Volcanic hazard from Late Pleistocene-Holocene monogenetic volcanism around the capital city of Kamchatka, Russia

Abstract:

More than 90% of populations (300k people) of Kamchatka live in Petropavlovsk-Kamchatsky, Vilyuchinsk and Elizovo on the coastal line of Avacha bay, surrounded by four major polygenic stratovolcanoes. Also, the Avacha bay is the main transport seaway to Kamchatka, and Asia N-America air transport corridor. While major volcanoes are monitored seismically, no analogous workshavebeen done forsmaller volcanic structures, even withinthe cities. Here we present first results of magma geochemistry and mineral assemblages, and compiled results for mapping those monogenetic cones. Most of them are related to the Malko-Petropavlovsk zone of transverse dislocations (MPZD), which is a natural arc-perpendicular graben boundary. It was formed on extension of Avachinsky submarine transform fault and divides the margin of accretions terrains arcs into northern segment of Kamchatka and sourthen long living arc. Locations of monogenic volcanoes are independent from the slab. There are on 197– 233 km from the trench. Most mafic, low alkaly magma (50–53 wt.% SiO₂, 6.5–7.7 wt.% MgO, 0.8–0.9 wt.% K₂O) belong to monogenic cinder cones in the valley of Paratunka and Bolshoy Vilyu rivers. Monogenic cinder cones were formed during two stages of activities: 7000–10000 BP and 2000–4000 BP (Dirksen, 2009). Extrusive domes (e.g. Mishennaya Mount and at least five others) are in north edging of Avacha bay on the 214-225 km from the trench. Mishennaya Mount is extrusive dome 600 ka years old according to K-Ar dating (Sheimovich, 2007), is in downtown of Petropavlovsk-Kamchatsky city and characterized by hornblende bearing andesites (~57 wt. % SiO₂, ~3 wt.% MgO, ~0.7 wt. % K₂O). Other cinder cones are related to bigger polygenic stratovolcanoes Avachinsky, Koryaksky with their specific chemic properties. These cinder cones located on 223-233 km from the trench, close to stratovolcanoes and magma compositions (52.74-56.05 wt. % SiO₂, 2.58-5.25 wt.% MgO, 0.53-1.29 wt.% K₂O). Most of monogenic volcanoes were utilized as high points for TV-mobile transmission, and quarried as scoria for constructions purposes. Considering population of Kamchatka living close to MPZD, it is necessary to set continuous monitoring using seismic data, gas, water analysis to predict potential dangerous of volcanic hazard from monogenetic volcanoes in the future.