IMPACT OF ICE BODIES ON THE SEABED OF THE NORTHERN CASPIAN SEA UNDER SEA LEVEL FLUCTUATION AND ICE COVERAGE CHANGES

The impact of sea ice on the coasts and bottom could be mechanical, thermal and physicalchemical. The most dangerous of these processes is ice gouging, i.e. mechanical destruction of the bottom grounds caused by the ice cover dynamics, hummocks and stamukhi formation under the influence of hydrometeorological factors and the topography of the coastal zone. During recent decades exploration of hydrocarbon reserves became more intensive within the Northern Caspian Sea region, including the design and construction of drilling platforms, underwater pipelines and other objects of oil and gas infrastructure. Reliable estimates of the impact of ice hummocks on the sea bottom and the depth of their penetration into the bottom grounds are necessary for designing underwater pipelines in freezing seas. Thus the assessment of ice impact (qualified as a natural hazard) is a key element of both geotechnical safety of oil and gas facilities and the environmental safety of marine areas. Underestimation of the glacial erosion could result in the damage of engineering constructions. Highly variable dynamics of ice cover of the Northern Caspian Sea and its impact on the bottom are discussed. Temperature regime during the cold season determines the state of the ice cover and the number of hummocks, so it influences the intensity of their impact on the coasts and the seabed. Under the same thermal conditions of ice formation the sea level becomes an important factor governing the intensity of ice gouging processes. During the exploitation period of hydrotechnical facilities the fluctuations of the Caspian Sea level could reach several meters. Thus the considerable changes of depths and the transformation of bottom relief could be expected, leading to the changes in ice hummocks formation and ice gouging of the bottom and coasts. At present the intensity of the ice cover impact on the bottom of the Northern Caspian Sea is still an open question. The problem is difficult to solve because, on the one hand, the interactions of ice cover and the bottom grounds of the sea are insufficiently known and, on the other, the extreme variability of the sea level and the ice cover makes the investigations particularly complicated. 

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