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.