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Debris Avalanche

Rock and ice debris avalanche (October 20, 1997) on the east side o...
Rock and ice debris avalanche (October 20, 1997) on the east side of Mount Adams. (Credit: Iverson, Richard. Public domain.)

Debris avalanches can be both large and small and pose relative sized threats. Small failures of the upper slopes of Mount Adams present hazards that exist primarily in unpopulated areas deep within the backcountry. However larger debris avalanches pose a very destructive and far-reaching hazard at Mount Adams. Recent research has detected a large mass of wet, hydrothermally altered rock on the upper southwest flank of Mount Adams, at the head of the White Salmon River, which is about 25 times greater than the mass that failed in 1921. A smaller, but similar mass, has been identified on the upper east flank at the head of a Klickitat River tributary. These rock masses have lost a significant amount of their original rock strength and are on very steep slopes. Every few years these masses of weakened rock spawn rock avalanches, some of which travel for several kilometers. A failure of a large volume from the southwest sector of the volcano could affect settled areas.