Catastrophic Geology: Case 11

In 2014, a landslide occurred near Collbran, Colorado.  The landslide was a debris flow, a conglomeration of soil, rock, and the wooded debris, that travels similar to a liquified sand mass. Some have theorized that vibrations within the mass allow it to travel as a debris flow.  The failure was instigated by a rotational global slope instability failure near the top of the mountain, producing a headwall scarp almost 600 feet tall at its maximum height.  A cascade of subsequent landslides produced the overall catastrophic landslide that traveled approximately 2.8 miles and killed 3 men.

Heavy rain likely reduced the shear strength along some of the failure plane within fissures in the sedimentary rock mass (shale) and instigated the failure.

A study by a team from the geology department at Colorado Mesa University found that the landslide produced new deposits up to 150 feet thick maximum in a matter of minutes (not millions of years).  The new deposit includes rock boulders and buried trees and other organic debris and if subsequently buried could form conglomerate or breccia type rock or resemble a glacial till.

The geology team also observed evidence that the original topography indicated the remnants of previous landslides (ancient slump blocks evident below steeper mountain slope).