The 1991--1993 eruption of Mount Etna, Sicily built a 7.2 km2 aa lava flow field within the Valle del Bove. This letter provides estimates of the power losses associated with various cooling mechanisms operating during the development of the flow field, derived from time-series analysis of nighttime satellite remote sensing data. Unlike sensors used in many previous remote sensing studies of active lava, the ERS-1 Along Track Scanning Radiometer (ATSR) provides unsaturated measurements of spectral radiance from even very hot surfaces. This allows for more accurate solution of the lava flow endmember thermal components. We find that radiative and conductive processes dominated, with our model suggesting energy losses of similar magnitude. Radiative losses peaked about one month into the eruption, when lava flowed in open channels. Conductive losses peaked after two months, with a marked decline caused by a significant decrease in the horizontal spreading rate of lava. By the end of the eruption the 235¿106 m3 of erupted lava is estimated to have lost only 28% of its initial thermal energy. A further 6.5¿1017 J must be lost before the lava reaches ambient temperature. ¿ 1997 American Geophysical Union