Mt St Helens
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Mount St. Helens, this 123 year dormant volcano, erupted on May 18, 1980 after being shaken by an earthquake measuring 5.1 on the Richter scale and with a 4.2 magnitude.
Scientists have determined that the history of Mount St. Helens began about 40,000 years ago with many eruptions. That continued until 2,500 years ago. During that activity, numerous explosive eruptions occurred for hundreds to thousands of years, but were separated by dormant times ranging in length from a few hundred to about 15,000 years. During the 40,000 years of its existence the volcano has gone through many eruptive periods.
The first is the The Ape Canyon eruptive period...