It was Mount Saint Helens

Thirty years ago today the United States experienced the largest volcano eruption ever recorded in the contiguous states. Approximately 65 people were killed. Following a 5.1 magnitude quake inside Mount Saint Helens, first came the landslide. The spot in which the landslide took place had been bulging before it broke off. You do not want your volcano to bulge. Then came the eruption. Turns out when lava mixes with snow and ice what you have is a lahar, which is reminiscent of wet cement. Don't let that comparatively benign description fool you though, the stuff was plenty hot. The lahars vaporized huge amounts of groundwater and when that steam blew, craters as large as 400 meters (1,300 feet) were blasted out. Nasty. The whole thing lasted about 9 hours. Here it is thirty years later and only a smattering of plants and animals have returned. So, not a garden spot but at least the lupines are back! And who doesn't like lupines.

Source:  A Fresh Look at Mount St. Helens. By Perkins, Sid. Science News, 4/24/2010
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