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Random pictures
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)
Tuesday, May 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. ... [more]
Saturday, Apr 20, 2013
(Very) tiny earthquakes occur regularly at the volcano, but nothing suggests anything unusual going on at the volcano for the moment. [more]
 

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 webcams / live data | Reports
Mount St. Helens volcano books
Last update: 5 Nov 2017 (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
TimeMag. / DepthDistanceLocation
Wed, 18 Apr
Wed, 18 Apr 20:32 UTCM 1.5 / 1 km37 kmExplosion - 22km ENE of Castle Rock, Washington
Wed, 18 Apr 11:37 UTCM 0.2 / 0.6 km1 km- 37km NNE of Amboy, Washington
Wed, 18 Apr 08:18 UTCM 1.4 / 17.5 km38 km- 14km WSW of Morton, Washington
Tue, 17 Apr
Tue, 17 Apr 23:43 UTCM 1.0 / 11 km12 km- 37km SSE of Morton, Washington
Mon, 16 Apr
Mon, 16 Apr 01:47 UTCM 1.6 / 8.6 km27 km- 3km NNE of Amboy, Washington
View all recent quakes
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.

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

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