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avalanche

An avalanche is the rapid flow of snow down a sloped surface. There are two general types of avalanches: slab avalanches and loose snow avalanches. Both begin when there is a mechanical failure in the layers of snow caused by when forces acting on the snow are greater than its strength. For slab avalanches, this leads to a cohesive layer of snow sliding down a slope. For loose snow avalanches, unconsolidated snow falls and gathers as it moves down the slope. Colorado, as a mountainous state, has an active avalanche environment.

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

Hazards

March 23, 2003

Case Study: Avalanche – Silver Plume

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.