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Diaporama
Earthquakes under Mount St. Helens volcano during 1988-2016; magmatic recharge swarms are marked, along with the most recent earthquake swarm. (image: USGS / Cascade Volcano Observatory via Eruptions Blog)
mardi, mai 10, 2016
Since the beginning of 2016, a swarm of small earthquakes has been occurring at under the volcano, suggesting that another phase of magma recharge is currently taking place. ... [details]
samedi, avril 20, 2013
(Very) tiny earthquakes occur regularly at the volcano, but nothing suggests anything unusual going on at the volcano for the moment. [details]
 

Mount St. Helens volcan

stratovolcan 2549 m / 8,363 ft
Washington, USA (mainland exept Alaska), 46.2°N / -122.18°W
Condition actuelle: normal / en sommeil (1 sur 5)
Mount St. Helens webcams / données en temps réel | Reports
Mount St. Helens livres
Last update: 5 nov. 2017 (small earthquake swarm)
Style éruptif tipique: Explosive
Eruptions du volcan Mount St. Helens: 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
HeureMag. / DepthDistanceLocation
Thu, 18 Jul 2019
Thu, 18 Jul 17:36 UTCM 0.5 / 4.5 km13 km32km NE of Amboy, Washington (USA)
Wed, 17 Jul 2019
Wed, 17 Jul 08:56 UTCM 0.8 / 4.8 km1 km37km NNE of Amboy, Washington (USA)
Tue, 16 Jul 2019
Tue, 16 Jul 16:43 UTCM 0.2 / 2.3 km0 km38km NNE of Amboy, Washington (USA)
Mon, 15 Jul 2019
Mon, 15 Jul 19:28 UTCM 0.1 / 2.2 km0 km38km NNE of Amboy, Washington (USA)
Mon, 15 Jul 13:49 UTCM 0.2 / 3.8 km5 km36km NE of Amboy, Washington (USA)
Voir tous
Mount St Helens volcano hardly needs introduction. In its spectacular eruption in 1980, it placed itself deep into collective memory, in particular within the NW states of the USA. Prior to this eruption and its gradual reawakening, little attention had been given to the volcanic nature and the beautiful mountain was a popular landmark for excursions.

Introduction:

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

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Plus d'info:
1980 eruption | News
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