History of Mount St. Helens

Mount St. Helens is a relatively young volcano. Scientists think that the current crater has formed over the last 2,200 years. In this time it is thought that over 60 individual tephra layers and several volcanically induced debris flows have been produced. It is though that at least 6 of these flows have reached the Columbia River, which is over one hundred kilometers downstream. Mount St. Helens has been the most active volcano in the Cascade range in recent history and for that reason it is the most intensively studied. The eruption that occured on May 18, 1980 came as no surprise. "Past eruptive activity of Mount St. Helens has been divided into 4 eruptive stages, each lasting about 2,000 years or more."[6] The most recent stage is called the Spirit Lake eruptive stage. During the last 1,700 years there have been several significant developments that helped form the volcano. It is thought that around 1,700 years ago the Cave Basalt was formed near the southwest base of the volcano. It is a lava tube system that is about eight kilometers long and contains the longest known uncollapsed lava tube in the world. The name of it is Ape Cave and it is about three and a half kilometers long.[6]

     Sugar Bowl dome is another significant feature of the volcano. It is located on the North side of the volcano, positioned slightly east of the mouth. It is thought that it occured about 1,200 years ago and was formed about the same time as the East Dome. Both of these domes were created by lateral blasts. The larger of the two blasts produced Sugar Bowl dome and spread debris as far as ten kilometers northeast of the volcano.
    The last significant eruptive period before the 1980 eruption was the Goat Rocks dome which formed between 1800 and 1857. The last signigicant activity before 1980 was in 1857 when Mount St. Helens produced dense smoke and fire. There have been a couple unconfirmed eruptions of the volcano and they were reported in 1898, 1903 and 1921.[6]
      The question is, will we heed the lessons of the past? Two volcanoes serve as great models from which we can learn. The first is Mount Vesuvius located about seven miles southeast of Naples, Italy. In 79 A.D. Vesuvius erupted killing an estimated 16,000 people. In 1631 it erupted again killing 18,000 people. It has erupted three times this century as well, killing more people and burying the city of Naples.[3] The amazing thing about Naples is that it is now built right on top of the old city. The lava provides the foundation for the current city.
    The second example is Mount Pele'e located on the French Island of Martinique in the Lesser Antillies. Mount Pele'e erupted in 1902 killing 25,000 residents in the city of St. Pierre. Undaunted, these people rebuilt the city over the next twenty years.[3] In both cases the towns have been rebuilt and the surrounding areas redeveloped which cost thousands more people their lives. It looks as if we are headed down the same destructive path with Mount St. Helens. Area residents may not be building a major city, but they are attracting millions of tourists to the volcano each year. The recent past has shown us that Mount St. Helens is an active volcano that erupts fairly regularly.   If Mount St. Helens follows the pattern of eruptions from the past, it will erupt within the next fifty to one hundred years. Only fifty-seven people died in the May 18, 1980 eruption, a relatively small number of people compared to others throughout history, but if we keep developing the area the next could claim many more.[4] We have built tourist resorts and encouraged development of the area. From this behavior it would seem that we have not learned anything from history and are destined to repeat it. We are defiant in the face of an inevitable evil.

This link provides the complete history of the formation of Mount Saint Helens. USGS Report

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