Geology

Volcanic structures

A period of volcanic activity started 72 Ma ago in the Tunka area reaching a peak at the end of the Mesozoic and the beginning of the Cenozoic. Most of the volcanic structures in the Tunka valley were formed during this time. Interbedded layers of lava and unconsolidated sediments form deposits of 100-150 m thickness. In the middle of the Cenozoic (Oligocene) the volcanic activity in this area stopped. Until this time over 20 cones and hills of volcanic origin were formed and can still be found in this area. They are divided by their location into 3 groups, Kuntinskaya, Talovskaya and Hobokskaya.

(position of the three different types of volcanoes)

The hills and cones are not higher than 40 or 50 meters. The Black mountain which belongs to the Hobokskaya group is the highest one with an altitude of nearly 150 m above its surrounding. Its Russian name is Kovrishka. Another mountain of this subgroup is Hara-Hobok.

(Hara-Hobok)

Hara-Hobok was formed at the end of the volcanic period in the Tunka region. The outcrop shows lava flows, tuff and volcanic bombs. Hara-Hobok is reported to be one of the few volcanic hills with a visible volcanic crater. The outcrop we saw, however, did not look like a crater and the assumed depth of 4 km for the generation of a basic magma would be very shallow.
The last hill of volcanic origin we visited is part of the same group and has a similar age but no crater to look at.

(hills of volcanic origin)

For Shamans this hill is a sacred place. After a layer of basalt with a very big thickness was formed there was an uplift of the mountains around. This layer is nowadays the central part of Khamar-Daban. The layer is 500 m thick and covers an area of over 3000 km². This layer of volcanic material caused a subsidence of the Tunka area which started in the Mio- and Pliocene and continues up to today. But there are also other hypothesis for the formation of volcanic structures in the Tunka area. One idea you can read at the homepage of the global volcanism program moderated by the Smithsonian Institution in Washington D.C.: “The Tunkin Depression volcanic field (also known as the Tunka Depression) covers a broad area immediately west of the SW tip of Lake Baikal. The Khobok group of basaltic cinder cones near the village of Tunka, one of five groups of cinder cones characterized by some sources as late-Pleistocene to Holocene in age, has the largest concentration of vents. Drill cores show that the upper 500 m of the basin is filled with Quaternary tuffs and a dozen lava flows; subsidence continues, partially burying volcanic features. Other well-preserved cinder cones of probable Pleistocene age are located to the SE in the Khamar-Dayan Range. The youngest cinder cones and lava flows are in the NE part of the Tunkin Depression. The age of the latest eruptions has variously been considered to be Pleistocene-to-Holocene or late-Pleistocene” Summarizing that all at least two periods of volcanic activity seem likely.

top