Mount St. Helen

Mount St. Helen

Mount St. Helens Location: Washington, United States Latitude: 46.20 N Longitude: 122.18 W height: 2,549 meters or 8,364 feet - 9,677 feet before May 18, 1980 Type: Stratovolcano Number of eruptions in past 200 years: 2-3 Latest Eruptions: Between 1660-1700, around 1800-1802, 1831, 1835, 1842-1844, 1847-1854, 1857, 1980-? Present thermal activity: strong steaming Nickname: Mount Fuji of the West Remarks: continuous intermittent activity since 1980 with occasional eruptions of steam and ash; occasional pyroclastic flows; intermittent dome forming. MSH is considered a young volcano that developed over the last 40,000 years and is one of the most active volcanoes in the Cascade Range. Geologists predicted that the volcano would erupt before the year 2000. The May 18, 1980 eruption of Mount SH was the most destructive in the history of the United States. In a matter of hours, MSH caused loss of lives and widespread destruction of valuable property because of the avalanche, lateral blast and mudflows. On March 20, 1980, starting with an earthquake that was followed by many others, MSH became active again after a quiet period of 123 years. On March 27, 1980, there was a huge explosion and MSH began blowing ash and steam. This lasted until May 14, 1980. The explosion in March opened up two craters that quickly became one huge crater. While this was happening, an enormous bulge on the north side of the mountain top appeared. It grew about six feet each day. Geologist kept measuring the bulge, recording the earthquakes and sampling the ash and gases. By May, the bulge was 300 feet wide and more than one mile in length. On May 18 at 8:32 in the morning, Mount St.. Helens erupted taking the top 1,200 feet off the volcan...

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...composite volcano because it erupts both lava and ash. Dormant and Extinct Volcanoes If a volcano shows no signs of life for thousands of years it is thought to be extinct. If a volcano shows activity, even slight movement, it is dormant. Volcanoes that have violent eruptions between long periods of no activity are usually stratovolcanoes. Volcanoes that are inactive and not expected to erupt in the near future are called dormant volcanoes. Volcanoes that are never expected to erupt again are called extinct. All of the volcanoes in the Cascade Range where MSH is found are dormant volcanoes. Approximately 50 or so volcanoes erupt every year. The International Association of Volcanology defines active volcanoes as one that has erupted in historic times. Historic can mean 200 years in Hawaii or 3,000 years in the Mediterranean depending if there are historical records.