Grimsvotn, a subglacial volcano in Iceland, has a partially exposed geothermal system, that has, until recently, been used to make estimates of heat flux using calorimetry. Increased melting in Grimsvotn in the aftermath of the 1998 eruption has changed the ice conditions considerably, resulting in major leakage of the ice dam that used to seal Grimsvotn caldera lake. This makes calorimetric estimates of melting more difficult. An aerial survey of Grimsvotn was carried out in June 2001. Thermal images of the Grimsvotn subglacial caldera show distinct areas of geothermal activity. Ground survey studies of the same area carried out by the Science Institute, University of Iceland, show that protruding ground above the ice, along with areas of open water, have high geothermal heat flux all year round. In these areas, heat is lost by radiation and geothermal steam emission. This component of heat flux cannot be detected by calorimetric estimates based on ice melting. Therefore an alternative method of calculating heat flux is adopted in this research based on a combination of remote sensing and meteorological information. Aerial photographs collected for Grimsvotn have been used to map the main features along the caldera walls, such as crevasses and slumps that cannot be accurately mapped from the ground because of inaccessibility. A high resolution DEM of the case study sites has been generated from the aerial photographic coverage using a stereoscope and parallax bar. The combined data sets have been analysed both visually and quantitatively using a combination of ERDAS Imagine and ARCGIS environments. Together, these data establish that remote sensing can be used to map and monitor an inaccessible volcano such as Grimsvotn, as well as aid in the understanding of the processes at work within one of the most powerful geothermal systems in the world.