Tunkin Depression

Tunka Range to the north and by the Khamar-Daban mountains to the south.^[1] The history of the Baikal Rift begins in the Mesozoic, when intracontinental extension took place at the rift. In the Cenozoic, rifting proper commenced generating basins that were filled by sediments and basaltic volcanism. The causes of the rifting are unclear and may involve either tectonic effects of the India-Asia collision, mantle plumes and asthenospheric processes.^[2]

Tunka and is named the Khobok group.^[3] The highest of these volcanoes is Khara-Boldok or Ulyborskiy, which is 125–120 metres (410–394 ft) high. This cone further features a 90–85 metres (295–279 ft) wide crater. Four other groups of volcanoes are found in the Tunkin Depression.^[4]

lava flows and tuffs.^[4] Subsidence is still occurring,^[3] and the volcanic cones are consequently lowering; one of the cones now rises only about 6 metres (20 ft) above terrain.^[1]

potassium-argon dating of some cones has yielded several ages, including 1.58 ± 0.14 million years ago and 700,000 ± 400,000 years before present.^[2]