Modeling of volcano edifice and flank stability, and hazard zonation at Mount Adams, Washington

Collapse of the edifice [summit] and flanks of volcanoes is common worldwide, including the Cascade Range. Many of these failures have transformed into devastating debris flows that may travel hundreds of miles from their source area and have killed or injured hundreds of thousands of people. Despite the danger posed by these failures and the incipient debris flows, limited geotechnical data exists to quantify hazards from edifice and flank failure.; Recent field work and investigation at Mount Adams, Washington focused on developing and refining a methodology for characterizing volcanic stability for geologic hazard analysis. This methodology may be applied at other volcanoes worldwide. Geotechnical data, including discontinuity and strength characteristics, Rock Mass Rating, point load index, direct shear, unconfined compression, and triaxial data were used to identify sectors based upon common geotechnical and geologic characteristics. The geotechnical information collected at Mount Adams adds to the limited data available worldwide and provides general strength ranges for use in initial stability studies at other volcanoes. In addition, a new point load index device was developed for use at high elevation and remote locations.; Stability of each identified sector was analyzed using limit equilibrium methods, based upon collected geotechnical and geologic data. Three previous failures were backanalysed to determine strength characteristics at the time of failure. Areas of immediate instability include The Castle and the Avalanche Glacier Headwall. Backanalysis of the Trout Lake Mudflow, which formed the Avalanche Glacier Headwall, suggests a seismic or eruption triggering mechanism. Stability analysis resulted in a failure hazard map quantifying the hazard in each sector from slope failure. This hazard map in combination with other data may be used by agencies and organizations involved in land-use planning in the Mount Adams area to protect lives and property.