Morphodynamic development of the Terkhiin Tsagaan Lake Depression, Central Mongolia: Implications for the relationships of Faulting, Volcanic Activity, and Lake Depression Formation

Data on the origin and morphology of lake depressions caused by volcanism are scarce in Mongolia. Previous studies focused on climate change patterns based on Terkhiin Tsagaan Lake sediment. We present a result of existing reconstructions of lake depression development and changes in the hydrology system during the Khorgo volcanic activation and the Holocene environmental change. A depression of the Terkhiin Tsagaan Lake is formed by a lava flow barrier from the Khorgo volcano. However, the Khorgo volcanic eruption and the lake depression that could shape a large lake have arisen instead from a fault. The morphometric analysis and field measurements indicate that the derivation of the Terkhiin Tsagaan Lake depression and Khorgo volcano may have evolved from movement on a sinistral strike-slip fault, which is about 70 km long. The southern mountains and rivers were displaced from northwest to southeast along the Terkh Fault. The offset along Terkh Fault is 4.02–5.28 km in the depression of the Terkhiin Tsagaan Lake. After movement, a wide valley of the Terkh River developed in the present landscape. The active Khorgo Volcano formed along the Khorgo Fault. The Terkhiin Tsagaan Lake is formed by blocked water from the Paleo-Terkh River after lava damming from the Khorgo Volcano. The initial paleo-lake area was about 195.7 km 2 , which was three times larger than the modern lake. The current water volume of the Terkhiin Tsagaan Lake is 0.351 km 3 while the volume of the paleo-lake was 2.248 km 3 . Based on this volume indicator the paleo-lake was 6.4 times larger than the current lake. Overflowing water from the lake depression formed the Suman River by a drying canyon through the lava plateau, but the canyon is along the Terkh Fault. Changes in the water volume of Terkhiin Tsagaan Lake and erosion of Suman River canyon are inversely related to each other. We present the morphometric relationships between the lava plateau of Khorgo Volcano and development of Terkhiin Tsagaan Lake depression.