Late Holocene Debris Flows and Valley Floor Development in the Northern Zailiiskiy Alatau, Tien Shan Mountains, Kazakhstan

ABSTRACT This study uses geomorphological, dendrochronological, and archival research to investigate the pattern, chronology, and sedimentology of debris-flow deposits in two reaches of the Zailiiskiy Alatau range of the Tien Shan mountains, Kazakhstan. Steep and narrow low-order tributary valleys in this environment promote rapid coarse sediment transfer to trunk streams and, in wider trunk valley reaches, locally result in development of debris-flow assemblages and terraced sequences of coarse-grained fluvial sediments. Since the mid-19th century the region has experienced 23 documented large-scale debris flows, including 14 in the study area, and these coincide with a period of climate warming. The majority of recorded events are attributed to the failure of moraine-dammed lakes, while the remainder were triggered by intense summer rainstorms. Landform-sediment assemblages investigated here have extended the documentary record by identifying at least 6 major debris-flow assemblages dating respectively ...