An account is given of magnetostratigraphic studies of Kamchatkan Holocene formations: the cover of soil and pyroclastics and the rocks of the cinder cones from the flank eruptions of Klyuchevskoi Volcano. А study was made of seven sections of the soil and pyroclastics and of samples from 17 cinder cones. А detailed account is given of the data processing procedure. Consideration is given to the reasons for the established incompleteness of the paleomagnetic record in the sections and it is demonstrated that adequately detailed reconstruction of the history of the geomagnetic 1ield is possible only provided that а study is made of а series of рагаllеl sections. The trajесtory of the geomagnetic field vector over the last 4000 years is determined on the basis of the material on radiocarbon datings. Seven cycles of paleosecular variations are distinguished in the age range investigated; each of these cycles has individual features by which they can be recognised and used for stratigraphic correlation. The, features taken were the direction of rotation of the vector, the shape and size of its loops, and the length of the cycles. Correlation of the sections based on paleomagnetic data was found to be in good agreement with the tephrostratigraphic correlation and enabled corrections to be made to the age of some horizons, including the archeological layers of the primitive settlement at Zhupanovo and the cinder cones. The metachronous magnetization present in some tephra layers was found to be an obstacle to any improvement in the accuracy and detail of magnetochronological reconstructions.

A thermal model has been constructed for a steady-state glacier of Ushkovskii Volcano. Analysis of ice mass balance components has revealed elevated heat flow (mean valce 10 W/m2) in the summit crater wich has remained nearly constant over the last 40 years. The measured accumulation rate and temperature distribution in the snow and firn body in the middle of the Gorshkov crater suggest the existence of a considerable uplift (a small embedded crater) overlain by the glaciers. The formulas proposed in this paper can be used to evaluate critical state parameters for unsteady ice masses on the slopes of Klyuchevskoi Volcano.

A matematical model is given of the formation of phreatic explosions in lava flows coming into contact with ice formations. Quantitative characteristics are derived for the various stages in the development of the explosion; by means of wich its strength and other parameters may be evaluated. The theoretical calculation results are in agreement with empirical data.

Современная активность вулкана связана с многоактным центральным эффузивным куполом. На северо-северо-восточной стороне его вершинной части расположен своеобразный кратер, имеющий форму радиальной щели длиной 250—270 м и шириной от 15 до 70 м. Известны слабые фреатические извержения в 1951, 1968, 1970, 1973 гг. Извержение 1989 г. началось 3 мая. Взрывы привели к образованию пепловогазового облака, высота которого 8 мая достигала 1,5 км. Уже при первых взрывах, на северном склоне вулкана возникла новая трещина длиной около 70 м. Извержение предварялось рядом землетрясений под вулканом в полосе, перпендикулярной Курильской островной дуге. По глубине очага землетрясения четко подразделяются на две группы — с глубинами, близкими к 30 км и с глубинами приблизительно 60—80 км. Слой в пределах от 30 до 55—60 км представляется асейсмичным. Это наводит на мысль, что в пределах глубин 30—60 км под вулканом расположен магматический очаг. Можно предполагать, что тектонические подвижки, связанные с поперечным разломом, привели к активизации вулкана. Приведен прогноз активности на ближайшее время.