Grímsvötn Volcano: Iceland’s hidden powerhouse sits on top of a mantle plume 

Grímsvötn, one of Iceland's most powerful and active volcanoes, lies hidden beneath the Vatnajökull glacier, Europe’s largest ice cap. The volcano sits right on top of the Iceland mantle plume.   Grímsvötn is part of the Grímsvötn-Laki volcanic system located in southeast Iceland. Although concealed by the glacier, its activity has far-reaching effects on Iceland’s environment and beyond. Its location beneath Vatnajökull influences its behaviour, often leading to glacial outburst floods, known as jökulhlaup, and ash plumes during eruptions.   

Type: Subglacial stratovolcano. Location: South-east Iceland

Volcanic System: Grímsvötn-Laki  

Elevation: 1,725 meters (5,659 feet) above sea level. 

Activity: Erupts approximately every 10 years. 

Caldera: 8 kilometres diameter 

Tephra Deposits: Grímsvötn eruptions produce significant tephra and ash, which can be carried far across Iceland and beyond.  

Grímsvötn eruptions in the modern era

Grímsvötn’s eruptions are frequent and powerful, 38% of historical eruptions in Iceland have been from Grímsvötn. Geologists estimate that Grímsvötn has erupted eighty-seven times in the past 8.000 years. The system is still highly active, there have been twelve eruptions in Grímsvötn since 1910. We are all waiting for the next one!   

Here are a few examples of the eruptions that originate in the Grímsvötn volcanic system:  

Lakagígar eruption (1783–1784)

The largest known eruption from this system. An effusive eruption that formed a 27km long fissure. People of the time recorded three weeks of earthquakes precursing the eruption. The hardship suffered by the Icelandic people caused by this eruption was terrible. This period is called the ‘Mist Hardship’ since the air was often thick with ash and other not-so healthy volcanic material and gases. Up to quarter of the Icelandic population perished in the famine which followed this immense eruption. 

Gjálp eruption 1996

The Gjálp fissure vent eruption revealed a possible interaction between Grímsvötn and Bárðarbunga. First subglacial eruption and jökulhlaup – glacial outburst flood - monitored with modern equipment. 

2011 eruption

The most powerful eruption of Grímsvötn in 100 years. Ash was ejected 20 kilometers into the atmosphere, disrupting air travel across Europe.  This eruption lasted 4 days and caused the cancellation of 900 flights. 

Impact of eruptions

Grímsvötn’s eruptions, while often hidden beneath ice, leave lasting marks on Iceland’s people, environment, and economy. 

Agriculture: Ashfall can damage crops and impact livestock 

Transportation: Ash clouds from eruptions have disrupted air travel globally, such as the 2011 event. 

Flooding: Glacial outburst floods (jökulhlaup) caused by melting ice during eruptions threaten roads, bridges, and farmland.

Scientific Research: Grímsvötn is a focal point for volcanological studies, advancing understanding of subglacial eruptions and jökulhlaups.  

Lava and tephra production

 Grímsvötn is a large producer of both lava and ash. Some notable examples include:

Lakagígar (1783–1784: produced an estimated 14km³ of lava. Lava fountains were estimated to reach 800-1400 meters (2,600 to 4,600 ft) high 

1996 Gjálp Eruption: Melted over 3 km³ (0.72 cubic mile) of glacial ice, triggering floods and reshaping the landscape.

2011 Eruption: Released approximately 0.7 km³ (0.168 cubic mile) of tephra, affecting flights, air quality and agriculture across Iceland.

 Comparisons to famous eruptions in history 

Grímsvötn’s eruptions hold their own against some of the most well-known volcanic events: 

Explosivity: Similar to Mount Pinatubo (1991), Grímsvötn’s eruptions can inject ash high into the stratosphere. 

Flooding: Comparable to the floods triggered by Eyjafjallajökull (2010), Grímsvötn’s jökulhlaups (glacial outburt floods) are among the largest in recorded history.