Until now, scientists have divided the eruption in two categories: violent (explosive) and effusive. The first type involves adorable kids ejection of ash and rock fragments high into the atmosphere (for example, the eruption of Mount St. Helens in 1980). Second — soft red hot lava flows that irrigate the slopes of the volcano (this, for example, are constantly in Hawaii).
Pumice stone to get to the unusual underwater volcano near McAuley in the southwest Pacific, the staff of the University of Victoria in Wellington (New Zealand) propose to introduce a third category, which they called tangaroanskim (Tangaroan) in honor of his research ship and the sea god Maori.
|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 author.)|
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, a similar species is formed only after violent eruptions. The number of holes, their size and shape allow geologists to understand the conditions under which the explosion occurred. If pumice found in the underwater volcano, then there also had a strong release of magma as a result of accumulation of gases, is not it?
No, not so. The holes in the volcanic pumice McAuley round and uniformly 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 observed elongated bubbles.
|Torn pieces of lava on the total weight and float.|
Perhaps the pressure of the water column is not allowed volcano explode. The case seems to have been the case (see illustration above). When the volcano rising magma, forming a kind of foam. Particles frothy lava quietly disappear from the total weight and float. From contact with sea water cools the edges of these formations, but inside the lava is still hot. With the rise of gas bubbles inside a uniformly increasing as the water pressure decreases. "Some 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, an extinct volcano in the rock off the coast of West Rota Mariana Islands. 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 Kermadec Island Arc, where McAuley, because there laid a lot of shipping routes and submarine cables.
As for pumice, then dip a few months, it either breaks or falls on the shore, or soaked with water and sinks to the bottom. Sometimes generated huge rafts of downed together pieces that play a role of a vehicle for marine life.
The study is published in the journal Nature Geoscience.
Prepared according to Our Amazing Planet.