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Frequently Asked Questions about the May 18, 1980 Eruption

How high was Mount St. Helens before the May 18, 1980 eruption. How high was it after?

Before May 18, 1980, Mount St. Helens' summit altitude of 2,950 m (9,677 ft) made it only the fifth highest peak in Washington State. It stood out handsomely, however, from surrounding hills because it rose thousands of feet above them and had a perennial cover of ice and snow. The peak rose more than 1525 m (5,000 ft) above its base, where the lower flanks merge with adjacent ridges. On May 18, 1980, the volcano lost an estimated 2.6 billion cubic meters (3.4 billion cubic yards or 0.63 cubic mile) of its cone (about 400 m or 1,300 ft in height), leaving behind a horseshoe-shaped crater (open to the north), with the highest part of the crater rim on the southwestern side being at 2,550 m (8,365 ft) elevation.

How much ash was there from the May 18, 1980 eruption of Mount St. Helens?

During the 9 hours of vigorous eruptive activity, about 540 million tons of ash fell over an area of more than 57,000 square kilometers (22,000 square miles). Total volume of the ash before its compaction by rainfall was about 1.25 cubic kilometers (0.3 cubic mile), equivalent to 500,000 olympic swimming pools or an area the size of a football field piled about 150 miles high with fluffy ash.

How far did the ash from Mount St. Helens travel?

The May 18, 1980 eruptive column at Mount St. Helens fluctuated in height through the day, but the eruption subsided by late afternoon. By early May 19, the eruption had stopped. By that time the ash cloud had spread to the central United States. Two days later, even though the ash cloud had become more diffuse, fine ash was detected by systems used to monitor air pollution in several cities of the northeastern United States. Some of the ash drifted around the globe within about 2 weeks.