Outburst floods of the Maly Yenisei. Part I
ABSTRACT The Yenisei, the largest river flowing to the Arctic Ocean, repeatedly hosted cataclysmic floods during the Pleistocene. The largest of the known floods likely originated from palaeolakes in northern Mongolia, at the headwaters of the Little, or Maly, Yenisei. These ancient floods are among the greatest known globally. They left giant gravel dunes and wide abandoned channels in the Kyzyl basin, and high terraces in the gorges upstream. However, few detailed field studies of the flood deposits and no measurements of their ages have been made thus far. The largest palaeolakes were impounded during major glaciations by outlet glaciers from the East Sayan ice field in southern Siberia. The shorelines suggest four distinct palaeolake depths of 290, 175, 145, and 65 m. The timing and location of the glacier impounding the deepest lakes are uncertain but at its maximum, the Tengis outlet glacier was likely capable of impounding the 175 m lake. The dating of glacial deposits in and around the basin reveals that the maximum late Pleistocene glaciers were during Marine Oxygen Isotope Stage (MIS) 3. The ages for deep lake sediments exposed in the basin behind the dam's location support this finding. During MIS 2 the Tengis glacier was large enough to impound at least the 145 m lake. However, the existence of a deep MIS 2 palaeolake in the basin has been challenged, because no evidence has been published of MIS 2 lake sediments from the cutbank outcrops and deep drilling cores. Additionally, the end moraines of the Tengis glacier, separated from the deeply eroded lateral moraines by the Maly Yenisei, remain undated; therefore it is uncertain exactly when this glacier crossed the river. This review is part I of a two part article; Part II presents new age data to constrain the ages of the glacial dam.