Grimsvotn: A Deep Dive into Iceland's Most Frequently Erupting Volcano
Beneath the Vatnajokull ice cap, Iceland's largest glacier, lies Grimsvotn, the most frequently erupting volcano in the country. Hidden under ice, it makes its presence known through powerful eruptions that punch through the glacier and through the glacial floods that its heat unleashes. Its 2011 eruption sent an ash plume high into the sky and briefly disrupted European air travel, a reminder of the reach of this ice-bound giant.
A volcano under the ice cap
Grimsvotn is a subglacial volcano, lying beneath the vast Vatnajokull ice cap in southeastern Iceland. Its caldera is filled with a subglacial lake, heated by the volcano below, which forms a defining feature of the system. Largely hidden from view, Grimsvotn is nonetheless one of the most active and important volcanoes in Iceland.
Iceland's most active volcano
Grimsvotn has erupted more frequently than any other volcano in Iceland in recent centuries, with eruptions occurring every few years to few decades. This high frequency, combined with its subglacial setting, makes it a central focus of Icelandic volcanology and a recurring source of both eruptions and glacial floods.
Jokulhlaups: the glacial floods
One of Grimsvotn's defining hazards is the jokulhlaup, a sudden glacial flood. Heat from the volcano melts the overlying ice, and meltwater accumulates in the subglacial lake until it bursts out beneath the glacier, sending enormous floods of water and debris across the outwash plains below. These floods are a characteristic and sometimes destructive feature of the Grimsvotn system.
The 2011 eruption
In 2011, Grimsvotn produced a powerful eruption that blasted an ash plume high into the atmosphere, the largest eruption of the volcano in many decades. The ash briefly disrupted air travel in parts of Europe, coming just a year after the Eyjafjallajokull eruption had caused far greater aviation chaos. The 2011 event demonstrated Grimsvotn's capacity for significant explosive activity.
Ice and magma
The interaction between Grimsvotn's magma and the overlying ice shapes its eruptions. When magma meets ice and meltwater, the explosive interaction can fragment the lava into fine ash, producing the ash plumes that pose a hazard to aviation. This ice-magma interaction is a key reason why subglacial volcanoes like Grimsvotn behave differently from those erupting in the open air.
Part of a larger system
Grimsvotn is closely linked to the Laki fissure system, the source of the catastrophic 1783 eruption that devastated Iceland and chilled the climate of the Northern Hemisphere. This connection underscores the power of the Grimsvotn system, which has the capacity for both frequent moderate eruptions and rare but immense fissure events.
Monitoring beneath the glacier
Iceland's Meteorological Office monitors Grimsvotn closely, tracking seismicity, ground deformation, and the level of its subglacial lake to anticipate both eruptions and jokulhlaups. Because the volcano is hidden beneath ice, this monitoring relies on indirect measurements, but it has proven effective in forecasting the floods and eruptions that the volcano regularly produces.
Explore on the map
Grimsvotn stands among Iceland's great volcanic systems, alongside Bardarbunga, Hekla, and the fissures of Laki. Explore it on the interactive map — filter by country to see Grimsvotn among Iceland's volcanoes and to appreciate the power of the volcanoes hidden beneath the island's glaciers.