The Peripheral Magma Chamber of Ploskii Tolbachik, a Kamchatka Basaltic Volcano: Activity, Location and Depth, Dimensions, and their Changes Based on Magma Discharge Observations

摘要

The Klyuchevskoi group of volcanoes (KGV) in Kamchatka is the most powerful existing island arc and subduction zone volcanic center. The Holocene volcanic activity in the southern part of the KGV is concentrated in a large basaltic volcano, Ploskii Tolbachik (PT), altitude 3085 m and in its Tolbachik zone of cinder cones (TZ), length 70 km, which are similar to Hawaiian-type volcanoes and their rifts. A variety of different basalt types are erupted at a rate of 18 × 10~6 t/yr. This paper provides information on the PT peripheral magma chamber obtained by several independent methods. We used data on the evolution, eruptions, magma discharge, deformation, and earthquakes in the PT and TZ, as well as calculations that give the size of the PT flow-through magma chamber. The use of seis- mological and geodetic data places the chamber under the PT summit caldera, gives its transverse size as below 6 km, and the top of the chamber at a depth of 2 km. Our calculations give 4.9–5.8 km for the transverse chamber dimension, 3.2–3.9 km for its vertical dimension, 40–70 km~3 for chamber volume, and about 4 km for the depth of chamber center. The information we provide makes the properties of this source of PT and TZ alumina-rich basalts clear, as well as those of the entire KGV complex plumbing system.