Mt Veniaminof is a large active stratovolcano located on the Alaska Peninsula (56.2° N, 159° W). We present results of the first geophysical survey of the icefield that fills much of the 10 km×8 km caldera that was most recently modified during the last major eruption roughly 3700 BP. The subglacial topography and ice volume are derived from an 8MHz radio-echo sounding survey conducted in July 2005. Prominent internal reflectors are assumed to be isochronal ash/acid deposits related to local eruptions. Accumulation rates and basal melt rates are calculated using a Nye one-dimensional steady-state accumulation model applied at a location that approximates an ice divide and calibrated by matching internal reflectors with published records of recent local volcanic eruptions. The model yields order of magnitude estimates of the accumulation rate of 4ma–1 water equivalent and 2 ma–1 of basal melt. The subsequent geothermal flux of ∽19Wm–2 is similar to active hydrothermal vents in volcanic lakes. We suggest that these values represent an upper limit for the geothermal flux within the ice-covered regions of the main caldera. We also analyze likely subglacial meltwater flow paths to examine the implications of recent eruption activity at an active intra-caldera cinder cone. Two lava-producing eruptions from the cinder cone in 1983–84 and 1993–94 melted roughly 0.17km3 of ice. The lack of significant deformation of the internal stratigraphy to the south and east of the melt hole suggests that any subglacial drainage in those directions was entirely within subglacial deposits. We suggest that the more likely drainage route was northwest into a large outlet glacier.