The Opala IV: An explosive caldera-generating super eruption,which was the largest in Kamchatka in the last 50000 years |
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Authors: | I. V. Melekestsev |
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Affiliation: | 1.Institute of Volcanology and Seismology, Far East Branch,Russian Academy of Sciences,Petropavlovsk-Kamchatskii,Russia |
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Abstract: | It is shown that the youngest (~40000 14C years BP) caldera of the Opala caldera complex, the Opala IV, was formed by a catastrophic explosive supereruption, the largest in Kamchatka during the last 50000 years of the seven dated similar-type eruptions that occurred during the Late Pleistocene paroxysm of explosive volcanism. It is thought that the ejected volume was on the order of 250 km3 of pyroclastic material. A smaller part of it went to form pumice-rich pyroclastic flows, with the greater part being transported as tephra. The principal axis of the ash fallout was oriented NNE (azimuth ~30°) where the tephra thickness was 20–30 cm at a distance of 300–320 km from the eruptive center. The uncontaminated juvenile material is rhyolite, the concentration of SiO2 was 75–76%, the total alkali content 7.3–8.3%, and the K2O/Na2O ratio 0.83–0.96. It was concluded that no such eruption can occur in the Opala caldera complex in the future for hundreds or thousands of years. |
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