VOLCANO MADNESS: Re: [Geology2] Ancient Colorado landslides

Thursday, April 4, 2013

Re: [Geology2] Ancient Colorado landslides

Could these be considered long run-out landslides? By definition a landslide that runs out beyond the same distance horizontally that it dropped vertically is considered to have not functioned as a frictional mass as is the case in conventional landslides.

On Wed, Apr 3, 2013 at 6:59 AM, Lin Kerns <linkerns@gmail.com> wrote:

DID YOU KNOW? There are two large landslide masses on the southeast side of Table Mountain ( 38.556218°, -104.966286°), about 15 miles southwest of Colorado Springs, that cover an area of roughly 2.3 mi2 with a conservative estimated depth of 10 ft, resulting in over 635,000,000 ft3 of mobilized debris. The headscarps are over 100 ft high! The landslides occur where resistant Dakota Sandstone is stratigraphically above several less-competent shales and mudstones including the Purgatoire, Morrison, and Lykins Formations. The Dakota Sandstone is highly jointed at these locations, allowing water to seep into and mobilize the underlying shales and mudstones. Some of the failures are rotational slumps where failure typically occurs along a vertical or nearly vertical fracture that intercepts a gently dipping shear plane within the shale and mudstone formations.

The images here are computer-generated using a 1-m resolution NAIP image draped over a 10-m digital elevation model (DEM).
The image at bottom is a color anaglyph in 3-D.

https://www.facebook.com/photo.php?fbid=541438982541482&set=a.362919700393412.92023.362778650407517&type=1&theater
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