Report on Askja (Iceland) — 1 September-7 September 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
1 September-7 September 2021
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2021. Report on Askja (Iceland). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 1 September-7 September 2021. Smithsonian Institution and US Geological Survey.
65.033°N, 16.783°W; summit elev. 1080 m
All times are local (unless otherwise noted)
On 3 September IMO reported that inflation at Askja had begun in early August based on ground deformation data derived from satellite images and continuous GPS data. The uplift was centered at the W edge of Oskjuvatn caldera and vertically deformed at a rate of about 5 cm per month. Data indicated that the source of the inflation was at a depth of about 3 km and caused a volume change of about 0.01 cubic kilometers per month; the source was unknown, though most likely was caused by an influx of magma. The Aviation Color Code remained at Green.
Geological Summary. Askja is a large basaltic central volcano that forms the Dyngjufjöll massif. It is truncated by three overlapping calderas, the largest of which is 8 km wide and may have been produced primarily from subglacial ring-fracture eruptions rather than by subsidence. A major rhyolitic explosive eruption from Dyngjufjöll about 10,000 years ago was in part associated with the formation of Askja caldera. Many postglacial eruptions also occurred along the ring-fracture. A major explosive eruption on the SE caldera margin in 1875 was one of Iceland's largest during historical time. It resulted in the formation of a smaller 4.5-km-wide caldera, now filled by Öskjuvatn lake, that truncates the rim of the larger central caldera. The 100-km-long Askja fissure swarm, which includes the Sveinagja graben, is also related to the Askja volcanic system, as are several small shield volcanoes such as Kollatadyngja. Twentieth-century eruptions have produced lava flows from vents located mostly near Öskjuvatn lake.