Copyright Information: All images are in the public domain and available for free. If you use this image, credit NOAA/NGDC, University of Colorado at Boulder. |
Buried cascade ashes between peat layers as they appeared in 1975 were a silent testimony of previous volcanism in the Cascades before the 1980 eruption of Mount Saint Helens. Volcanic activity at the Mount Saint Helens site began during the last major glaciation of the Ice Age. There have been nine periods of eruptive activity, the most recent of which ended in 1857. Two geologic reports in the 1970s identified Mount Saint Helens as the most likely volcano to reawaken in the conterminous United States. Image Credit: University of Colorado at Boulder May 18, 1980 Mount Saint Helens USA volcano An earthquake occurred at 15 32 UT, only seconds before the explosion that began the eruption of Mount St. Helens volcano. This eruption and blast blew off the top of the volcano, reducing its elevation by 396 meters, killed 31 people and caused an estimated property damage of between $0.5 billion and $2 billion. About 53 earthquakes having magnitude larger than 4.5 were located near Mount St. Helens before the main event and eruption. No earthquakes having magnitudes higher than 4.5 were located following the eruption. |
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