Large Scale Collapses of Avachinsky and Koryaksky Volcanoes and the Associated Catastrophic Eruptions – The Main Danger for Cities of Petropavlovsk-Kamchatsky and Elizovo

It is well known that large scale collapses of volcanic edifices (with volume more than 0.01 km) are common natural phenomenon and usual stage in geological history of many volcanoes. Volcanic collapses produce high-velocity, devastating debris avalanches, which travel long distances. In many cases, large scale collapses also provoke strong explosive eruptions. We report geological data about deposits of a large scale edifice collapse (debris avalanche) of Avachinsky volcano with volume 12 km. A major part of the city of Petropavlovsk-Kamchatsky is built on top of this debris avalanche deposit. We also report a new determination of the radiocarbon age of the organic-rich deposit underlying the avalanche deposit, which indicates that Avachinsky volcano collapsed 16500 C years BP. We presume that modern edifices of Avachinsky and Koryaksky volcanoes are potentially ready for future large scale collapses. The considered scenarios of possible future collapses show that the resulted debris avalanches will be able to reach the cities Petropavlovsk-Kamchatsky and Elizovo. The results of our investigations allow to upgrade the existing maps of volcanic hazards for this area.