DOCSLIB.ORG

A Brief Guide to Parent Material and Landforms Developed for the New Mexico Envirothon Introduction

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Brief Guide to Parent Material and Landforms Developed for the New Mexico Envirothon Introduction A Brief Guide to Parent Material and Landforms Developed for the New Mexico Envirothon Logan Peterson, NRCS Introduction When soil scientists make maps of soil, we search above the ground for clues before we dig holes. As explained in “From the Surface Down,” a soil gets its unique properties from the interaction of five major factors: climate, living organisms, landscape position, parent material, and time. Once we learn how to read a landscape, we can identify differences in each of these factors and, thus, predict differences in soil properties. A steep north-facing slope will be cooler and support different vegetation than a steep south- facing slope of the same mountain. Because these two slopes will differ in their landscape position, microclimate, and living organisms, we can expect that they will have different soil properties. As another example, let’s compare two landforms: a mountain slope and a floodplain along a stream. The mountain slope is made up of bedrock which is several million years old, while the floodplain is made up of sediments which were recently deposited by water. The mountain slope is relatively steep, and water readily runs off of it, while the floodplain is flat and often flooded. Lastly, the hillslope hasn’t changed much in shape for several thousand years, while the floodplain was deposited during a heavy rainstorm just thirty years ago. We can see that the soils on these two landforms differ in their parent material, landscape position, and in the amount of time they have had to form. Because of its landscape position, the floodplain soil receives much more water, so it will grow a very different plant community (organisms) than the mountain slope soil. For all of these reasons, we can expect that these two soils will have very different properties. Case in point, the best way to predict where different soil types will appear is often to look for differences in landforms. In the table below, I have summarized the differences between these two soils—in terms of soil forming factors and soil properties. Mountain Soil Floodplain Soil Parent Material Decomposed bedrock (residuum) Sediment (alluvium) Age of Soil (Time) 20,000 years 30 years Effective Moisture 16 inches per year 50 inches per year Plant Community Ponderosa pine forest Willows and grasses Soil Horizons O, A, B, C, R A, C Depth to Bedrock (R) 85 cm 400 cm Depth to aquifer 400 feet 80 cm Textures (top-down) fibrous organic matter, loam, clay sandy loam, loamy sand loam, sandy loam, bedrock 1 Parent Material In simple terms, parent material is the stuff that soils develop out of. Most soils form in decomposing mineral deposits. Because various life forms such as plants and earthworms live and die in and on the soil, soils also contain different types and amounts of decomposing organic matter. In this sense, parent material can be divided into two basic categories: mineral and organic. Parent material is also categorized by how it ended up where it is. There are four kinds of parent material which are defined based on their mechanism of transport. Alluvium is a kind of parent material which was deposited by water (washed into place). Rocks which have been bounced along the bottoms of waterways for miles become rounded, so rounded rocks in a soil profile are good indicators of an alluvial soil. As a rule, faster-moving water can carry larger particles. As water slows down (picture rapids flowing into a deep pool), it deposits the larger particles it carries. The speed of water flowing over a given spot tends to fluctuate for a number of reasons. The result is that alluvial deposits tend to be stratified: divided into horizontally-stacked layers which are dominated by different particle sizes. For example, a gravelly layer may have been deposited by fast- moving flood waters; it sits directly on top of a silty layer that was laid down when the river was low and calm. Over the years, the fluctuation of water speeds can lead to a repeating pattern of gravelly-silty- gravelly-silty-… The translocation of clay particles through a soil profile can cause differences in texture to occur between soil horizons in non-alluvial soils, but the stratification of different sizes of rounded rocks is a telltale sign of an alluvial deposit. Colluvium is parent material which was deposited by gravity rather than flowing water. A familiar example of colluvium would be a pile of rocks at the base of a cliff. As the cliff face is weathered, pieces of rock break off and pile up at the base. Soils that develop in colluvium often contain rocks of various sizes. Because these rocks weren’t carried and deposited by water, they are generally not rounded, nor are they stratified. Residuum is parent material composed of weathering bedrock. This material can range in age from just a few hundred years (as in fresh lava flows that are just beginning to decompose) to a few billion years (as in Precambrian metamorphic rock). Soils that formed in residuum are often relatively shallow to hard bedrock. Residuum is a dominant parent material on upper mountain slopes, and on the tops of plateaus and mesas. Eolian Deposits are parent materials that were moved by wind; sand dunes are a familiar example. Only the most powerful winds can carry mineral particles larger than sands, so rock fragments larger than 2 mm in a soil horizon are a pretty good sign that the parent material in this layer is not eolian. Many of New Mexico’s soils formed in thin eolian deposits on top of other materials. For example, many of the soils on top of mesas in Northeastern NM formed in eolian deposits which were deposited on top of residuum. Because silts and very fine sands are easily eroded and carried by wind, they tend to dominate eolian deposits. 2 Alluvium Colluvium Residuum Figure 1. Three soil profiles derived from three kinds of mineral parent material. Illustration by Logan Peterson. 3 Figure 2. Two soils with alluvial parent material. Note that the rocks in both are rounded, and that the alluvium on the left is stratified. Photos by Logan Peterson. Figure 3. On the left is a pile of fresh colluvium beneath cliffs in Montana. On the right is a soil formed in this type of parent material. Photos by Logan Peterson. 4 Figure 4. A soil formed in residuum. Tape is in inches. Photo by Charles Hibner. Figure 5. Eolian deposits (sand dunes) near the southeastern border of NM. Photo by Dr. Lynn Loomis. 5 Common Landforms of New Mexico If you pay attention to the Earth’s surface as you drive across New Mexico, you’ll notice that it is made up of a number of distinct shapes. Many parts of the state, such as the plains around Roswell, are quite flat. Other areas are dominated by rounded shapes of foothills or steep shapes of mountains. Geologists have come up with a number of names for such shapes, or landforms. We generally define a landform based on its shape, as well as the way that it formed. For example, mesas and floodplains are both flat surfaces which often have steep slopes along their edges. However, a floodplain was deposited by water, while a mesa is made up of bedrock. Below are some examples of landforms you are likely to encounter at the New Mexico Envirothon competition. Landforms can be divided into two categories, based on how they formed. Landforms which got their shapes by being carved away by erosion are referred to as erosional. Landforms which were deposited by moving water are referred to as depositional. Floodplains, stream terraces, and alluvial fans are depositional landforms; mountains and mesas are erosional. Floodplains are relatively new alluvial deposits which lie along the channel of a stream, river, or arroyo. They are relatively flat, and their slopes usually have the same gradient (steepness) and aspect (direction) as the channel below. Floodplains often have steep walls (or “cut-banks”) along the channel. The flat upper surface of a floodplain is low enough that it floods often (at least once per 100 years). Because floodplain soils are made up of alluvium, they are often stratified and frequently contain rounded rocks. Stream Terraces are similar to floodplains, but they are older and rarely flooded. In fact, all stream terraces were floodplains in earlier times. However, as adjacent channels gradually cut deeper into the Earth, it took progressively larger flows to flood these landforms. A stream terrace floods less than once per 100 years. Stream terraces are shaped like floodplains, with flat tops that have similar slopes to the channels below. The soils of stream terraces are quite similar to those of floodplains, but are older, so they usually have horizons which are more distinct. Alluvial Fans form as water rushing off of steep slopes deposits parent material onto the valley floor below. As torrents of floodwaters come rushing down steep slopes, they erode materials and carry them off. These floodwaters converge in steep canyons and arroyos, which direct them to flat valleys at the bases of the slopes. When these floodwaters hit level ground, they slow down, depositing the largest fragments in their sediment loads first. During the next flood event, waters will be directed around the piles of sediments left by the last flood. In this way, temporary channels meander back and forth across the growing alluvial fan, depositing sediment as they move. Alluvial fans are shaped roughly like hand-held fans; they are steepest and contain the largest fragments at their highest points.
Load more

Recommended publications
  • Visualizing Texas Parent Materials Julieta Collazo, Jonathan Gross, Cristine L
    Visualizing Texas Parent Materials Julieta Collazo, Jonathan Gross, Cristine L. S. Morgan Agrilife Research, Texas A&M University, College Station, TX Figure 2: INTRODUCTION Water MAJOR LAND RESOURCE AREAS A soil parent material map for Texas was created Wind Blown PARENT MATERIALS OF TEXAS SOIL to further the ISEE2 goal of better visualization Aeolian Sand for teaching soil science. Texas has a diverse Loess depositional history which includes residuum, as Coastal Sediments well as water and wind transported materials Coarse Coastal Sediments (Fig. 1). The most difficultly was found in Fine Coastal Sediments differentiating alluvial sediments in the Coastal Alluvium Plains. While these materials were classified Young Alluvium similarly by the United States Department of Old Alluvium Agriculture, differentiation of the two processes Deltaic Alluvium is important for teaching purposes. Another Lacustrine Alluvium 42 Desertic Basin problem that was encountered in the decision 77 High Plains 85 Grand Prairie Valley Fill Alluvium 78 Central Rolling Red Plains making process was delineating general 86 Blackland Prairie Alluvial Fans 80 Prairies 87 Claypan 81 Edward Plateau categories that are instructive for land use Undifferentiated Residuum 133 Coastal Plain 82 Central Basin 150 Gulf Coast Prairie decisions. Residuum Clastic 83 Rio Grand Plains and Valley 151 Gulf Coast Marshes 84 Cross Timbers Residuum Igneous or Metamorphic 152 Gulf Coast Flatwoods The overall goal of this project was to develop a Residuum Tuff decision tree to convert Official Series Colluvium Figure 3: 1st ORDER CLASSIFICATION Descriptions (OSD) to parent materials, to aid Organic Material teaching, as well as be congruent with Anthropogenic Windblown material, neighboring states and the United States.
    [Show full text]
  • Surficial Geology of Marine Quadrangle
    Introduction Clearing of forests during early European colonization and possibly earlier during 2004b). An electrical earth resistivity study of Neudecker’s Mountain, for example, Stream Valleys References Amerindian civilization centered at the Cahokia Site in western Madison County, led could not resolve specific sand bodies within the mound, although sand found in nearby The Silver Creek valley is filled with fine-grained postglacial stream sediment (Cahokia This map depicts geologic materials found within 5 feet of the ground surface in the to extensive upland erosion and sediment accumulation in creek valleys. Relatively boreholes may be correlatable to the mound. (cross section B-B’; ISGS Groundwater Formation) that overlies coarse-grained glacial stream sediment (Pearl Formation, Berg, R.C., J.P. Kempton, and K. Cartwright, 1984, Potential for Contamination of Marine 7.5-minute Quadrangle, Madison County, southwestern Illinois (fig. 1). The cross recent stream incision into these sediments and older deposits is attributed to large water Section, unpublished data). Other similar but smaller mounds also occur across the undifferentiated). The occurrence of the Pearl Formation (undifferentiated) in Silver Shallow Aquifers in Illinois: Illinois State Geological Survey Circular 532, 30 p. discharges with initially low sediment loads brought about by recent climate changes, quadrangle, but they have not been distinguished here because there is no supporting Creek is evidence that the valley was as a meltwater outlet during the Illinois Episode. sections show the extent of surficial and buried units down to bedrock.This product Fox, J., E.D. McKay, J. Hines, and M.M. Killey, unpublished, Work maps of geology for URFICIAL EOLOGY OF ARINE UADRANGLE land use changes, or both.
    [Show full text]
  • 1 Understanding the Regolith in Tropical and Sub
    UNDERSTANDING THE REGOLITH IN TROPICAL AND SUB-TROPICAL TERRAINS: THE KEY TO EXPLORATION UNDER COVER. C.R.M. Butt Cooperative Research Centre for Landscape Environments and Mineral Exploration CSIRO Exploration and Mining PO Box 1130 Bentley Western Australia 6151 Regolith distribution and characteristics Large areas of the world, especially the largely tropical to sub-tropical zone between latitudes 40º north and south, are characterized by a thick regolith cover. Much of this regolith is residual and consists of intensely weathered bedrock, but there may also be an overlying component of transported material, itself weathered to varying degrees. The regolith is most extensive in continental regions of low to moderate relief, such as the Precambrian shields, and adjacent and overlying Phanerozoic sedimentary basins, of South America, Africa, India, south east Asia and Australia. Remnants are present in some areas of stronger relief, perhaps most significantly in parts of the circum-Pacific belt, where ophiolitic rocks have weathered to form high grade nickel laterites. Commonly, such regolith is absent from tectonically active and mountainous areas. Thick residual regolith is also generally absent from very arid terrains in the tropics and sub-tropics, such as the Sahara and Arabian deserts, although transported materials, including fluvial deposits and dune sands, are widespread. Nevertheless, isolated occurrences of strongly weathered regolith are recorded from these desert regions, either exposed or buried beneath the younger sediments, indicating that it was once more widespread. There is also increasing recognition of the presence of similar regolith, mainly as thick saprolite, in North America and Europe. Much of the residual regolith has broadly lateritic characteristics, with a thick, clay-rich saprolite, generally with an overlying iron and /or aluminium-enriched horizon, although the latter may be only patchily developed or have been removed by later erosion.
    [Show full text]
  • Geology and Stratigraphy Column
    Capitol Reef National Park National Park Service U.S. Department of the Interior Geology “Geology knows no such word as forever.” —Wallace Stegner Capitol Reef National Park’s geologic story reveals a nearly complete set of Mesozoic-era sedimentary layers. For 200 million years, rock layers formed at or near sea level. About 75-35 million years ago tectonic forces uplifted them, forming the Waterpocket Fold. Forces of erosion have been sculpting this spectacular landscape ever since. Deposition If you could travel in time and visit Capitol Visiting Capitol Reef 180 million years ago, Reef 245 million years ago, you would not when the Navajo Sandstone was deposited, recognize the landscape. Imagine a coastal you would have been surrounded by a giant park, with beaches and tidal flats; the water sand sea, the largest in Earth’s history. In this moves in and out gently, shaping ripple marks hot, dry climate, wind blew over sand dunes, in the wet sand. This is the environment creating large, sweeping crossbeds now in which the sediments of the Moenkopi preserved in the sandstone of Capitol Dome Formation were deposited. and Fern’s Nipple. Now jump ahead 20 million years, to 225 All the sedimentary rock layers were laid million years ago. The tidal flats are gone and down at or near sea level. Younger layers were the climate supports a tropical jungle, filled deposited on top of older layers. The Moenkopi with swamps, primitive trees, and giant ferns. is the oldest layer visible from the visitor center, The water is stagnant and a humid breeze with the younger Chinle Formation above it.
    [Show full text]
  • Chapter 7 – Geomechanics
    Chapter 7 GEOMECHANICS GEOTECHNICAL DESIGN MANUAL January 2019 Geotechnical Design Manual GEOMECHANICS Table of Contents Section Page 7.1 Introduction ....................................................................................................... 7-1 7.2 Geotechnical Design Approach......................................................................... 7-1 7.3 Geotechnical Engineering Quality Control ........................................................ 7-2 7.4 Development Of Subsurface Profiles ................................................................ 7-2 7.5 Site Variability ................................................................................................... 7-2 7.6 Preliminary Geotechnical Subsurface Exploration............................................. 7-3 7.7 Final Geotechnical Subsurface Exploration ...................................................... 7-4 7.8 Field Data Corrections and Normalization ......................................................... 7-4 7.8.1 SPT Corrections .................................................................................... 7-4 7.8.2 CPTu Corrections .................................................................................. 7-7 7.8.3 Correlations for Relative Density From SPT and CPTu ....................... 7-10 7.8.4 Dilatometer Correlation Parameters .................................................... 7-11 7.9 Soil Loading Conditions And Soil Shear Strength Selection ............................ 7-12 7.9.1 Soil Loading .......................................................................................
    [Show full text]
  • Part 629 – Glossary of Landform and Geologic Terms
    Title 430 – National Soil Survey Handbook Part 629 – Glossary of Landform and Geologic Terms Subpart A – General Information 629.0 Definition and Purpose This glossary provides the NCSS soil survey program, soil scientists, and natural resource specialists with landform, geologic, and related terms and their definitions to— (1) Improve soil landscape description with a standard, single source landform and geologic glossary. (2) Enhance geomorphic content and clarity of soil map unit descriptions by use of accurate, defined terms. (3) Establish consistent geomorphic term usage in soil science and the National Cooperative Soil Survey (NCSS). (4) Provide standard geomorphic definitions for databases and soil survey technical publications. (5) Train soil scientists and related professionals in soils as landscape and geomorphic entities. 629.1 Responsibilities This glossary serves as the official NCSS reference for landform, geologic, and related terms. The staff of the National Soil Survey Center, located in Lincoln, NE, is responsible for maintaining and updating this glossary. Soil Science Division staff and NCSS participants are encouraged to propose additions and changes to the glossary for use in pedon descriptions, soil map unit descriptions, and soil survey publications. The Glossary of Geology (GG, 2005) serves as a major source for many glossary terms. The American Geologic Institute (AGI) granted the USDA Natural Resources Conservation Service (formerly the Soil Conservation Service) permission (in letters dated September 11, 1985, and September 22, 1993) to use existing definitions. Sources of, and modifications to, original definitions are explained immediately below. 629.2 Definitions A. Reference Codes Sources from which definitions were taken, whole or in part, are identified by a code (e.g., GG) following each definition.
    [Show full text]
  • Economic Impact of Mountain Biking in the Grand Mesa, Uncompahgre & Gunnison National Forests
    Economic Impact of Mountain Biking in the Grand Mesa, Uncompahgre & Gunnison National Forests JAMES N. MAPLES, PhD MICHAEL J. BRADLEY, PhD Report submitted to Outdoor Alliance: November 2018 Study funded by Outdoor Alliance Image Credit: Carl Zoch 1 Executive Summary of Study Grand Mesa, Uncompahgre and Gunnison National Forest (GMUG) is an important American mountain biking destination. Mountain bikers visited the GMUG over 150,000 times per year. An estimated 70% of these visits were from persons living outside the GMUG and surrounding region. Over 576 mountain bikers from around the nation responded to our survey collecting their economic expenditures on their most recent trip to the GMUG. Based on the economic impact analysis and NVUM visitation figures, the research team estimates: 1. Mountain bike visitors who are not local residents annually spend $24 million in the GMUG. 2. Mountain bike visitors’ expenditures in the GMUG support 315 jobs and $7.9 million in job income within the region. REPORT CONTENTS Meet Your Research Team 2 Methodological Notes 3 Study Regions 4 Visitor Mean Expenditures 5 Economic Impact Terminology 8 Economic Impact Modeling 9 Taxation Generation within the Study Areas 10 Visitor Expenditures beyond Study Area but in State 11 Local Resident Expenditures by Study Area 12 Local Resident Expenditures beyond Study Area but Inside State 15 Omissions, Considerations 16 1 Meet Your Research Team DR. JAMES N. MAPLES is an associate professor of sociology at Eastern Kentucky University, where he examines the political economy of renewable tourism. His research interests include the economic impact of outdoor recreation and social change in rural areas.
    [Show full text]
  • Subsurface Exploration and Geotechnical Engineering Evalution
    SUBSURFACE EXPLORATION AND GEOTECHNICAL ENGINEERING EVALUTION DeKalb County Fire Station No. 7 Decatur, DeKalb County, Georgia November 23, 2016 Submitted to: DeKalb County Facilities Management Department DeKalb County, Georgia Submitted by: Willmer Engineering Inc. Project No. 71.4175 November 23, 2016 VIA EMAIL Dulce M. Guzman Senior Project Manager Architectural & Engineering Services DeKalb County Facilities Management Department Clark W. Harrison Building 330 W. Ponce de Leon Avenue, 4 th Floor Decatur, Georgia 30030 SUBJECT: Subsurface Exploration and Geotechnical Engineering Evaluation Fire Station No. 7 Decatur, DeKalb County, Georgia Willmer Project No. 71.4175 Dear Ms. Guzman: Willmer Engineering Inc. (Willmer) is pleased to provide this report of subsurface exploration and geotechnical engineering evaluation for the proposed Fire Station No. 7 project located east of the intersection of Columbia Drive and Peachcrest Road in Decatur, DeKalb County, Georgia. This work was performed for DeKalb County under our Master Services Agreement in general accordance with our proposal dated October 6, 2016. The results of our evaluation and our recommendations are summarized in this report. This engineering report is divided into five sections. Section 1 contains the project background information and a summary of the objectives and scope of our work. Summaries of the field exploration and laboratory testing programs are provided in Sections 2 and 3, respectively. Section 4 presents regional geologic conditions and subsurface conditions at the site, and the results of our geotechnical engineering evaluations and our recommendations are presented in Section 5. We greatly appreciate the opportunity to be of service to you on this project. Please contact us if you have any questions concerning this report or require further assistance.
    [Show full text]
  • Hogback Is Ridge Formed by Near- Vertical, Resistant Sedimentary Rock
    Chapter 16 Landscape Evolution: Geomorphology Topography is a Balance Between Erosion and Tectonic Uplift 1 Topography is a Balance Between Erosion and Tectonic Uplift 2 Relief • The relief in an area is the maximum difference between the highest and lowest elevation. – We have about 7000 feet of relief between Boulder and the Continental divide. Relief 3 Mountains and Valleys • A mountain is a large mass of rock that projects above surrounding terrain. • A mountain range is a continuous area of high elevation and high relief. • A valley is an area of low relief typically formed by and drained by a single stream. • A basin is a large low-lying area of low relief. In arid areas basins commonly have closed topography (no river outlet to the sea). Mountains • Typically occur in ranges. • Glaciated forms –Horn –Arête • Desert Mountains – Vertical Cliffs – Alluvial Fans 4 Mountain Landforms: Horn Deserts: Vertical Cliffs and Alluvial Fans 5 Valleys and Basins • River Valleys – U-shape (Glacial) – V-shape (Active Water erosion) – Flat-floored (depositional flood plain) • Tectonic (Fault) Valleys (Basins) – Tectonic origin – San Luis Valley – Jackson Hole – Great Basin U-shaped Valley: Glacial Erosion 6 V-shaped Valley: Active water erosion Flat-floored Valley: Depositional Flood Plain 7 Desert and Semi-arid Landforms • A plateau is a broad area of uplift with relatively little internal relief. • A mesa is a small (<10 km2)plateau bounded by cliffs, commonly in an area of flat-lying sedimentary rocks. • A butte is a small (<1000m2) hill bounded by cliffs Plateau, Mesa, Butte 8 Colorado National Monument Canyonlands 9 Desert and Semi-arid Landforms • A cuesta is an asymmetric ridge in dipping sedimentary rocks as the Flatirons.
    [Show full text]
  • A Geomorphic Classification System
    A Geomorphic Classification System U.S.D.A. Forest Service Geomorphology Working Group Haskins, Donald M.1, Correll, Cynthia S.2, Foster, Richard A.3, Chatoian, John M.4, Fincher, James M.5, Strenger, Steven 6, Keys, James E. Jr.7, Maxwell, James R.8 and King, Thomas 9 February 1998 Version 1.4 1 Forest Geologist, Shasta-Trinity National Forests, Pacific Southwest Region, Redding, CA; 2 Soil Scientist, Range Staff, Washington Office, Prineville, OR; 3 Area Soil Scientist, Chatham Area, Tongass National Forest, Alaska Region, Sitka, AK; 4 Regional Geologist, Pacific Southwest Region, San Francisco, CA; 5 Integrated Resource Inventory Program Manager, Alaska Region, Juneau, AK; 6 Supervisory Soil Scientist, Southwest Region, Albuquerque, NM; 7 Interagency Liaison for Washington Office ECOMAP Group, Southern Region, Atlanta, GA; 8 Water Program Leader, Rocky Mountain Region, Golden, CO; and 9 Geology Program Manager, Washington Office, Washington, DC. A Geomorphic Classification System 1 Table of Contents Abstract .......................................................................................................................................... 5 I. INTRODUCTION................................................................................................................. 6 History of Classification Efforts in the Forest Service ............................................................... 6 History of Development .............................................................................................................. 7 Goals
    [Show full text]
  • Colorado Plateau
    MLRA 36 – Southwestern Plateaus, Mesas and Foothills MLRA 36 – Southwestern Plateaus, Mesas and Foothills (Utah portion) Ecological Zone Desert Semidesert* Upland* Mountain* Precipitation 5 -9 inches 9 -13 inches 13-16 inches 16-22 inches Elevation 3,000 -5,000 4,500 -6,500 5,800 - 7,000 6,500 – 8,000 Soil Moisture Regime Ustic Aridic Ustic Ustic Ustic Soil Temp Regime Mesic Mesic Mesic Frigid Freeze free Days 120-220 120-160 100-130 60-90 Percent of Pinyon Percent of Juniper production is Shadscale and production is usually usually greater than blackbrush Notes greater than the Pinyon the Juniper Ponderosa Pine production production 300 – 500 lbs/ac 400 – 700 lbs/ac 100 – 500 lbs/ac 800 – 1,000 lbs/ac *the aspect (north or south) can greatly influence site characteristics. All values in this table are approximate and should be used as guidelines. Different combinations of temperature, precipitation and soil type can place an ecological site into different zones. Southern Major Land Resource AreasRocky (MLRA) D36 Mountains Basins and Plateaus s D36 - Southwestern Plateaus, Mesas, and Foothills Colorado Plateau 05010025 Miles 36—Southwestern Plateaus, Mesas, and Foothills This area is in New Mexico (58 percent), Colorado (32 percent), and Utah (10 percent). It makes up about 23,885 square miles (61,895 square kilometers). The major towns in the area are Cortez and Durango, Colorado; Santa Fe and Los Alamos, New Mexico; and Monticello, Utah. Grand Junction, Colorado, and Interstate 70 are just outside the northern tip of this area. Interstates 40 and 25 cross the middle of the area.
    [Show full text]
  • Unexpected but Foreseeable Mat Settlements on Piedmont Residuum
    Unexpected but foreseeable mat settlements on Piedmont residuum Paul W. Mayne, Professor, Georgia Institute of Technology, USA ABSTRACT: A large mat foundation was constructed to support a 13-story dormitory on Piedmont residual silty soils in Atlanta, Georgia. Prior to construction, the geotechnical consultant of record estimated maximum expected settlements of the mat on the order of 1.8 inches (46 mm), while the building proceeded to deflect as much as 10 inches (250 mm) at the center and 5 inches (127 mm) at the corners near the end of construction. Details on the case history are reviewed by an outside observer and placed within the context of geotechnical practice. In addition to routine soil borings, the use of enhanced in-situ testing (in this case, flat dilatometer tests) in concert with elastic continuum solutions would have provided calculated values in line with the observed performance. KEYWORDS: foundations, displacements, elasticity, in-situ tests, mats, rafts, settlements. INTRODUCTION In preparation for the 1996 Summer Olympics, the construction of many office and residential buildings were underway in downtown Atlanta in order to accommodate a large number of visiting athletes, participants, and spectators. A site located south of the Olympic Village was to receive four mid-rise buildings that were eventually turned over to Georgia State University (GSU) for use as dormitories. The site was previously occupied by small one- and two-story residential and commercial buildings that were demolished prior to the new construction. Based on the results of soil test borings with standard penetration tests (SPT), the consultant recommended different systems for each of these buildings.
    [Show full text]