Ash from Mount St. Helens volcano travelled a great distance

On Sunday, May 18, 1980, one of the best-monitored volcanic eruptions in history occurred at Mount St. Helens in Washington. A tremor that morning caused a side of the mountain to slump along a fault, sending a massive landslide of hot ash and expanding gas down the hillside at over 200 kilometers per hour. For nearly 20 kilometers outward, the wall of volcanic ash covered the surrounding area, including lakes, rivers and trees. At the same time, the slump exposed the magma chamber directly to the atmosphere, and the rising hot magma exploded skyward, jetting a dark gray ash cloud nearly 24 kilometers into the atmosphere. In the end, almost 390 square kilometers of forest had been destroyed, traces of ash had fallen as far as Colorado and Oklahoma, and 60 people had lost their lives.

Credit: Dylan Prentiss, Department of Geography, University of California, Santa Barbara. Modified from Tilling, Topinka, and Swanson, 1990, "Mount St. Helens: Past, Present and Future."

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