If you studied volcanoes at school (whether you were deeply bored or totally enthralled) you will probably remember that volcanic explosions fall broadly into one of two types – either effusive (such as those which tend to characterise Hawaiian volcanoes) or explosive (characteristic of many of the planet’s most memorable eruptions, from Vesuvius to Mount St Helen’s).
Now, however, science teachers the world over may have to revisit their lesson plans. New Zealand researchers investigating underwater eruptions in the south-western Pacific Ocean have identified a third type of eruption, termed the Tangaroan, which falls between the other two.
What is a Tangaroan Eruption?
The results of the study, supported by a grant from the Royal Society of New Zealand Marsden Fund, are published in the journal Nature Geoscience. Researchers looked at submarine Macauley volcano in the Kermadec island arc, evaluating the erupted clasts (pieces of rock) in terms of their texture and density – the latter determined by the number of holes, or vesicles, left by escaping gases.
What they found was a pattern among these clasts that suggested they behaved differently from the other effusive or explosive eruptions. According to lead author Melissa Rotella, the erupted lumps of volcanic lava (known as ‘blebs’) are sufficiently buoyant relative to the surrounding water to rise slowly and form a kind of lava ‘foam’ before eventually sinking. “The water medium the magma is erupted into causes the exterior of the blebs to quench, sealing the bleb and allowing the interior of the bleb to vesiculate (grow bubbles) internally without losing the gas through the bleb rind,” she told Decoded Science.
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