Cascade Range Current Update

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.

A picture of this feature can be obtained from:
ftp://ftpext.usgs.gov/pub/wr/wa/vancouver/MSH_Images/MSH04_dome_glacier_south_side_9-29-04.jpg

Amendment made at 12:45 P.M. This area is the source of the steam and ash emission that began shortly after noon. We continue to monitor the situation closely and will issue additional updates as warranted




Mount St. Helens Information Statement,
October 1, 2004, 1:45 P.M., PDT

Mount St. Helens remains at Alert Level 2—Volcano Advisory

Shortly before noon today, Mount St. Helens emitted a plume of steam and minor ash from an area of new crevasses in the crater glacier south of the 1980-86 lava dome. This area was described in the prior Information Statement issued at 12:45 P.M. The event lasted from 11:57 to 12:21 PDT and created a pale-gray cloud that reached an altitude of about 9700 ft (from pilot reports). It drifted southwestward, where nearby residents should receive no more than a minor dusting of ash. USGS scientists making thermal measurements witnessed the emission and noted that the clouds were not particularly hot. Blocks of rock and ice ejected by the event fell in the crater and rim areas. The emission was accompanied by an abrupt drop in seismicity, which remains at low levels.

Similar events are possible in the future. We will monitor the situation closely over the next several hours anddays in order to determine the outlook for future behavior. Additional updates will be issued as needed.



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