Structural and heat flow implications of infrared anomalies at Mt. Hood, Oregon, 1972–1977

Abstract

Surface thermal features occupied an area of approximately 9700 m 2 at Mt. Hood in April 1973 and 9200 m 2 in September 1977, as determined by aerial infrared line scan surveys. The distribution of thermal anomalies below the summit of Mt. Hood suggests structural control by a fracture system and a brecciated zone peripheral to a young hornblende‐dacite plug dome and by a concentric fracture system associated with the development of the present crater. We estimate a heat discharge of 5 to 10 MW from the extent and temperature of the thermal areas, including a heat loss of 2–4 MW via conduction, diffusion, evaporation, and radiation to the atmosphere, and a somewhat less certain loss of 3–6 MW via fumarolic mass transfer and surface advection. Additional heat is transferred to groundwater. The first part of the estimate is based on two‐point models for differential radiant exitance and differential geothermal flux from heat balance of the ground surface and on a shallow temperature probe traverse across the Devils Kitchen fumarole field. Alternate methods for estimating volcanogenic flux that assume a quasi steady state heat flow yield values in the 5‐ to 12‐MW range. The estimated heat loss due to cooling of the 220±150 year old dacite plug dome is insufficient to account for the heat flux at the fumarole field. The heat source is judged to be deep seated.