| Title | Deciphering the Heat Sources Behind Time-Variant Subglacial Geothermal Areas in Iceland |
|---|---|
| Authors | Hannah I. REYNOLDS, Magnús T. GUDMUNDSSON, ThórdÃs HÖGNADÓTTIR, Gudni AXELSSON |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Volcano-ice interaction, Geothermal, Heat flux, Ice cauldrons, Iceland |
| Abstract | Thermal anomalies at the Earth’s surface are observed at volcanoes all over the world but are usually difficult to quantify. However, where thermal signals occur beneath glaciers, ice cauldrons (depressions on the ice surface) form due to melting at the glacier base; the ice acts as a calorimeter which allows for heat flux estimates to be made with considerable accuracy. This study explores the heat sources behind time-variant subglacial geothermal activity. The gradual collapse of the subglacial Bárdarbunga caldera in 2014–2015 lead to major changes in the geothermal activity around the caldera rim. Several weeks after the start of the collapse, significant growth occurred in three cauldrons on the caldera rims, with four smaller cauldrons forming in 2015–2017. Five years after the Bárdarbunga event, some cauldrons continue to grow whereas others do not. The cauldrons have reached volumes between 1.0±0.2 and 27±3 million m3. Similarities are found between the activity at Bárdarbunga and rapid changes in geothermal activity at GrÃmsvötn, also associated with volcanic eruptions. In contrast, much longer-term geothermal activity has also been observed at GrÃmsvötn, and at Skaftárkatlar, where two cauldrons have been active for more than 80 years. HYDROTHERM numerical modelling software was used to simulate heat and mass transport in geothermal systems to investigate possible scenarios to explain the variations in geothermal activity observed at different time-scales. Shallow intrusions connected to high-permeability pathways were found to greatly enhance surface thermal signals. Pre-intrusion temperature of the surrounding bedrock has a major effect on heat transfer to the surface, where temperature conditions close to the boiling point of water produce efficient heat transfer due to the formation of steam plumes. This work improves the understanding of both rapid and years-to-decades scale variations in geothermal power. |