USGS/Cascades Volcano Observatory, Vancouver, Washington
REPORT:
Recent Eruptive History of Mount Hood, Oregon,
and Potential Hazards From Future Eruptions
-- Dwight R. Crandell, 1980,
Recent Eruptive History of Mount Hood, Oregon,
and Potential Hazards from Future Eruptions:
U.S. Geological Survey Bulletin 1492
Abstract
Each of three major eruptive periods at Mount Hood (12,000-15,000(?),
1,500-1,800, and 200-300 years ago) produced dacite domes, pyroclastic flows,
and mudflows, but virtually no pumice. Most of the fine lithic ash that mantles
the slopes of the volcano and the adjacent mountains fell from ash clouds that
accompanied the pyroclastic flows. Widely scattered pumice lapilli that are
present at the ground surface on the south, east, and north sides of Mount Hood
may have been erupted during the mid-1800's, when the last known activity of the
volcano occurred.
The geologically recent history of Mount Hood suggests that the most likely
eruptive event in the future will be the formation of another dome, probably
within the present south-facing crater. The principal hazards that could
accompany dome formation include pyroclastic flows and mudflows moving from the
upper slopes of the volcano down the floors of valleys. Ash clouds which
accompany pyroclastic flows may deposit as much as a meter of fine ash close to
their source, and as much as 20 centimeters at a distance of 11 kilometers
downwind from the pyroclastic flows. Other hazards that could result from such
eruptions include laterally directed explosive blasts that could propel rock
fragments outward from the sides of a dome at high speed, and toxic volcanic
gases. The scarcity of pumiceous ash erupted during the last 15,000 years
suggests that explosive pumice eruptions are not a major hazard at Mount Hood;
thus, there seems to be little danger that such an eruption will significantly
affect the Portland (Oregon) metropolitan area in the near future.
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07/28/00, Lyn Topinka