34 Years Ago Today

In 1980, a major volcanic eruption occurred at Mount St. Helens, a volcano located in state of Washington, in the United States. The eruption (which was a VEI 5 event) was the only significant one to occur in the contiguous 48 U.S. states since the 1915 eruption of Lassen Peak in California.  The eruption was preceded by a two-month series of earthquakes and steam-venting episodes, caused by an injection of magma at shallow depth below the volcano that created a huge bulge and a fracture system on the mountain's north slope.

Prior to the eruption, USGS scientists convinced local authorities to close Mount St. Helens to the general public and to maintain the closure in spite of local pressure to re-open it; their work saved thousands of lives. An earthquake at 8:32:17 a.m. PDT on Sunday, May 18, 1980, caused the entire weakened north face to slide away, suddenly exposing the partly molten, gas- and steam-rich rock in the volcano to lower pressure. The rock responded by exploding a hot mix of lava and pulverized older rock toward Spirit Lake so fast that it overtook the avalanching north face.

An eruption column rose 80,000 feet (24 km; 15 mi) into the atmosphere and deposited ash in 11 U.S. states.  At the same time, snow, ice and several entire glaciers on the volcano melted, forming a series of large lahars (volcanic mudslides) that reached as far as the Columbia River, nearly 50 miles (80 km) to the southwest. Less-severe outbursts continued into the next day, only to be followed by other large, but not as destructive, eruptions later in 1980.

Fifty-seven people were killed, including innkeeper Harry R. Truman, photographer Reid Blackburn and geologist David A. Johnston.  Hundreds of square miles were reduced to wasteland causing over a billion U.S. dollars in damage ($2.88 billion in 2014 dollars), thousands of game animals were killed, and Mount St. Helens was left with a crater on its north side. At the time of the eruption, the summit of the volcano was owned by the Burlington Northern Railroad, but afterward the land passed to the United States Forest Service.  The area was later preserved, as it was, in the Mount St. Helens National Volcanic Monument.  Thanks to Wikipedia for this information.