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Posts Tagged ‘Mount St. Helens’

Magma Reservoir Re-pressurizing Beneath Mount St. Helens

Posted by feww on May 2, 2014

SEISMIC HAZARD
HEIGHTENED GLOBAL SEISMICITY
VOLCANIC HAZARD
NIGHTMARE SCENARIOS 07, 08
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Mount St. Helens remains active, but no signs of impending eruption: CVO

The magma reservoir beneath Mount St. Helens has been slowly re-pressurizing over the past 6 years, according to the Cascades Volcano Observatory (CVO).

The re-pressurization is probably due to the arrival of a small amount of additional magma some 4 to 8 km  beneath the surface, said CVO.

“Since the end of the 2004-2008 dome-building eruption at Mount St. Helens, scientists at the USGS Cascades Volcano Observatory (CVO) and the Pacific Northwest Seismic Network (PNSN) have been monitoring subtle inflation of the ground surface and minor earthquake activity reminiscent of that seen in the years following the 1980-1986 eruptions. Careful analysis of these two lines of evidence now gives us confidence to say that the magma reservoir beneath Mount St. Helens has been slowly re-pressurizing since 2008.”

The re-pressurization in not unexpected because Mount St. Helens is in an active period, as it has been since 1980, said CVO, adding that there was no indication the volcano could erupt anytime soon.

St Helens 1980 Eruption

The eruption on May 18, 1980, which was heralded by a magnitude 5.2 earthquake, covered an area larger than 600 km² with volcanic matter, destroying entire  forests, killing 57 people and causing about $1.2buillion in property damage.

st helens
Prior to 1980, Mount St. Helens had the shape of a conical, youthful volcano sometimes referred to as the Mount Fuji of America. During the 1980 eruption the upper 400 m (1,300 ft) of the summit was removed by a huge debris avalanche, leaving a 2 x 3.5 km (1.2 x 2.2 mi) horseshoe-shaped crater now partially filled by a lava dome and a glacier. It is primarily an explosive dacite volcano with a complex magmatic system.

Mount St. Helens was formed during four eruptive stages beginning about 275,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to about 12,800 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older St. Helens edifice, but a few lava flows extended beyond the base of the volcano. The bulk of the modern edifice (above the 1980 crater floor) was constructed during the last 3,000 years, when the volcano erupted a wide variety of products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the north flank, and were witnessed by early settlers. (Source: CVO/USGS)

Volcano Details (CVO)

Location: Washington, Skamania County
Latitude: 46.2° N
Longitude: 122.18° W
Elevation: 2,549 (m) 8,363 (f)
Volcano type: Stratovolcano
Composition: Basalt to Rhyodacite
Most recent eruption: 1980 (May 18), 2004-2008
Nearby towns: Castle Rock, WA; Olympia, WA; Vancouver, WA; Yakima, WA; Portland, OR
Alert Level: Normal (2014-04-30 09:05:42)


Mount St. Helens, Washington simplified hazards map showing potential impact area for ground-based hazards during a volcanic event.

Posted in Global Disaster watch, Seismic Hazard, Significant Event Imagery, significant events, volcanic hazard, volcanism | Tagged: , , , , , | 1 Comment »

Mount St. Helens: “The Ides of March?”

Posted by feww on February 17, 2011

VolcanoWatch Weekly [17 Feb 2011]

Shinmoedake Update:

Some 2,500 people living near Shinmoedake volcano on Japan’s Kyushu island were advised earlier today to evacuate their homes after heavy rain threatened lahar avalanches, reports say.

VoW: Mount St. Helens


Mount St. Helens and Spirit Lake, as seen from Bear Cove. Image Source: U.S. Forest Service via USGS/CVO.


Phreatic eruption of Mount St. Helens, March 28, 1980, as seen from the north. Image by C.Dan Miller, USGS/CVO

Mount St. Helens, Washington  Ash Plume Path May 18, 1980


Click image to enlarge.

Mount St. Helens Volcano
Position: 46°12′ N 122°10’48” W,
Summit Elevation: 2,549 m (8,363 ft )
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN
Source: USGS/CVO

Recent observations:

An M4.3 earthquake struck the Mount St. Helens region this morning, 14 February 2011, at 10:35 a.m. PST (18:35 UTC) and was felt widely through southwestern Washington and Northwestern Oregon (http://earthquake.usgs.gov/earthquakes/dyfi/events/uw/02141835/us/index.html). Its exact magnitude may change by a few tenths from this value as records are further analyzed. The earthquake was followed by several aftershocks up to M2.8 over the next few hours (http://www.pnsn.org/recenteqs/latest.htm), the three largest of which were also reported felt. All of the earthquakes are located in an area about 8 kilometers (5 miles) north of the crater of Mount St. Helens, near the Johnston Ridge Observatory, at a depth of about 4 to 6 kilometers (2.5 to 4 miles).

Today’s earthquakes are in the same place as a small swarm that took place about two weeks earlier, on 29 January. These earthquakes are reminiscent of a swarm that took place about 30 years ago, when a swarm of small earthquakes began in August 1980, a few miles northwest of today’s activity. The 1980-1981 sequence climaxed with an M5.5 earthquake on 14 February 1981. Analysis of the 1981 events suggested that they occurred along existing faults in the Mount St. Helens seismic zone, a northwest to southeast trending system of faults in which Mount St. Helens lies. The Mount St. Helens seismic zone exhibits strike-slip motion, with the southwestern rocks slipping horizontally northwest relative to the rocks northeast of the fault zone. The fault zone likely exerts control on the location of Mount St. Helens volcano. Studies following the 1980 eruption suggested that the magma removed during the May 1980 eruption and subsequent lava-dome building caused faults along the seismic zone to slip in response to the magma withdrawal. Similar interaction of volcanic activity and tectonic fault movement is possible in the case of today’s earthquakes, but at present there appears to be no signs of unrest in the volcanic system.  USGS/Cascades Volcano Observatory, Vancouver, Washington

Summary of Weekly Volcanic Activity Report – 9 February to 15 February 2011

[Source: SI/USGS]

New Activity/Unrest:

Map of Volcanoes


Map of Volcanoes.
Background Map: University of Michigan. Designed and enhanced by Fire Earth Blog. Click image to enlarge.

Ongoing Activity:

For additional information, see source.

Related Links:

FEWW Volcanic Activity Forecast

Other Related Links:

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