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02 October 2004

Mount St. Helens Volcanic Advisory

Mount St. Helens Volcano Advisory (Alert Level Two) : September 29, 2004 10:40 A.M., PDT -- U.S. Geological Survey Cascades Volcano Observatory, Vancouver, Washington / University of Washington Dept. of Earth and Space Sciences, Seattle, Washington

Over night, seismic activity at Mount St. Helens has accelerated significantly, which increases our level of concern that current unrest could culminate in an eruption. We are increasing the alert level to the second of three levels, which is similar to Color Code Orange of the alert system used by the Alaska Volcano Observatory and analogous to the National Weather Service's hazard watch. Earthquakes are occurring at about four per minute. The largest events are approaching Magnitude 2.5 and they are becoming more frequent. All are still at shallow levels in and below the lava dome that grew in the crater between 1980 and 1986. This suggests that the ongoing intense earthquake activity has weakened the dome, increasing the likelihood of explosions or perhaps the extrusion of lava from the dome. The cause and outcome of the accelerating unrest is uncertain. Explosions from the lava dome could occur suddenly and without further warning.

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