USGS/Cascades Volcano Observatory, Vancouver, Washington
REPORT:
Growth of the lava dome at Mount St. Helens, Washington, (USA) 1981-1983
--
Swanson, D.A., Dzurisin, D., Holcomb, R.T., Iwatsubo, E.Y.,
Chadwick, Jr., W.W., Casadevall, T.J., Ewert, J.W., and Heliker, C.C., 1987,
Growth of the lava dome at Mount St. Helens, Washington, (USA), 1981-1983:
IN: Fink, J.H. (ed.), 1987, Emplacement of Silicic Domes and Lava Flows:
The Geological Society of America, Special Paper 212
Abstract
Nine dominantly nonexplosive episodes of dome growth at Mount St. Helens
during 1981-83 added about 40 million cubic meters of dacite lava to the active
composite dome in the volcano's 1980 crater. Endogenous and exogenous growth,
the latter mostly in the form of stubby lava flows that accumulated on the
dome, combined to build an edifice 880 m long, 830 m wide, and 224 m high by
December 1983; the total volume (1980-1983) was about 44 million cubic meters.
Every 1-5 months during 1981-82, periods of increasing seismicity and ground
deformation lasting 1-3 weeks culminated in extrusions lasting a few days.
Endogenous growth became increasingly important during this interval, and in
February 1983, the style of activity changed from episodic to essentially
continuous endogenous and exogenous growth.
In March 1982 and February 1983, extrusions were preceded by lateral
explosions that triggered snow avalanches from the crater wall and mudflows
down the volcano's north flank. Collapse of part of the north face of the dome
during rapid endogenous growth in April 1982 produced a hot rock avalanche
and small mudflow. Ejections of gas and comminuted dome rock from the top of
the dome were frequent throughout 1981-1983, and averaged several per day in
1983.
As the dome continues to grow, its capacity to accommodate newly supplied
magma without rupturing, and hence the ratio of endogenous to exogenous growth,
will probably continue to increase. Endogenous growth will be especially
favored when magma supply is continuous and slow; extrusive activity will be
favored when supply rate becomes significantly higher than the current rate
of about 0.9 million cubic meters per month. Future explosive activity is
possible and perhaps even likely in view of Mount St. Helens' history and
the histories of similar contemporary domes at other volcanoes, but at this
time we can foresee no change from the pattern of mostly nonexplosive dome
growth that characterized activity during 1981-1983.
Return to:
[Report Menu] ...
URL for CVO HomePage is:
<http://vulcan.wr.usgs.gov/home.html>
URL for this page is:
<http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/GSA212/abstract.html>
If you have questions or comments please contact:
<GS-CVO-WEB@usgs.gov>
04/16/01, Lyn Topinka