Jun 192017
 

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 landslides 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.

The ledge of jointed sandstone along with several large displaced blocks is seen at the center of the image. Photo credit Jon White.

The ledge of jointed sandstone along with several large displaced blocks is seen at the center of the image. Photo credit Jon White.

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Feb 012017
 

By Jill Carlson

On March 23, 2003, a large avalanche occurred about one mile west of the Town of Silver Plume. The avalanche brought trees, rock, soil and snow to the valley floor, knocked down overhead utility lines, blocked the I-70 frontage road, damaged the town’s water treatment plant (WTP), and dammed Clear Creek. The dam was breached using explosives before the plant’s electric pump motors were flooded. With damage to the WTP’s chlorine contact tank and building, Silver Plume residents had to boil their tap water for over a month.

The avalanche occurred three days after near-record snowfall. It was triggered by additional snow loading in the starting zone caused by a change in wind direction, and began in a known avalanche path above timberline on Pendleton Mountain. Its unusually large volume and velocity caused it to unexpectedly reach the valley floor, along a path not previously identified as an avalanche chute. Rick Gaubatz, the Town’s water commissioner, counted 110 rings in a spruce tree that was found in the avalanche debris at the damaged WTP, indicating that an avalanche of similar magnitude had not occurred in the immediate area in at least 110 years.

Avalanche debris in the runout zone taken by Xcel Energy from a helicopter on the morning after the avalanche occurred, 24 March, 2003.

Avalanche debris in the runout zone taken by Xcel Energy from a helicopter on the morning after the avalanche occurred, 24 March 2003.

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