I travelled to the Askja volcano to perform crustal deformation measurements with GPS and levelling. We were four persons who went to Askja: Steini, Sveinbjörn, Siqi and I. Summer 2019 has been fantastic in Reykjavík. It seems that if one part of the country is enjoying good weather, another part must suffer. This year the summer in the northeast came short in terms of good. The Askja caldera had more or less continued snow cover until first week of July. The first snow of autumn had fallen (Fig. 1).
Measurements with GPS can in theory be made in all types of weather, while leveling is much more weather dependent. It was decided to combine GPS measurements in Vonaskarð with the work in Askja. Sveinbjörn and Siqi left on the 20th of August (Tuesday) to deploy instruments in Vonaskarð. They continued Thursday to Askja, moving 12 instruments and leaving 13 in Vonaskarð to be picked up on the way back. Steini and I left Reykjavik on the 22nd of August for Mývatn (Reykjahlið) and we deployed a GPS instrument at Ishólsvatn (ISHO). The next day we continued to Askja and me up with Sveinbjörn and Siqi. At 2 o’clock we started the leveling, as the weather had become sufficient good. We almost succeeded in doing half of the 1.2 km long profile (measuring forward and back). The next day (Saturday) we completed the long levelling line and proceeded to a location at the lake, called Bátshraun. At this site we did a short levelling profile and erected a GPS instrument. In the late afternoon, Steini and I took two GPS units to the southern slopes of the Askja volcano, while Sveinbjörn and Siqi placed a GPS instrument 600 m in Holuhraun. We returned to Dreki before 8 o’clock. We had invited the rangers for dinner this evening, but as we would be ten persons we decided to use the rangers’ hut. They had prepared the meat and lit the coal, so we could start barbecuing directly upon our arrival. The dinner was extremely successful. The next day at lunchtime two GPS instruments were retrieved from the caldera and in the late afternoon two additional instruments were picked up. With all tings loaded Steini and I went to Mývatn (Reykjahlið). We decided to bring in the Ishólsvatn instrument the same evening, so we had a late dinner. On Monday we returned to Reykjavík, while Sveinbjörn and Siqi went to Vonaskarð bringing in all six instruments.
The leveling line measured is 1.2 km long and was installed in the lava field 1961. This eruption lasted between 26 October to the first days of December and produced 0.09 km3 lava from the craters Vikraborgir located at the end of the road. The first part of profile was installed 1966, comprising 12 benchmarks and extended to 30 in 1968. It is more or less orientated radially out from the center of the caldera, under which the shallow magma chamber is located at 3 km depth. This makes it sensitive to changes in the shallow magma chamber. This line is far to short to detect displacements caused by the deeper magma reservoir located at about 16 km depth. The annual measurements were discontinued between 1973 and 1982 but resumed in 1983. From 1983 until this year, the center of the caldera has subsided. This subsidence has decreased from a subsidence rate of 8.5 cm/yr in 1983 to this year 2019 where a rate was 2 cm/yr was measured. This is the lowest subsidence rate observed so far meaning no new magma has accumulated up to present.