Mt. St Helens Erupts

"On May 18, 1980, after nearly 2 months of local earthquakes and steam eruptions, picturesque Mount St. Helens, ... suddenly began a major explosive eruption directed first northward and then upward. The lateral blast, which lasted only the first few minutes of a 9-hour continuous eruption, devastated more htan 150 square miles of forest and recreation area, killed countless animals, and left about 60 persons dead or missing. The 9-hour eruption, the huge debris avalanche that immediatedly preceded it, and intermittent eruptions during the following 3 days removed about 4 billion cubic yards (0.7 cubic mile) of new magmatic material and of the upper and northern parts of the mountain, including about 170 million cubic yards (0.03 cubic mile) of glacial snow and ice. The eruption caused pyroclastic flows and many mudflows, the largest of which produced deposits so extensive and voluminous that they reached and blocked the shipping channel of the Columbia River about 70 river miles from the volcano. The May 18 eruption blew volcanic ash, consisting of pulverized old rock from the mountain's core as well as solidified new lava, more than 15 miles into the air. Winds carried the ash generally eastward across the United States and, in trace amounts, around the world. The ash, which fell in troublesome amounts as far east as western Montana, severely disrupted travel, caused widespread economic loss, and resulted in other problems that persisted ..."

-Foxworthy and Hill, 1982, Volcanic Eruptions of 1980 at Mount St. Helens, The First 100 Days: USGS Professional Paper 1249