We are in close
contact with USGS/Cascades
Volcano Observatory, in Vancouver, Washington and
the University
of Washington Pacific Northwest Seismograph Network.
Mount St. Helens Volcano Activity
Current status is Volcano Advisory (Alert Level 2); aviation
color code ORANGE
Growth of
the new lava dome inside the crater of Mount St. Helens
continues. As long as this eruption is in progress,
episodic changes in the level of activity can occur
over days, weeks, or even months. Increase in the intensity
of eruption could occur suddenly or with very little
warning and may include explosive events that produce
hazardous conditions within several miles of the volcano.
Small lahars (volcanic debris flows) could suddenly
descend the Toutle River valley if triggered by heavy
rain or by interaction of hot rocks with snow or glacier
ice. These lahars pose a negligible hazard below the
Sediment Retention Structure (SRS), but could pose a
hazard to people along the river channel upstream of
the SRS. At this time of year, it is not unusual for
rivers draining the volcano to contain high concentrations
of sediment that turn the water murky.
Although considered less likely at this time, the current
eruptive activity could evolve into a more explosive
phase that affects areas farther from the volcano and
sends significant ash thousands of feet above the crater
where it could be a hazard to aircraft and to downwind
communities.
Wind forecasts from the National Oceanic and Atmospheric
Administration (NOAA), coupled with eruption models,
show that ash clouds that rise above the crater rim
today would drift southward from the volcano.
Seismicity remains at a low level compared to that observed
early in this unrest. The current seismicity is consistent
with a continuing, slow rise of magma driving uplift
of the crater floor and feeding a surface extrusion
of lava. The overall low rates of seismicity and gas
emission suggest that the lava reaching the surface
is gas poor, thereby reducing the probability of highly
explosive eruptions in the near term.
Preliminary reduction of LIDAR data from October 14
indicates that the volume increase of the new dome (uplifted
glacial ice, rock debris, and new lava) was approximately
11 million cubic meters at that time, giving a growth
rate of about 7 cubic meters per second.
Crews had a productive day in the field yesterday. Work
included installation of two new GPS stations to measure
ground deformation on the surface of the growing dome,
geologic observations and sampling, collection of oblique
stereophotos for tracking growth of the new dome, thermal-infrared
mapping to determine temperature distribution in the
new and old (1980-86) domes, a gas-measurement flight,
and telemetry maintenance. Results include the following:
the new GPS station on the southern part of the new
dome shows motion downward and to the southeast; a station
near the summit of the old dome has moved northward
about 7 cm since October 20; thermal imaging showed
an elongate band of elevated surface temperature, locally
as great as 775º C along the west face of the new
dome coincident with the area of exposed newly extruded
lava; gas-emission rates measured yesterday are similar
to recent previous measurements (SO2 about 250 tons
per day, CO2 about 300 tons per day, H2S about 2 tons
per day); samples of dome rock similar in appearance
to the rock of the older dome were collected from two
localities in the vicinity of the exposed new lava.
In the aggregate, the above results indicate that the
character and rise of magma is continuing as it has
over tha past few weeks. The visible steam plume is
caused by condensation of moisture in the cold air above
the hot dome.
No field work is planned for today.
The U.S. Geological
Survey and the University of Washington continue to
monitor the situation closely and will issue additional
updates and changes in alert level as warranted.
Telephone recordings
with the latest update on Mount St. Helens and phone
contacts for additional information can be heard by
calling:
Media (360) 891-5180
General public
(360) 891-5202
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