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).

Evidence of Catastrophic Geology: Case 10

Sedimentary deposits such as alluvial terrace deposits (regional flood deposits), debris flows (landslide during flood along river or stream valley), or mud flows (saturated fine-grained soils in a landslide during a flood along a river or stream valley) can produce layers several feet thick in a single event.  At Mount Rainer for example in 2006 the Tahoma Creek was subjected to severe flooding, in some places flooding the river valley 400 feet across.  Flood flow aggredation deposited 4 feet of granular soil in a single event near the bridge at the photograph below.  The level the man is standing at was 4 feet higher than before the flood.

A park geo-scientist reported in a video presentation of the event up to 6 feet of deposition in some areas, and an accumulated 38 feet total aggredation in some areas since 1910.  That is a 38-ft thick channelized or wide valley sedimentary deposit stratum or bedded strata in less than 100 years.  Although the Tahoma Creek drainage valley is the downstream drainage feature of the local glacier, granular flood deposts can be produced along any river or stream valley where source rock is available upstream where rivers are present through rock geology.  "Aggredation" is a term used to describe the accumulation of sediment.