The net geothermal flux through palagonitized basaltic tephra rims of the Surtur I and Surtur II craters at Surtsey, Iceland, in 1972, is estimated at 780 ±325 μcal cm-2s-1, indicating a decline since 1969 when a flux of 1,500 μcal cm-2s-1 was estimated. Heat flux in this range characterizes the postvolcanic environment on Surtsey in which the subaerial palagonitization of basaltic tephra is associated with mass transfer of hydrothermal vapor, either of meteoric or sea-water origin, only a few years after cessation of eruptive activity. The flux estimation is the result of the Surtsey data-relay experiment via Landsat-1 which was carried. out in several phases. Successful field installation and test transmissions demonstrated the feasibility of repetitive long-distance (that is, 4,800-km) data transmission and reception from a volcanic environment in Iceland via the Landsat Data Collection System. Temperature data were transmitted for a 38-day period in November and December 1972. A near-surface vertical gradient of 69.4 °C/m was obtained, suggesting a mixed mechanism of heat transfer, partitioned between conduction and convection. Comparison of four methods for estimating fluxes between 500 and 1,500 μcal cm-2s-1, using temperature data derived from the Data Collection Platform, suggests that, where the only temperature available are from the surface and a depth of 1 m, methods of estimating the net geothermal flux from examination of spectral radiance are superior to methods that assume dominant convection or conduction. A computerized thermal-modeling technique to construct parametric diurnal surface-temperature curves is particularly applicable. Flux-estimation methods that assume dominant convection or conduction are limited by the lack of temperature data at greater depths and lack of knowledge of the exact energy partition.
