Selected Examples of Mass Wasting
on Mount Shasta

A Term Paper
by Bob Musgrove
Geography 581 Geomorphology
Professor: Dr. Mairs
Southern Oregon University 
 Introduction | Snow Avalanches | Jokulhlaups | A Unique Debris Flow | Conclusion | Sources


Avalanches as a Mountain Hazard

The Cyberspace Avalanche Center reported 205 snow avalanche fatalities worldwide during the 1998-1999 season. In October 1999 the climbing community was saddened by the death of Alex Lowe in a snow avalanche while on expedition in Tibet (Avalanche Incident 1999). When white settlers moved into the Western United States they learned about the dangers of avalanche terrain the hard way; for example an estimated 225-250 people were killed in snow avalanches in Little Cottonwood Canyon, Utah, between 1865 and 1915 (Armstrong and Williams 1986). Steep, high volcanoes, such as those in the Cascade Range, present a significant avalanche threat to modern recreational visitors.

Figure 1.
The above shows the snow depth in the runout zone of a large avalanche that occured on Mt. Shasta on January 1, 1997. Photograph by Eric White. That's a pair of skis in the foreground.

Figure 2.
Shastina viewed from the south before the
catastrophic events of January 1, 1997.

Figure 3.
Shastina after the large avalanches of January 1, 1997. This avalanch has been dubbed the "chicken foot" or the "alien footprint".

Photos by Jane English.

Avalanches on Mount Shasta

That Mount Shasta has long been the scene of avalanche activity is evident from consulting the United States Geological Survey 15' series Mount Shasta map. The main climbing route ascends aptly named Avalanche Gulch, and even the most casual map reader will notice the finger-like tendrils of treeless terrain that project from the lower reaches of almost every gulch, chute, or draw on the mountain. In recent years conditions have been just right for the incidence of unusually large snow avalanches on Mount Shasta.

In January, 1995, the snow depth on Shasta was at a 20-year high, and conditions were optimal for record-setting avalanches. The Mount Shasta Herald interviewed U.S. Forest Service officials for information as to the extent of the destruction and for details on avalanche conditions. Forest Service scientist Peter Van Susteren reported that one of the largest avalanches crossed the Everitt Memorial Highway, plucking boulders from the soil, destroying 300-year-old growth forest, and leaving a path of devastation 150 feet wide and up to 25 feet deep. During the same time period another very large avalanche scoured the slopes of Shastina, leaving six distinct paths through old growth forest.

The rain-related events of of January 1, 1997 are memorable to anyone who was living in southern Oregon or northern California at that time. A particularly enormous wet snow avalanche occurred in Avalanche Gulch on January 1 during a rain-on-snow event at high altitude (Towner 1999). According to my own field observations at the time and subsequent figuring with a topographic map, the avalanche's starting zone was at an altitude of approximately 12,700 feet and it finally came to a stop at 7,400 feet , a little over a vertical mile below. The avalanche's track was over four miles long, making for a "vertical drop" to "horizontal run" ratio of .25 to 1. This avalanche deposited snow to an estimated depth of 20 feet at the lower elevations and the terminal mounds of snow persisted into the following winter. Large avalanches such as those described above represent an ongoing threat to backcountry visitors. The 1995 slide buried the site of a then-proposed ski lodge, as reported in the Mount Shasta Herald story referred to above.

Figure 4. The green line on the map show the path of the January 1997 slide in Avalanche Gulch. The red line refers to the debris flow discussed elswhere on the website. (USGSmap)

Causes of Avalanches on Mount Shasta

In North America and Europe, a small community of avalanche professionals is dedicated to the science of avalanche forecasting and control (Armstrong and Williams 1986), and each year studies are conducted and papers presented at conferences (ISSW 1996). A complete discourse on avalanche snow science would be a good topic for a thesis, and is beyond the scope of this paper. On the other hand, it would be helpful to readers to gain an elementary understanding of the causes of the large avalanches on Mount Shasta and what causal elements snow avalanches share with the two other types of mass wasting discussed in this paper.

  Avalanche forecasters divide avalanches into 3 main parts: the starting zone with slopes of 30 to 50 degrees, the track with slopes of 20 to 30 degrees, and the runout zone with slopes less than 20 degrees (Armstrong and Williams 1986). An avalanche might start when a more dense snowfall is deposited on top of a less dense layer of snow, resulting the formation of a slab that is not well bonded to the weaker snow below (Armstrong and Williams 1986). On the slopes of Mount Shasta, shear strength holds snow in place, and shear failure can occur if the stress is strong enough to overwhelm the forces of cohesion and resistance in the layers of snow (Easterbrook 1999). On Mount Shasta factors that may increase stress leading to shear failure include the deposition of rain on snow and the warming and partial melting of the upper layers of snow. 


 Introduction | Snow Avalanches | Jokulhlaups | A Unique Debris Flow | Conclusion | Sources

web page authored by Bob Musgrove