Рассмотрено движение однофазной вязкой магмы по щели постоянного сечения. Вязкость магмы описана двучленной формулой, учитывающей резкое возрастание вязкости вблизи точки замерзания магмы и плавное уменьшение вязкости в области высоких температур. Составлена система уравнений, описывающих движение магмы с учетом вязкого нагрева и теплопотерь через стенки щели. Задачи решены на ЭВМ для широкого диапазона начальных условий в питающем очаге. На основании результатов решения получено приближенное аналитическое соотношение, связывающее главные параметры задачи (глубину залегания Н питающего очага, избыточное давление Р и температуру То магмы в нем, толщину W и время существования t дайки, а также скорость v движения магмы по дайке). Определены границы стабильного движения магмы. Получена приближенная формула, связывающая предельные параметры Vmin и pmin (минимальную скорость стабильного движения и давление, при котором движение магмы прекращается) с параметрами дайки и питающего очага.

The paper discusses the results of geodetic investigations performed in the region of the large 1975-1976 Tolbachik fissure eruption in Kamchatka. Using data from repeated triangu-lation and trigonometric levelings, horizontal and vertical displacements have been detected in an area of 3,500 km2. Two zones have been recognized: the tension and uplift zone that is probably due to magma intrusion from depths to the surface along the line of new cones and the extensive compensative subsidence zone located at a distance of 20-50 km from the nearest newly-formed cones.??Measurements made with small distance measuring device showed the dynamics of feeding basalt dykes intrusion and made it possible to determine their width (a little greater than 1 m) and magma and gas overpressure (50-250 bar). Data have been obtained on dimensions and growth of cones and on vertical ground deformation in the area of new cones during and after the eruption.??

The paper describes the course of the Large Tolbachik fissure eruption taking place in Kamchatka from July 6, 1975 to December 10, 1976. The eruption zone extended for 30 km. The formation of monogenic scoria cones nearly 300 m high, lava tubes and basalt sheets up to 80 m thick and more than 40 km2 in area and subsidence of the Plosky Tolbachik summit caldera to a depth of more than 400 m were observed during the eruption. The volume of eruption products amounted to more than 2 km3. It was the largest basalt eruption which has taken place in the Kurile-Kamchatka volcanic belt in historic time.

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.