GeoSpectrum

When people think of Colorado and geologic hazards, they tend to think of catastrophic landslides, avalanches, and rockfalls. But little-known geologic hazards associated with certain types of soils are more costly to Colorado residents and can cause havoc with homes, commercial buildings, and infrastructure if not identified prior to construction.

One of these places is in Garfield County, where the burgeoning oil and gas development of the Piceance Basin is spurring rapid growth along the Colorado River Corridor. Neighborhoods in Rifle, Silt, and Battlement Mesa, as well as the Interstate 70 roadways, have experienced varying levels of damage related to ground subsidence from soil settlement. Garfield County schools in the corridor have also required remedial work to repair sinking foundations and concrete slabs.

“Collapsible soil is responsible for settlement-related damage to roads and pipelines, structure foundations, and many homes throughout this valley corridor,” said Jonathan White, senior engineering geologist for the CGS. “Garfield County is especially affected because the geologic, topographic, and climatic conditions are ideal for the deposition of low density, dry soils that may have collapse characteristics.”

These types of soils in the semi-arid to arid climates of Colorado have the property to compact and settle when they get wet. Also known as hydrocompactive soils, the soil settlement can be so rapid the soil seems to collapse, and can ruin your house and possibly your whole neighborhood. The Colorado Geological Survey (CGS) has been collecting information on this hazard for a number of years and announced today the publication of “Collapsible Soil Susceptibility Map of the Colorado River Corridor in the Vicinity of Rifle, Garfield County, Colorado.” This is the second map of a series of regional collapsible soil susceptibility maps that will become available from CGS. The first map (Map Series-34) was also made in Garfield County along the Roaring Fork River corridor from Glenwood Springs to Basalt where collapsible soils are also a significant hazard.

This publication includes a 1:50,000-scale hazards map plate, and a second plate with map discussion that also describes the geologic processes that form collapsible soil, the engineering properties, and considerations for proposed and existing development, as well as a terrain block diagram of the map area to illustrate the types of landforms where collapsible soils occur. The publication is in a CD/ROM format that includes digital copies of the map in Adobe Acrobat (.pdf) format. Geographic Information Systems (GIS) data are also included on the CD-ROM. This data is in ESRI’s Shapefile and Geodatabase format and can be accessed using GIS software such as ESRI’s ArcGIS or the free ArcReader map-viewer utility available on the internet.

“This map will be an important tool for the practicing professional engineer and geologist, but will also be useful to land-use planners, land developers or purchasers, landscape architects, and contractors that work along the Colorado River corridor in the Piceance Basin,” said Vince Matthews, director of the Colorado Geological Survey. “Property owners can also use the map to identify whether their homes lie in collapse-susceptible soil and more carefully manage water use to reduce potential for settlement. For those people that want to know more about the hazards of collapsible soil, I encourage them to see another recent CGS publication, Engineering Geology 14, Collapsible Soils in Colorado, which is a more comprehensive statewide study of this phenomenon.”

CDs of Map Series 47, “Collapsible Soil Susceptibility map of the Colorado River Corridor in the Vicinity of Rifle, Garfield County, Colorado” are available for $18 at the CGS office in Denver. Telephone, online, or mail orders require an additional $3.50 (minimum) for shipping and handling. VISA and MasterCard are accepted. Order online at http://dnr.state.co.us/geostore . You can also call (303-866-2611, x8321), fax (303-866-2461), or post your order to the Publication Section, Colorado Geological Survey, 1313 Sherman Street, Room 715, Denver, CO 80203.

A complete list of CGS publications and publication order forms are available online at the CGS website, http://www.colorado.gov/geosurvey