Subglacial eruptions, those of ice-covered

volcanoes A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

, result in the interaction of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

with ice and snow, leading to meltwater formation, jökulhlaups, and lahars. Flooding associated with meltwater is a significant hazard in some volcanic areas, including

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...

, and parts of the

Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...

. Jökulhlaups (glacial outburst floods) have been identified as the most frequently occurring volcanic hazard in Iceland, with major events where peak discharges of meltwater can reach 10,000 – 100,000 m³/s occurring when there are large eruptions beneath

glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

s. It is important to explore volcano-ice interactions to improve the effectiveness of monitoring these events and to undertake hazard assessments. This is particularly relevant given that subglacial eruptions have demonstrated their ability to cause widespread impact, with the ash cloud associated with Iceland's

Eyjafjallajökull Eyjafjallajökull (; "glacier of (the mountain) Eyjafjöll"), sometimes referred to by the numeronym E15, is one of the smaller ice caps of Iceland, north of Skógar and west of Mýrdalsjökull. The ice cap covers the caldera of a volcano wi ...

eruption in 2010 resulting in significant impacts to aviation across Europe.

Examples

Deception Island, Antarctica (1969)

Given that subglacial eruptions occur in often sparsely populated regions, they are not commonly observed or monitored; thus timings and sequences of events for an eruption of this type are poorly constrained. Research of the 1969

Deception Island Deception Island is in the South Shetland Islands close to the Antarctic Peninsula with a large and usually "safe" natural harbour, which is occasionally affected by the underlying active volcano. This island is the caldera of an active volc ...

eruption demonstrates that the impact of a subglacial eruption is not limited purely by

thickness, but that the pre-volcanic ice structure and densification (proportion of impermeable ice) play a role as well. In this case, even though the glacier was thin, a large jökulhlaup was observed as the glacier was largely made up of impermeable (unfractured) ice with a sudden supraglacial flood once the cavity has reached capacity. The resulting flood severely damaged buildings on the island, with complete destruction of a British scientific station.

Grímsvötn, Iceland (1996)

Over a period of 13 days in 1996, 3 km² of ice was melted with erupted magma fracturing into glass to form a 7 km long and 300 m high

hyaloclastite Hyaloclastite is a volcanoclastic accumulation or breccia consisting of glass (from the Greek ''hyalus'') fragments (clasts) formed by quench fragmentation of lava flow surfaces during submarine or subglacial extrusion. It occurs as thin marg ...

ridge under 750 m of ice at Gjalp

fissure vent A fissure vent, also known as a volcanic fissure, eruption fissure or simply a fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is often a few metres wide and may be many kilo ...

Grímsvötn Grímsvötn (; ''vötn'' = "waters", singular: ) is an active volcano with a (partially subglacial) fissure system located in Vatnajökull National Park, Iceland. The central volcano is completely subglacial and located under the northwestern side ...

volcano in Iceland. Meltwater flowed along a narrow basal glacier bed into a

subglacial lake A subglacial lake is a lake that is found under a glacier, typically beneath an ice cap or ice sheet. Subglacial lakes form at the boundary between ice and the underlying bedrock, where liquid water can exist above the lower melting point of ic ...

for five weeks, before being released as a sudden flood, or jökulhlaup. Although it has been proposed that subglacial volcanism may play a role in the dynamics of West Antarctic ice streams by supplying water to their base, for the Gjalp eruption, no rapid basal sliding was observed at the regional scale, with the formation of ice cauldrons over eruptive fissures due to the sudden removal of mass at the base. Research demonstrated that for warm-based glaciers, the effects of subglacial volcanic eruptions are localised, with eruptions forming deep depressions and causing jökulhlaups. For there to be significant changes in the extent and shape of an

ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...

, extensive subglacial volcanism would be required, melting a considerable fraction of the total ice volume over a short period of time.

Eyjafjallajökull, Iceland (2010)

In the first two days of the eruption, ice cauldrons were formed over the volcanic vents. Radar images reveal the development of these cauldrons in a 200 m thick ice cover within the summit

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

. They can also be used to document the subglacial and supraglacial passage of meltwater away from the eruption site. Research shows the eruption breached the ice surface four hours after the initial eruption onset, whilst meltwater release was characterised by accumulation and subsequent drainage, with most of the volcanic material in the ice cauldrons being drained in hyperconcentrated floods.Magnusson, E., M. T. Gudmundsson, M. J. Roberts, G. Sigurosson, F. Hoskuldsson, and B. Oddsson. 2012. Ice-volcano interactions during the 2010 Eyjafjallajökull Eruption, as revealed by airborne imaging radar. ''Journal of Geophysical Research: Solid Earth'', 117, B07405.

References

{{Glaciers Phreatomagmatic eruptions Glaciovolcanism

Examples

Deception Island, Antarctica (1969)

Grímsvötn, Iceland (1996)

Eyjafjallajökull, Iceland (2010)

See also

References