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U.S. Geological Survey, Vancouver, Washington
University of Washington, Pacific Northwest Seismograph Network, Seattle, Washington
Mount St. Helens Information Statement
October 1, 2004, 12:45 P.M., PDT
This Information Statement describes a new feature that has developed in the crater of Mount St. Helens over the past few days. Photographs taken by scientists during gas flights show that an area of about 5 to10 acres on the crater glacier, just south of the 1980-86 lava dome, has risen up to several tens of feet (exact amount is not known) and has become increasingly crevassed (cracked). The crevasses are up to several feet wide and perhaps tens of feet deep. We think that this localized deformation is caused by a portion of the south side of the lava dome and crater floor pushing upward in a piston-like motionand lifting overlying snow, glacier ice, and rock debris that is tens to several hundred feet thick. Because there is no sign of steaming or rapid melting, we infer that old, cold dome rock is in contact with the glacier and not new lava, which would be hot enough to cause steaming. This morning a USGS scientist from the Alaska Volcano Observatory is flying over the crater with an instrument that measures surface temperatures of the dome and crater floor.
This deformation accompanies the intense seismic activity of the past week and suggests that the dome has been weakened sufficiently that forces at depth are large enough to allow upward displacement of part of the dome and crater floor. Evidence from GPS instruments on the flanks of the volcano indicate that this deformation is limited to a relatively small area between the lava dome and south crater wall and that other sites are stable.
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