Johnston Ridge Observatory
24000 Spirit Lake Highway
P.O. Box 326
Toutle, WA 98649
VolcanoCam Movies Archive
Eruption Event Movie - October 10, 2004
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the frame rate will increase to its defined rate of six frames/second.
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preset to loop indefinitely.
Below the Flash movie may be a copy of the press release as issued the same day
by the U.S. Geological Survey, Cascades Volcano Observatory, Vancouver, Washington.
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(As issued by the U.S. Geological Survey, Vancouver, Washington
University of Washington, Pacific Northwest Seismograph Network, Seattle, Washington)
Seismic activity has decreased slightly over the past 20 hours to low
levels, similar to those observed during the evening hours of October
7. Earthquakes continue to occur at a rate of about 1 per minute, but
most have magnitudes of 1.0 or less. With the improving weather, a gas
measuring flight is planned within the next two days.
Additional analysis of lidar and photographs of the intensely uplifting
area on the south side of the lava dome suggests that the total volume
change represented by the deformation between late September and October
6 is about 16 million cubic meters (21 million cubic yards). The average
rate of change is about 2 million cubic meters per day (2.6 million cubic
yards per day). If this figure represents the rate of intrusion of magma
into shallow levels of the dome and(or) underlying crater floor, it is
an intrusion rate about twice that measured during dome-building eruptions
at Mount St. Helens in the 1980s. Cartographers with the USGS office
in Denver are working to develop precise volume change estimates for
the uplifted area from stereo airphotos acquired between 1 and 5 October.
As a result of the intense unrest of the past 11 days, we infer that
magma is at a very shallow level. During times of unrest, Mount St. Helens
and similar volcanoes elsewhere typically go through episodic changes
in level of unrest over periods of days to weeks, or even months. Such
changes are in part driven by variations in the rate of magma movement.
We expect fluctuations in the level of unrest to continue during coming
days. Escalation in the degree of unrest and perhaps an eruption could
occur suddenly or with very little warning. There may be little time
to raise the alert level before a hazardous event occurs. Therefore,
we continue to monitor the situation closely and will issue additional
updates and changes in alert level as warranted.