Study is made for the first time on morphological peculiarities of microstructure of three samples from the unbroken marker ash layers of the Shiveluch volcano. In this paper we give the qualitative analysis of tephra structure, i.e. size and shape of particles and type of microstructure, describe structural relationships between deposit components, etc. and make the quantitative analysis of porosity of Sh2 and Sh1 tephra at magnification of 200 and 1,000. Hollow globules of volcanic glass were found for the first time in Sh2 ashes.

KUDRIAVY volcano on Iturup island in the Kuril arc is an active calc-alkaline volcano. It has not erupted this century; its current volcanic activity is characterized by hot (up to 910oC) gas jets which have been stable for at least 30 years. The composition of the gaseous emissions is typical of high-temperature fumaroles, but we report here the discovery of unusual subsurface sublimates associated with one gas jet—a sulphide mineral containing rhenium as the only cation. To our knowledge, this is the first reported occurrence of a pure rhenium mineral. The concentration of rhen-ium in the fumarole gas is only 2–10 p.p.b., so the condensation of pure rhenium sulphide from this gas requires both enrichment of rhenium by eight orders of magnitude and remarkable selectivity. Rhenium is generally believed to exist in only trace amounts at the Earth's surface, but our findings demonstrate that it can be readily mobilized, dispersed and concentrated by degassing magmas.

Previous data are summarized and new evidence is presented on the Avacha eruptions of 1926-1927, 1938, and 1945. The last eruption of January 1991 is described. The dynamics of the Avacha eruptive activity is considered for a period of 1737-1991. The eruptions are classified into different types. The type and size of a future event are predicted and the related hazard is assessed. It is recommended that the southwestern and southern sectors of the Avacha surrounding should be declared forbidden for residential or industrial construction because of a high volcanic hazard. -Journal summary

Some of the previous views on the style of the Avacha eruptions during 1737-1909 are revised on the basis of new data obtained by the authors. The types of eruptions, their geological and geomorphological effects, and the related volcanic hazards are reassessed. All eruptions were explosive events, except for the 1894-1895 extrusive-explosive eruption. The eruptions of 1737, 1779, and 1827 are classified as large, the others, as mild or medium-size events. -from Journal summary

The eruptive history of Ebeko Volcano is described since its origin about 2400 years ago until the beginning of the 17th century. Six stages of increased activity each lasting 200-300 years were separated by repose periods of the same duration. The eruption of juvenile material (lava and pyroclastics) took place at the first stage only (420-200 B.C.). All eruptions that followed were phreatic events of varying vigor. It is shown that, except for the first eruptive stage, the main volcanic hazard for the Ebeko area and the town of Severo-Kurilsk near by comes from large lahars and tephra fallout. -from Journal summary

Consequences of the Ebeko eruptions in the 17th-20th centuries have been reconstructed, using historical records, tephrochronological study, and air photographs. It is shown that all eruptions were phreatic and phreatomagmatic with a heat source of a strongly heated dike-sill complex of more than 1 km3 volume. It is supposed that the main potential hazard for Severo-Kurilsk city and adjacent area may be connected with large-volume lahar flows along the Kuzminka and Matrosskaya Rivers, which are sourced on Ebeko Volcano. Lesser hazard is expected from ashfalls of this and other volcanoes of the north Kurils and south Kamchatka. -from Journal summary

Lava flows from sixteen sites at Gorely Volcano, Kamchatka were sampled. Initial analysis showed high within-site scatter for NRM specimen directions. Alternating field and thermal demagnetization of specimens showed single-component magnetization indicating that specimens had not moved or were not exposed to changes in the magnetic field during acquisition of a magnetic direction. Scatter is thought to be either due to movement of the specimen with respect to the magnetic field or change in the magnetic field with respect to the specimen. Four factors were found that would contribute to scatter in specimen directions. These are 1) cooling rate, 2) range of unblocking temperatures, 3) relative time of emplacement, and 4) how the specimen moved or was affected by changes in the magnetic field. Only two sites showed that scatter was due to movement of the specimen. It appears that scatter in other sites resulted from changes in the magnetic field generated from a magma-induced electrical current due to lava flowing in the earth’s magnetic field. These changes in the magnetic field are shown to have more affect on material sampled at the surface than on material sampled at depth because massive interiors of flows showed less dispersion in specimen directions than levees or pull-aparts.

Предложен новый механизм потери устойчивости конической постройки стратовулкана за счет развития пластовых магматических интрузий из питающей системы вулкана. На основе данного механизма рассмотрена возможность катастрофического обрушения склона Ключевского вулкана и представлены оценки геометрических размеров лавинообразных потоков.