The dynamics of hostorical eruptions for Chikurachki Volcano has been analyzed. It is shown that these were either weak Strombolian-type eruptions (at intervals of a few years to a few tens of years) or powerful Plinian-type eruptions (at intervals of 100-200 years) discharging basaltic magma (50-54% SiO2). We have studied the tephra deposits and determined the parameters of the 1853 and 1986 Plinian-type eruption phases whose values have turned out to be similar: the minimum volume of erupted magma was 0.03 and 0.04 km3, respectively, the magma discharge was 5 x106 kg/s for both eruption types, the eruptive column height was about 13-14 km for wind velocities of 35-40 and 15 m/s, the Plinian-type phases lasting 5 and 7 hours. Information is provided on the morphology of the volcanic edifice and the structure of the soil-pyroclastic cover in the area. The condition of the crater in the summer of 2000 is described. It is concluded that high, pyroclastics-charged clouds of Plinian-type eruptions are the leading risk factor associated with Chikurachki Volcano.

This stady has proved that the EPR technique can be used to date volcanic formations within the Elbrus Volcanic Center (EVC) by investigating rock-forming quartz in volcanites, xenoliths of Paleozoic granite contained in these, and quartz in underlying older, metamorphic lavas. This is the firts time in Russia that the EPR dating technique has corroborated cycles of activity in the behavior of the Elbrus Volcanic Center previously identified from geological data, has determined the relevant time intervals, and deciphered the history of this stratovolcano. It is for the firts time that the EPR technique was used to determine the timing of paleofumarole activity and the age of deposits left by paleothermal springs (geyserites) during the EVC history. EPR dating results yielded a much earlier beginning of activity for Elbrus Volcano (mid-Middle Neopleistocene, 220.000 to 200.000 B. P.) and accordingly, a shorter duration compared with the opinion of previous researchers who based their findings on the K-Ar technique and the geomorphic method.

The geological and geophysical research carried out during the five cruises of R/V/ Vulkanolog in the 1980s and early 1990s provided new evidence of the structure and evolution of the Chernye Bratya volcanic massif. Five phases have been identified in its evolution. The first phase which began in the Early - Middle Pleistocene, or possibly Neogene, involvel the generation of a major shield-shaped, mostly laval, volcanic massif with dimensions 30 km by 35 km. The secondphase seems to have been a catastrophic explosive eruption producing the older caldera (Gorshkov Outer Caldera) of dimensions 15 km by 20 km. It is not younger than the mid-Late Pleistocene. A large volcanic structure formed during the third phase in the north and central parts of the older caldera, filling most of the caldera and overlapping its rim. A major explosive eruption occurred during the fourth phase producing the younger caldera (Gorshkov Caldera) of dimensions 7.5 km by 11.5 km. The generations time of that caldera corresponds to a powerful burst of acid explosive volcanism in the Kuril-Kamchatka region about 45.000 to 30.000 years ago. The final phase involved high volcanic activity within the younger caldera producing the present-day volcanic edifices of Chirpoy and Brat Chirpoev islands near the caldera rim. The total volume of ejecta discharged in the area may be in excess of 1000-1300 km 3; of these, 400-600 km 3 consist of pyroclastic material produced by the caldera-generating eruptions.