Swelling Soils

Innocuous as it sounds, Colorado’s most significant geologic hazard is swelling soil-soil laced with layers of various clays. These clays cause more property damage than any other natural hazard. Bentonite and montmorillonite (weathered volcanic ash) clays underlie many populated areas of Colorado. The can expand up to 20 percent in volume when exposed to water and exert up to 30,000 pounds of force per square foot, more than enough to break up any structure they encounter. One zip code in a Denver suburb has the dubious distinction of suffering more annual monetary loss from swelling soil than any other in the nation.


Sound building techniques can prevent swelling-soil damage to homes, but it is crucial that builders follow these techniques faithfully. CGS geologists wrote a booklet about this hazard for homeowners entitled A Guide to Swelling Soils for Colorado Homebuyers and Homeowners that has sold more than 175,000 copies and won several national awards.

Please enjoy this video produced
by the Colorado Geological Survey:

Hazardous Soils in Colorado