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Monday, June 18, 2012

MT. SAINT HELENS AND TOPOGRAPHIC CHANGES


Photo: Mt. St. Helens.  Image credit: NASA/JPL/NGA 
FROM:  NASA
Mount Saint Helens
Mount Saint Helens exemplifies how Earth's topographic form can change greatly even within our lifetimes. The mountain is one of several prominent volcanoes of the Cascade Range that stretches from British Columbia, Canada, southward through Washington, Oregon and into northern California. Mount Adams (left background) and Mount Hood (right background) are also seen in this view, which was created entirely from elevation data produced by the Shuttle Radar Topography Mission.

Prior to 1980, Mount Saint Helens had a shape roughly similar to other Cascade peaks, a tall, bold, irregular conic form that rose to 9,677 feet (2,950 meters). However, the explosive eruption of May 18, 1980, caused the upper 1,300 feet (400 meters) of the mountain to collapse, slide and spread northward, covering much of the adjacent terrain (lower left), leaving a crater atop the greatly shortened mountain. Subsequent eruptions built a volcanic dome within the crater, and the high rainfall of this area lead to substantial erosion of the poorly consolidated landslide material.

Eruptions at Mount Saint Helens subsided in 1986, but renewed volcanic activity here and at other Cascade volcanoes is inevitable. Predicting such eruptions still presents challenges, but migration of magma within these volcanoes often produces distinctive seismic activity and minor but measurable topographic changes that can give warning of a potential eruption.