The rise of Askja continues
Text and photos by Erik Sturkell
The annual research trip to the volcano Askja in the Icelandic highlands took place from the 17th to the 28th of August this year. Fieldwork this late in the summer was dictated by the possibility to combine geodesy (levelling and GPS) with a microgravity survey. I flew into Iceland on the morning of the 16 August and got a fantastic view of the cloud over the volcanic eruption site at Meradalir (Fig. 1). Before lunch we had a planning meeting led by Freysteinn and with Halldor and the two students Cat and Yilin, who were to take part in the measurements at Askja. Since beginning of August 2021, magma has been accumulating under Askja. As a response to this activity, we made a measuring trip in late September 2021. During this trip and the current, Elske and her students from the Netherlands came with two gravimeters to determine the mass changes. The next day Wednesday on the 17th we drove north to Reykjahlid in Mývatn with two GPS units and the levelling equipment. In Askja we picked up instruments from two continues sites. The sites (Fig. 2) are operated by the Iceland Meteorological Office, but the instrument belongs to the University of Iceland. On Thursday after a supply expedition to Húsavík we went to Askja and set out the GPS instruments in terrible weather which did not improve. For several days we had snow and the instruments were deployed in a winter landscape (Fig. 3). In the evening we were joined by Michelle, Adrian and Ásta Rut. The next day they helped with the levelling and we managed almost half of the long levelling line of 35 benchmarks. On Saturday the weather was terrible, and we couldn’t do any levelling and Michelle, Adrian and Ásta Rut left us. But in the evening after a wet day, we were invited by the rangers to their annual X-mas party. The rangers who work only in the summer have realised they will not have a X-mas party in December, so they started this tradition more than twenty years ago. We met the Cambridge group in Dreki on the last day of their fieldwork. Sveinbjörn took part in their fieldwork and drew back to Reykjavik just to turn around to join us. He came with Elske’s microgravity group (Mathijs and Josefa) and with four GPS instruments. We moved the GPS at MASK (middle of Askja) to Olafsgigar, finished the levelling and joined them in Rekjahlid on Monday evening. I got a flat tire up in Askja but with help of my pump I could put air in the tier, it lost about a pound per hour. The next day Tuesday I got it attended in Rekjahlid and we left for Askja at 9:30AM. Sveinbjörn brought up four GPS instruments that was set out the same day in the southern part of Askja (Fig. 4). The next day (the 24th) Cat, Yilin, Sveinbjörn and I hiked to the GPS and levelling line on the Bátshraun lava. The GPS was taken down and Cat and Yilin went to take down the GPS at Olofgigar. The GPS was taken down just after the microgravity team arrived so perfect timing. Sveinbjörn and I levelled the short line at Bátshraun and we measured the relative lake level at the same location. In the evening Melissa from the meteorological office arrived to make gas measurement, with her followed Santiago, a student and Adrian returned. It was fantastic to get Adrian back in the field! On Thursday the 25th we made the outer ring around Askja. We had two instruments in the house and when we went to retrieve two receivers in the south and deployed four west and north of the volcan. This was done in terrible weather (Fig. 5). On Friday we did a levelling station to the east of the volcano. The distance is too long to get a signal of the current magma inflow – it is needed more uplift before it can be detected at this location. A GPS station at a one-way distance of 1½ hour out in the lava fields was picked up. In the afternoon the weather changed, and it became fantastic (Fig. 6). On Saturday in fantastic weather, we left Askja and drew the northern road, retrieved the four GPS instruments and did tilt measurements at three sites. It was a slow drive and we returned late in the afternoon, but in time to get to the shopping mall in Reykjahlid. The results from the levelling can be calculated directly. The displacement of the benchmarks in the line has never been this large. The difference between the benchmarks closest and furthest away from the uplift is measured to almost 4.5 cm/yr. The benchmarks closed the central part of the caldera has risen. This is in contrasts to the situation from 1983 to 2021 with the closest point subsiding. Over the years the subsidence between the points has decayed from 1983-84 with 1.2 cm/yr to 2020-21 with 0.2 cm/yr. This uplift agrees with GPS and InSAR measurements. The short levelling line on the Bátshraun lava showed uplift towards the northern part of lake Öskjuvötn.
Magma assembles under the caldera floor with an uplift rate of several decimeters per year.
Thanks to all who helped in this campaign – we did it despite the poor weather!
Figure 1. The cloud that forms above the eruption site as hot vapor rises from the volcano and condensates some distance in the air.
Figure 2. In the evening of the 18th, we took down the permanent station KASC to get a third receiver to rotate.
Figure 3. The GPS instrument at MASK (Middle of ASKja) Sunday the 21st of August in the new fallen snow.
Figure 4. The cairn to honor and remember the Germans that disappeared in 1907, set up 1951. In the background the lava field called Mývetningahraun which flow out 1922.
Figure 5. The GPS station at Lokatindur along the northern road. A GPS station can be set up even in truly terrible weather.
Figure 6. The weather is changing the clouds and rain moves away, the photograph is from out side the house.