Glaciological and related observations from 1961 to 2005 at the summit of Mt Wrangell (62.00° N, 144.02°W; 4317m a.s.l.), a massive glacier-covered shield volcano in south-central Alaska, show marked changes that appear to have been initiated by the Great Alaska Earthquake (Mw = 9.2) of 27 March 1964. The 4×6 km diameter, ice-filled Summit Caldera with several post-caldera craters on its rim, comprises the summit region where annual snow accumulation is 1–2m of water equivalent and the mean annual temperature, measured 10 m below the snow surface, is –20°C. Precision surveying, aerial photogrammetry and measurements of temperature and snow accumulation were used to measure the loss of glacier ice equivalent to about 0.03 km3 of water from the North Crater in a decade. Glacier calorimetry was used to calculate the associated heat flux, which varied within the range 20–140Wm–2; total heat flow was in the range 20–100MW. Seismicity data from the crater’s rim show two distinct responses to large earthquakes at time scales from minutes to months. Chemistry of water and gas from fumaroles indicates a shallow magma heat source and seismicity data are consistent with this interpretation.