ИСТИНА

The research is based on field survey in 2016, with the involvement of satellite images 1984-2017 and topographic maps 1833-1999. Part of the White sea named The Gorlo is a water area with very active hydrodynamics, where Northern and Western waves are superimposed on high speeds of tidal currents. The Holocene accumulative terrace of Intsy cape occupies 12 km of the shore between the eroded areas; its width exceeds 3 km. Climate and sea level changes cause erosion of previously formed accumulative coast. The sea terrace includes remnants of the moraine ridges up to 25 m high, one of which is located the Intsy lighthouse, built in 1900. At the time of construction, the distance from the lighthouse to the coast was more than 250 m and the moraine hill was not eroded by the sea. Our research has established: The average rate of retreat of the coastal ledge, cut out in the moraine hillside, for 185 years was 2.4 m/year. With the same speed the ledge has receded also in 2009-2016. For these 7 years the area of the hill has decreased by 14.5%, annual losses due to erosion and landslides are estimated at 0.32 ha. If the rate of destruction of the shore remains the same, the lighthouse of Intsy will be destroyed in 25 years. On the surface of the terrace up to 3 m high above sea level there are several generations of palaeo coastal ramparts marking the stage of extension of the shore. At this time of the 12 km of the terrace, only about 3.5 km remain stable, the rest are eroding. The retreat of the shore increases the deflation of sand on the littoral and the beach. The exposed sand is accumulated in the depth of the terrace forming vast massifs of dunes up to 12 m high. The main conclusion of the study is that in this area, due to changes in lithodynamic factors, the accumulation that prevailed during the Holocene was replaced by erosion of the shore. The work was partially supported by the RFBR 18-05-60221 and 19-05-00966 projects.