Grimsvötn volcano (Iceland): accelerating rates of subsidence increase likelihood of glacial flood and perhaps an eruption

Mon, 29 Nov 2021, 17:45
17:45 PM | BY: T
Vertical deformation on the summit of Grimsvötn volcano's ice sheet (image: IMO)
Vertical deformation on the summit of Grimsvötn volcano's ice sheet (image: IMO)
The ice sheet on top of the volcano continues to subside and does so at accelerating rate: Compared to a week ago, the surface has sunk by 4 meters, but more than half of that occurred during the past 48 hours, and it is not clear how much is yet to come.
In any case, it suggests that more and more melt water normally trapped above the summit area is now flowing away to different locations further at the side of the ice shield. This makes a glacial flood very likely in the next days - once enough water has accumulated beneath the rims of the glacier, it can lift it and surge out, and/or melt and erode itself a channel through its bottom, to exit in a massive, violent glacial flood known as jökulhlaup (literally "glacial run").
According to geologist Björn Oddsson from Civil Defense in an article on, "melt water is accumulating under an ice cave that lies at the top. There's a GPS measuring device over the ice cave which indicates the situation with the water. When the water accumulates, the ice cave rises." He estimated that the total volume of water involved was about one cubic kilometer.
There are concerns that the pressure changes on the volcano involved by sudden changes in overlying weight also increase the likelihood of the volcano, by many thought to be "overdue".

Previous news

Thu, 25 Nov 2021, 16:36
Grimsvötn volcano in August 2021 (image: IMO)
The ice-sheet above the volcano has been subsiding in the past days, likely because a pool of glacial melt water has moved away and might soon break out as a glacial flood. ... Read all
Wed, 24 Nov 2021, 06:00
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. ... Read all
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