SLOPES AND SHORE MORPHODYNAMICS OF THE NAGAEV BAY (SEA OF OKHOTSK)¹

The results of the morphodynamics analysis of denudation slopes and the coastal zone of Nagaev Bay, as well as estimated distances and rate of the eastern coastline retreat for the period from 1939 to 2016 are presented. The main methods of the work are morphographic and morphometric using aerial photographs of different years of flight, modern satellite images and snapshots. It is established that the morphostructure of the southern and northern shores of Nagaev Bay is determined by active faults striking in sub-latitudinal direction and framing the bay. The polygenetic mountain slopes adjacent to the coastline differ in length and angle of inclination. The slopes are covered with active kurums (stone runs) that slide towards the bay. In the lower part of the northern slope there is a zone of the Nagaevsky active fault, which causes a high dynamics of slope processes with a predominance of active kurums and landslides. The northern slope has been cut by a road built during the construction of the seaport and the Port Highway. As a result, widespread technogenically triggered landslides, rock falls and scree are often disrupting traffic on the highway. Thus, the territory of the commercial seaport and the Port Highway are at a risk of a sudden movement of large-volume of detrital material down the mountain slope. The eastern coastal zone is formed by a coastal ledge composed of unconsolidated deposits of the Nagaevskaya strata, an incomplete profile beach, and a littoral, the width of which reaches 200–250 m at low tide. The marine boundary of the zone runs at a distance of about 500 m from the coastal ledge. The eastern shore is actively moving towards the city of Magadan. During the period from 1939 to 2016, it shifted by 56 m with an average speed of 0.73 m/year. During the first stage (1939–1974), it advanced 29.0 m with an average speed of about 0.83 m/year. During the second stage (1974–2016), the coast moved for about 27.0 m with an average speed of 0.64 m/year. In recent years, large-scale work has been carried out on the eastern shore of Nagayev Bay in order to reinforce the shore and protect it from abrasion by erecting a breakwater wall. The engineering structure results in breaking of the established dynamic balance of coastal processes, which will eventually lead to the complete disappearance of the beach, and on the remaining unprotected sections of the coast – to increased abrasion and faster movement of the coastline towards the city.