The central volcano is completely subglacial and located under the northwestern side of the Vatnajökull ice cap.

The massive climate-impacting Laki fissure eruption of 1783–1784 took place in a part of the same Grímsvötn-Laki volcanic system.

Because most of the volcanic system lies underneath Vatnajökull, most of its eruptions have been subglacial and the interaction of magma and meltwater from the ice causes phreatomagmatic explosive activity.

[12] At the same time, sudden inflation was measured by GPS in the volcano, indicating magma movement under the caldera.

On 1 November 2010 meltwater from the Vatnajökull glacier was flowing into a lake, suggesting that an eruption of the underlying volcano could be imminent.

[17] Disruption to air travel in Iceland[18] commenced on 22 May, followed by Greenland, Scotland,[19] Norway, Svalbard[20] and a small part of Denmark on subsequent days.

[22][23][24] In June 2020, the Icelandic Meteorological Office (IMO) issued a warning that an eruption might take place in the coming weeks or months, following scientists reporting high levels of sulfur dioxide, which is indicative of the presence of shallow magma.

The water contains elevated levels of dissolved hydrogen sulfide, suggesting increased volcanic activity under the ice.

Two days later, the Icelandic Meteorological Office increased the alert level for Grímsvötn from yellow to orange, after a series of earthquakes was detected.

[1] The Laki eruptions which were both effusive and explosive between June 1783 and February 1784,[31] produced the Skaftáreldahraun lava flows, which cover a large part of south-east Iceland.

[3] There are two recent pre-historic but undated Bergvatnsárhraun lava flows just on the south-eastern edge of the Vatnajökull glacier, related to the line of the Rauðhólar-Eldgígur fissures.

[38] The volcano erupts predominantly tholeiitic basalt,[3] and a close chemical affinity exists with the other lavas of the Grímsvötn-Laki volcanic system.

[42] Studies indicate that volcanic activity in Iceland rises and falls so that the frequency and size of eruptions in and around the Vatnajökull ice cap varies with time.

Seismic activity has been increasing in the area in recent years, indicating the entry of magma.