Three of four Plinian eruptions from Ksudach Volcano are among the four largest explosive eruptions in southern Kamchatka during the past 2000 years. The earliest of the eruptions was voluminous and was accompanied by an ignimbrite and the fifth and most recent caldera collapse event at Ksudach. The isopach pattern is consistent with a column height of 23 km. The three more recent and smaller eruptions were from the Shtyubel' Cone, within the fifth caldera. Using isopach and grain size isopleth patterns, column heights ranged from ≥ 10 to 22 km. Although the oldest eruption may have produced a large acidity peak in the Greenland ice, the three Shtyubel' events may not be related to major acid deposition. Thus it is possible that few if any of the uncorrelated acidity peaks of the past 2000 years in Greenland ice cores result from eruptions in southern Kamchatka.

Based on thepalynological studies, the age dismembering is made of volcanogenic-sedimentary deposits in the Uzon-Geysernaya Caldera Depression. The paleogeographical setting of the time of sedimentation is described. The age of deposits was established to be Late Pleitocene-Holocene. The dating was made of the main events of the post-caldera volcanic activity in the Uzon Caldera.

High hydrothermal activity is concentrated in the crater of Ushishir volcano which represents an almost closed bay connected with the ocean through a narrow and shallow strait. In their composition the thermal waters can be divided into two groups: (1) thermal waters of sea origin of high mineralization altered as a result of high-temperature interaction with rocks and (2) waters of sea origin heated in the near-surface conditions and mixed with fresh meteoric water. Ion and gas geothermometry as well as mixing plots in Na - 1ма_к and CI - coordinates suggest that these thermal vents are fed by steam-water geothermal reservoir with temperature of about 260°C; mineralization of the fluid in equilibrium zone is 23 g/l, C02 pressure being about 4 bar. Calculations of the equilibrium solution composition in the closed "water-andesite" system indicate that the observed Mg concentration could be formed in a wide temperature range but at low, lower than 0,01, mass rock-water ratios. Reequilibration of the solution at temperatures of 170-200°C in the near-surface conditions is most probable. The main discharge takes place primarily in the intersection zone of the ring-shaped and linear faults. Through the ring-shaped fracture mostly gas and steam-heated waters are discharged.