GEOLOGIC HAZARDS OF THE STATE ROUTE 9 CORRIDOR, LA VERKIN CITY TO TOWN OF SPRINGDALE, WASHINGTON COUNTY, UTAH by Tyler R. Knudsen and William R. Lund SPECIAL STUDY 148 UTAH GEOLOGICAL SURVEY a division of UTAH DEPARTMENT OF NATURAL RESOURCES 2013 GEOLOGIC HAZARDS OF THE STATE ROUTE 9 CORRIDOR, LA VERKIN CITY TO TOWN OF SPRINGDALE, WASHINGTON COUNTY, UTAH by Tyler R. Knudsen and William R. Lund Cover photo: The Watchman landslide in Springdale, Utah, developed in the spring of 2005 and is one of several historically active landslides in the State Route 9 Corridor Geologic-Hazard Study Area. ISBN: 978-1-55791-880-2 SPECIAL STUDY 148 UTAH GEOLOGICAL SURVEY a division of UTAH DEPARTMENT OF NATURAL RESOURCES 2013 Gary R. Herbert, Governor Michael Styler, Executive Director Richard G. Allis, Director contact Natural Resources Map & Bookstore 1594 W. North Temple Salt Lake City, UT 84114 telephone: 801-537-3320 toll-free: 1-888-UTAH MAP website: mapstore.utah.gov email: [email protected] contact 1594 W. North Temple, Suite 3110 Salt Lake City, UT 84114 telephone: 801-537-3300 website: geology.utah.gov Although this product represents the work of professional scientists, the Utah Department of Natural Resources, Utah Geological Survey, makes no warranty, expressed or implied, regarding its suitability for a particular use. The Utah Department of Natural Resources, Utah Geological Survey, shall not be liable under any circumstances for any direct, indirect, special, incidental, or consequential damages with respect to claims by users of this product. CONTENTS ABSTRACT ..................................................................................................................................................................................1 INTRODUCTION ........................................................................................................................................................................ 1 Purpose ................................................................................................................................................................................. 1 Background ............................................................................................................................................................................2 Scope of Work........................................................................................................................................................................ 4 SOURCES OF INFORMATION ..................................................................................................................................................4 SETTING ......................................................................................................................................................................................4 GEOLOGY ................................................................................................................................................................................... 5 EARTHQUAKE-GROUND-SHAKING HAZARD ....................................................................................................................8 Introduction ............................................................................................................................................................................8 Sources of Information .......................................................................................................................................................... 8 Earthquakes in Southwestern Utah ........................................................................................................................................9 Potential Sources of Strong Earthquake Ground Shaking .....................................................................................................9 Ground Shaking Hazard Reduction .....................................................................................................................................10 SUMMARY ................................................................................................................................................................................ 11 ACKNOWLEDGMENTS .......................................................................................................................................................... 11 REFERENCES ........................................................................................................................................................................... 11 FIGURES Figure 1. Boundaries, principal developed areas, transportation corridors, index to U.S. Geological Survey 7.5' quadrangle maps, and UGS 7.5' geologic quadrangle maps in the State Route 9 Corridor Geologic-Hazard Study Area. ............. 3 Figure 2. Relation of the State Route 9 Corridor Geologic-Hazard Study Area to previous UGS geologic-hazard studies, major transportation corridors, nearby communities, principal drainages, physiographic province boundaries, and large potentially active faults in the State Route 9 Corridor region ...............................................................................3 Figure 3. Hurricane Cliffs mark the trace of the Hurricane fault in the City of La Verkin, about a mile west of the State Route 9 Corridor Geologic-Hazard Study Area western boundary ................................................................................5 Figure 4. Simplified geologic map of the State Route 9 Corridor Geologic-Hazard Study Area .................................................6 Figure 5. Lithologic column of geologic units that crop out in the State Route 9 Corridor Geologic-Hazard Study Area. .........7 Figure 6. Jointed cliffs of Navajo Sandstone (upper cliffs) have produced numerous rock falls within Zion Canyon ................7 Figure 7. Normal-slip faults in and near the State Route 9 Corridor Geologic-Hazard Study Area ............................................ 8 Figure 8. The Intermountain Seismic Belt and major historical ISB earthquakes. .......................................................................9 TABLES Table 1. Principal geologic hazards in the State Route 9 Corridor Geologic-Hazard Study Area................................................ 2 Table 2. Census data and growth projections for communities in the State Route 9 Corridor Geologic-Hazard Study Area...... 2 Table 3. International Building Code site-class definitions ........................................................................................................ 10 PLATES Plate 1. Flood and debris-flow hazards, State Route 9 Corridor Geologic-Hazard Study Area ...........................................on CD Plate 2. Landslide hazard, State Route 9 Corridor Geologic-Hazard Study Area ................................................................on CD Plate 3. Rock-fall hazard, State Route 9 Corridor Geologic-Hazard Study Area .................................................................on CD Plate 4. Collapsible-soil susceptibility, State Route 9 Corridor Geologic-Hazard Study Area ............................................on CD Plate 5. Expansive-soil-and-rock hazard, State Route 9 Corridor Geologic-Hazard Study Area .........................................on CD Plate 6. Gypsiferous soil and rock, State Route 9 Corridor Geologic-Hazard Study Area. ..................................................on CD Plate 7. Piping, erosion, and wind-blown-sand susceptibility, State Route 9 Corridor Geologic-Hazard Study Area .........on CD Plate 8. Surface-fault-rupture hazard, State Route 9 Corridor Geologic-Hazard Study Area ..............................................on CD Plate 9. Liquefaction susceptibility, State Route 9 Corridor Geologic-Hazard Study Area .................................................on CD GEOLOGIC HAZARDS OF THE STATE ROUTE 9 CORRIDOR, LA VERKIN CITY TO TOWN OF SPRINGDALE, WASHINGTON COUNTY, UTAH by Tyler R. Knudsen and William R. Lund ABSTRACT tigations are necessary. We recommend a site-specific geo- technical investigation for all new construction in the study Historically, the communities of La Verkin, Virgin, Rockville, area, and a geologic assessment to identify potential geologic and Springdale have been affected by a variety of geologic hazards at sites within special-study areas shown on the maps hazards. The 1992 St. George earthquake, recent damaging accompanying this report. Site-specific investigations can re- rock falls, riverine floods most recently in 2005 and 2010, re- solve uncertainties inherent in these 1:24,000-scale maps, and current flash floods and landslides, and problems associated help increase safety by identifying the need for special con- with collapsible soil and expansive soil and rock demonstrate struction design or hazard mitigation. that the communities are vulnerable to geologic hazards, and that public officials require reliable hazard information as Because of their wide distribution, frequent occurrence, and they plan for and manage future growth. The purpose of this destructive potential, we expect floods, rock falls, landslides, study is to provide municipal, county, and regional adminis- collapsible soil, and expansive soil and rock to be the princi- trative, safety, and planning officials, as well as consultants, pal geologic hazards that will affect the SR-9 study area in the landowners, and others with geographic information system future. With the exception of the effects of a rare but