Geological structure and origin of the Islands
Unlike the Islands of Japan, where considerable areas are covered by ancient, crumpled in folds sedimentary marine rocks, and from Kamchatka, West and center of which are composed of marine sediments, sedimentary formations on the Kuril ridge are common only in the extreme North (North) and South (Shikotan) Islands; on the other they put a small area of lowlands and separate spots are found around the volcanoes, on the shores of the bays, mouths of rivers and on the terraces of the coast.
Ancient sedimentary rocks are usually more or less altered by the action of high temperature and pressure. The composition of their heterogeneous: there are shales, Sands, gravels, in some places the accumulation of limestone: the main Islands are composed of volcanic rocks. In addition to the lava, there are large areas of volcanic tuff, layers of ash and coarse-grained material, often cemented compacted ash or pumice.
In the distant past geological history of the earth, the sea covered the whole northeast Asia. Sometimes it receded, and in place of Kamchatka and the Okhotsk sea was drying up. Kamchatka and the Islands of Japan itself became part of the sushi into the second half of the tertiary period (middle Miocene) and was to the mainland of ASIA one. Sea of Okhotsk at this time it was a Bay of the ocean.
Now the bed of the sea of Okhotsk is separated from the bed of the Great ocean Grand ledge. The sharp change of depth to the West and to the East of the Islands is the result of a fracture in the earth’s crust and lowering of the bed adjacent to the Islands of the Great ocean. Split the earth’s crust occurred on the verge of the tertiary and Quaternary time. He was accompanied by outpourings of lava on the sea floor; a branch from the land of the larger Islands, a jumble of volcanic rocks and the formation of garlands of volcanic Islands, which restricted the “bowl” of the sea of Okhotsk. Magma, breaking through the thick marine sedimentary rocks, in some places lifted her and crushed.
The location of the Islands, the depths of the sea of Okhotsk and the ocean can be established that the main fault line of the earth’s crust was accompanied by parallel cracks and discharges a smaller scale. Basic fault line stretches the chain of Islands from Shumshu and Paramushir to Iturup and Kunashir. Several West of it runs a parallel line of fracture to the Islands of Atlasova and Antsiferov, it is accompanied by the East fault, along which stretched from the island of Shikotan until Nemuro Peninsula on Hokkaido island. The movement of the earth’s crust and the formation of Islands continued throughout the Quaternary period and has not ended to the present, manifesting itself in frequent earthquakes and volcanic eruptions.