Estimates of heat release to the atmosphere related to effusive volcanic eruptions and intrusive activity during the 1975-84 rifting episode of Krafla, NE-Iceland

The heat transfer dynamics in volcanic geothermal areas determine the options for geothermal energy exploration. Intrusive and eruptive events provide additional heat input into the geothermal system, as cooling and solidification of the magma heats the surrounding host rock and water in the porous matrix. The evaporation of the water leads to convection and an advective rise of steam in the fissures. Steam rises further and diffuses into the atmosphere depending on wind conditions. The heat lost by steam released to the atmosphere is in many cases one of the significant parameters that determine the heat budget of a geothermal system. The Krafla fires describe a period of volcanic activity at the Krafla volcano in North-East Iceland from 1975 to 1984 with nine volcanic eruptions and several more intrusive events. This activity was part of a major rifting episode where several meters of widening occurred along the Krafla fissure swarm. The rifting and associated intrusive activity had a significant effect on the geothermal system. Aerial photographs taken during or a few months after each eruption are used to determine the position and size of the fumaroles and associated steam generation. The heat output of the steam clouds is empirically related to its area, expressed as a power-law function (Hochstein & Bromley, 2001). The escape of water vapor, and thus the prevalence of fumaroles associated with these events, is mainly evident on the eruptive fissures. Surface alteration is prevalent and a sign of current or recent steaming. The results for heat lost to the atmosphere can be compared with the heat released by the cooling of the magmatic intrusions formed in the upper crust, providing heat to the existing geothermal area.