of trees near the Podkamennaya Tunguska (Stony Tunguska) in central Siberia. Most scientists believe this resulted from the air burst of a meteor or a comet. Even though no crater has ever been found, the landscape in the (sparsely inhabited) area still bears the scars of this event. Soviet Union In the early decades of the Soviet Union (especially in the 1930s and 1940s), the government used the Gulag state agency to administer a system of penal labour camps, replacing the previous katorga system. According to semi-official Soviet estimates, which did not become public until after the fall of the Soviet government in 1991, from 1929 to 1953 more than 14 million people passed through these camps and prisons, many of them in Siberia. Another seven to eight million people were internally deported to remote areas of the Soviet Union (including entire nationalities or ethnicities in several cases). Half a million (516,841) prisoners died in camps from 1941 to 1943 during World War II. At other periods, mortality was comparatively lower. The size, scope, and scale of the Gulag slave-labour camps remain subjects of much research and debate. Many Gulag camps operated in extremely remote areas of northeastern Siberia. The best-known clusters included Sevvostlag (the North-East Camps) along the Kolyma and Norillag near Norilsk, where 69,000 prisoners lived in 1952. Major industrial cities of Northern Siberia, such as Norilsk and Magadan, developed from camps built by prisoners and run by former prisoners. Geography Siberia spans an area of , covering the vast majority of Russia's total territory, and almost 9% of Earth's land surface (). It geographically falls in Asia, but is culturally and politically considered European, since it is a part of Russia. Major geographical zones within Siberia include the West Siberian Plain and the Central Siberian Plateau. Eastern and central Sakha comprises numerous north–south mountain ranges of various ages. These mountains extend up to almost , but above a few hundred metres they are almost completely devoid of vegetation. The Verkhoyansk Range was extensively glaciated in the Pleistocene, but the climate was too dry for glaciation to extend to low elevations. At these low elevations are numerous valleys, many of them deep and covered with larch forest, except in the extreme north where the tundra dominates. Soils are mainly turbels (a type of gelisol). The active layer tends to be less than one metre deep, except near rivers.