Koriak Mountains

highlands in the northeastern Asiatic USSR, in Kamchatka and Magadan oblasts, extending along the coast of the Bering Sea from the Gulf of Anadyr’ to the Kamchatka Peninsula. The mountains are 880 km long and up to 270 km wide. Elevations range from 600 to 1,800 m; the highest peak is Mount Ledianaia (2,562 m) in the central part.

The Koriak Mountains lie in the northwestern part of the Pacific geosynclinal belt, whose basement is composed of ophiolite and terrigenous formations of the Paleozoic and Lower Mesozoic. Above these formations is an Upper Jurassic and Cretaceous geosynclinal complex, consisting of terrigenous and siliceous-volcanic rock, which forms a cluster of linear folds compressed in the southwest and diverging toward the northeast. In the northern and central parts of the mountains the Paleogene and Neocene are represented by volcanic rock and molasse (frequently carboniferous). In the south the main geosynclinal stage was completed in the Neocene and is represented by thick volcanic-siliceous and terrigenous rock of the Paleogene and Miocene, crushed into linear folds and extending in a northeastern direction. Lying unconformably on these rocks are sloping, dislocated molasse of the Neocene and effusives of the Anthropogene. Intrusions consist of basic and ultrabasic rocks and, sometimes, of granitoids from the Paleozoic, Early and Late Cretaceous, and Cenozoic.

Minerals include placer gold and shows of native gold, silver, tin, copper, polymetals, and molybdenum, associated with Cretaceous, Paleogene, and Neocene granitoids and Neocene effusive and subvolcanic rock. Mineralization by mercuric compounds (sometimes with antimony) is controlled by zones of fractures and confined to Cretaceous deposits and layers of Neocene and Anthropogene volcanic rock. Copper pyrite and ironmanganese ores are found in volcanic-siliceous formations. Sulfur is associated with Late Neocene and Anthropogene effusions. Bituminous coal, lignite, and shows of oil and gas occur in terrigenous deposits from the Cretaceous, Paleogene, and Neocene.

Ranges divided by deep depressions extend from the central areas to the southwest and northeast. The longest of them stretch to the southwest: Vetveiskii (elevations to 1,443 m), Pakhachinskii (to 1,715 m), Pylginskii (to 1,355 m), jutting out into the sea as the Goven Peninsula, and the Oliutorskii (to 1,558 m), forming the Oliutorskii Peninsula. The most important depression is the Vivenka, 200 km long and up to 40 km wide. Ranges running to the northeast include the Neprokhodimyi (to 1,450 m), Koiverlanskii (to 1,062 m), and luzhno-Main (to 1,265 m), which joins the basalt Main Tableland (Parkhanoi Plateau).

The relief is dominated by sharp ridges, steep slopes covered with moving rock debris, deep gorges, and glacial valleys formed by the intensity of recent tectonic movements and by glaciation. The region has a cold coastal climate, with cool summers and much fog, rain, and snow. In the winter there are strong winds and relatively mild frosts. Annual precipitation on the southeast slope exceeds 700 mm and on the northwest slope, 400 mm. The snowline occurs at altitudes of 1,400 m on the northern slopes and at elevations of up to 1,980 m on the southern. Contemporary glaciation covers an area of 205 sq km, with glaciers up to 4 km long descending to elevations of 1,000-700 m. Cold mountain deserts and tundras are widespread. Valley floors are covered with grass and shrub tundra, and Siberian dwarf pine grows widely at heights of up to 200 m in the north and 400 m in the south. Flood-plain forests with chosenea, poplars, and shrubs are occasionally found in river valleys.