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Alert Level: NORMAL, Color Code: GREEN
2014-04-30 16:05:42 UTC





CASCADES VOLCANO OBSERVATORY INFORMATION STATEMENT
U.S. Geological Survey
Wednesday, April 30, 2014, 9:05 AM PDT (Wednesday, April 30, 2014, 16:05 UTC)


MOUNT ST. HELENS VOLCANO (VNUM #321050)
46°12' N 122°10'48" W, Summit Elevation 8363 ft (2549 m)
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN

Posted via the USGS Volcano Notification Service (VNS) http://volcanoes.usgs.gov/vns/


Analysis of current behavior at Mount St. Helens indicates that the volcano remains active and is showing signs of long-term uplift and earthquake activity, but there are no signs of impending eruption. 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. It is likely that re-pressurization is caused by arrival of a small amount of additional magma 4-8 km (2.5-5 miles) beneath the surface. This is to be expected while Mount St. Helens is in an active period, as it has been since 1980, and it does not indicate that the volcano is likely to erupt anytime soon. Re-pressurization of a volcano's magma reservoir is commonly observed at other volcanoes that have erupted recently, and it can continue for many years without an eruption.

USGS and PNSN are continuing to monitor ground deformation and seismicity at Mount St. Helens. In an effort to learn more about activity beneath the volcano, they will conduct two additional types of measurements this summer. Surveys will measure the types and amounts of volcanic gases being released, and the strength of the gravity field at the volcano. Both types of measurements are sensitive to changes in the amount or depth of subsurface magma. The information collected at Mount St. Helens continues to help scientists interpret behaviors at other volcanoes and to improve eruption forecasting capabilities. Additional research results will be posted in USGS Updates, Information Statements, and on the USGS-CVO website.

In a previously planned but related development, an experiment called "Imaging Magma Under St. Helens" (iMUSH) will start this summer and run for the next few years. The experiment, jointly funded by the National Science Foundation and USGS, is designed to produce a better picture of the magma plumbing system under the volcano. It may also provide new insights into the ongoing re-pressurization process.

The USGS Cascades Volcano Observatory and Pacific Northwest Seismic Network continue to monitor Mount St. Helens and other volcanoes of the Cascade Range for signs of increased unrest. The likelihood of detecting short-term precursory phenomena before the next eruption at Mount St. Helens is enhanced by the existence of an effective monitoring network established in response to recent eruptions. Efforts are underway to bring networks at other dangerous volcanoes in the Cascade Range up to a similar standard.


The USGS and the Pacific Northwest Seismic Network at University of Washington continue to watch conditions at Mount St. Helens closely.

For Further Information: Carolyn Driedger at USGS-CVO (360) 993-8907 driedger@usgs.gov
Bill Steele at UW-PNSN (206) 685-2255 wsteele@uw.edu







CASCADES VOLCANO OBSERVATORY INFORMATION STATEMENT
U.S. Geological Survey
Monday, February 14, 2011, 5:48 PM PST (Tuesday, February 15, 2011, 01:48 UTC)


MOUNT ST. HELENS VOLCANO (VNUM #321050)
46°12' N 122°10'48" W, Summit Elevation 8363 ft (2549 m)
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN

The 40-month-long lava-dome eruption of Mount St. Helens that began in autumn 2004 ended in late January of 2008. Earthquakes, volcanic gas emissions, and ground deformation are all at pre-eruptive background levels. The alert level and aviation color code were reduced to NORMAL/GREEN on July 10, 2008, following five months with no sign of renewed activity.

Even with the end of lava dome growth, some hazards persist. The new lava dome remains hot in places and capable of producing small hot avalanches or minor explosions that could dust areas with ash up to tens of miles downwind. Rock fall from the crater walls can produce clouds of dust that rise above the crater rim, especially during dry, windy days, as has happened in the past. Also, heavy rainfall or rapid snowmelt can send small debris flows onto the Pumice Plain north of the crater.


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.

The USGS and the Pacific Northwest Seismic Network at University of Washington continue to watch conditions at Mount St. Helens closely.