Rerouting of Volcanic Heat Fluxes in the Mt.~Wrangell Caldera Glaciation after the 1964 Alaska Earthquake

The ice-filled caldera at the 4000 m summit of Mt. Wrangell, Alaska underwent significant changes in the years after the magnitude 9.2 Good Friday earth quake in 1964. Measured surface velocities in the Caldera center changed both in magnitude and direction between 1965 and 1976, but remained stable since. Since the ice is very cold (-20° C 20 m below the surface) these changes can only be due to altered boundary condition at the glacier base. There, ice is melted at a high rate (about 0.6 m/a) which was inferred from observed accumulation rates and velocity fields. Between 1965 and 1976 the surface flow field changed from horizontal convergence to divergence in the Caldera center. Between 1976 and 2004 the submergence velocities decreased by 20 - 50 %, while the ice thickness increased by 8m. Both observations lead to the conclusion that the melt rate at the Caldera base has significantly decreased. Also within 12 years after the earthquake 40· 106 m3 of ice melted in the North Crater. Simultaneously, the ice volume increased in the West Crater which had been the most active of the three craters along the Caldera rim. We speculate that the changes of ice volumes in the craters and of the flow velocity field in the Caldera resulted from changes in the hydrothermal system of the volcano.