

Given the popularity of winter recreational activities it is likely that backcountry travelers will continue to encounter avalanches in Teton County, primarily within the Teton Range. Based on historic events, avalanche fatalities occur about once every 2.7 years in Teton County. Wyoming Department of Transportation has mapped the slide prone areas associated with state highways in the county. This allows them to anticipate and monitor areas that will need heavy equipment and personnel, prioritize, and respond rapidly when avalanches do occur. This pre-planning may help minimize loss and damage.

Summary

PROPERTY AFFECTED: Low POPULATION AFFECTED: Low PROBABILITY: High JURISDICTION AFFECTED: Unincorporated areas, Highway 22 over Teton Pass.

Teton County MHMP 11.5

Chapter 12. Tornadoes

Tornadoes are the most intense storm on earth having been recorded at velocities exceeding 315 mph. The phenomena results in a destructive rotating column of air ranging in diameter from a few yards to greater than a mile, usually associated with a downward extension of cumulonimbus cloud. Tornadoes are classified by their intensity by using the Fujita (F) Scale, with F0 being the least intense and the F6 being the most intense (Table 12.1).

According to the Wyoming Climate Atlas, the State of Wyoming ranks 25th in the number of annual tornadoes (10), 33rd in fatalities (six deaths per million people), 37th in injuries, and 36th in property damage ($49,339,505) (figure from Wyoming State Geological Survey) in the US from 1950-1994 (excerpted from the Wyoming Climate Atlas).

Table 12.1 Fujita Scale of Tornado Intensity Fujita Wind Speed Damage Scale F0 40-72 Light F1 73-112 Moderate F2 113-157 Considerable F3 158-206 Severe F4 207-260 Devastating F5 261-318 Incredible F6 319-379 Inconceivable

Tornado statistics, especially prior to the 1970s, must be viewed as incomplete since many twisters must have occurred without being witnessed. Wyoming's open rangelands experience little if any damage from these storms so many go unreported. In the 1990s, the Internet and Doppler radar increased the public's awareness of tornadoes with the potential of more being observed and reported. However, the trend in annual tornadoes has decreased by one third since 1976 and appears to have coincided with a major hemispheric weather pattern shift, despite the increased reporting based on Doppler radar vortex (circulation) signatures (excerpted from the Wyoming Climate Atlas).

History

In a database composed of information derived from the National Oceanic and Atmospheric Administration’s (NOAA) National Climactic Data Center (NCDC), the Wyoming Climate Atlas, and the Wyoming Office of Homeland Security, there have been two recorded damaging tornado events in Teton County. Damage is defined by those events that resulted in loss of property or life. Table 12.2 provides a statewide county summary of reported tornadoes including those with associated damage. Figure 12.1 shows the reported tornadoes by county. Table 12.3 describes the one tornado that actually caused damage in Teton County, a rare high altitude F4 event that caused

Teton County MHMP 12.1

massive forest damage. Fortunately tornadoes are rare in mountainous environments such as Teton County. Tornadoes are most likely to occur in May, June, and July.

Table 12.2 Wyoming Tornado Data Totals (1907-2003) Property Damage Crop Damage Total Damage County Events Deaths Injuries (USD) (USD) (USD) Teton 1 0 0 500,000 0 500,000 Statewide Total 512 6 122 51,108,075 977,850 52,085,925

Teton County MHMP 12.2

Table 12.3 Teton County Damaging Tornado Events Estimated Estimated Crop Total Estimated County Location T Date Deaths Injuries Property Fujita Scale Information Damage Damage Damage Some unusually severe thunderstorms swarmed over northwest Wyoming during the afternoon. One of the first indications of these severe thunderstorms was the 60-mph wind gusts reported by a radio station in Jackson at 1300 MST. As these severe thunderstorms moved northeast, additional reports of hail between 1 and 2.25 inches in diameter were observed along with winds gusting above 58 mph. Also, torrential rains were noted from Jackson northeast to Cody. When these severe thunderstorms moved northeast of Jackson over the Teton Wilderness Area it spawned the highest elevation F4 tornado ever documented. The devastating winds from the tornado Jackson July 21, produced a massive blow down of 15,000 acres of mostly mature Teton 45NE; Teton 0 0 $500,000 $0 $500,000 F4 1987 lodgepole pines which ranged from 80 to 100 feet tall. The Wilderness massive blow down stretched slightly over 24 miles from Box Creek Trailhead, 10 miles ENE of Moran Junction, on the south to beyond the Yellowstone River on the north and was about 1 to 2 miles wide, 2.5 miles at the widest. An eye-witness to the blow down stated, "You could look up a hillside where there had been a dense forest and count the trees left standing." Later, as these severe thunderstorms moved over the East Entrance of Yellowstone National Park, torrential rains produced mudslides that closed highways for a few hours. The Park County Sheriff reported that some of these mudslides buried about 50 yards of highway to a depth of 2 feet. Between S Teton Entrance and Aug 4, 2007 0 0 Unknown 0 Unknown Unknown Trees downed, winds estimated at 60 mph. Grant Village

Teton County MHMP 12.3

Impacts

Although different counties in the state have been affected to lesser or greater extents by tornado intensity, frequency, and damage, tornadoes have struck every county in Wyoming, thus proving to be a considerable hazard. In 2004 dollars, Teton County ranks 11th out of 23 counties for reported damage (Table 12.4 and Figure 12.2).

Table 12.4 Tornado Damage by County in 2004 USD (1907 - 2003) County Damage Teton 822,368

Statewide Total 134,008,519

Future Impacts

Historical data demonstrates that the most critical area of the state for tornado hazard is the eastern one third, with the five most threatened being Laramie, Campbell, Goshen, Converse and Platte. The five least threatened include Teton, Uinta, Sublette, Hot Springs, and Washakie (Table 12.5). Laramie, Campbell, Goshen, Crook, and Niobrara are the five counties that have received the most damage, while Sublette, Uinta, Johnson, Lincoln, and Hot Springs are the sustained the least damage.

Tornadoes rarely occur in Teton County and there are not enough historic records to calculate a statistically significant recurrence interval. The only documented damaging tornado caused $500,000 in damage 1987, or $831,000 in 2004 dollars. This should be considered to be an indicator of damage from a future event, but the potential for more damaging tornadoes exists if the tornado hits a developed area. Because of the random nature of tornadoes it is difficult to predict where the next one will hit, or how damaging it will be.

Summary

PROPERTY AFFECTED: Medium POPULATION AFFECTED: Medium PROBABILITY: Low JURISDICTION AFFECTED: All

Teton County MHMP 12.4

Figure 12.1 Wyoming Tornado Data

Teton County MHMP 12.5

Teton County MHMP 12.6

Chapter 13. Wildland Fires

Teton County, because of its semi-arid climate, available fuels and rural character, is vulnerable to catastrophic wildland fires, and, of all the fires in Wyoming, over 50% involve wildland areas. As defined by the National Interagency Fire Center (NIFC), a ―wildland fire‖ is any non-structure fire, other than prescribed fire, that occurs in the wildland. Before discussing wildland fire hazard in Teton County, some key terms should be identified. The term ―wildland/urban interface‖ or WUI is widely used within the wildland fire management community to describe any area where man-made buildings are constructed close to or within a boundary of natural terrain and fuel, where high potential for wildland fires exists. ―Aspect‖ refers to the direction in which a slope faces. ―Fuel‖ consists of combustible material, including vegetation, such as grass, leaves, ground litter, plants, shrubs, and trees that feed a fire.

As the population and the wildland/urban interface in Wyoming increases, the more significant the risk of wildland fire hazard. The past 100 years of wildland fire suppression has led to heavy vegetation growth and thus has greatly increased the potential fuel-load for a wildfire to burn. As the wildland/urban interface has grown into these densely packed forests, the potential for catastrophic wildland fires has increased as well.

Wyoming wildland fires are managed and supported to varying extents through cooperative efforts by the:

Bureau of Land Management (BLM) Wyoming Fire Program Geospatial Multi-Agency Coordination (GeoMAC) Wildland Fire Support Maps Wyoming Fire Academy Wyoming Wildland Fire Plan Action Team National Park Service (NPS) Fire Management Program US Fish and Wildlife Service (FWS) Fire Management Branch National Interagency Fire Center (NIFC) Bureau of Indian Affairs (BIA) Fire and Aviation Management – NIFC USDA Forest Service (USFS) Fire and Aviation Management Wyoming State Forestry Division

Currently, the principal action plan for the State is the Wyoming Wildland Urban Interface Hazard Assessment produced by a joint venture of the Wyoming State Forestry Division, USFS, BLM, NPS, and other interested parties, with the BLM hosting the data. This is a Geographic Information System (GIS)-based mapping mission building on The Front Range Redzone Project in Colorado—the first fire-hazard mapping program of its kind. The Assessment maps fire hazard incorporating population density against slope, aspect, and fuels. With the mapping analysis evaluating areas of varying wildfire vulnerability, the final output will result in a Risk, Hazard, and Value (RHV) map displaying areas of concern (Redzones) for catastrophic wildland fires.

Teton County MHMP 13.1

The Wyoming Wildland Urban Interface Hazard Assessment builds on the work of earlier hazard methodologies and provides new and updated data to further enhance accuracy and scale.

Teton County completed a collaborative Community Wildfire Protection Plan or CWPP in 2005 with Forest Service, National Park, and State Forester partners. Approximately 20% of the citizens in the county live in the wildland urban interface (WUI.) The CWPP identified and mapped WUI areas in the county and ranked them according to priority for mitigation work. Notification and evacuation triggers were developed for each interface area. Each WUI area is described with respect to hazard level, fuels, and existing infrastructure. Thirty-one communities at risk or areas (taken from the Federal Register) are listed for the county. The CWPP also contains appendix material helpful for property owners who wish to mitigate the threat of wildland fire to their property.

Jackson Hole Fire/EMS reviews plans to all new or altered subdivisions, all new structures to be built in the interface, and alterations to existing structures in the interface. The Department is a combined paid staff and volunteer organization. There are 125 volunteer fire fighters and EMTs. Fourteen positions are paid. The Department has seven fire stations. Grand Teton National Park and the Bridger-Teton National Forest also have paid fire fighters and fire apparatus.

History

The wildland fire history for the State of Wyoming has been compiled in the Wyoming Multi-Hazard Mitigation Plan from various state and federal sources. Unfortunately the data does not provide detail to the county level. Wyoming has had damaging fire seasons, often coinciding with times of drought. One of the worst fire seasons occurred during 1988, when fifty fires started in Yellowstone National Park. These fires, along with other natural and human-caused fires that began outside the Park boundaries eventually burned more than a third of the Park, nearly 800,000 acres. Another 700,000 acres outside the Park also burned. Approximately 25,000 firefighters worked to put out the fires. The costs exceeded $120 million. Table 13.1 includes recent wildland fire incidents in Teton County based on lightning-caused fires recorded in a National Weather Service severe weather database.

Teton County MHMP 13.2

Table 13.1—Wildfire events in Teton County Total Total Estimated estimated Number Number Estimated estimated County Location Date property damage Information killed injured crop damage damage damage (current year (2004 USD) USD) A blaze sparked by a lightning strike burned 1080 acres in Grand Teton August 30, Teton 0 0 $140,000 $0 $140,000 $243,056 National Park, destroying 10 cabins and 1985 inflicting an estimated $140,000 worth of damage. During the month of July, at least 59 fires were started by lightning from mostly high-based thunderstorms that produced little rainfall. These included very large forest fires such as the Clover Mist Blaze in Yellowstone National Park and the Lost Fire over the Big Horn Mountains of northern Wyoming. On a week-by-week basis, the breakdown of lightning fire is as follows. Before and Park, Teton, including the 2nd, fourteen lightning fires Carbon, were started. During the 10th through July 01, 1988 0 0 $364,430 $0 $364,430 $575,719 Sweetwater, and the 16th, 18 such fires were reported. Natrona From the 17th through the 23rd, there were eight fires. Between the 24th and 30th, ten lightning blazes occurred. Finally, on the 31st, there were four fires. According to the BLM for Wyoming, 3,644.3 acres were torched with an estimated lost resource value of $364,430. This does not include the fires started by lightning in Yellowstone National Park because this information is not yet available. Park, Teton, Sweetwater, Same as Sheridan, Natrona, July 03, 1988 0 0 1 July $0 $0 See 1 July 1988 description Fremont, Albany, 1988 Laramie, Crook, and Johnson Park, Teton, Sweetwater, Fremont, Johnson, Laramie, July 10, 1988 0 0 $0 $0 See 1 July 1988 description Washakie, Converse and counties

Teton County MHMP 13.3

Table 13.1—Wildfire events in Teton County Total Total Estimated estimated Number Number Estimated estimated County Location Date property damage Information killed injured crop damage damage damage (current year (2004 USD) USD) Park, Teton, Fremont, Same as Sweetwater, July 17, 1988 0 0 1 July $0 $0 See 1 July 1988 description Washakie and 1988 Natrona Park, Teton, Uinta, Same as Johnson, and July 24, 1988 0 0 1 July $0 $0 See 1 July 1988 description Sublette 1988 Same as Park and Teton July 31, 1988 0 0 1 July $0 $0 See 1 July 1988 description 1988 Park, Teton, Campbell, Crook, August 01, Natrona, 0 0 $415,900 $0 $415,900 $657,030 See 1 July 1988 description 1988 Sweetwater and Weston Park, Teton, Converse, Same as August 07, Sweetwater, 0 0 1 August $0 $0 See 1 July 1988 description 1988 Lincoln and 1988 Carbon Teton, Park, Sweetwater, Same as August 14, Lincoln, Fremont, 0 0 1 August $0 $0 See 1 July 1988 description 1988 Washakie and Hot 1988 Springs Same as Teton, Park and August 21, 0 0 1 August $0 $0 See 1 July 1988 description Sweetwater 1988 1988 Lightning started the Mormon Row fire in August 28, the Antelope Flats area on the 28th and Teton Moose $60,000 $60,000 $75,662 1994 the fire grew quickly to 3200 acres by the end of the month. Teton 2001 Greenknoll Fire The Blacktail Wildfire was started by lightning on August 10. On August 11, Gros Ventre Campground had to be August 10, evacuated as the fire approached. Teton 3 S Moose 0 0 $0 2003 Smoke impacted air traffic at Jackson Airport and Highway 26/89/91 was temporarily closed on August 12. The fire burned 2,650 acres.

Teton County MHMP 13.4

Table 13.1—Wildfire events in Teton County Total Total Estimated estimated Number Number Estimated estimated County Location Date property damage Information killed injured crop damage damage damage (current year (2004 USD) USD) The East Wildfire, located near the East Entrance of Yellowstone National Park, was started on August 11 by lightning. Thirty-one residences and 43 commercial buildings need protection as gusty winds caused rapid fire growth. 10 E August 11, The wildfire burned four private vehicles. Teton Fishing 0 0 $0 2003 On August 15, the East Entrance of Bridge Yellowstone National Park was closed, only to be opened temporarily, 3 hours in the morning and 3 hours in the afternoon, from August 29-31. The fire burned 23,500 acres. The estimated cost of fighting the fire was $6.6 million. Purdy Fire burned apprx 8,000 acres in Gros Ventre Bridger-Teton and Shoshone National Teton Aug. 4, 2006 0 0 Unknown 0 Unknown Unknown Drainage Forests. Plans made for evacuations on Dubois side of fire.

Teton County MHMP 13.5

Impacts

GIS is a tool that is used to compare, capture, input, output, store, manipulate, analyze, model, and display spatial data. In the case of the Wildland Urban Interface Hazard Assessment, wildfire hazard vulnerability is determined by comparing values such as slope, vegetation, housing density, and aspect. The following is from the Wyoming Wildland Urban Interface Hazard Assessment Methodology—a report written by the Wyoming State Forestry Division:

The Wildland Urban Interface Hazard Assessment uses three main layers to determine fire danger—Risk, Hazard, and Values. The following lists include the data used to create each of the three layers.

1. Risk – Probability of Ignition a. Lightning Strike density b. Road density c. Historic fire density d. Hazard – Vegetative and topological features affecting intensity and rate of spread e. Slope f. Aspect g. Fuels – Interpreted from GAP Vegetation information. 2. Values – Natural or man-made components of the ecosystem on which a value can be placed. a. Housing Density – Life and property 3. Non-flammable areas Mask – a mask was created to aid in the analysis for areas that will not carry fire such as water and rock areas. These areas show in the final assessment as a zero value for hazard.

The statewide Wildland Urban Interface Hazard Assessment and its resultant outputs serve two primary purposes: assisting in prioritizing and planning mitigation projects and creating a communications tool to which agencies can relate to common information and data. With the mapping analysis evaluating areas of varying wildfire vulnerability, the final output will result in a Risk, Hazard, and Value (RHV) map displaying areas of concern (Redzones) for catastrophic wildland fires. The Redzone map for Teton County follows. Another method of estimating potential future impact is to determine the value of structures that are located within Redzones, or wildland fire building exposure values. Wildland fire building exposure value is the value of buildings that can be potentially damaged by wildland fire in an area. Building exposure values are based on Census Block level data from HAZUS. The methodology utilized is similar to that used to model flood exposure described in the flood chapter.

Teton County MHMP 13.6

Figure 13.1 Teton County Wildland Fire Base Map with Redzones (Wyoming Wildland – Urban Interface Hazard Assessment)

Teton County MHMP 13.7

Figure 13.2 Wildland Fire Building Exposure Map

Teton County MHMP 13.8

Future Impacts

Small wildfires occur within the county every year. Large fires are less frequent, but with climate change, fire seasons are becoming longer and larger fires may be more common with more extreme fire behavior. Based on GIS analysis performed by the State of Wyoming, Teton County has over $1.5 billion in building value potentially at risk to wildland fires. Though it is not likely that the areas at risk will simultaneously face a completely destructive event, this figure provides the upper end of what could be affected. Future wildfires could damage forests and watersheds within the County, and contribute to soil erosion and deposition problems. Future losses could result from property loss and damage, loss of natural resources such as timber and forage, forfeited recreation and tourism revenues to the local economy, medical costs related to smoke and burns, and fire suppression costs. Taken together future losses for a large- scale wildland fire could easily exceed $10 million.

Summary

PROPERTY AFFECTED: High POPULATION AFFECTED: High PROBABILITY: High JURISDICTION AFFECTED: unincorporated areas, Jackson

Wildland Urban Interface area on the south edge of Jackson.

Teton County MHMP 13.9

Chapter 14. Winter Storms and Blizzards

Severe winter storms affect far more people in Wyoming than their summer counterparts, even though they are inherently less violent. Blizzard conditions bring the triple threat of heavy snowfall, strong winds and low temperatures. Poor visibility and huge snowdrifts are major hazards caused by blowing snow. These storms disrupt work, make travel difficult or impossible, isolate communities, kill livestock by the hundreds or thousands and sometimes leave human fatalities in their wake.

Data show that Lake Yellowstone and Lander lead the state in frequency of major snowstorms with an average of about five such days per year. The time of year when they receive these storms, however is quite different. In Yellowstone and throughout most of western Wyoming, major snowstorms strike most often in the mid-winter months. Springtime snowstorms are particularly destructive for ranchers because they coincide with calving and lambing. Damaging winter weather has occurred in September and October as well. Climbers in the Teton Range can experience winter weather conditions almost any time of year at high elevations.

History

The winter storm history in Teton County extends from 1886 to present. Teton County has a winter storm of significance about every two and half years, based on 51 events during a 121- year period. There have been a few winter storms in the county that have caused great damage, economic impact, and brought about change in livestock practices. A complete history of storms that caused damage, significant closure of highways, and/or impacts to the livestock industry is in Table 14.1. The data were derived from the monthly Storm Data reports from National Oceanic and Atmospheric Administration’s (NOAA) National Climatic Data Center (NCDC). Other sources are unpublished reports from the Wyoming Office of Homeland Security, newspaper accounts, and periodicals from public libraries. One of the most significant storms is described below.

The winter of 1886-1887 was one of the most significant early storms recorded. The snow that winter came early and grew very deep. Then, a freak thaw turned much of this to water. As cold weather moved back in, this froze into a crust of ice, which prevented cattle getting through to the forage underneath. These conditions, accompanied by a blizzard of unusual severity, caused a loss of over 50% among the State's livestock operations. The snow was six feet deep on the level between Mountain Home and Woods Landing. On February 12, 1887 the storms were still raging over the State, and the snow was packed so hard that stages could drive over it. Trains were stalled on their tracks. The winter of 1886- 1887 sounded the death knell of the open range cattle business as it had been during previous years.

TetonTeton CounTetontonTn 14

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops The winter of 1886 to 1887 was the earliest severe economic disruption. The snow that winter came early and grew very deep. Then, a freak thaw turned much of this to water. As cold weather moved back in, this froze into a crust of ice, which prevented cattle getting through to the forage underneath. These conditions, accompanied by blizzard of unusual severity, caused a loss of more than 50% among the State's livestock Loss of operations. The snow was 6 feet deep on the level between 50% of Snow, Mountain Home and Woods Landing. On February 12, 1887 the Statewide Statewide 1886 1887 Several Several livestock Blizzard storms were still raging over the State, and the snow was operations packed so hard that stages could drive over it. Trains were stalled on their tracks. The winter sounded the death knell of the open range cattle business as it had been during previous years. The real disaster to cattlemen had been in the winter of 1886 which has been called "The Equalizer". My father a boy of 8 at the time recalls the spring of 1887. In certain sheltered area he and companions amused themselves stepping from one carcass to another without ever setting foot to the ground. In January of 1887, F.J. Haynes joined a cross-country ski expedition led by Frederick Schwatka, the artic explorer. Soon after the eight man expedition left Mammoth Hot Springs for Norris, a brutal winter storm hit.That night temps fell to -37°F and several inches of snow fell the next day causing the expedition to take three days to reach Norris. They made it to the Upper Geyser Basin Hotel, but were shut in for five days during the continuous snow storm. After two clear days in which Haynes took many photographs of the geysers in eruption, they returned to Norris, and then east to the Grand Canyon. After a Snow, couple of days at the nearly buried Canyon Hotel, they decided Park and Yellowstone 1887-Jan-01 31 Jan 1887 Blizzard, to return to Mammoth by way of crossing the Washburn Range. Teton National Park cold The clear day soon became a blinding blizzard, with visibility cut to 30 feet. Huddling beneath the outstretched branches of an alpine fir, they built a small fire to keep warm and nibbled carefully at their food, for they had only brought one days provisions. They stayed awake the whole night, fearing that a few moments sleep would become eternal in the subzero tempratures. The next day they set out, and the storm grew even worse. WIth no idea where they were, they wandered on, hoping against hope that they might find civilization. Finally, the sun emerged from the clouds and showed them the way to Tower Fall and eventually to Mammoth.

Teton County MHMP 14.2

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops great This blizzard covered a number of states. The combination of Thousand Snow, Statewide Statewide 1888-Jan-11 13 Jan 1888 loss of strong winds, snow and rapid temperature drops made it very s of cattle Blizzard life dangerous. Loss of life was great and thousands of cattle died. This blizzard covered several states. Temperatures dropped March 28, Snow, Statewide Statewide 1931-Mar-25 2 rapidly. Strong winds drifted snow badly, blocking highways for 1931 Blizzard several days. Two people died in Wyoming. Heavy snow and strong winds covered much of several states, including Wyoming. Snowfall up to 60 inches fell in Wyoming. March 27, Statewide Statewide 1950-Mar-25 1 Snow, Wind There was widespread damage to power lines and many cars 1950 and trains were stranded. Drifts were up to 16 feet and one person died in the state. This blizzard covered several states, including Wyoming. Up to February Snow, Statewide Statewide 1955-Feb-18 4 11 inches of snow fell with winds to 65 mph and temperatures 20, 1955 Blizzard below zero. There were four deaths in Wyoming. Heavy snow fell over several states, including Wyoming. Drifts March 25, Statewide Statewide 1957-Mar-22 Snow were from 10 to 25 feet deep and many motorists were trapped 1957 in cars or snow bound in towns. Snow accompanied by high winds began early afternoon and Snow, continued through the evening. Three people were killed and Statewide Statewide 1961-Oct-28 5 4 $27,500 $0 Heavy and four were injured in auto accidents caused by low visibility. Two high winds hunters were lost and died in the storm. A cold wave moved over the state the evening of the 15th and caused considerable damage to crops, trees, power and phone lines, stopped much of the transportation by closing roads, Snow, September caused an estimated 5% shrinkage in marketable livestock and Statewide Statewide 1965-Sep-15 0 0 $2,750,000 C heavy; 17, 1965 a few death losses in livestock. Temperature dropped quite low Severe cold for so early in the season and the heavy (18"-22") band of snow from the southwest part of the state to the northeast part was by far the heaviest so early in the season. Heavy snow and strong winds blanketed the state, with roads, March 14, Snow, Statewide Statewide 1973-Mar-13 0 0 $275,000 C streets, and farms and ranches blocked. There were numerous 1973 Blizzard power and communications outages as well as livestock losses. Heavy snow with strong winds began early on December 31, 1975 and continued through most of the State through most of Most of January 01, Snow, Statewide 1975-Dec-31 0 0 $275,000 $0 the storm. Livestock losses were minimal and most of the Wyoming 1976 Blizzard damage is attributed to loss of time, cars stuck, rescue missions and snow removal.

Teton County MHMP 14.3

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops A severe blizzard with winds 40 to 50 mph and gusts to 75 mph, snow and temperatures down to 0 degrees started the morning of the 27th and continued to the evening of the 28th. Highways were blocked and some people stranded for varying times but March 28, Snow, Statewide Statewide 1975-Mar-27 0 0 $2,750,000 C all rescued. Some damage to signs, windows, trees, etc., but 1975 Blizzard most damage to livestock, especially new born, and to cows (udders frostbitten, etc.). The storm was most severe over the eastern half of the state and most of the damage was there also. Snow with large accumulations entered the state the afternoon on the 16th, accompanied by very cold temperatures. Some blowing and drifting caused hazardous driving conditions in many areas. The snow ended by the morning of the 18th but was quickly followed by strong, gusty, westerly winds which November Statewide Statewide 1977-Nov-16 1 0 $275,000 $0 Snow, Wind moved the large amounts of loose snow into ground blizzards 19, 1977 with severe problems on highways, ranches, etc. One man was killed at Rawlins as he tried to walk into town along the interstate from the west. Numerous people were stranded along the highways and in towns and ranches until the roads were opened. This very heavy snow storm dumped over a foot of snow across much of the state causing road and airport closures in many areas throughout the state. Winds gusting to 75 mph caused December Snow, High Statewide Statewide 1978-Dec-05 0 0 $275,000 $0 extensive blowing and drifting snow, stopping both local and 07, 1978 Wind interstate travel. This storm isolated livestock from ranchers, contributing to subsequent substantial losses of cattle and sheep in Wyoming. Numerous heavy snows combined with prolonged extremely cold temperatures have caused widespread damage across much of Wyoming during the month of January. Estimated loss of 2700 sheep and 2000 cattle with projected losses of calves January 31, Statewide Statewide 1979-Jan-01 0 0 $2,500,000 C Snow; Cold and lambs to 35,000 head are reported. Also, numerous towns 1979 and communities across the state have extensive damages to their water systems due to frozen water mains and sewer systems. Emergency Winter Storm Relief Aid of $2.5 million is currently being asked for by the State. Snow began on the 6th and ended on the 15th. Four feet of snow closed all roads into Jackson Hole for one day. Winds in Snow, high excess of 100 mph were clocked by the U.S. Forest Service at January 15, teton 1980-Jan-06 0 0 ? wind, the top of Rendezvous Mountain, while residents at Moose 1980 avalanche reported gusts to 76 mph. Major avalanches closed Teton Pass indefinitely and slide in the Snake River Canyon closed that route.

Teton County MHMP 14.4

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops Much of the state was paralyzed. Freak thunderstorms occurred in Casper, Riverton, and Lander areas. Roads were closed and some motorists stranded. Interstate 25 from Laramie to the Utah state line was closed by winds approaching 80mph in Statewide Statewide 1980-Jan-10 0 0 ? Snow south-central Wyoming. An estimated 60 vehicles were in the ditch along I-80 west of Rawlins. Reported 90 mph winds in Medicine Bow blew out car and truck windows and a large window in a cafe. Many schools were closed. Snow and blowing snow from the morning of the 25th to the evening of the 27th swept across Wyoming dumping a record 11 inches of snow on Cheyenne in a 12-hour period. Heavy snow and slick road surfaces due to bitter cold temperatures closed many highways and interstates, including I-80 from the Nebraska state line to Rock Springs. Near Bitter Creek Hill, 38 miles east of Rock Springs, 21 cars and trucks were involved in a pile-up on the afternoon of the 25th. Two men were killed at 1900 MST on the 26th, 9 miles east of Powell when the driver lost control, ejecting both men. One fatality occurred on the 27th at 11:30 a.m. on I-80 near Rock Springs when a car slowed Snow, down because of poor visibility and slick roads and the truck January 27, Statewide Statewide 1980-Jan-25 4 ? ? Heavy, driver, trailing the vehicle, failed to slow down in time and 1980 bitter cold crushed the back end of the car in which the victim was riding. A man died about 1245 MST on the 27th when the flatbed truck he was driving 95 miles south of Gillette jack-knifed on a left- hand curve and rolled on its top. Schools in Cheyenne were closed at noon on Friday and did not reopen until Wednesday. Most churches in Cheyenne remained closed on Sunday. Casper thermometers dipped to record lows of -27° on Saturday, -28° on Sunday night, and -32° Monday morning. Cheyenne reported temperatures at 0 or below zero for a period of 79 hours. Weather-related problems may have caused the derailment of 12 empty freight cars at Point of Rocks at 0645 MST on the 25th.

Teton County MHMP 14.5

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops Snow beginning on the evening of the 14th moved across the state leaving 13 inches in Laramie and 11 inches in Rawlins. Most other areas received from 1-3 inches. Some highways were closed on the 16th, including I-80 between Cheyenne and Walcott Junction (100 miles). One person was killed and three others injured in a storm-related two-vehicle accident southwest of Cody on the 15th. The storm apparently contributed to a light October 16, Snow, Statewide Statewide 1980-Oct-14 4 5 ? $0 plane crash that killed one man near the airport at Rock Springs 1980 blizzard at 2110 MST on the 15th. Blizzard-like conditions were contributing factors when a freight train plowed into the caboose of a grain train 13 miles southeast of Laramie about 1600 MST on the 16th, killing two crew members and injuring two others. Schools in Laramie, including the University of Wyoming, were closed on the 16th. Many hunters were stranded. Tree limbs snapped causing power outages in Rawlins and Sinclair. Extreme cold to -42°F caused electrical power outages overnight to the Jackson area and from 0600 to 1400 MST Teton, Jackson, February Extreme Friday in the Pinedale area. The extreme cold caused 1982-Feb-11 0 0 $2,750 $0 Sublette Pinedale 12, 1982 Cold conductors to break at the splice joints, failure of oil protective systems in the circuits, and failure of a power switch to open after repairs. Wind; Wind near 100 mph in open areas, combined with snow, Snow; blowing snow and avalanche problems isolated Jackson from Teton Jackson 1982-Jan-05 0 0 ? Flood, the world Monday. The avalanche slid inside the Town of local, Jackson just after 1300 MST from the Gros Venture Butte and avalanche caused over flooding near the Meadowbrook Condominiums. Yellowstone This late summer snow storm dumped heavy wet snow in Park, Hot National Park, northwest, north central and central Wyoming which stranded Springs, Park, Hot hundreds of motorists, left thousands of people without Fremont, Big Springs, electricity and closed several roads and schools. The areas Horn, Fremont, Big September $2,750,00 Snow, most affected along with some snow depth reports as of noon 1982-Sep-13 0 6 $2,750,000 Sheridan, Horn, 14, 1982 0 Heavy Wet on the 14th include: Lander 16.9 inches; Story 10; South Fork of Johnson, Sheridan, the Shoshone River 12 to 18; Powell 5; Sheridan 4.5; Cody 3.5, Natrona, Johnson, and Casper 1. Damages from the storm to the property and Teton Natrona,Teton crops are estimated in the millions of dollars. The six known counties injuries were from storm related vehicle accidents.

Teton County MHMP 14.6

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops The worst arctic outbreak ever in December hit Wyoming full- force with almost all of the state remaining below zero for five days. Overnight lows in the 20 to 40 below range were common, with quite a few towns setting record Dec lows. Most Wyoming residents fared much better in the cold than December Subzero mechanical items. A malfunctioning transformer left the town of Statewide Statewide 1983-Dec-20 0 ? $2,750,000 $0 25, 1983 Cold Lander without power for 12 hours, and numerous vehicles were damaged by the extreme temperatures. The greatest damage, however, occurred to homes and businesses as hundreds of water pipes froze and burst. The State Capitol Building in Cheyenne, for example, suffered almost $250,000 in damage due to burst water pipes. Converse, Natrona, Niobrara, Hot Springs, Johnson, Sheridan, A spring snowstorm swept through northern, central and Washakie, western Wyoming dumping an average of 6 to 12 inches of Campbell, All of WY snow. Up to 18 inches fell in some western mountain towns. Crook, except the Snow, 1983-May-11 0 0 ? $0 Near blizzard conditions occurred in southwest Wyoming as Weston, Big Southeast Heavy northeast winds of 30 to 40 mph whipped up 2 to 4 foot drifts. At Horn, Park, Quarter least two interstate highways were closed for a period of time, Teton, and lots of traffic accidents were reported across the state. Carbon, Fremont, Sublette, Lincoln, Sweetwater, Uinta Up to 2 feet of snow fell in northwest Wyoming late on the 7th Northwest February and early on the 8th. The 2-foot snowfall was recorded at Teton Teton, Park 1985-Feb-07 0 0 ? $0 Snow Wyoming 08, 1985 Village, just outside of Jackson, in Teton County. Blowing and drifting snow closed most of the roads in the area. Six inches of snow fell during the day on Rendezvous Peak, west of Teton Village. Wind gusts to 100 mph during the morning damaged cabin roofs and mobile homes. A ski Snow, wind, patrolman was buried and died in an avalanche near Teton 1986-Feb-17 1 0 $27,500 $0 blizzard, Rendezvous Peak, where 74 inches of snow had fallen in the avalanche past 6 days. A series of avalanches kept passes in and out of Jackson Hole closed. Blizzard conditions prevented the reopening of the passes and caused an extreme avalanche hazard.

Teton County MHMP 14.7

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops A fairly moist but strong upper level westerly flow dumped 4 to 8 inches of new snow over Yellowstone National Park. This strong westerly flow produced wind gusts around 60 mph from 0130 to 0500 MST at Cody Regional Airport. These strong Park, Teton, westerly winds continued to move into southeast Wyoming Natrona, Yellowstone during the morning and the afternoon. Shortly before 0300 MST Carbon, National Park, High wind; Natrona County Airport near Casper recorded a wind gust to 43 1987-Dec-21 0 0 $2,750 $0 Albany, Southeast Snow mph. From 0500 to 1330 MST sustained winds of 35 to 45 mph Laramie, Wyoming were clocked from Rawlins to Cheyenne along I-80. These Platte strong winds were also observed from Wheatland to Cheyenne. Very strong wind gusts from 0500 to 1030 MST reached speeds of 58 to 64 mph at the Cheyenne airport. Construction damage due to these high wind were reported in the Cheyenne area between 0400 to 0600 MST. A cold front associated with a strong upper level westerly flow dropped between 8 to 14 inches from Evanston to Yellowstone Uinta, National Park. Slick roads about half a mile west of Jackson Lincoln, West were blamed for the fatal automobile accident of a Montana 1987-Dec-22 1 2 $27,500 $0 Snow Teton, Park, Wyoming woman. Two other persons were also seriously injured in a car Sweetwater accidents in Teton County. The Town of Green River alone had at least 18 weather related traffic accidents between 1600 to 1800 MST with damages greater than $12,550. A moist storm developed over Nevada on the 23rd and moved over Wyoming through the 25th. This moist storm combined with favorable upslope flow and dumped from 6 to 26 inches of snow. The storm unloaded a new record snowfall total in Northwest Lander of over 26 inches. At one point heavy snow was Fremont, mountains to February Snow, 1987-Feb-23 0 ? $0 $0 observed in Lander on the 24th from 1900 to 2300 MST, where Teton Wind River 25, 1987 Heavy 8 inches of new snow fell. Some other individual snowfall Basin reports were 11 inches at Rendezvous Peak with 10 to 14 inches at Crowheart and Riverton. The storm caused numerous road closures and frequent cancellation of schools and public meetings across the far west and Wind River Basin.

Teton County MHMP 14.8

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops A cold front blitzed into far west Wyoming and produced thunderstorms and eight to twenty inches of new snow from Kemmerer north to Yellowstone National Park. Around 0500 MST wind gusts of 115 mph were recorded at the top of Rendezvous Peak at the Teton Village Ski Resort. Wind gusts of 50 to 55 mph raked across the Green River to Wind River Park, Teton, Basin around 0530 MST. These strong winds caused short Lincoln, power outages at Big Piney and Pinedale during the morning of Uinta, the 11th. Also, wind gusts to 55 mph were noted in the Gillette High Wind; Sublette, West January 11, area around 0700 MST. As this cold front moved through 1988-Jan-10 0 0 $0 $0 Snow, Campbell, Wyoming 1988 southeast Wyoming and Carbon County sustained winds of 35 Heavy Carbon, to 45 mph with gusts of 55 to around 70 mph were logged. One Albany, peak wind gust over the southeast part of Casper reached 68 Natrona mph at 1000 MST with 71 mph at Rawlins airport at 1300 MST. During these high winds several tractor trailer trucks were knocked down between Wamsutter and Laramie along I-80. Truck drivers along the Interstate complained the strong winds were treating their semi-tractor trailers "like kites pulling whichever way the wind was blowing." One man was injured on I-80 when two tractor trailers collided. The strong low pressure system both at the surface and aloft moved slowly northeastward to extreme southeast Montana by the 7th. This storm unleashed very heavy snow over most areas with elevations above 6000 feet MSL in the north and west sections of Wyoming. Since this storm had begun the morning Big Horn, of the 6th more than 20 inches of new snow had fallen in the Sheridan, Big Horn Mountains of northern Wyoming, while there was 6 to Northern and Johnson, 10 inches of snow at Yellowstone National Park. Additionally, west-central Park, Teton, May 07, Snow, more than 10 inches of new snow was on the ground near Wyoming, 1988-May-06 0 0 $0 $0 Carbon, 1988 Heavy Pinedale, located in west-central Wyoming, and the Snowy South-central Albany, Range to the west of Laramie. More snow fell at these locations mountains Sublette, during the 7th. By 1335 MST on the 7th, Arrowhead Lodge in Crook the Big Horn Mountains had a total of 3 feet of new snow on the ground. Bear Lodge, located in the Wyoming Black Hills, had 24 to 30 inches of new snow by the afternoon of the 7th. Numerous trees and power lines were downed by very wet snow, with several communities without electricity through much of the 7th.

Teton County MHMP 14.9

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops The combination of a series of mid- and upper-level disturbances and a fast, very moist westerly upslope flow triggered a prolonged snow event over the northwest and west parts of the State from the 12th through the 14th. Many valley floors received more than 1 foot of new snow with numerous mountain location accumulations more than 3 feet. New snow amounts included 16 inches at Jackson Hole, 22 inches at Moran Junction, and a ski area in extreme northwest Wyoming Uinta, measured about 5 feet on the top of one of its mountains. Western Lincoln, Bridger Teton National Forest recorded about 30 inches of Mountains, Teton, Park, November snow in their mountains while many sections of Yellowstone Green River 1988-Nov-12 0 0 $0 $0 Snow Sweetwater, 14, 1988 National Park accumulated 10 to 20 inches. This storm caused Basin, Red Fremont, the Jackson Hole airport to be closed, and there were Desert Sublette numerous automobile and truck accidents. Some of the accidents did cause personal injuries. The snowstorm considerably eased the drought situation. The storm was the greatest snowfall event since November 1985. Other snowfall amounts included 2 feet in the Wind River Mountains and 8 inches at Dubois. Finally, Evanston accumulated 6 to 7 inches of snowfall from this storm. Other lower elevation locations over west-central and southwest Wyoming generally picked up 1 to 6 inches of new snow during this three-day period. As a result of the combination of calm winds, a bitterly cold arctic air mass and deep snow cover, extremely low minimum temperatures occurred across the cowboy state during the morning of the 22nd. Many of these temperatures were not only record lows for the date, but also the coldest ever for December Extreme December. The lowest temperatures were generally over the Statewide Statewide 1989-Dec-21 0 0 $0 $0 22, 1989 Cold Eastern two-thirds of Wyoming. Recluse, in the far Northeast corner, had a low of 50° below zero. Other lows included 47° below in Redbird, 40° below at Douglas, 35° below at both Sheridan and Gillette, 34° below zero in Laramie, 28° below at both Casper and Cheyenne, 23° below in Cody, 14° below at Farson and 13° below zero in Lander.

Teton County MHMP 14.10

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops Record cold temperatures gripped the state from the 2nd through the morning of the 6th, the coldest in at least 5 years. Many locations had at least 80 to 100 consecutive hours of subzero readings. Wind chills from 50° to 90° below zero accompanied the cold. Most overnight lows were between minus 20° and minus 40° with maximum temperatures struggling above 15° or 20° below zero. On the morning of the 3rd, Sheridan set a record low of minus 32°, eclipsing the old record of 24° below zero, set in 1985. Casper had a record low 27° below zero. The minimum at Cheyenne was minus 24°, one degree shy of the record low for the 3rd, dating back to 1883. February Extreme Additionally, Weston, located over far northern Wyoming, Statewide Statewide 1989-Feb-02 0 0 $0 $0 06, 1989 Cold dropped to 47° below zero while locations in Yellowstone National Park dipped lower than minus 40°. These low temperatures, including several records, were typical through the 6th. The maximum temperature for Cheyenne on the 3rd was 18° below zero. Not only was that a record low maximum, but the second coldest such reading since weather records have been kept at Cheyenne, back more than 100 years. During the morning of the 6th, the temperature at the capitol city finally rose above zero. The record is 120 hours, set in December 1983. Due to this Arctic episode, this was the coldest February ever for Casper. It was also the worst cold spell for Gillette in a decade. A major winter storm followed by a bitterly-cold Arctic outbreak, plagued most of Wyoming for about two to four days. Heavy snows with strong winds occurred on the 18th over the far western part of the state, with up to a foot in the mountains. Light snows of 2 to 6 inches generally occurred over the rest of the state, except in the far southwest where storm totals approached 15 to 20 inches by 1800 MST on the 19th. Bitterly- cold Arctic air started spilling into the state after 1200 MST on the 18th on brisk northern winds. On the 19th and 20th, wind Snow, chills dropped to -40° to -75° at times in many areas. The December Statewide Statewide 1990-Dec-18 0 0 $27,500 $0 Heavy, coldest temperatures occurred on the 21st and 22nd, with most 22, 1990 Bitter Cold areas from -25° to -45°. Minus 50° readings were reported at Worland and near Jackson. Casper set an all-time record-low of -41° on the 21st. Major roads affected by the snow and winds were confined to the far west and southwest. The worst conditions occurred along I-80 from Rock Springs to Rawlins on the night of the 19th and 20th where snow and strong winds closed the road, stranding many people. The bitter cold caused power outages in some places, most notably in Jackson. Schools and other events were widely canceled due to the cold weather.

Teton County MHMP 14.11

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops Converse, Natrona, Niobrara, Hot Springs, Heavy snow and strong winds caused blizzard conditions over Johnson, much of Wyoming. Snowfall amounts ranged from four inches Sheridan, at Rock Springs and Gillette to 17 inches at Casper Mountain. Washakie, Generally, 6 to 10 inches of snowfall was common. Winds Campbell, gusted to 55 mph and caused blizzard conditions with drifts up Crook, All except the October 23, Snow, to 5 feet deep. Reported drifts of 2 to 4r feet were common. Weston, Big Southwest 1995-Oct-21 0 0 $1,000,000 $0 1995 Blizzard Many roads were closed from the 22nd to the afternoon of the Horn, Park, Corner 23rd due to drifting and near-zero visibilities. Many travelers Teton, were stranded across the state until the 23rd and a number of Carbon, hunters had to be rescued. Power was out for a time in various Albany, places, due to downed power lines from the heavy snow and Goshen, strong winds. Laramie, Platte, Fremont, Sublette Yellowstone National Park Mt Id, North Absarokas, South Low temperatures dropped to between 10° below zero and 45° Absarokas, below zero during this time across the state. On the 1st, strong Cody Foothills, winds lowered wind chill temperatures to as low as 60° below Park, North Big Horn zero in some locations. Some young livestock were frozen. The Fremont, Basin, cold also froze many pipes and caused some water lines to Sublette, Hot Teton/Mountai February Extreme break or leak. A number of schools and events were cancelled Springs, 1996-Feb-01 1 0 $50,000 ns, Jackson 04, 1996 Cold across the state during this time. About 40 residences were Washakie, Valley, Owl without natural gas in the Big Horn Basin on the 3rd due to the Big Horn, Creek cold causing a valve malfunction. Many accidents occurred on Teton Mountains, the 1st due to poor visibilities. One person froze to death just South Big north of Buffalo early on the 2nd after walking for help after his Horn Basin, car broke down. Dubois, Wind River Mtns East, Lander Foothills

Teton County MHMP 14.12

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops Yellowstone National Park Mt Id, North Absarokas, South Heavy snow and strong winds were over the western mountains Absarokas, and the Snowy Range. Fifteen to 40 inches of snow fell, with Albany, Teton/Mountai the greatest amount being 40 inches in some of the west facing Carbon, ns, Jackson mountains. Jackson saw 24 inches of snow fell in 24 hours Fremont, January 28, Valley, Wind 1996-Jan-27 0 0 Snow, wind which was the largest 24-hour snowfall ever recorded for that Lincoln, Park, 1996 River Mtns city. Some roads in the area were closed on the 28th. In Sublette, East, Star addition, winds were from 55 to 70 mph with gusts more than Teton Valley, Salt 100 mph over the open, higher areas. The strong winds caused River Range, considerable blowing and drifting snow. Wind River Mountains West, Snowy Range. Yellowstone National Park Mt Id, Cody Two-day storm dumped up to 3 feet of snow on parts of Foothills, Johnson County, with the heaviest amounts near the town of Jackson Fremont, Buffalo. Roads (including I-25 and I-90) and schools were Valley, Dubois, April 15, Snow, Johnson, 1998-Apr-14 0 1 closed, and tree limbs and power lines were down in Buffalo. Lander 1998 Heavy Park, Teton Lesser amounts fell over northwest Wyoming, with 7 to 12 Foothills, inches reported from central parts of Jackson Hole northward Southeast Big into Yellowstone National Park. Horn Mountains, East Johnson Yellowstone National Park Mt Id, North Absarokas, South Winter storm northwestern part of state over two days, with the Absarokas, heaviest snow falling Saturday afternoon through Sunday. Big Horn, Cody Foothills, Hardest hit were Jackson Hole, northern and western Park Lincoln, Park, North Big Horn January 11, 1998-Jan-10 0 0 Snow County, and northern Sublette County, with up to 2 feet of snow Sublette, Basin, 1998 reported in these areas over the weekend. In Jackson, storm Teton Teton/Mountai was characterized as the "biggest in years." Whiteout ns, Jackson conditions reported parts of northern Park County on Sunday. Valley, Salt River Range, Wind River Mountains West

Teton County MHMP 14.13

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops North Absarokas, South Absarokas, Big Horn, Late spring storm dropped 1 to 3 feet of snow on Beartooth Teton/Mountai Fremont, Hot Highway in northwest Park Co…10 inches of snow in the Owl ns, Owl Creek June 04, Snow, Spriongs, 1998-Jun-03 0 0 Creek Mountains near Thermopolis and 7 to 9 inches of snow in Mountains, 1998 Heavy Park, Teton, the Wind River Mountains and Lander Foothills. Power outages Wind River Washakie in Fremont county due to downed power lines. Mtns East, Lander Foothills, Wind River Basin Yellowstone National Park Late spring snow storm dropped up to 30 inches of snow in the Mt Id, North June 14, Snow, Park, Teton 2001-Jun-12 0 0 Northwest Wyoming mountains. Yellowstone National Park was Absarokas, 2001 Heavy closed for part of June 13th. Teton/Mountai ns A Pacific storm system brought heavy snow and strong winds to Yellowstone the western Wyoming mountains. Snowfall amounts included National Park upwards of 2 feet at Grand Targhee Ski Resort and 1 to 2 feet Park, Teton, Mt Id, January 22, Snow, 2002-Jan-20 0 0 elsewhere. The combination of strong winds and heavy snow Lincoln Teton/Mountai 2002 Winds closed both Teton and Togwotee Passes and the highway ns, Salt River between Moose and Moran Junction. Both Grand Targhee and Range Jackson Hole ski areas closed ski lifts due to the strong winds. Two hikers climbing Grand Teton were caught in a winter storm on August 29. On the summit of Grand Teton, two feet of snow Teton and Teton, August 31, Snow, was deposited between August 29-31. The climbers sought Gros Ventre 2003-Aug-29 0 1 Sublette 2003 heavy refuge inside a dry cave until skies cleared on August 31. Ranges However, one of the climbers was seriously injured when he fell during the descent. Three vigorous weather systems slammed into the western mountains and valleys of Wyoming, dropping significant snowfall as 2003 came to a close. Holiday travel was significantly impacted as snow began with the first storm on Lincoln, Christmas Night. The final storm pushed out of western Sublette, Wyoming on January 1, 2004. Total snowfall accumulation Western December Snow, Fremont, 2003-Dec-25 0 0 $0 $0 during this eight day stretch approached 4 to 5 feet in the Wyoming 31, 2003 Heavy Teton western mountains and northern Star Valley. Two to 3 feet of counties snow was recorded in the rest of the western valleys during this time frame. Several roads were closed across western and central Wyoming including Highway 29 at South Pass and Highway 22 at Teton Pass. The conclusion of this event is provided in the January 2004 Storm Data Publication.

Teton County MHMP 14.14

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops Yellowstone National Park, Absaroka Mountains, Teton and A strong westerly flow and abundant pacific moisture brought Gros Ventre heavy snow to the mountains of western Wyoming. Snowfall Mountains, ranged from 15 to 40 inches in the mountains to 6 to 12 inches Jackson Hole, in the valleys. In addition, strong winds produced considerable Wind River Fremont, Snow, blowing and drifting snow, causing blizzard conditions in the Mountains March 07, Lincoln, Park, 2003-Mar-05 0 0 heavy, Jackson Valley on the morning of March 6th. During the same West, Wind 2003 Teton blizzard morning, snow drifts of 3 to 4 feet stranded several motorists River north of Afton. On March 6th around 11 p.m. MST, the summit Mountains of Rendezvous Peak at the Jackson Hole Ski Resort reported a East, Star wind gust of 93 mph. The summit also clocked a wind gust of Valley, Salt 84 mph on March 7th around midnight MST. River and Wyoming Ranges, Upper Green River Basin Foot Yellowstone National Park, Absaroka Mountains, Cody Foothills, A spring storm brought heavy snow to western and central Southwest Big Wyoming. The heavy snow was the result of an upper level Horn Basin, disturbance that dropped south from Montana and moved Fremont, Hot Owl Creek and across Wyoming. The storm track created a favorable upslope Springs, Snow, Bridger March 27, flow for areas east of the Continental Divide. Snowfall ranged Johnson, 2003-Mar-26 0 0 Heavy, Mountains, Big 2003 from 4 to 10 inches in the lower elevations to 24 to 30 inches in Teton, Park, Wind Horn the Teton Range of western Wyoming. Also, snowfall was Washakie Mountains around 1 foot in Lander and Meeteetse. The combination of Southeast, wind and snow closed many state highways around the area on Northeast and the morning of March 27th. Southeast Johnson County, Teton county Snow storm drops six feet of snow in 8 days. Caused Heavy Teton Teton Jan. 2006 0 0 cancellation and delay of flights, transportation issues. No snow major vehicle accidents. Intense snow storm interrupted power service, broke tree Sept. 23, Teton Teton 0 0 Snow branches, and forced closure of Teton Pass. More than a 2006 dozen drivers slid off or lost control on Teton Pass.

Teton County MHMP 14.15

Table 14.1 Teton County Winter Storms Estimated Estimated Character of County Location Start Date End Date Deaths Injured Damage - Damage – Information Storm Property Crops March 28, Snow and Teton Jackson 0 0 Widespread heavy snow and gusty winds. 2007 wind Heavy snowfall and gusts up to 80 mph. Avalanche on Hwy 22 Snow, wind, Teton Teton Co. Jan. 28, 2008 0 0 over Teton Pass closed road for 10 hours. Slide was 120 feet avalanche long by 6 feet deep. Ski lifts closed, airport shut down.

Teton County MHMP 14.16

Impacts

Winter storms usually cover a significant part of the state, and as such are difficult to describe regionally. The historic dollar impact of winter storms statewide is $158,944,800. In 2004 dollars the statewide impact is $400,972,900. The actual statewide impacts are much greater because of the effects on transportation and because of loss of life and injuries. The impacts from loss of livestock can carry over for many years. Winter storm deaths in the table above do not include vehicle accident fatalities. The Wyoming Department of Transportation provided statistics for crash deaths and injuries for the years 1994-2007. During this period, there were five fatal crashes, and 267 injury crashes in the county due to icy, slushy, or snowy roadway conditions. (Thomas Carpenter, WYDOT Highway Safety Program, 2008)

Future Impacts

Based on the history of winter storms, Teton County will continue to experience damaging winter storms about every two and half years. Based on the worst-case regional event that involved Teton County (1982) the dollar impacts—not counting loss of human life--could be in excess of $1.3 million (assuming an equal distribution of the total losses of $10.7 million, in 2004 dollars, across the 8 counties involved), enough power lines could be toppled that emergency intervention could be required, significant property damage could occur, and the livestock industry could lose 15%-20% of its inventory. Life safety will continue to be a concern for motorists, outdoor enthusiasts, or ranchers stranded by winter storms. Injuries and deaths will likely continue to occur during storm-related vehicle accidents.

Summary

PROPERTY AFFECTED: Medium POPULATION AFFECTED: High PROBABILITY: High JURISDICTION AFFECTED: County

Teton County MHMP 14.16

Chapter 15. Terrorism

Terrorism is a willful act committed by a person (domestic--U.S. citizen or non- U/S/ citizen) intended to cause disruption, fear and panic, damage and/or loss of life.

Following the bombing of the Twin Towers in New York, all counties in the country—including Teton County--completed a threat and risk assessment for potential terrorist attacks. Teton County identified approximately 30 potential targets. Terrorism can be propagated by foreigners and also U.S. citizens hostile towards the government or other entities.

History

New York’s Twin Towers have been targeted twice and the Federal Building in Oklahoma City once. Both of these attacks resulted in a large number of fatalities. Americans have also been killed in other terrorist aircraft incidents. A number of attempts have been stopped. In addition to these high profile cases, domestic terrorists have targeted entities such as laboratories, a resort development, and auto dealerships--making statements in favor of environmental protection. None of these types of attacks has occurred in Teton County. However, both the National Parks and individuals who live in or frequent the county could be potential targets for terrorism.

Impacts

Impacts of a terrorist attack in Teton County could include fear and panic, civil unrest, property loss and damage, damage or destruction of infrastructure, loss of life, and interruption of communications and business. There is no history upon which to develop a dollar loss estimate for Teton County. Losses would depend on the type and location of the terrorist action.

Future Impacts

Future impacts could include those listed above, plus resulting associated natural resource disasters. If a dam was targeted for example, flooding could also occur.

Summary

PROPERTY AFFECTED: Medium POPULATION AFFECTED: Medium PROBABILITY: Low JURISDICTION AFFECTED: All

Teton County MHMP 15.1

Chapter 16. Goals and Mitigation Actions

How the Goals and Mitigation Actions Were Developed

The goals and actions that follow were developed by the contractor, deputy county coordinator, and the advisory committee after consideration of:

the history of hazards in the county, the probability of future occurrences, the vulnerability of key systems and facilities, the projects that were identified in the 2004 plan, available resources and capacities, and several disaster scenarios.

Problem Statements

At the October 21 meeting, the Advisory Committee generated three possible disaster scenarios. Potential impacts of each scenario were listed. From these impacts, problem statements were developed.

Many impacts or problems would be common to more than one of the following scenarios or even other scenarios that were not discussed. The problems that could occur in more than one scenario suggest mitigation actions that are “robust” because they address a number of disaster possibilities and are likely to be cost-effective. The problem statements that apply to more than one scenario are given at the end of the scenarios. The problem statements that apply to only one scenario are provided under that scenario.

Scenario One: A 7.5 magnitude earthquake occurs along the Teton Fault.

A number of areas become inaccessible because the earthquake severely damages or destroys a number of highway and other bridges. The earthquake causes one or more of the high hazard dams to breach or wash out.

Scenario Two: A severe winter storm closes all highways in and out of the valley.

Scenario Three: A hazardous material spill or terrorist attack occurs on Town Square when it is filled with people.

A half-mile radius must be evacuated. That half-mile contains key transportation intersections, the Emergency Operations Center, Sheriff’s Office, Police Station, and town and county government offices.

Teton County MHMP 16.1

Problems that could occur under two or more scenarios.

Power is lost in the valley. With the loss of electricity, people lose primary heat source. Cell, landline and radio communications could be compromised or inadequate. Natural gas pipeline breaks. There is no ability to warn people. Significant damage could occur to public and private buildings and there is not an adequate number of inspectors to determine what is safe. The airport is closed either due to inclement weather or runway damage, eliminating a means of getting people and supplies in and out of the valley. Landslides close roads. Emergency response personnel can not report to work. DOT and public works equipment operators can not get to the equipment and can not get the roads and highways cleared of debris and/or snow. Commuting workers in the valley can not get home. A large number of visitors may be stranded in Jackson or other areas of the valley. Some areas do not have the ability to shelter. Some stranded visitors and/or residents may not speak English. Alta could be shut off from the rest of the county. Mass casualties overwhelm medical resources. Key emergency response facilities may be damaged or unavailable. Food and supplies can not get into the valley and run low or run out. People panic.

Additional Problems

New construction may be occurring in areas with natural hazards because there is no comprehensive map of hazard areas for the county. Large numbers of skiers could be trapped at Grand Targhee if the access road becomes impassable. Stormwater back-up flooding central areas of Jackson.

Teton County MHMP 16.2

Each goal statement below is followed by a table giving information about the specific mitigation actions or projects. The actions vary in cost and in priority. Costs were estimated to fall within three ranges and assigned a low, medium, or high rating.

High priority projects from the 2004 plan that have not been completed, are not underway, are still appropriate, and are specific enough to bring forward are incorporated into the project lists under each goal.

Low Cost Projects: from $0 to $5000

Medium Cost Projects: from $5001 to $25,000

High Cost Projects: $25,001 and over.

Priority rankings were also assigned by the contractor and Deputy County Emergency Management Coordinator based on a low, medium, and high system.

High Priority Projects: projects identified in response to one or more of the highest probability hazards combined with the ability to save lives.

Medium Priority Projects: projects associated with a less probable hazard with potential to save lives or damage to property.

Low Priority Projects: projects associated with low or infrequent hazard probability and least likely to prevent loss of life.

A full range of types of mitigation actions or projects were identified by the participants in the planning process. Project type is shown in the tables in this chapter designated by one or more letters corresponding to the following types;

P Prevention PR Preparation PP Property Protection EA Education and Awareness NRP Natural Resource Protection S Structural Projects C Coordination

Teton County MHMP 16.3

GOAL ONE: Increase the disaster-resistance of the transportation infrastructure and prepare to respond effectively when transportation routes are compromised.

Table 16.1 Goal One Projects # Description Priority Cost Type Who 1.a Assess all state highway High High P, PR, WYDOT bridges for seismic NRP, S FHWA vulnerability Geol. Survey

1.b Assess secondary road Med High P, PR, WYDOT and private bridges for NRP, S Geol. Survey, seismic vulnerability Teton Co Road and Levy 1.c Assess the town bridges for Med Med Jackson Public seismic vulnerability Works

1.d Prioritize mitigation of High High P, PR, LEPC, WYDOT seismic issues on public NRP, S FHWA and private bridges and Geol. Survey, begin mitigation County Road and Levy, Jackson Public Works 1.e Identify nearest resources Med Med P, PR, WYDOT, for installation of temporary NRP, S Emergency bridges Management, National Guard 1.f Work with town/county Med Med PR, PP, WYDOT, building inspectors to train S, C Emergency volunteer cadre for Management, emergency bridge Jackson and Teton inspections County building depts. 1.g Develop transportation High Low P, PR, C LEPC alternatives plan to get emergency responders into the valley

1.h Complete Fire/EMS Capital High High P, PR, Town, County, Project priority 14, PP, NR, Fire/EMS reconstruct Wilson Fire S Station

1.i Complete emergency plan High Low P, EA, C Resort, EM, Red for Targhee Resort Cross

Teton County MHMP 16.4

Teton Pass from Idaho state line. This route carries workers to and from Jackson daily.

GOAL TWO: Be prepared for isolation of and within the valley.

Table 16.2 Goal Two Projects # Description Priority Cost Type Who 2.a Negotiate agreements with Med Low PR, C Emergency the lodging association for Management, rates during emergencies Lodging Association 2.b Calculate the # of hotel beds Med Low PR, C Emergency available for emergency Management, housing and use this as a Red Cross trigger for opening shelters

2.c Negotiate and sign an High Low PR, C Emergency agreement with one lodging Management establishment to provide the lodging for emergency responders without homes in the valley during an emergency.

Teton County MHMP 16.5

# Description Priority Cost Type Who 2.d Work with local food bank Med Low PR, C Emergency and grocery stores to Management, develop a plan for providing Public Health, food during an emergency. Grocery Stores, Food Bank, Red Cross 2.e Work with hospital and High Low PR, C Emergency pharmacies to develop a plan Management, to ensure medicines can be St. Johns, obtained, delivered during an Pharmacies, emergency. Public Health

2.f Acquire a helicopter (with Med High PR, C Emergency neighboring counties) to airlift Management, critical personnel and Town and supplies into valley. County

2.g Ensure commuting workers High Low P, PR, Emergency are prepared to be cut-off C Management, from home. Stress Red Cross contingency and communication plans and 72- hour kits.

2.h Develop a resource list of Med Low C Red Cross, volunteer capabilities for Emergency emergency support in the Management valley.

2.i Complete Fire/EMS Capital High High P, PR, Town, County, Project Priority #1, new PP, Emergency station at Hoback NRP, S Management

2.j Complete Fire/EMS Capital High High P, PR, Town, County, Project #21, new fire station PP, Emergency at Jackson Hole Golf and NRP, S Management Tennis

2.k Develop a list of individuals High Low P, PR, Emergency unable to self evacuate EA, C Management, (UTSE) Red Cross, St. Johns

Teton County MHMP 16.6

# Description Priority Cost Type Who 2.l Purchase/install mobile High Med PR, C Town, incident command capability Emergency in five police Management vehicles(@$500/ea)

2.m Monitor state policy Med Low PR, Emergency development on amateur C Management, radio operations and ECHOJH emergency management. Integrate amateur radio resources into the communications system.

2.n Host a demonstration of Low Low C ECHOJH IRLP capability

2.o Create a small cache of pre- Med High PR, C Emergency programmed back-up Management, portable radios Fire/EMS, Law enforcement

Consolidated Fire/EMS Administration building

Teton County MHMP 16.7

GOAL THREE: Increase levels of general preparedness and awareness for a variety of potential hazard situations.

Table 16.3 Goal Three Projects # Description Priority Cost Type Who 3.a Offer 2 CERT courses/year High Low P, EA Emerg. Mgmt Red Cross 3.b Offer 2-4 weather spotter Med Low P, EA Emergency courses/year Management NOAA 3.c Offer course assembling 72- High Low P, EA Emergency hour kits—address back-up Management heat sources

3.d Develop and run avalanche High Low P Emergency public service announcmts Management, Avalanche Center 3.e Produce a detailed county High High PR, PP, Co. Planning, hazard map to ensure NRP, C Emergency development is not occurring in Management, hazard areas WYOHS, Geol. Survey 3.f Support Lower Valley Energy High High P, PR, Lower Valley in accomplishing the Caribou PP, S Energy, Project (new station at Soda C Emergency Springs) to provide contingent Management, electrical power Bonneville Power Adm. 3.g All town, county employees Med Low PR, EA Town, complete ICS 100 and NIMS County 700 online courses

3.h Complete a Continuity of Govt. Med Med P, PR, Emergency Plan for the county C Management, Teton Co. 3.i Complete a Continuity of Govt. Med Med P, PR, Emergency Plan for the town C Management, Town 3.j Maintain on-going exercise program (drill, table top, functional, and full-scale)

3.k If/when loss of life or a disaster Low Low P, EA Emergency occurs follow-up with news Management releases on prevention

Teton County MHMP 16.8

GOAL FOUR: Be ready to respond to the inevitable winter storms.

Table 16.4 Goal Four Projects # Description Priority Cost Type Who 4a Continue to monitor slide High Low PR, WYDOT, County areas, close roads as NRP Road and Levy, necessary, and prioritize Jackson Public response to incidents Works

4b Install snow support structures High Med P WYDOT, Forest to stop slides on S89 Service

GOAL FIVE: Reduce potential damage, injury and loss of life from earthquake hazard.

Table 16.5 Goal Five Projects # Description Priority Cost Type Who 5.a Identify critical private facilities Med High P, PR, WY Geol. Survey, and infrastructure. PP, S Emergency Assess seismic vulnerability. Management, (hospital, utilities, etc.) Property Owners

5.b Identify critical public Med High PR, PP, Town and county, infrastructure NRP, S Emergency (water, sewer, roads) Management

5.c Identify and pursue fund Med Low C Town and County, sources for seismic mitigation Emergency projects Management, WYOHS, FEMA 5.d Train volunteer cadre of Low Med PR, P, Town and county structure inspectors to do S, C inspectors, safety assessments of critical Emergency buildings following a seismic Management event

Teton County MHMP 16.9

GOAL SIX: Be prepared to respond to a Hazmat incident.

Table 16.6 Goal Six Projects # Description Priority Cost Type Who 6.a Conduct a placard count to Med Med PR Emergency determine the amount and type Management of hazmat moving through the Fire Department county WYDOT

6.b Purchase specialty response High Med PR Town and equipment County (suits, etc.)

6.c Fund and implement Fire/EMS High High P, PR, Town, County, Capital Improvements Project NRP Emergency #6 Management Training Facility Improvemt

6.d. Train 12 individuals to the High Med PR Town and Technician Level County, WYOHS

GOAL SEVEN: Minimize potential losses from flooding and wind events.

Table 16.7 Goal Seven Projects # Description Priority Cost Type Who 7.a Continue participation in High Low P, PP, Town, County, National Flood Insurance S property owners Program

7.b Continue monitoring frazile ice Med Med PP, WYOHS, FEMA, build-up in Flat Creek. NRP Town, U.S. Army Implement mitigation plan to Corp prevent flooding from the ice.

7.c Complete North Cache storm High High PR, S Town, water upgrade to reduce WYOHS/FEMA flooding in town

7.d Bury all overhead electrical Med High P, PP, Town, Utility, lines in the corporate limits of S FEMA Jackson

7.e Finish implementation of Med Med P, PP, Town hazard tree reduction program S in Jackson

Teton County MHMP 16.10

Snake River looking south from Wilson bridge.

GOAL EIGHT: Reduce vulnerability to terrorism.

Table 16.8 Goal Eight Projects # Description Priority Cost Type Who 8.a Review and upgrade security High Med PR, S Emergency procedures for access to local Management, government buildings and sites Jackson PD, Teton Co, Sheriff 8.b Proceed with hardening Med High PR, S Town and potential targets identified in County Law homeland security assessment Enforcement, WYOHS 8.c Provide training in WMD Med Med PR WYHOS

8.d Identify mental health Med Low PR, C Emergency resources available locally Management, Red Cross

Teton County MHMP 16.11

Project Selection and Implementation

Some of the projects identified above are already underway and/or planned for in the near-term. And, it should be noted that the Fire Department has consistently applied for and received grant funds outside of the pre-disaster mitigation process, successfully enhancing training, equipment, coordination, and services. The jurisdictions will need to determine the priority of the identified mitigation actions for their jurisdictions on an annual basis in light of the available resources. Each spring prior to the annual budget setting, the County Emergency Management Coordinator will contact the mayor of Jackson Hole and the Chair of the Board of County Commissioners by letter or appearance at a regularly-scheduled meeting. The purpose of the contact will be to update the elected officials on projects that are either underway or completed, request the local project priorities for the coming year’s budget, and determine what if any support will be needed from the County Emergency Management program. The county can assist the local jurisdiction, Jackson, in applying for grant funds, obtaining information and technical expertise.

The county can also make available information regarding the STAPLEE method for evaluating and prioritizing mitigation actions. The method looks at social, technical, administrative, political, legal, economic, and environmental aspects of projects as a means of weighing the pros and cons of implementing specific mitigation actions. Information on this analysis method can be found in FEMA’s Developing the Mitigation Plan (FEMA 386-3). The local jurisdictions will need to consider compatibility with goals and objectives in the state’s mitigation plan, compatibility with goals in this MHMP, impacts of the project on other jurisdictions, costs and benefits, funding priorities, and compatibility with other local or county plans and programs.

Teton County MHMP 16.12

Chapter 17. Plan Monitoring, Maintenance, Revision, and Coordination

Responsible Parties

The Teton County Commissioners in cooperation with the mayor of Jackson Hole are responsible for ensuring that the MHMP is kept current. With adoption of the plan, the Commissioners designate the Teton County Emergency Management Coordinator—with the assistance of the Local Emergency Planning Committee— as the lead in accomplishing the on-going responsibility.

Plan Monitoring and Evaluation

There are two types of plan monitoring and evaluation; effectiveness and implementation. Effectiveness monitoring looks at whether the plan has addressed needed items. Implementation monitoring looks at whether projects in the plan are being undertaken and completed. The County Emergency Management Coordinator with the help of the LEPC will ask the following questions to evaluate the effectiveness and implementation of the plan.

Have any potential hazards developed that were not addressed in the plan? Have any natural disasters occurred that were not addressed in the plan? Has any unanticipated development occurred that is vulnerable to hazards? Are there any additional mitigation ideas that need to be incorporated? Have projects been initiated and/or completed? What are the barriers to completing projects identified in the plan?

Each January the LEPC will meet to ask and answer the questions listed above. The discussion will be documented so that when the plan is revised, the findings of the monitoring can be incorporated into the revision. The County Emergency Management Coordinator will ask the LEPC Chair to convene the LEPC for this purpose.

Plan Update Review Triggers

Any of the following three situations could trigger a review and update of the plan.

Occurrence of a major natural disaster in or near Teton County Passage of five years Change in state or federal regulations which must be complied with.

Teton County MHMP 17.1

Revision Procedures

Should a major natural disaster occur in Teton County, the LEPC shall meet following the disaster to determine whether a review of the MHMP is warranted. In the absence of a major natural disaster, the five-year review will take place during the six-month period preceding the FEMA approval anniversary date.

The Teton County Emergency Management Coordinator will publish a legal ad in the Jackson Hole News and Guide notifying the public that an update is being initiated and providing information on meeting schedules, how and where to get information on the project, and how to provide input. The coordinator will then convene the LEPC and with their assistance and/or the assistance of the WYOHS or a contractor as determined necessary, carry out the following tasks;

1. Review the Hazard Mitigation Plan Review Crosswalk form completed by WYOHS and FEMA during their most recent review of the plan.

2. Examine and revise the risk assessment and development trends data as needed to ensure it is current.

3. Update the mitigation strategies to incorporate completion of actions and add any needed strategies or projects.

4. Identify problems that may be hindering or affecting implementation of the plan, and recommend actions for resolving those problems.

5. Recommend any necessary revisions to the MHMP.

6. Comply with all applicable regulations and statutes.

Forty-five days prior to the five-year anniversary date, a final draft of the revised plan will be submitted to the WYOHS.

An annual review will be conducted by the County Emergency Management Coordinator for the purpose of summarizing the status and effectiveness of the plan mitigation goals or strategies.

Incorporation into Other Plans

Teton County is updating its comprehensive land use plan simultaneously with this MHMP revision. The county planner has been made aware of this plan and has contributed to its content. The Deputy County Emergency Management Coordinator and hazard mitigation contractor provided comments to the county for the land use plan update. The Deputy County Emergency Management Coordinator was extensively involved in the preparation of this plan and has a

Teton County MHMP 17.2

thorough knowledge of its contents. The Deputy Coordinator and the county commissioner liaison will ensure that hazard mitigation strategies are considered in any appropriate county plans developed or revised during the next five-year period.

One of the high priority projects in this mitigation plan is the development of a detailed hazard map for the county. This map will be used to evaluate future development proposals to ensure that they are not approved in areas of high hazard without adequate mitigation. Once this map has been created, the county will be able to specifically articulate the hazards of concern—most likely during the pre-planning stages and/or incorporated into regulation of the development process—to ensure that the developers address them.

The MHMP has identified the need for a number of additional planning efforts, primarily related to Emergency Operations and preparedness. As the driver for development of these other plans, the MHMP will provide valuable background and support and should be reviewed by other planners and incorporated by reference at a minimum. The Deputy or County Emergency Management Coordinator will be a participant—most likely the lead--in those planning processes and can ensure close coordination, referencing, and inclusion of MHMP plan elements as necessary.

Teton County MHMP 17.3 Chapter 16. Goals and Mitigation Actions

How the Goals and Mitigation Actions Were Developed

The goals and actions that follow were developed by the contractor, deputy county coordinator, and the advisory committee after consideration of: • the history of hazards in the county, • the probability of future occurrences, • the vulnerability of key systems and facilities, • the projects that were identified in the 2004 plan, • available resources and capacities, and • several disaster scenarios.

Problem Statements

At the October 21 meeting, the Advisory Committee generated three possible disaster scenarios. Potential impacts of each scenario were listed. From these impacts, problem statements were developed.

Many impacts or problems would be common to more than one of the following scenarios or even other scenarios that were not discussed. The Geologists of Jackson Hole correctly pointed out during the comment period that the worst scenarios would occur when disasters compounded each other or happened simultaneously. For example, and earthquake could also cause dam failure or occur during a mid-winter storm.

The problems that could occur in more than one scenario suggest mitigation actions that are “robust” because they address a number of disaster possibilities and are likely to be cost-effective. The problem statements that apply to more than one scenario are given at the end of the scenarios. The problem statements that apply to only one scenario are provided under that scenario.

Scenario One: A 7.5 magnitude earthquake occurs along the Teton Fault.

• A number of areas become inaccessible because the earthquake severely damages or destroys a number of highway and other bridges. • The earthquake causes one or more of the high hazard dams to breach or wash out.

Scenario Two: A severe winter storm closes all highways in and out of the valley.

Scenario Three: A hazardous material spill or terrorist attack occurs on Town Square when it is filled with people.

Teton County MHMP 16. 1 • A half-mile radius must be evacuated. That half-mile contains key transportation intersections, the Emergency Operations Center, Sheriff’s Office, Police Station, and town and county government offices.

Problems that could occur under two or more scenarios. • Power is lost in the valley. • With the loss of electricity, people lose primary heat source. • Cell, landline and radio communications could be compromised or inadequate. • Natural gas pipeline breaks. • There is no ability to warn people. • Significant damage could occur to public and private buildings and there is not an adequate number of inspectors to determine what is safe. • The airport is closed either due to inclement weather or runway damage, eliminating a means of getting people and supplies in and out of the valley. • Landslides close roads. • Emergency response personnel can not report to work. • DOT and public works equipment operators can not get to the equipment and can not get the roads and highways cleared of debris and/or snow. • Commuting workers in the valley can not get home. • A large number of visitors may be stranded in Jackson or other areas of the valley. Some areas do not have the ability to shelter. Some stranded visitors and/or residents may not speak English. • Alta could be shut off from the rest of the county. • Mass casualties overwhelm medical resources. • Key emergency response facilities may be damaged or unavailable. • Food and supplies can not get into the valley and run low or run out. • People panic.

Additional Problems

• New construction may be occurring in areas with natural hazards because there is no comprehensive map of hazard areas for the county . • Large numbers of skiers could be trapped at Grand Targhee if the access road becomes impassable. • Stormwater back-up flooding central areas of Jackson.

Teton County MHMP 16. 2 Each goal statement below is followed by a table giving information about the specific mitigation actions or projects. The actions vary in cost and in priority. Costs were estimated to fall within three ranges and assigned a low, medium, or high rating.

High priority projects from the 2004 plan that have not been completed, are not underway, are still appropriate, and are specific enough to bring forward are incorporated into the project lists under each goal.

Low Cost Projects : from $0 to $5000

Medium Cost Projects : from $5001 to $25,000

High Cost Projects : $25,001 and over.

Priority rankings were also assigned by the contractor and Deputy County Emergency Management Coordinator based on a low, medium, and high system. The Advisory Committee concurred with the rankings.

High Priority Projects : projects identified in response to one or more of the highest probability hazards combined with the ability to save lives.

Medium Priority Projects : projects associated with a less probable hazard with potential to save lives or damage to property.

Low Priority Projects : projects associated with low or infrequent hazard probability and least likely to prevent loss of life.

A full range of types of mitigation actions or projects were identified by the participants in the planning process. Project type is shown in the tables in this chapter designated by one or more letters corresponding to the following types;

• P Prevention • PR Preparation • PP Property Protection • EA Education and Awareness • NRP Natural Resource Protection • S Structural Projects • C Coordination

Acronyms in the following project tables are found at the bottom on Table 16.1.

Teton County MHMP 16. 3 GOAL ONE: Create disaster-resistant infrastructure. Enhance existing infrastructure.

Table 16.1 Goal One Projects # Description Benefits Priority Cost Type Responsible agency for implementation coordination 1.a Assess all state Better High High P, PR, WYDOT highway bridges for understand NRP, S seismic vulnerability vulnerability

1.b Assess secondary Better Med High P, PR, WYDOT road and private understand NRP, S Teton County bridges for seismic vulnerability Engineering vulnerability

1.c Assess the town Better Med Med P, PR, Jackson Public bridges for seismic understand NRP, S Works vulnerability vulnerability

1.d Prioritize mitigation Increase High High P, PR, LEPC, WYDOT of seismic issues on disaster – NRP, S FHWA, Geol. public and private resistance of Survey, County bridges and begin transportation Road and Levy, mitigation system Jackson Public Works 1.e Identify nearest Be prepared High Low P, PR, WYDOT, TCEM, resources for to quickly re- NRP, S National Guard installation of establish temporary bridges transportation system 1.f Work with Be able to Med Med PR, PP, WYDOT, TCEM, town/county building quickly S, C Jackson and Teton inspectors to train assess County building volunteer cadre for building depts. building inspections. safety. Save lives. 1.g Work with WYDOT to Be able to Med Med PR, PP, WYDOT, Town train quick response quickly asses S, C Public Works, bridge inspection bridge safety. Teton County cadre Save lives Engineering, and property County Road and Levy 1.h Develop Enhance High Low P, PR, C START transportation response LEPC alternatives plan to effectiveness get responders into the valley

Teton County MHMP 16. 4

# Description Benefits Priority Cost Type Responsible agency for implementation coordination 1.i Complete Fire/EMS Enhance High High P, PR, Town, County, Capital Project response PP, NR, Fire/EMS priority 14, effectiveness S reconstruct Wilson for Wilson Fire Station area

1.j Identify critical public Better High High P, PR, WY Geol. Survey, and private understand PP, S, TCEM, Property infrastructure and vulnerability NRP Owners, facilities (water, Town, County sewer, roads, hospital, utilities) Asesss seismic vulnerability

1.k Identify and pursue Increase Med Low C Town, County fund sources for disaster- Planning Depts, seismic structural resistance. County Grants mitigation projects Save lives Specialist, TCEM, and property. WOHS, FEMA 1.l Complete and Respond High Med PR.C TCEM maintain a more comprehensive effectively inventory of disaster response equipment

Acronyms: ARC is the American Red Cross, EMS is Emergency Medical Services, FEMA is the Federal Emergency Management Agency, FHWA is the Federal Highway Administration, IRLP is xxxx, LEPC is the Local Emergency Planning Committee, NOAA is the National Oceanic and Atmospheric Administration (parent to the National Weather Service) PD is the Police Department, SO is the Sheriff’s Office, START is the Teton Area Transit , TCEM is Teton County Emergency Management, WOHS is the Wyoming Office of Homeland Security, WYDOT is the Wyoming Department of Transportation

Teton Pass from Idaho state line. The route carries workers to and from Jackson daily.

Teton County MHMP 16. 5 GOAL TWO: Be prepared for isolation of and within the valley.

Table 16.2 Goal Two Projects # Description Benefits Priority Cost Type Responsible agency for implementation coordination 2.a Calculate the total # of Open shelters Med Low PR, C TCEM, ARC, hotel beds available for when truly Jackson Hole emergency housing and needed Central use this as a trigger for Reservations opening shelters

2.b Negotiate, sign Ensure High Low PR, C Individual Town agreements with lodging responders and County establishments to have lodging in agencies provide the emergency the valley lodging for responders during without homes in the emergencies valley

2.c Work with local food Ensure food is High Low PR, C TCEM, Teton bank and grocery stores available if County Public to develop a plan for transportation Health, Grocery providing food during an is cut off Stores, Food emergency. Bank, ARC

2.d Work with hospital and Ensure critical High Low PR, C St. Johns, pharmacies to develop a medicines are Pharmacies, plan to ensure available if Teton County medicines can be transportation Public Health obtained and delivered is cut off during an emergency. 2.e Ensure commuting Reduce stress High Low P, PR, TCEM, ARC workers are prepared to on responders C be cut-off from home. and families Stress 72-hour kits, contingency plans, and communication plans.

2.f Develop a resource list Get appropriate Med Low C ARC of volunteer capabilities resources for emergency support in where needed the valley. faster

2.g Complete Fire/EMS Provide High High P, PR, Town, County, Capital Project Priority response PP, Jackson Hole #1, new station at capability to NRP, S Fire/EMS Hoback area that may be isolated during disaster

Teton County MHMP 16. 6

# Description Benefits Priority Cost Type Responsible agency for implementation coordination 2.h Complete Fire/EMS Provide High High P, PR, Town, County, Capital Project #21, new response PP, Jackson Hole fire station at Jackson capability to NRP, S Fire/EMS Hole Golf and Tennis area that may be isolated during disaster 2.j Purchase/install mobile Be able to High Med PR, C Jackson PD IC command capability manage in five police vehicles disasters in @$500/ea isolated areas

2.k Monitor state policy Maximize Med Low PR, TCEM, RACES development on amateur ability of C radio operations and amateur radio emergency operators to management. Integrate assist during amateur radio resources disasters into the communications system.

2.l Annually demonstrate Improve Low Low C RACES IRLP capability understanding of capability to assist 2.m Create a small cache of Enhance Med High PR, C TCEM, pre-programmed back- communication Fire/EMS, PD, up portable radios capability for SO disasters 2.n Install snow support Reduce High Med P, NRP WYDOT, Forest structures to stop slides potential for Service on S89 loss of life

2.o Obtain year-round Support High High C, P, TCSO availability of helicopter operations PR during disaster, support Search and Rescue

Teton County MHMP 16. 7 GOAL THREE: Improve awareness and preparedness for natural disasters.

Table 16.3 Goal Three Projects # Description Benefits Priority Cost Type Responsible agency for implementation coordination 3.a Offer two CERT Raised High Low P, EA TCEM, Jackson courses/year awareness, Hole Fire/EMS response capability 3.b Offer 2-4 weather Raised High Low P, EA TCEM spotter courses/year awareness, NOAA better data 3.c Offer course Citizens will be High Low P, EA TCEM assembling 72-hour better prepared kits—address back- up heat sources

3.d Develop and run Prevent injuries Med Med P TCEM, Avalanche avalanche public and fatalities Center, SO-Search service and Rescue announcements 3.e Produce a detailed Prevent future High High PR, PP, County Planning, county hazard map property NRP, C WOHS, Geol. to ensure damage Survey development is not occurring in hazard areas

3.f Support Lower Ensure High High P, PR, Lower Valley Valley Energy in adequate PP, S Energy, WOHS, accomplishing the power for heat, C Bonneville Power Caribou Project communication, Adm. (new station at and other Soda Springs) to needs provide contingent electrical power

3.g Develop and Ensure local High Med PR, EA TCEM enforce govt employees Town/County preparedness can assist Human Resources requirements for during town and county disasters employees

3.h Complete a Continue to High Low P, PR, C TCEM, County Continuity of Govt. provide Plan for the county essential

3.i Complete a Continue to High Low P, PR, C TCEM, Town Continuity of Govt. provide Plan for the town essential services

Teton County MHMP 16. 8 # Description Benefits Priority Cost Type Responsible agency for implementation coordination 3.j Maintain on-going Be ready to High High PR,C TCEM, Town, exercise program respond safely County (drill, table top, and effectively functional, and full- to future scale) disasters

3.k Continue to monitor Save lives High Low PR, WYDOT, County slide areas, close NRP Road and Levy, roads as necessary, Jackson Public and prioritize Works response to incidents 3.m Continue Prevent High Low P, PP, S Town, County, participation in property loss property owners National Flood and damage Insurance Program

3.n Mitigate frazile ice Prevent Med Med PP, WOHS, FEMA, build-up property loss NRP Town, U.S. Army and damage Corp of Engineers 3.o Complete North Prevent High High PR, S Town Planning, Cache storm water property loss, WOHS, FEMA upgrade to reduce damage, and flooding in town business interruption 3.p Bury all overhead Prevent injury Med High P, PP, S Town, Utility, FEMA electrical lines in the and property corporate limits of damage Jackson

3.q Finish Prevent injury Med Med P, PP, Town implementation of and property S hazard tree damage reduction program in Jackson

3.r Develop a list of Save lives High Low P, PR, TCEM, Teton individuals unable to during EA, C County Public self evacuate disasters Health, (UTSE) St. Johns

Teton County MHMP 16. 9

Snake River looking south from Wilson bridge.

Consolidated Fire/EMS Administration building

Teton County MHMP 16. 10 GOAL FOUR: Improve awareness and preparedness for human-caused disasters.

Table 16.4 Goal F our Projects # Description Benefits Priority Cost Type Responsible agency for implementation coordination 4.a Conduct a More Med Med PR TCEM, Jackson Hole placard count to effective, Fire/EMS, determine the safer spill WYDOT amount and type response LEPC of hazmat moving through the county

4.b Develop and More High High PR, Town, County, WOHS equip a local 12- effective, NRP person hazmat safer spill response team. response

4.c Fund and Better High High P, Town, County, Jackson Hole implement capability to PR, Fire/EMS Fire/EMS Capital respond to NRP Improvements all types of Project #6 disasters. Training Facility Responder Improvement safety improved 4.d Review and Reduced Med Med PR, S TCEM, PD, SO upgrade security chances of procedures for domestic access to local terror attack government buildings and sites

4.e Harden identified Reduced Med High PR, S PD, SO, WOHS targets chances of terrorist attack 4.f Provide training Better Med Low PR TCEM in WMD capability to detect and respond 4.g Identify mental More Med Low PR, C Teton County Public Health, health resources effective ARC available locally response to all types of incidents

Teton County MHMP 16. 11 Project Selection and Implementation

Some of the projects identified above are already underway and/or planned for in the near-term. And, it should be noted that the Fire Department has consistently applied for and received grant funds outside of the pre-disaster mitigation process, successfully enhancing training, equipment, coordination, and services. The jurisdictions will need to determine the priority of the identified mitigation actions for their jurisdictions on an annual basis in light of the available resources. Each spring prior to the annual budget setting, the County Emergency Management Coordinator will contact the mayor of Jackson and the Chair of the Board of County Commissioners by letter or appearance at a regularly-scheduled meeting. The purpose of the contact will be to update the elected officials on projects that are either underway or completed, request the local project priorities for the coming year’s budget, and determine what if any support will be needed from the County Emergency Management program. The county can assist the local jurisdiction, Jackson, in applying for grant funds, obtaining information and technical expertise.

The county can also make available information regarding the STAPLEE method for evaluating and prioritizing mitigation actions. The method looks at social, technical, administrative, political, legal, economic, and environmental aspects of projects as a means of weighing the pros and cons of implementing specific mitigation actions. Information on this analysis method can be found in FEMA’s Developing the Mitigation Plan (FEMA 386-3). The local jurisdictions will need to consider compatibility with goals and objectives in the state’s mitigation plan, compatibility with goals in this MHMP, impacts of the project on other jurisdictions, costs and benefits, funding priorities, and compatibility with other local or county plans and programs.

Teton County MHMP 16. 12