We consider a problem of disturbance of a continuous medium which surrounds a magma chamber or channel. This disturbance is caused by excess internal pressure in the magma chamber. We used Godunov's entropy criterion to estimate the value of the shear strain required. Relations were found to determine critical pressure in the chamber and the time needed to achieve the critical state. The zone of rocks which surrounds the magma chamber and which is located next the melting zone has to be fracturing-resistant.

The results of mathematical modeling are given foi magma ascent in a fissure or dike for the case of temperature-dependent viscosity. Th( parameters chosen for calculations are as follows: the dike widths in the range 0.5-4.0 m, the magma viscosity 23-9.6 ± 106 Pa s (230-108 Poises), the depth to the magma chambei 30 km, and the temperature and pressure excess in the magma chamber 1300° С and 200 bars respectively. The distribution of one-phase flow velocities, temperature and viscosity of magmi inside dikes, the magma freezing on the dike walls and in its head, and the conditions undei which the magma ceases to move in dikes of different widths are investigated. It is shown tha the central faster streams of magma in dikes can reach the earth's surface, preserving thi temperature of a deep chamber (with the deduction of slight adiabatic cooling).

The new mechanism of the edifice stability loss of stratovolcario have been suggested at the expence of the magma intrusive sheet development from the feeding system. On the base of (hat mechanism there have been considered the opportunity of the catastrophic slope collapse of the Klyuchevskov volcano and there have been given an estimation of ihc geometric parameters of landslide deposils.

Mechanism of activity of the giant basaltic Klyuchevskoy volcano is stadied. Magma overpressure in its feeding system, surrounding rocks heating, amount and concentration of numerous radial dykes beneath the volcano at distances up to 20 km are calculated. It is shown that basaltic magmas of the Klyushevskoy volcano should be formed during their ascent through the crust and have to be accumulated in it. Results are compared with data on volcano eruptions, on the structure of the crust and earthquakes beneath the volcano. The state of the volcano and its unstable upper cone, and probable features of its next large eruptions are estimated.