[ED: This brief report from 1995 was written by Jon White, (Senior Engineering Geologist, emeritus). It looks at a specific rockfall situation in the central Front Range town of Manitou Springs. There are hundreds of similar instances like this where gravity rules in mountainous terrain. Geotechnical solutions are of some help in the long-term scale of the hazards, but are extremely expensive to implement. Development pressures that are affecting building in areas threatened by natural disasters—of small and large scale—continue apace in the US West.]

Manitou Springs occupies a narrow valley where Fountain Creek emerges from the foothills northeast of Pikes Peak and west of Colorado Springs. The valley slopes are composed of interbedded resistant sandstone and conglomerates (i.e., gravelly sandstone), and weaker mudstones and shale. The outcropping sandstone is most prevalent on the steeper slopes on the north side of the valley.

During the wet spring of 1995, rockfall and landslide incidents increased throughout Colorado, some resulting in fatalities. In Manitou Springs, a fortunate set of circumstances occurred before the Memorial Day holiday weekend when local residents observed the movements of a large, dangerous block of rock before it actually could fall. The observation set into motion an emergency declaration by the town, resulting in a compulsory evacuation of homes located below the rocky slope, the closing of the road in the area, and an immediate rock stabilization project. During this emergency situation, the Colorado Geological Survey was asked to provide expert assistance to help stabilize the rock. The emergency evacuation decree remained in effect until the rock was stabilized and the area subsequently declared safe.

more “Case Study: Rockfall – Manitou Springs”