Herlen

Course

The river originates in the south slopes of the Khentii mountains, near the Burkhan Khaldun mountain in the Khan Khentii Strictly Protected Area, about 180 kilometres or 112 miles northeast of Ulaanbaatar. This area constitutes the divide between the Arctic (Tuul River) and Pacific (Kherlen, Onon) basins and is consequently named "Three River Basins".

From there the Kherlen flows in a mostly eastern direction through the Khentii aimag. Further downriver, it crosses the eastern Mongolian steppe past Ulaan Ereg and Choibalsan, entering China at 48°3′N 115°36′E and emptying into Hulun Nuur after another 164 kilometres or 102 miles.

The mean streamflow of Kherlen River has decreased by more than a half from 2000 to 2008 when compared with prior decades.

Soda lakes, uranium and associated geology

in basins formed in basalt, pyroclastic material and rhyolite erupted from the Choibalsan–Onon volcanic chain during the late Cretaceous; among these lakes are the Tsaidam lakes, the Gurvany lakes and the Shar Burdiin lake.

The groundwater that feeds the soda lakes comes from a shallow unconfined aquifer recharged by rainfall and snowmelt, and from precipitation in the highlands north of the lakes. But the local climate is semi-arid, with only 207 mm mean annual precipitation distributed unequally throughout the year. This means that groundwater recharge is relatively rare: only the largest precipitation events and snowmelt periods result in significant recharge.