On Sunday, May 25, 2014, a large mudslide rushed down a Colorado mountain near the town of Collbran covering an area three miles long and one-half to three-quarters of a mile wide. It claimed the lives of three ranchers and triggered a small earthquake.
The extent of the mudslide is evident in the top image, which was acquired by the Landsat 8 satellite on June 7. The lower image, taken by Landsat 8 on June 20, 2013, shows the slide region before the slide. The top edge of the slide, the scarp, is on the lower side of the image. The debris flowed north and ended at the toe, partially covering a natural gas well.
The slide happened in the Grand Mesa region of western Colorado, an area extremely prone to landslides. In fact, the recent mudslide began at the scarp of a previous landslide. The region is unstable because of its underlying geology. A layer of basalt lies on top of soft claystone that erodes easily. The basalt slumps when water erodes the soft rock beneath it, as illustrated in these diagrams. Landslides are most prevalent in this region during the spring and early summer when the ground is moist from snowmelt and runoff.
On average, Colorado experiences thousands of landslides every year. According to the Colorado Landslide Inventory, most of the slides occur in the mountainous western half of the state.
- Colorado Geological Survery Colorado landslide inventory. Accessed June 19, 2014.
- Colorado Geological Survey Definition. Accessed June 19, 2014.
- Denver Post (2014, May 26) Photos: Grand Mesa mudslide, 3 dead. Accessed June 19, 2014.
- Earthly Musings (2014, May 27) The Grand Mesa Colorado mudslide beneath Sugarloaf Peak. Accessed June 19, 2014.
- The Landslide Blog (2014, May 28) Grand Mesa: an unusually large and mobile mudslide. Accessed June 19, 2014.
- NBC 9News (2014, May 29) Landslide-created lake endangers Mesa County town. Accessed June 19, 2014.
- Reading the Washington Landscape (2014, May 29) Notes on the Mesa County, Colorado Landslide. Accessed June 19, 2014.
- Ready Colorado Landslide/rockslide. Accessed June 19, 2014.
- USGS Earthquake Hazards Program (2014, May 25) M2.8 Landslide – 30km NNE of Cedaredge, Colorado. Accessed June 19, 2014.
- U.S. Geological Survey (1996) Geologic map of slump-block deposits in part of the Grand Mesa area, Delta and Mesa Counties, Colorado. Accessed June 19, 2014.