Prediction and characteristics of the 1975 eruption of Tolbachik volcano, Kamchatka

Abstract

According to a long-term prediction. Tolbachik volcano was expected to erupt with a 0.7 probability, some time in the period 1964–1978. An eruption of Tolbachik commenced at 21.45 GMT on July 5, 1975. It took place on the southwestern Hank of the volcano at an altitude of 880 m a.s.l. about 18 km from the central crater. An earthquake swarm preceded it. The place and time of eruption were predicted three days belore it began on the basis of epicenter locations and characteristics of recorded seismic activity. During the period July 5–28 gases and incandescent magma were continuously ejected to a height of 2,000 m above ground level. Ash clouds rose to a height of 6 to 8 km, with a train of ash extending over a horizontal distance of 300 km. The velocity of jets from the crater was about 200 m/see. During the first days of the eruption the quantity of materials erupted and the eruption power amounted to 1.25 · 105 kg/see and 2.1 · 1011W, respectively. The vertical growth of the scoria cone was consistent with the lawH=2.153√vt, where the time and height are expressed in seconds and meters, respectively. The mouth of the volcano conduit was estimated to be 12 m in diameter. Lava began to erupt at 22h23m on July 28. During the period July 5–31 about 3 · 1011 kg of magmatic material, consisting of ash, scoria and lava, was erupted onto the earth’s surface. The energy released over the period of eruption accounted for 5 · 1017 J.