REMOTE 3-D SURFACE MAPPING OF HYDROTHERMALLY WEAKENED ROCK AT MOUNT HOOD, OREGON: IMPLICATIONS FOR VOLCANIC HAZARDS

Mount Hood, the fourth highest Quaternary stratovolcano in the Cascade Range, is located 75 km east of Portland, Oregon. Although the volcano last erupted just prior to the arrival of Lewis and Clark in 1805, the potential for lahars and debris avalanches continues to presents a hazard. Debris avalanches threaten proximal areas at Mount Hood, while lahars are capable of traveling much further along drainages and river valleys (Scott et al., 1997). Typically, these flows originate near the summits of stratovolcanoes where hydrothermal alteration has weakened rocks.

We used 1996 Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data to identify and map the distribution hydrothermal alteration minerals near Mount Hood’s summit. Because the AVIRIS sensors were flown on an ER-2 aircraft at an altitude of 20 km, we applied an atmospheric radiation transfer models to the data to correct for water vapor and carbon dioxide molecular scattering. Prior to image processing, we converted the data in the image cube to reflectance using the field spectra from a relatively homogneous target at Mount Hood.

Results indicate the presence of iron oxides, alunite, and hydrothermal clays. Where possible, we analyzed samples returned from the field to check for accuracy. Finally, we “draped” a hydrothermal mineral map over a co-registered 30 m U.S. Geological Survey DEM (digital elevation model) to produce a 3-D map. Rotation of the 3-D map provides opportunities to view potential edifice failures from a variety of perspectives.