NUMERICAL SIMULATION OF TSUNAMI GENERATION BY COLD VOLCANIC MASS FLOWS AT AUGUSTINE VOLCANO, ALASKA

Many of the world's active volcanoes are located on or near coastlines and are surrounded by oceans or other large bodies of water. Volcanic mass flows, such as pyroclastic flows, debris avalanches, and lahars, produced during eruptions are capable of delivering large volumes of fast-moving material to the sea and are thus a potential source mechanism for tsunamis. In the Aleutian arc of Alaska, the deposits of both hot and cold volcanic mass flows are exposed at many locations along the coastlines of the North Pacific Ocean and Bering Sea indicating that the flows reached the sea and in some cases may have initiated tsunamis. Here, we describe numerically the process of tsunami generation by cold, granular, gravity driven, subaerial volcanic mass flows (debris avalanches) and evaluate how cold volcanic mass flows interact with water as they move from the volcano flank into the sea. We present a center of mass description of debris avalanche motion, describe tsunami generation in the near field, and give results for tsunami propagation and inundation of far-field coastlines. The numerical simulation scheme GEOWAVE is used to evaluate tsunami generation at Augustine Volcano and to evaluate potential tsunami hazards along the southern Cook Inlet coastline. Augustine is the most historically active volcano in the Cook Inlet region of Alaska and debris avalanches that flowed into the sea have occurred at least 12 times since about 3500 cal. yr. B.P. Our numerical simulation results indicate that tsunami generation is limited by the shallow water (<25 m) surrounding Augustine Island and far-field waves reaching the Kenai Peninsula have only modest amplitudes (<1 m) for tsunamis initiated by north and northwest directed mass flows. For tsunamis generated by east-directed mass flows, far-field waves reaching the Kenai Peninsula have larger amplitudes (up to 5 m) and would pose a greater coastal hazard.