Subglacial volcano

A subglacial volcano is a volcano whose main crater lies under a glacier.

Occurrence

Areas in which there are particularly many subglacial volcanoes, are in the polar regions, especially on the island of Iceland, Alaska, and Antarctica. But even high-altitude mountainous regions including Japan, with the Fujiyama, one of the most famous volcanoes in the world, the Kamchatka Peninsula in Russia or the Andes, for example, in Chile, Bolivia and Peru have to have such volcanoes.

Geological characteristics

One must distinguish between covered only in the summit area of glaciers mountains such as in the Andes peaks or on the Kamchatka the case on the one hand, and lying almost entirely below the ice mountains in Antarctica or Iceland on here. In the first case you can see the structure of the mountains generally involves. clearly seen, usually it is Strato or Calderavulkane. In contrast, the structure can be under the ice lying mountains only with the help of computer and satellite technology almost divine.

Strato volcanoes are made up of alternating lava and ash layers. If there is a central volcano, it is mainly composed such as the Torfajökull from rhyolite and at least one - have formed Caldera - usually in the case filled with ice.

However, at the meantime exposed mountains from the ice age, you realize that if they were below a glacier, consist of Palagonittuff or Hyaloklastiten and pillow lava, which have formed over a vent cone, over a fissure Palagonitrücken, such as Sveifluháls at Krísuvík in the southwest of Iceland.

Typical onset forms

It is explosive and phreatomagmatic eruptions, which are usually accompanied by glacier runs or lahars and can cause enormous damage, as you had to find some in the volcanic disaster of Armero in Colombia during the eruption of the glacier -capped Andes volcano Nevado del Ruiz in 1985.

Sequence of subglacial eruptions

Magma that rises through vents during a volcanic eruption or column and reaches the border between stratum and often several hundred meters thick ice sheet melts first a cavity in the ice. At the same time the ice falls on its surface more or less fast and strong, and it forms a kind of boiler. The cavity above the magma fills with large flares and corresponding thickness of the ice up to 9 /10 with melt water. From this ratio, however, the glacier floats on the melt water on that same breaks through the ice barrier and rushes in a giant tidal wave down the slopes. This process could be observed, for example, in 1996 the eruption of lying under the Vatnajokull glacier shield volcano Gjálp.

As long as the water pressure on the magma is still sufficient to form pillow lava over the eruption site. If the eruption stop at this stage, a back or a cone of such lavas remains. An example would be Sigalda near the volcano Hekla in Iceland.

But falls below the water pressure a certain limit, we find a phase change takes place in one or explosive phreatomagmatic phase. Here, in more or less large amount of tephra or other materials such as volcanic Locker Brecchien or slag is produced. If the eruption pauses here, the results are Palagonitrücken.

Keeps the eruption, however, continues to rise, lava begins to flow out, fills the crater and flows down the flanks or over the glacier. If the crater was initially filled with (melt ) water, the lavas have to build first in the form of pillow lava up to the water surface and only then are they on lava produced, which then accumulate as on dry land. But because of the glacier, which holds materials in strict form, the flanks of the volcano, thus building up panel will be very steep. Examples of such board volcanoes are about The Table in the Canadian Cascades mountain range or Herðubreið in Iceland.

Other well-known examples

In Iceland, especially 4 glaciated volcanoes in the last centuries were active: Grímsvötn and Öræfajökull, both from the enormous glaciers of Vatnajökull plate ( approximately 8,000 km2) are covered, Eyjafjallajökull and Katla.

In recent times, that is in March and April 2010, has mainly been talk of Eyjafjallajökull. In the case of a stratovolcano located under a medium-sized glacier dome. The outbreak in the spring of 2010 produced up to 8,000 m high ash clouds, an outbreak rather medium size (see Vulkanexplosivitätsindex ), which, however, because on the one hand the composition of the clouds of very fine-grained andesite particles and on the other hand, unfavorable wind directions air traffic in Europe for almost a week severely disabled.

Mount Redoubt in Alaska about has experienced major outbreaks in 1990 and 2009, which, inter alia, ash fell on Anchorage.

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