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Time vs. # of Events & vs. Seismic Strain Energy Release
1981 through 1991 (11 years)
Graphs show average number of events occurring
per day (blue) and average seismic strain energy release
(square root of seismic energy) per day (red). The times and types of
eruptions are shown at the top of each figure with the length of the
symbol roughly proportional to the size of the eruption. Magmatic
explosive eruptions are those which had a significant amount of new,
juvenile magma ejected into an ash cloud. Phreatic explosions are
steam or gas explosions involving little or no magmatic material.
Dome growth eruptions are relatively quiet non-explosive eruptions
of lava onto the lava dome.
This plot overlaps the plot for the
past decade at the same time scale
for easy comparison. Note that the average daily number of events
during the early and mid 1980s is dominated by the sharp peaks during
precursors to dome-building eruptions. Even though many of these
active periods lasted only a few days to a week or so the peaks are much
higher than the levels during the 1990s. The peaks in energy release
during the precursory periods contrast even more due to the
fact that many more earthquakes were much larger than the small
earthquakes occuring in the late 1980s and 1990s.
This can be contrasted to the seismicity during the period of
explosive eruptions in 1980.
Back to:
UW Dept. of Earth and Space Sciences
PNW
Earthquake Info
University of Washington Dept. of Earth and Space Sciences, Box 351310, Seattle, WA 98195-1310
This is file SEIS/PNSN/HELENS/energynum.81-92.html.
If you see any problems e-mail:
seis_web@ess.washington.edu
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