Monday, May 12, 2014

When Hawaiian volcanoes explode, it's gas

Hawaiian volcanoes are sometimes casually called drive-in volcanoes, for their comparatively tame eruptions, but sometimes they’re anything but tame.

Sometimes they fountain aggressively, and occasionally, they explode, tossing boulders like so many grains of sand.

(Image: Fountaining at the 1959 eruption of Kīlauea. Credit Hawaiian Volcano Observatory, U.S.G.S.)
A new study sheds some light on how the volcano determines when to be calm and when to have a temper.

It suggests that Kīlauea Volcano’s most explosive eruptions may come from far deeper in the Earth than previously thought, and may determine their explosive nature when still at depth.

A team of researchers studied 25 eruptions in the last 600 years, and concluded that the amount of dissolved gas in the molten rock is a key indicator of explosiveness. 

The researchers include Don A. Swanson of the Hawaiian Volcano Observatory, Bruce Houghton of the University of Hawai`i Department of Geology and Geophysics, and . R. Sides, M. Edmonds and J. Maclennan, of the University of Cambridge Earth Sciences Department.

Their paper, Eruption style at Kīlauea Volcano in Hawai‘i linked to primary melt composition, was published in the journal Nature Geoscience.

They argue that explosive eruptions seem to be from lavas formed deep, which rise fast to the surface, and bypass storage in a magma reservoir that may feed many less violent eruptions.

“We conclude that the eruption style and magma-supply rate at Kīlauea are fundamentally linked to the geochemistry of the primary melts formed deep below the volcano. Magmas might therefore be predisposed towards explosivity right at the point of formation in their mantle source region,” they say.

Or, put more simply, “Gas-rich magmas are “predisposed” to rise quickly through the Earth’s mantle and crust and erupt powerfully,” Houghton said in a University of Hawai`i press release.

© Jan TenBruggencate 2014

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