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).

A mathematical model and a method of computation are developed for the flow of magma with temperature-dependent viscosity in the conduit of a volcano. An example involves the following parameters: conduit radius is 10 m, depth to the magma chamber is 30 km, the overpressure, magma temperature and viscosity in the chamber are 20 bars, 1300° C, and 104, Ю5, 106Pa s, respectively. The initial phase of conduit operation lasting less than 10 years is considered. Conditions are determined under which the conduit freezes (stopping the extrusion), a quasistationary behavior sets in (steady flow), and the flow heats the conduit wall intensively.