Seismological observations provided consistent information on the course and mechanism of the complicated large fissure eruption at Tolbachik volcano in Kamchatka from July 6, 1975 to December 10, 1976. Seismicity indicates that the initial magnesian basalts were rising ten days before the eruption from depths of more than 20 km. The formation of new feeding dykes was accompanied by earthquake swarms which decreased sharply one to two days before the opening of new eruptive fissures. The seismological data indicate that the main source of the different erupted basalts (2 km) was a vast system (diameter ca. 80 km) of hydraulically connected magma
chambers located in the lower crustal layers or in the crust-mantle transition layer.

The results of geological and geophysical studies, including recent ones, which make it possible to verify the existence of a liquid magma chamber below the Avachinsky volcano on Kamchatka, and to estimate the chamber depth and approximate dimensions, are analyzed. The heat stored in the host rock heated by the volcanic magma chamber from the time of chamber origination to the present is estimated, taking variable chamber dimensions during the process of evolution into account. The geological-geophysical prerequisites for using the thermal energy of the heated rock which surrounds the magma chamber to supply heat and power to Petropavlovsk-Kamchatskii are analyzed. The creation of an underground geothermal circulation system (fracture heat exchanger) using deep boreholes is proposed.

Изучены термальные источники - Карымские и Академии Наук. В кальдере Карымской выявлен новый тип разгрузки высокотемпературной гидротермальной системы в виде высокодебитных углекислых минеральных источников, отличающихся повышенным содержанием магния. Естественная тепловая мощность источников около 200 МВт, температура - 42-9" С. Карымские термы сформировались в результате смешения глубинных, насыщенных СО2, хлоридных натриевых вод с инфильтрационными, и взаимодействия их охлажденной смеси с метасоматитами предыдущих этапов развития гидротермальной системы. По общим геолого-структурным позициям, истории магматизма-вулканизма, гидротермальной деятельности, тепловой мощности, гидротермальная система кальдер Карымская - Академии Наук сходна с системами кальдер Узон - Гейзерная и Большого Семячика. Их отличают гидрогеологические условия разгрузки, сложившиеся на последних этапах развития (в голоцене).

Most of the hot .springs and all high-temperature hydrothermal systems are located within the three volcanic belts: East Kamchatka, South Kamchatka and Srcdinny Ridge connected with the zones of subduction. At the present time subduction beneath the Sredinny Ridge has stopped and the Central Kamchatka depression is now a relict of the continental slope of deep-sea trench. This is supported not only by the geological data but also by the fact that heat release by hot springs in the Sredinny Ridge is an order of magnitude lower then within East and South Kamchatka. Distribution of the hot springs is similar in all three belts. At 90-100 km width of the volcanic belts and of zones of the hydrothermal activity over 95% of heat is released by the sources located within the 45-km wide near-frontal zones. Voicanic fronts of the arcs are the clear boundaries beyond which heat release discontinues sharply. The descreate heat release is observed along the volcanic belts at the typical distances of 70-100 km between the maxim of heat release. Quantitative estimation of the probable heat and water contribution into the hydrothermal system formation showed that the only real heal source are the near surface magmatic chambers. Scenario of the probable heat and mass transfer leading to the formation of the hydrothermal systems and connected with them ore deposits has been considered.