ИСТИНА

Volcanic activity is the unique factor of river runoff formation and redistribution in areas under volcanic affect. There are 68 active volcanoes in Russia, and rivers with specific features of river runoff and hydrological regime are formed there. The major eruptions in the region occurred in the XX – the start of the XXI century e.g. Bezymyanny (March, 1956), Shiveluch (November, 1964), Tolbachick (1974–1975), and Pik Sarycheva (2009) volcanoes. Those eruptions could influence on river basins directly through ashfalls, lava flows, and transportation of chemical elements; indirect impact is usually connected with changes of conditions in the river basin, such as, infiltration, transpiration, characteristics of soils and vegetation, and etc. Two specific types of hydrological regime are observed in some rivers draining volcanic flanks in Kamchatka peninsula. One of them is characterized by almost uniform distribution of the water runoff within the year due to the dominance of groundwater feeding. Another type, so called “dry” rivers, is formed due to strong infiltration of surface runoff under subsurface connected with very high infiltration rates of friable volcanic deposits. There are three studied types of hydrological regime in the Kuril Islands: 1) extended flood with flash floods in warm part of the year; 2) spring flood with relatively small flash floods; 3) flood regime without a significant spring flood. Rivers of volcanic regions are usually characterized by very high suspended sediment yield. Analysis of the stationary observation data demonstrates the highest values are usually measured after major volcanic eruptions in the region. The suspended sediment concentration of 200 kg m-3 was measured during our field investigations in rivers of the Kliuchevskoy volcano group. This value is absolute maximum for Kamchatka peninsula. Volcanic eruptions can influence on major ions and microelements in water significantly due to transportation of various chemical elements and acidic gases during eruptions. The variability of the major ions in the Kamchatka River basin demonstrates increased background values in the section of volcanic impact on river runoff, where sharp increase in mineralization and some ions (in about 1.5 times) is observed in river cross-sections near the Kliuchevskoy volcano group. The unusual increase of some ions and mineralization is observed after major eruptions in the river, which is not connected with water runoff fluctuations. Recent studies on the subject demonstrates exceed of the background for P, Sr, Ba, Va, Pb, Mn, Cd, As, Zn, Cr, Li, Ni, Se, and Cu. It is estimated about 85% of solved matter comes into the river system in the region of the Kliuchevskoy volcano group and Shiveluch volcano action. Few data on major ions content in two rivers of the Kuril Islands demonstrates the difference in their hydrogeochemestry. One of them (the Kitovaya R.) is hydrocarbonate class of the sodium group, while another one (the Lesnaya R.) has increased content of sulphates and chlorides due to tributaries draining the sulphate fields. Special investigations of the thermal springs in the Kuril Islands show they can often influence natural water significantly. This work was supported by the grant of the The Government of the Russian Federation (Agreement № 075-15-2025-008 date 27.02.2025).