STUDY AND MECHANISM OF THE SIMULTANEOUS 1996 KARYMSKY VOLCANO AND AKADEMII NAUK CALDERA ERUPTIONS IN KAMCHATKA

Abstract

This paper describes eruptions that commenced simultaneously in the Kamchatskiy volcanic center in 1996. A significant swarm of earthquakes with magnitudes as high as 6.9 occurred there on January 1, 1996, and was followed on January 2 by a uniform summit eruption at Karymsky Volcano, which continued up until March 1997 and later with a rate of andesite-dacite lava discharge of 0.8 tonnes/s. On January 2-3 a phreatomagmatic eruption occurred in the Akademii Nauk caldera with a rate of pyroclastic discharge greater than 800 tonnes/s. The eruption occurred after 28,000 years of dormancy, and resulted from the injection of basalt through a fissure. The distance between the craters of these two eruptions was 6 km. The base surges of subaqueous explosions were observed, major tsunamis were caused, and a new peninsula was formed in the caldera lake. It was found that the ground surface had experienced an extension of more than 2.3 m. The fresh caldera lake, with a volume of 0.47 km3 was transformed into an acid lake (of pH 3.2). The situation within the volcanic center at the end of 1995 is briefly described here, and a successful forecast is reported. Estimates are presented for the depth of a pressure center in the main magma source (18.3 ± 0.8 km), for the volume of the crustal magma chambers (400 km3), and for the dimensions of a dyke that was injected through the consolidated crust (this was 0.7 m thick and 4700 m long). The mechanisms of the eruptions and associated volcanic activity are discussed.