What is the current status of Mount St. Helens
Matt
and Leigh
Dear Matt and Leigh,
Sorry for the delay. I knew that there was an increase in the number of
earthquakes at Mount St. Helens but it took awhile for the information to
become available.
The U.S. Geological Survey's Cascade Volcano Observatory reports that the
number of small magnitude earthquakes (less than magnitude 1) beneath
Mount St. Helens has increased slowly and steadily from less than 10
events per month in January to about 100 events per month in September.
They point out that the volcano has been quiet during this period and
that no explosion or emission of gas or ash has occurred from the lava
dome. Similar seismic activity was observed prior to and during a series
of small gas explosions from the dome in 1989-1991. Although these
explosions were relatively small, they did throw dome rocks 1 foot (30
cm) in diameter 0.5 miles (0.8 km) from the dome and sent ash plumes as
high as 20,000 feet (6,100 m) above the sea level. Because these events
can happen without warning some trails in the area have been closed. For
additional information visit the
CVO homepage
.
Steve Mattox, University of North Dakota
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