Summary
Mount Jefferson is a prominent feature of the
landscape seen from highways east and west of
the Cascades. Mount Jefferson (one of thirteen
major volcanic centers in the Cascade Range) has
erupted repeatedly for hundreds of thousands of
years, with its last eruptive episode during the
last major glaciation which culminated about
15,000 years ago. Geologic evidence shows that
Mount Jefferson is capable of large explosive
eruptions. The largest such eruption occurred
between 35,000 and 100,000 years ago, and
caused ash to fall as far away as the present-day
town of Arco in southeast Idaho. Although there
has not been an eruption at Mount Jefferson for
some time, experience at explosive volcanoes
elsewhere suggests that Mount Jefferson cannot
be regarded as extinct. If Mount Jefferson erupts
again, areas close to the eruptive vent will be
severely affected, and even areas tens of
kilometers (tens of miles) downstream along
river valleys or hundreds of kilometers (hundreds
of miles) downwind may be at risk.
Numerous small volcanoes occupy the area
between Mount Jefferson and Mount Hood to the
north, and between Mount Jefferson and the
Three Sisters region to the south. These small
volcanoes tend not to pose the far-reaching
hazards associated with Mount Jefferson, but are
nonetheless locally important.
A concern at Mount Jefferson, but not at the
smaller volcanoes, is the possibility that small to-
moderate sized landslides could occur even
during periods of no volcanic activity. Such
landslides may transform as they move into
lahars (watery flows of rock, mud, and debris)
that can inundate areas far downstream. The
population at immediate risk in the Mount
Jefferson region is small, but these residents as
well as other people who visit the area for
recreation and work purposes should be aware of
the potential hazards. Probably the greatest
concern in the Mount Jefferson region is the
possibility that large lahars might enter reservoirs
on either side of the volcano, namely, Detroit Lake
to the west and Lake Billy Chinook to the east.
Lahars entering these lakes could set up large
waves that could overtop dams and possibly cause
dam failure, with catastrophic effects downstream.
Such events have very low probabilities but great
potential consequences.
This report describes the kinds of hazardous
geologic events that have occurred in the Mount
Jefferson area in the past and shows, in the
accompanying volcano-hazards-zonation maps,
which areas will likely be at risk when hazardous
events occur again in the future.
Link to the Data
- Schilling, S.P., Doelger, S., Walder, J.S., Gardner, C.A.,Conrey, R.M., and Fisher, B.J., 2008, Digital data for volcano hazards in the Mount Jefferson region, Oregon: U.S. Geological Survey Open-File Report 2007-1224, https://pubs.usgs.gov/of/2007/1224/
|
First posted February 22, 2000
Part or all of this report is presented in Portable Document Format (PDF). For best results viewing and printing PDF documents, it is recommended that you download the documents to your computer and open them with Adobe Reader. PDF documents opened from your browser may not display or print as intended. Download the latest version of Adobe Reader, free of charge.
|