Geoscience and Environment

Cascade Range - Mount Shasta


"Small glaciers appear to account for a third to a half of the sea level rise observed since 1884...", (Meier, M. Contribution of Small Glaciers to Global Sea Leval, Science, 226:4681.

The awakening of Mount St Helen's in 1980 alerted the world to the risk of volcanic eruptions in the western United States. The United States Geological Survey (USGS) identified 75 centers of potential volcanic activity from the coastal states of Washington, Oregon, and California to Wyoming. Highest on the list of potential explosive eruptions is the Long Valley Caldera in California and next are Mount Shasta and its near neighbor, Lassen Peak, also in California, (Richard Kerr, Volcanoes to Keep an Eye on, Science, 221:4611). USGS: Volcanoes

While volcanic eruptions are often catastophic events, they tend to be infrequent. Mount Shasta last erupted about 200 years ago, and has erupted only once per 600 years during the last 4,500 years. (USGS: Shasta Hazards).

On this basis we might conclude that there is little risk, since Mount Shasta is not due to erupt again for another 400 years.

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However, there are two factors that prevent us from accepting this conclusion. First, volcanic events are not regular events - they can occur at irregular intervals. Second, there are more frequently occurring hazards: debris avalanches and mudflows. (Some authors appear to class mudflows as a type of debris flow; others consider them to be different phenomena.)

Debris avalanches and lahars are more frequent than volcanic eruptions. Both depend on climatic conditions, including release of water from mountain glaciers and precipitation. During the last 400 years the mean interval beteen debris flow events at Mount Shasta has been six years, (C. R. Hupp et al, Dendrogeomorphic Evidence and Dating of Recent Debris Flows on Mount Shata, Northern California, USGS Professional Paper 1396-B, 1987. This paper does not distinguish mudflows as separate phenomena.)

Under certain conditions wet debris flows down the mountainside gathering speed as it flows. No human structures can withstand its force. Few have time to escape. (W. R. Osterkamp et al, Magnitude and Frequency of Debris Flows and Areas of Hazard on Mount Shasta, Northern California, USGS Professional Paper 1396-A, 1986, Related report, James Blodgett, et al). More geology.


The complex history of Mount Shasta during the last 400,000 years is partly revealed by the patterns of absorption and reflectance of light recorded in satellite images (Landat/ASTER). The landforms of the region also have a story to tell and, while Crandell and others have discussed topographical evidence of Mount Shasta's past, good quality and detailed digital elevation models (DEMs) have not been available until recently. The aim of this study is to outline the potential of DEMs for the study of the landforms with brief reference to errors in DEMs.


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