Changes in Geothermal Activity at Bárdarbunga, Iceland, Following the 2014-2015 Caldera Collapse, Investigated Using Geothermal System Modeling

摘要

The gradual collapse of the subglacial Bárdarbunga caldera in 2014-2015 provided an opportunity to explore the geothermal signals produced by large‐scale volcanic events. In August 2014, four ice cauldrons (shallow depressions on the ice surface) formed on the caldera flank. These cauldrons reached their maximum volume rapidly and then shrank, indicating that they were created during minor subglacial eruptions. Several weeks after the start of the collapse, three cauldrons on the caldera rim grew in volume, with four smaller cauldrons forming in 2015-2017. The cauldrons reached volumes in the range of 1.0 ± 0.2 to 27 ± 3 million m3. HYDROTHERM numerical simulations of fluid flow and heat transport in the uppermost 1 km of the crust were performed to explore possible causes for these thermal signals and in particular assess the role of shallow magmatic intrusions. The heat transfer required to create the more rapidly formed caldera‐rim cauldrons can be reproduced with shallow intrusions into high‐permeability pathways, which greatly enhance the surface thermal signal. The preintrusion temperature of the surrounding bedrock has a major effect on heat transfer to the surface, with cold bedrock causing a buffering effect, whereas temperature conditions close to the boiling point of water produce far more efficient heat transfer due to the formation of steam plumes. Not all observed behavior is reproduced by our models, suggesting that geothermal reservoirs below 1‐km depth may play a significant role in the observed thermal anomalies.