Magma Reservoir Re-pressurizing Beneath Mount St. Helens

SEISMIC HAZARD
HEIGHTENED GLOBAL SEISMICITY
VOLCANIC HAZARD
NIGHTMARE SCENARIOS 07, 08
.

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.

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.