Coastal Geology and Geomorphology of the Kasatka Bay (Iturup Island, South Kuril Islands, SE Russia)

Abstract

Iturup is the largest and most explored island of the Kuril Archipelago. It is known for the activity of tectonic processes, active volcanoes and geothermal sources, and is rich in minerals. However, much less attention is paid to the study of the geological and geomorphological structure of the coast. As a result of our studies, we identified 3 morpholithogenetic types of coasts in Kasatka Bay, of which 49% are in the accumulative coasts with sand-pebbles beaches, and 51% are on the erosion and erosion-denudation coasts (bay flanks and Chertovka rock). Using the joint use of geomorphological and geophysical methods, the geological and geomorphological structure of marine terraces in the central part of the bay has been clarified. Geological and geomorphological sections of low sea terraces were obtained on the basis of GPR sounding using the common midpoint method. It has been established that a 5–15 m accumulative terrace level lies on top of an ancient bench, developed, most likely, in proluvial pre-Holocene deposits. The measurements showed that the pyroclastic cover with buried soils at terrace levels of 25–40 m and 45–60 m has a subhorizontal flat-layered structure from 3 to 5–6 m thick. with a thickness of 3 to 5–6 m. Studies of terrace 45–60 m structure above Chertovka rock showed the presence of ancient lahar deposits under pyroclastic cover with buried soils.