Volcano landslides often create horseshoe-shaped craters

Horse-shoe shaped crater of Mount St. Helens volcano, Washington
Photograph by C.D. Miller in 1980

View is looking south into the crater of Mount St. Helens formed by an enormous landslide on May 18, 1980. The newly-formed crater is about 2 km wide (east-west), 3 km long (north-south), and about 600 m deep. The landslide removed about 2.3 km3 from the volcano's cone, which towered 1,035 m above the crater floor!

Large horseshoe-shaped craters, open at one end, have long been noted in many volcanic regions around the world. The origin of these breached craters has been controversial, but since the landslide and eruption of Mount St. Helens in 1980, many have been interpreted by scientists as the result of a landslide.

If a large landslide creates a horseshoe-shaped crater that exposes a volcano's eruptive vent, the deep crater will likely direct subsequent volcanic activity (lava flows, pyroclastic flows, or lahars) toward its breached opening. A new hazard assessment may be necessary to determine the way in which volcano-hazard areas downslope from the crater may have changed.

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U.S. Department of the Interior, U.S. Geological Survey, Menlo Park, California, USA
URL http://volcanoes.usgs.gov/Imgs/Jpg/MSH/30210600_056_caption.html
Contact: VHP WWW Team
Last modification: 16 December 1999 (SRB)