Geothermal mapping and remote sensing of surface thermal anomalies at Grændalur area, Hveragerði, SW Iceland

Abstract

The Grændalur Valley is located in southwest Iceland, immediately north of the town of Hveragerði. It is located at the contact of the eastern margin of the Western Volcanic Zone (WVZ) and the South Icelandic Seismic Zone (SISZ). The area is seismically active, the most recent significant earthquake swarm occurred on May 29, 2008 with magnitudes of 6.3 and 5.5 between the towns of Selfoss and Hveragerði. The Grændalur valley is one of the areas in the Hveragerði region with intense geothermal activity. Geothermal mapping has been carried out in this area to map surface geothermal manifestations such as hot and warm springs, mud pools, fumarole, steam vents, steaming ground and structures. Remote optical sensors (Landsat and ASTER satellite images) were used to identify thermal anomalies in this area. The analysis of thermal anomalies made on daytime and nighttime satellite images from 2005 to 2020 has detected a new geothermal activity in the north near the center that would have certainly been created after the earthquakes of May 29, 2008. The thermal infrared (TIR) image taken with a TIR camera carried by a DJI Matrice 200 drone with a Zenmus XT thermal camera at 120 m height, was compared with temperature measurements taken directly on the ground after the flight to calibrate the TIR image for accuracy. The TIR image was used to identify and estimate the surface temperature of a geothermal manifestation whose accessibility was difficult. The surface temperature of this geothermal manifestation is about 43°C.

Í Grændal við Hveragerði er virkt hverasvæði og nokkur jarðskjálftavirkni, enda liggur dalurinn á mörkum vesturgosbeltisins og Suðurlandsbrotabeltisins. Öflug skjálftahrina gekk yfir svæðið vorið 2008, er skjálftar að stærð 6,3 og 5,5 M riðu yfir, en upptök þeirra voru á milli Selfoss og Hveragerðis. Markmið verkefnisins var að kortleggja ummerki jarðhita í Grændal, svo sem leir- og gufuhveri, yfirborðsvatn og jarðfræðilega formgerð, og kanna jafnframt hvort vísbendingar væri að finna um breytingar á virkni svæðisins vegna skjálftahrinunnar 2008. Ýmsum fjarkönnunargögnum var beitt við rannsóknina: Úr gervitunglum (LANDSAT, ASTER), loftmyndum (Loftmyndir ehf., Samsýn ehf.) og dróna (Matrice), en jafnframt var farið í vettvangsferð um svæðið. Greining hitamynda úr gervitunglum, frá tímabilinu 2005-2020, sýndi myndun nýrra hverasvæða í kjölfar skjálftanna 2008. Hitakortlagning var unnin með gögnum úr dróna DJI M200 dróna með Zenmuse XT hitamyndavél úr 120 m hæð, og kvörðuð með mælingum af jörðu niðri. Yfirborðshiti reyndist vera um 43°C.