http://vulcan.wr.usgs.gov/Volcanoes/Cascades/CurrentActivity/Mount St. Helens Notice of Volcano Alert, October 2, 2004
A notice of Volcano Alert (Alert Level 3) was issued today at 2:00 p.m. PDT
Immediately after the small steam emission at 12:15, seismic activity changed
from principally rock breakage events to continuous low-frequency tremor, which
is indicative of magma movement. We are increasing the alert level to Volcano
Alert the highest alert level indicating that an eruption could be imminent.
The cause and outcome of the accelerating unrest is uncertain. Explosions from
the vent could occur suddenly and without further warning. During such
explosions the dome and crater floor are at greatest risk from ballistic
projectiles, but the rim of the crater and flanks of the volcano could also be
at risk. Explosions would also be expected to produce ash clouds that rise
several to tens of thousands of feet above the crater rim and drift downwind.
Currently wind forecasts from the National Weather Service, combined with
eruption models, show that ash clouds will move to the northwest. If ash
emissions are large, drifting ash could affect downwind communities. Minor
melting of the glacier could trigger debris flows from the crater that are
large enough to reach the Pumice Plain. There is very low probability that
downstream communities would be impacted by these hydrologic events. .
We continue to monitor the situation very closely and will issue additional
updates as warranted, whether activity escalates or returns to background
levels.
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Mount St. Helens Update, October 2, 2004, 7:30 A.M.
Current status is Alert-Level 2-Volcano Advisory
Yesterday the increasingly energetic seismic swarm of the past week culminated
in a small 25-miunute-long eruption around noon from a vent just south of the
lava dome. Seismicity dropped to a low level for several hours after the
eruption, but quickly increased with earthquakes reaching a peak around 11 pm
last night. Currently earthquakes are occurring at a rate of 1-2 per minute
with maximum earthquake magnitudes about M3. All earthquake locations remain
shallow. The current level of seismic energy release is slightly above where it
was prior to the eruption yesterday. We infer that the system has
repressurized. As a result, additional steam-and-ash eruptions similar to
yesterdays's could occur at any time.
Yesterday field crews in a helicopter took thermal images of the dome and
crater both during and several hours after the eruption. Temperatures were
consistent with those expected from the steam explosion and well below magmatic
temperatures. Another flight for thermal imagery will occur this morning. A
deformation crew will be in the field today to collect data. Yesterday's gas
flight detected no magmatic gases in the area of the eruptive vent, but did
detect some carbon dioxide (CO2) from a small fumarole on the NW face of the
dome. The amount of CO2 will probably be too small to quantify. At times the
flight crew thought they smelled a weak sulfurous odor in the vicinity of this
fumarole, but the sensors did not detect any SO2 or H2S.
Updated wind forecasts from the National Oceanic and Atmospheric Administration
coupled with an eruption model indicate that the wind direction are from the
east so that any ash clouds produced today will drift westwardly.
There will be a press conference at CVO this morning at 9:30 am.
Viele Grüße,
Angie