Heat from dyke intrusions released by boiling of warm groundwater and steaming into the atmosphere during the 1975–1984 eruptive and intrusive activity at Krafla, Iceland
Patricia Fehrentz , Magnús T. Gudmundsson , Hannah I. Reynolds , Anette K. Mortensen , Sydney R. Gunnarson , Joaquin M.C. Belart , Michaela A. Chodora
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引用次数: 0
Abstract
The Krafla volcano-tectonic episode in NE-Iceland in 1975–1984 was associated with approximately 10 m widening of the plate boundary within the Krafla caldera, where a high-temperature geothermal system is located. A composite dyke was formed, with an estimated volume 0.15–0.31 km3 within the geothermal reservoir, releasing thermal energy of 0.5–1.0 × 1018 J. An empirical relation between the area of steam clouds in air photos and their heat output was used to assess heat loss to the atmosphere by steaming during the Krafla fires. The applicability of this method for Krafla was tested in 2024 at selected locations where steam flow could be measured directly. Analyses of vertical air photos obtained several times in 1976–1985, notably during and after the eruptive events, show that steaming was mainly prevalent in the vicinity of the eruptive fissures. The heat loss to the atmosphere within the geothermal area was ∼0.9 MW/m during eruptions, declining to a more long-term value (∼0.05 MW/m) in 50–100 days. This enhanced steaming after the dyke injection/ eruption is considered to be caused by the interaction of the groundwater/shallow geothermal fluid with the uppermost 110–400 m of the dyke and appears to account for about one-third of the total heat lost in this way to the atmosphere. The remaining two-thirds were lost gradually throughout the rifting episode. The heat lost to the atmosphere (∼5–10 % of the total energy) was an order of magnitude smaller than the 90–95 % of the thermal energy added to the geothermal reservoir by the dyke.
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