st helens ...1980 eruption..?
can anybody tell me anything about the 1980 st helens eruption.... like why it was caused....how far the effects where caused...and any other geological things about the eruption..thx..
- 10 years agoFavorite Answer
The 1980 eruption of Mount St. Helens, a stratovolcano located in Washington state, in the United States, was a major volcanic eruption. 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 California's Lassen Peak.
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 Mount St. Helens' north slope. An earthquake at 8:32:17 a.m. on 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 quickly that it overtook the avalanching north face.
An eruption column rose 80,000 feet (24,400 m) 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 fifty miles (eighty kilometers) to the south. 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 (including innkeeper Harry R. Truman and geologist David A. Johnston) and thousands of animals were killed. Hundreds of square miles were reduced to wasteland, causing over a billion U.S. dollars in damage ($2.74 billion in 2007 dollars), 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.