Strongest earthquake since 1991 and glacial outburst flood at Grímsvötn volcano, Iceland

A glacial outburst flood has begun at Grímsvötn volcano, located beneath the Vatnajökull glacier in Iceland. In addition, the volcano was hit by a M4.3 earthquake on January 11 — the strongest since measurements began in 1991. Glacial outburst floods are known to increase the likelihood of volcanic eruptions. As a result, the Aviation Color Code for the volcano has been raised to Yellow.

A brief seismic swarm at Grímsvötn was recorded by the seismic network beginning at 16:00 UTC on January 4, 2024, prompting the Icelandic Meteorological Office (IMO) to raise the Aviation Color Code to Yellow (the second level on a four-color scale). Since activity did not escalate on January 5 and only one M0.6 earthquake was detected, the Aviation Color Code was lowered to Green.

Glacial outburst flood was confirmed by IMO on January 11, following M4.3 earthquake at 06:54 UTC. This is the largest earthquake at the volcano since measurements began in 1991.

The earthquake is believed to be a result of pressure relief following the start of the glacier flood.

The volcano has experienced similar floods in October 2022 and late 2021. The current amount of water in Grímsvötn, estimated at 0.29 km³, is half more than the 2022 run but less than the volume in late 2021. Professor Magnús Tumi Guðmundsson noted that while water levels have risen in Gígjukvísl river, the event is comparable to a small or medium-sized glacial outburst flood.

Due to difficulties in contacting the Earth Science Institute’s GPS device on the ice sheet, estimating the flow speed from the lakes is challenging. However, it’s anticipated that the maximum flow from Grímsvötn will occur around or shortly after the upcoming weekend, with the peak flow in Gígjukvísl at Þjóðveg 1 highway reaching about 1 – 2 days later. The maximum flow is not expected to exceed 1 000 m³/s and should not impact structures like roads and bridges.

Historically, volcanic eruptions in Grímsvötn have followed glacial floods, with the last such event occurring in 2004. However, eruptions without preceding floods are more common, with 12 eruptions since 2004 not linked to floods. The last volcanic eruption in Grímsvötn was in 2011, unrelated to a glacial run.

Due to glacial flood and increased seismic activity, the Aviation Color Code was again raised to Yellow.

References:

¹ Hlaup hafið úr Grímsvötnum – Jarðskjálfti af stærð 4,3 varð í morgun – IMO – January 11, 2024

² Glacial Outburst Flood Has Begun in Grímsvötn – Iceland Review – January 11, 2024

³ Global Volcanism Program, 2024. Report on Grimsvotn (Iceland) (Sennert, S, ed.). Weekly Volcanic Activity Report, 3 January-9 January 2024. Smithsonian Institution and US Geological Survey

Featured image credit: IMO