ИСТИНА

The retreat of the coastal line is occurred due to thermal denudation and thermal abrasion of coastal deposits. Thermal abrasion intensity depends from several main factors in the permafrost area, i.e.: ice regime, properties and composition of the seashore rocks, tidal activity of the sea level as well as water temperature and its salinity. Thermal denudation depends from radiation-heat transfer to the surface of slope, mechanical properties of grounds, ice content in ground and lithology of deposits. Ice activity of the sea have the significant influence on the retreat of the seashore (Are, 1980; D. Zachar, 1982; Dallimore et al., 1996; Jones et al., 2009; Arp et al., 2011 et al). On the other hand, the most important phenomena are ice cover duration and ice coverage during the summer season. The easiest to erode are silty clay, sand and loam clays. These sediments are typical for genetic types of Quaternary permafrost sediments on Kara seacoast. They often have high ice content represented by ice layers, ice wedges and massive ice texture of frozen ground (Romanovsky, 1993). Very important role in thermal abrasion is played by remove and ebbing work of the sea. It is not clear the role of sea level rising due to glaciers thawing. Besides that factor, it was found that seawater temperature and salinity do influence on the seashore erosion rate (F.E.Are, 1980). Thermal denudation is spreading for shore composed by frozen rocks with rich ice content (Gunter et al., 2013). It include some exogenesis cryogenic gravitational processes (slumping, sliding, solifluction, erosion etc.) which develop in course of rock thawing as well as nivation (snow bank processes) which induces seashore destruction and material migration to the lower areas (beach). Thermal denudation impact on the above-water part of the littoral zone results in scarp flattening with their stability also affected by abrasion (Romanovsky, 1993). Development of thermal denudation processes acquires some specific features in massive ice areas since on such areas these processes turn to be very intensive. Thermal cirques and thermal terraces are confining to massive ice exposure areas with rate of their back land retreat much higher than rate of thermal abrasion-inspired scarp retreat in the neighboring areas. For evaluation of rate of seashore retreat F.E. Are et al (2004) suggested and implemented the method based on thermal terrace dimensions and their lifetime data. Thermal denudation resulting from snow melting and summer rains is more active in the areas without any vegetation. Vegetative ground cover induces block caving in the top of thermal cirques. Often they are large blocks, which are delineate by frost fissures that caves down (Khomutov and Leibman, 2008). In accordance, the above-mentioned method the complex scientific research of the coastal retreat carried out on the western coast of Baydara Bay of Kara Sea. That works focused on detailed study of cryogenic destruction of seashore permafrost. That includes different programs of works: geocryological, geodetic surveying, drilling, thermometric and laboratory researches and study of hydro physical, mechanical, thermophysical and other properties of the rocks in both samples and in-situ. The purpose of research carried out in the Kara sea coast are complex study and investigation of seashore to illuminate the dependence between the lithology of the coastal deposits and height of the coast and the retreat rate for this sites. It based on 2013-2015 season observations.