Ascension Island: Fiery and highly explosive

Scientists explore the origins of the volcanic island

Volcanic island of Ascension Barry Weaver
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1, 600 kilometers of water in the east, 1, 600 kilometers of water in the west, and a black-brown patch of land in between: That's Ascension Island, a volcanic island seven degrees south of the equator. In the past, the inhospitable island was hit by massive explosive volcanic eruptions. Two budding geoscientists at the University of Bonn are now investigating the mechanisms behind these outbreaks.

It was not until 1815 that Ascension Island was settled. Therefore, there are no eyewitnesses to the huge volcanic eruptions that must have taken place there in the last few centuries. To date, only a sparse vegetation on the brown-black lava masses could gain a foothold. Kirsten Pedroza and Sebastian Bernhardt disturb the little: The budding geoscientists are anyway more interested in the volcanic rocks that were once brought to light by massive eruptions. They will spend almost two months in the remote spot in the middle of the Atlantic Ocean; They will be flown by a British military machine next Thursday. The two report on their experiences in an internet diary.

On the trail of the outbreak mechanisms

What makes Ascension Island so interesting for research is the way the island volcanoes erupted in the past. "There is a high percentage of pimples on the island; this is foamed volcanic rock that is produced by strong, explosive eruptions, "explains Holger Paulick from the Mineralogical Petrological Institute of the University of Bonn. The scientist supervises the diploma students and has been to a preliminary examination on the remote island several years ago. "Our job is to understand the mechanisms behind these outbreaks and make predictions about when the volcano might erupt."

When the plug is blown off ...

On the explosive power of 500 Hiroshima bombs experts estimate the energy that was released 20 years ago at the outbreak of Mt. St. Helens. The volcano in the northwestern United States lost 400 meters in height during the eruption, a 20-kilometer ash cloud obscured the sun. Such an explosion can occur when viscous magma clogs the volcanic vent. At some point, the plug will not withstand the rising pressure; the magma makes its way to the surface. In a fatal chain reaction, the gas dissolved in the magma bubbles up abruptly. Like a carelessly opened champagne bottle, the lava splatters out of the vent with extreme force. "That's why the resulting pimples are up to 80 percent air bubbles, " explains Kirsten Pedroza. "The foamed rocks are so light that they even swim."

Cutting torch melts earth crust

It is also exciting to ask why there are volcanoes on Ascension Island. Normally, the mountains of fire form on the edges of the crustal plates. Here the mantle is partially melted, and magma rises to the surface. However, Ascension Island is about 80 kilometers from the nearest seam - the Mid-Atlantic Ridge. "Perhaps this is a so-called mantle plume, " explains Sebastian Bernhardt. Over these volcanoes, hot mantle rocks, finger-shaped, rise from great depths and burn through the overlying crust of the earth. Hawaii is over such a "hot spot", The earth's crust has been sliding over this hot spot for millions of years, melting like a cutting torch. Therefore, Hawaii pulls a rat tail of now extinct volcanoes behind it. display

Whether Ascension is actually a "mantle plume" will be shown by the analysis of the rocks in the geochemical isotope laboratory of the University of Bonn. Schmuckst ck is a brand new high-precision mass spectrometer worth 1.2 million euros, which was financed from DFG funds. Among other things, the researchers can find out from which depth the volcanic rock originates: hot-spot volcanoes tapping the lower layers of the mantle at a depth of about 2, 900 kilometers. On the other hand, volcanoes at plate boundaries are more likely to be boring on the surface: with them, the eruption material comes to a maximum depth of 200 kilometers.

The internet blog of Kirsten Pedroza and Sebastian Bernhard can be found here.

(University Bonn, 06.02.2007 - NPO)