The Opala IV: An explosive caldera-generating super eruption,which was the largest in Kamchatka in the last 50000 years

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.