Grímsvötn, Iceland

Grímsvötn, Aviation Code Raised to Orange 6th December 2021 (Since Lowered to Yellow)

Good morning!

Update 8 December 2021

The alert level has been lowered to Yellow. To date no eruption has followed the jökulhlaup or increased seismicity. As Grímsvötn may erupt with little warning, the situation remains closely monitored.

Original Post 6 December 2021

Fig 1: Líndal. A. (1 June 2011). Grímsvötn: photo 3 of 14. Retrieved from http://icelandicvolcanoes.is/?volcano=GRV

The alert level for Grímsvötn  has been raised to orange following the draining of the caldera lake over the past few days, the resulting jökulhlaup, and increased seismicity today.

Fig 2: Aviation codes for Icelandic Volcanoes.  Grímsvötn is orange.  Source: IMO

The ice-cap has subsided by c. 77 metres.  The water drained via the Gígjukvísl river; the discharge in Gígjukvísl river yesterday around noon was 2800 m3/s, reducing later in the day.

Fig 3:  Measurements of the jökulhlaup as it impacted the Gígjukvísl river.  Source: Línurit (vedur.is)

At the time of writing, there have been 25 earthquakes in the last 48 hours in the vicinity of Grímsfjall.  A magnitude 2.3 occurred at 06:15, followed shortly afterwards at 06:16 by a magnitude 3.6.  There have been a few aftershocks.  No volcanic tremor has been detected.

Fig 4: Map of earthquakes at Vatnajökull.  Grímsfjall is roughly where the green star is; the green star is the location of the 3.6M earthquake.  Source: Vatnajökull (vedur.is)

Volcanic eruptions have occurred after draining of the caldera lake in the past, attributed to the sudden decrease in pressure destabilising the system; IMO cite the 2004, 1934 and 1922 eruptions.

Armchair Volcanologist

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Sources

Icelandic Met Office: IMO

Icelandic Volcanoes: Icelandic Volcanoes (icelandicvolcanos.is)