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Continuously accumulating eruption-threat in the South American Altiplano-Puna which never came to an outburst

Laguna Cuicocha in Ecuador, the caldera of a volcanic eruption. Foto: Andreas D. / Wikimedia Commons

Geoscientists discover magma volumes of supervolcanic proportions in the Andes

International geoscientists have discovered accumulations of magma in the Andes sufficient to have set off a super-eruption but which, in fact, did not. Such eruptions, which expel enormous quantities of magma, are the largest volcanic events on earth. Together with colleagues from the USA, researchers from the Institute of Earth Sciences in Heidelberg, Germany discovered that magma volumes of supervolcanic proportions have been continuously accumulating in the Altiplano-Puna region since the last super-eruption nearly 2.9 million years ago.

These magmas, however, did not reach the surface to trigger a catastrophic eruption but instead slowly cooled at depth and hardened into plutonic rock. The results of the research were published in the journal „Geology”.

Such plutonic rocks have large crystals as their cooling down from hot magma to cold stone had very much time to finalize. They are very hard, often used as cobblestones for streets or for building plinths. Granites, Gabbros or Diorites are such materials later lifted to the Earth’s surface over millions of years.

Prof. Dr Axel Schmitt of the Institute of Earth Sciences indicates that there have been at least seven super-eruptions in the Altiplano-Puna region within the last ten million years, the most recent one about 2.9 million years ago. What remains unclear is why no further major eruptions have occurred since then and whether the region can now be considered inactive for such events.

Using samples from five comparatively small lava domes in northern Chile and southeast Bolivia, the researchers investigated the most recent eruptions whose chemical composition matches the supervolcanic magmas from the region. They determined the age of very small zircon crystals from these lava flows with the aid of a high-spatial-resolution mass spectrometer. „The mineral zircon forms almost exclusively in magmas, so its age revealss when those magmas were present under the volcano,“ explains Axel Schmitt. „The astonishing result was that the ages of the zircons measured from all five of the smaller volcanoes extended continuously from the time of the eruption 75,000 years ago back to the last supervolcanic eruption.”

Translation: pebe

(20.10.2016, USA: 10.20.2016)