VOLCANO HAZARD ASSESSMENTS OF OREGON VOLCANOES

The USGS Volcano Hazards Program has prepared volcano hazard assessments for the five major Quaternary volcanic centers of the Oregon Cascades from Mount Hood to Crater Lake. All assessments were written for lay audiences and discuss volcano processes and associated hazards, a brief eruptive history of the volcano, and an evaluation of the most likely future activity. Each assessment contains a volcano hazards zonation map that shows areas that may be affected by future lava flows, pyroclastic flows, debris avalanches, and lahars. Because of the far-reaching effects of lahars, several hazards zones, each corresponding to a different lahar volume, are shown. Most reports also contain probabilistic regional tephra hazard maps.

Although there is much similarity in the reports, collectively they point out unique aspects of individual volcanic centers. For example, of the five centers studied (Mount Hood, Mount Jefferson, Three Sisters, Newberry Volcano, and Crater Lake), only Mount Jefferson has not erupted in Holocene time. However, renewed explosive activity, similar to what has occurred in the past at Mount Jefferson, could potentially affect a large area. Although largely unpopulated, the area at risk contains important infrastructure such as large reservoirs. Mount Hood is the least explosive of the five volcano centers, but has had the most significant flank failures. Three Sisters, Mount Jefferson, and Mount Hood all have glaciers and perennial snowfields, and thus the potential for hot rock to melt snow and ice and to thereby form lahars is a concern for these three volcanoes year round. Newberry Volcano and Crater Lake are snow and ice free in the summer. But unlike the other three centers they have crater lakes that could contribute large volumes of water to form lahars during an eruption. In addition to the major volcanic centers, the reports discuss hazards associated with regional mafic volcanism, which is especially prevalent in central Oregon.

The assessments are 'living documents' that can be reissued quickly if new information significantly enhances or alters the interpretation of one of the centers. All maps are in GIS format and all reports and maps can be found on the USGS Cascades Volcano Observatory web site at http://vulcan.wr.usgs.gov.