Underwater volcanoes erupt differently

Macauley Island — caldera, formed after the eruption of an underwater volcano of the same name 6100 years ago (here and below the image of the authors.)

January 21, 2013. Until now, scientists were divided eruption into two categories: violent (explosive) and effusive. The first type involves adorable kids emission of ash and rock fragments high into the atmosphere (for example, eruption of Mount St. Helens in 1980). The second — the soft glow of red lava streams that irrigate the slopes of the volcano (this, for example, constantly going on in Hawaii).

To get to the unusual pumice near the underwater volcano McAuley in the southwest Pacific Ocean, the staff Victoria University of Wellington (New Zealand) propose to introduce a third category, which they called tangaroanskim (Tangaroan) in honor of his research vessel and sea god Maori.

The bubbles in the pumice suggest that one of the recent eruptions McAuley was not explosive and effusive, and some in between.

You probably know that there are holes in the pumice — the void left by the gas bubbles during the solidification of lava. On land such species is formed only after violent eruptions. Number of holes, their size and shape allow geologists to understand the conditions under which the explosion occurred. If pumice was found in a submerged volcano, then there also had a strong release of magma as a result of accumulation of gases, is not it?

No wrong. The holes in the volcanic pumice McAuley rounded and evenly frothy, with the texture of a well-made mousse or meringue, says co-author Colin Wilson. Along the edge, where there was a rapid cooling, there are elongated bubbles.

Chunks of lava come off the total weight and float.

Probably the pressure of the water column is not allowed volcano explode. It seems to be as follows (see figure above). When the volcano magma rises, forming a kind of foam. Particles of frothy lava quietly disappear from the total weight and float. Due to the contact with sea water cools the edges of these formations, but inside the lava is still hot. As the gas bubbles rise inside uniformly expand, as the water pressure decreases. "Some kind of hellish popcorn" — says Mr. Wilson.

In the case of the volcano McAuley these pieces are about 10 cm in diameter, but the authors found reports that in other places there are fragments of meter size — for example, in the breed extinct volcano off the coast of West Rota Mariana Archipelago. And in 1998, near the island of Terceira in the Azores saw pieces of three meters in diameter.

Therefore, we can breathe a sigh of relief: not every underwater volcano, around which is scattered pumice, can lead to the rapid eruption. This is important for many volcanic archipelagos, including the island arc Kermadec, where McAuley, because there laid a lot of shipping routes and submarine cables.

See also: In the Pacific Ocean found drifting island

As for the pumice, then swim a few months, she either breaks or falls on the shore, or soaked with water and sinks to the bottom. Sometimes form giant rafts of downed together pieces that play a role vehicle for marine life.

The study is published in the journal Nature Geoscience.

Based on: Our Amazing Planet
Source: Kompyulenta

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