| Title | Ground Deformation at the Theistareykir Volcanic System, Iceland, Following Onset of Geothermal Utilization |
|---|---|
| Authors | Vincent DROUIN, Freysteinn SIGMUNDSSON, Siqi LI |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Crustal deformation, InSAR, GPS, volcano, Sentinel-1, Theistareykir, Iceland |
| Abstract | A 90 MW power-plant operated by Landsvirkjun, the National Power Company of Iceland, began production in November 2017 at the active geothermal area in the Theistareykir central volcano, in the Norther Volcanic Zone of Iceland. Eruptive activity of the central volcano is low: the last eruption took place about 2500 years ago and other lava flows are more than 10,000 years old. Rifting events without eruptions may have occurred in the area in 1618 and 1885 but it is uncertain if these originated from the Theistareykir central volcano or from a nearby off-shore volcano. However, geodetic measurements show two possible inflation episodes during the last 25 years: in 1995-1996 and in 2006-2008. In order to obtain a good overview of the deformation prior to the onset of production at the power-plant, the Theistareykir area has been well monitored since 2009-2011. Network of GPS geodetic stations was densified in 2010 and 2011 for annual summer campaign measurements. TerraSAR-X SAR images have also been acquired yearly since 2009. Starting in 2015, the Sentinel-1 SAR mission has provided very good observations of the local deformation, with images acquired every 6-12 days. We observe that the area has been deforming at fairly stable rate between 2009 and 2017. In addition to plate spreading, the main noticeable feature is a slow subsidence in the north-west part of the central volcano in a similar location as an inflation episode took place in 2006-2008. This deformation field is then compared to the summer 2017 - summer 2018 deformation field to detect changes possibly related to geothermal fluid extraction. Results indicate additional subsidence at the Theistareykir geothermal area: the subsiding area is elongated north-south along the fissure swarm but appears not to be centered next to the most productive wells. The area subsided at a rate less than 5 mm/yr, a low rate when compared to what has been observed at the onset of production at other geothermal power-plants operating in Iceland. Knowing the deformation induced by geothermal fluid extraction is important to estimate the effect of the current production rate on the geothermal reservoir and assess its sustainability and the potential of increasing the production in the future. Monitoring the activity of the volcano also gives us insight on how much potential heat is added in the system during intrusive episodes. |