Studying magma formation beneath Mount St. Helens
University and government scientists are embarking on a collaborative research expedition to improve volcanic eruption forecasting by learning more about how a deep-underground feeder system creates and supplies magma to Mount St. Helens.
They hope the research will produce science that will lead to better understanding of eruptions, which in turn could lead to greater public safety.
The Imaging Magma Under St. Helens project involves three distinct components: active-source seismic monitoring, passive-source seismic monitoring and magnetotelluric monitoring, using fluctuations in Earth's electromagnetic field to produce images of structures beneath the surface.
Researchers are beginning passive-source and magnetotelluric monitoring, while active-source monitoring -- measuring seismic waves generated by underground detonations -- will be conducted later.
Passive-source monitoring involves burying seismometers at 70 different sites throughout a 60-by-60-mile area centered on Mount St. Helens in southwestern Washington. The seismometers will record data from a variety of seismic events.
"We will record local earthquakes, as well as distant earthquakes. Patterns in the earthquake signatures will reveal in greater detail the geological structures beneath St. Helens," said John Vidale, director of the University of Washington-based Pacific Northwest Seismic Network.
Magnetotelluric monitoring will be done at 150 sites spread over an area running 125 miles north to south and 110 miles east to west, which includes both Mount Rainier and Mount Adams. Most of the sites will only be used for a day, with instruments recording electric and magnetic field signals that will produce images of subsurface structures.
Besides the UW, collaborating institutions are Oregon State University, Lamont-Doherty Earth Observatory at Columbia University, Rice University, Columbia University, the U.S. Geological Survey and ETH-Zurich in Switzerland. The work is being funded by the National Science Foundation.
Mount St. Helens has been the most active volcano in the Cascade Range during the last 2,000 years and has erupted twice in the last 35 years. It also is more accessible than most volcanoes for people and equipment, making it a prime target for scientists trying to better understand how volcanoes get their supply of magma.
The magma that eventually comes to the surface probably originates 60 to 70 miles deep beneath St. Helens, at the interface between the Juan de Fuca and North American tectonic plates. The plates first come into contact off the Pacific Northwest coast, where the Juan de Fuca plate subducts beneath the North American plate and reaches great depth under the Cascades. As the magma works its way upward, it likely accumulates as a mass several miles beneath the surface.
As the molten rock works its way toward the surface, it is possible that it gathers in a large chamber a few miles beneath the surface. The path from great depth to this chamber is almost completely unknown and is a main subject of the study. The project is expected to conclude in the summer of 2016.
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The above story is based on materials provided by University of Washington. Note: Materials may be edited for content and length.
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Sabancaya Volcano in southern Peru becomes active
June 18, 2014
By Rachel Chase
(Photo: El Comercio)
Geological authorities are reporting that the Sabancaya volcano in southern Peru has become active after 15 years of silence.
According to information released by the Peruvian Geophysical Institute (IGP), Sabancaya has erupted several times. The first recorded activity at Sabancaya was in 1750, and the volcano became active again in 1784. 200 years later, in 1986, the volcano once again displayed activity. Now, the volcano is once again active, having gradually intensified since late February.
Speaking to El Comercio, IGP investigator Orlando Macedo said "All this activity is part of an expected process. Before the eruption, tremors were occurring closer and closer to the volcano and the crater. However, the process is taking longer than that which we saw at the Ubinas Volcano, when everything happened in a matter of days. In the case of Sabancaya, this could go on for several months."
In addition to seismic activity, Sabancaya has also emitted plumes of smoke. No thermic anomalies have been observed by the IGP.
According to the IGP, three seismic monitoring stations are keeping watch over activity at Sabancaya.
Sabancaya, located in the southern region of Arequipa, is part of a volcanic complex that includes Hualca-Hualca and Ampato.
http://www.peruthisweek.com/news-sabancaya-volcano-in-southern-peru-becomes-active-103283Enigma of Changbaishan volcano and a gap in stagnant slab
NECESS Array: the Earth's interior seen from Northeast China
Earthquake Research Institute
2014/06/17
A cartoon image of the subducting Pacific slab and the mantle upwelling beneath the Changbaishan volcano, showing the Pacific slab (blue) and low velocity zone of the mantle to its west (red). This indicates that the stagnant slab is interrupted either by warm or soft substance.
Reprinted by permission from Macmillan Publishers Ltd: Nature Geoscience 7, May 2014, copyright 2014.
Researchers at Earthquake Research Institute (ERI) of the University of Tokoyo working together with Chinese and U.S colleagues, conducted a temporal deployment of over 120 broadband seismometers in northeast China (NorthEast China Extended SeiSmic Array: NECESSArray) over a period of two year from September, 2009 to August, 2011. This seismic array enabled visualization of the three-dimensional structure of the deep mantle of the earth in detail, at far better resolution than ever before.
Using the data from this seismic array, ERI Ocean Hemisphere Research Center Professor Hitoshi Kawakatsu's research group discovered a large a gap in the stagnant slab (a stagnating section of the subducted Pacific plate) in the mantle transition zone beneath NE China.
Changbaishan volcano at the border between China and North Korea, is located further away from the subduction zone of the plate boundary where volcanoes are usually formed. Why the volcano was formed in such place was unknown until now.
Previous tomographic models indicated the presence of a horizontally laying slab, and this time, a gap of the stagnant slab in the mantle transition zone beneath Changbaishan volcano was found. This finding sheds new light on the origin of the enigmatic Changbaishan volcano.
Paper
Youcai Tang, Masayuki Obayashi, Fenglin Niu, Stephen P. Grand, Yongshun John Chen, Hitoshi Kawakatsu, Satoru Tanaka, Jieyuan Ning & James F. Ni,
"Changbaishan volcanism in northeast China linked to subduction-induced mantle upwelling",
Nature Geoscience Online Edition: 2014/5/18, doi: 10.1038/ngeo2166.
Article link
Links
Ocean Hemisphere Research Center, Earthquake Research Institute
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