Report on Grimsvotn (Iceland) — 24 November-30 November 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
24 November-30 November 2021
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2021. Report on Grimsvotn (Iceland). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 24 November-30 November 2021. Smithsonian Institution and US Geological Survey.
64.416°N, 17.316°W; summit elev. 1719 m
All times are local (unless otherwise noted)
On 24 November Icelandic Meteorological Office (IMO) reported that the ice sheet in Grímsvötn's caldera had subsided 60 cm in the previous few days and the rate of subsidence had accelerated in the last day. By 29 November the ice had sunk a total of 5 m and by 1 December the subsidence totaled 10 m. Data indicated that water had likely begun exiting the caldera and will result in a jökulhlaup (glacial outburst flood) that will cause flooding conditions in drainages. Water levels in the Gígjukvísl drainage rose overnight during 30 November-1 December.
Geological Summary. Grímsvötn, Iceland's most frequently active volcano in recent history, lies largely beneath the vast Vatnajökull icecap. The caldera lake is covered by a 200-m-thick ice shelf, and only the southern rim of the 6 x 8 km caldera is exposed. The geothermal area in the caldera causes frequent jökulhlaups (glacier outburst floods) when melting raises the water level high enough to lift its ice dam. Long NE-SW-trending fissure systems extend from the central volcano. The most prominent of these is the noted Laki (Skaftar) fissure, which extends to the SW and produced the world's largest known historical lava flow in 1783. The 15 km3 basaltic Laki lavas were erupted over a 7-month period from a 27-km-long fissure system. Extensive crop damage and livestock losses caused a severe famine that resulted in the loss of one-fifth of the population of Iceland.