Mount St. Helens volcano
stratovolcano 2549 m / 8,363 ft
Washington, USA (mainland exept Alaska), 46.2°N / -122.18°W
Current status: dormant (1 out of 5)
Mount St. Helens volcano books
Washington, USA (mainland exept Alaska), 46.2°N / -122.18°W
Current status: dormant (1 out of 5)
Mount St. Helens volcano books
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Last update: 10 May 2016 (small earthquake swarm)
Typical eruption style: Explosive
Mount St. Helens volcano eruptions: 2004-08, 1990-91, 1989-90, 1980-86 (18 May 1980: Plinian eruption), 1921(?), 1903(?), 1898(?), 1857, 1854, 1853, 1850, 1849(?), 1848, 1847, 1842-45, 1835, 1831
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Typical eruption style: Explosive
Mount St. Helens volcano eruptions: 2004-08, 1990-91, 1989-90, 1980-86 (18 May 1980: Plinian eruption), 1921(?), 1903(?), 1898(?), 1857, 1854, 1853, 1850, 1849(?), 1848, 1847, 1842-45, 1835, 1831
| Time | Mag. / Depth | Distance | Location |
| Tue, 22 Aug | |||
| Tue, 22 Aug 04:02 UTC | M 0.8 / 10.8 km | 11 km | - 26km NNW of Carson, Washington |
| Tue, 22 Aug 03:50 UTC | M 0.6 / 3.4 km | 3 km | - 37km NE of Amboy, Washington |
| Mon, 21 Aug | |||
| Mon, 21 Aug 10:36 UTC | M 0.5 / 0.5 km | 1 km | - 37km NNE of Amboy, Washington |
| Mon, 21 Aug 07:16 UTC | M 0.9 / 8.3 km | 38 km | - 2km SSE of Morton, Washington |
| Sun, 20 Aug | |||
| Sun, 20 Aug 16:29 UTC | M 0.4 / 15.5 km | 17 km | - 26km S of Morton, Washington |
Background:
The eruption in 1980 followed a long repose interval, typical of the volcanoes in the Cascades Range, and is now one the best studied eruptions in history. It started with steam and ash explosions on 27 March 1980, the first eruption in the contiguous USA since the 1914-17 activity of Lassen Peak, California. Activity gradually built up, including the formation of an enormous growing bulge of the northern sector, which at the end measured more than 50 m, caused by intruding magma. The eruption culminated on 18 May when almost the entire northern sector of the mountain collapsed in a giant debris avalanche reaching 30 km. The flank collapse triggered a massive lateral blast wave that totally destroyed everything within a 10 km radius and knocked down trees as far as 30 km. Simultaneously, a vertical Plinian eruption column was erupted from the crater and reached 23 km altitude.Despite extensive evacuation measures, several people were killed in the eruption, including volcanologist David Johnston (USGS) who was on his turn monitoring the volcano when the eruption occurred.
Prior to the 1980 eruption, Mount St. Helens formed a conical, youthful volcano sometimes called the Fuji-san of America. During the 1980 eruption the upper 400 m of the summit was removed by collapse of the slope, that left a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens is a very young volcano and only about 40-50,000 years old.
It has been the most active volcano in the Cascade Range during the past 10,000 years, and the modern edifice was constructed during the last 2,200 years, when the volcano produced basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century were witnessed by early settlers.
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Sources:
USGS Cascades Volcano Observatory
St. Helens Information from the Global Volcanism Program
1980 eruption of Mount St Helens
A chronology and brief description of the 1980 eruption of Mount St. Helens has been put on its own page.
A chronology and brief description of the 1980 eruption of Mount St. Helens has been put on its own page.
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