Lake Issyk Kul: Neotectonic deformation of (paleo-) shorelines and their link with intermontane basin closure and lake-level fluctuations
Final Report Abstract
Lake Issyk Kul in northern Kyrgyzstan is a potential ICDP drilling site to examine the climatic and erosional history of Central Asia over the past few Myr. Shorelines and lacustrine deposits furnish ample evidence for major lake-level fluctuations during the Quaternary, and help identify transient fluvial connectivity with other basins and overflow conditions, which are paramount for correctly assessing changing environmental conditions in the lake basin. These phenomena furnish premier geomorphic reference horizons that are ideally suited to record deformation associated with repeating earthquakes and may thus offer insight into tectonically forced short-term variations in sedimentation rates in the lacustrine system. The E-W elongated Lake Issyk Kul occupies one of the many intermontane basins in the Kyrgyz Tien Shan, a seismically active intra-continental orogen in the interior of Central Asia. Located at an elevation of 1607 m, the present-day lake is situated within an internally drained basin, surrounded by reverse-fault bounded mountain ranges with peaks exceeding 4000 m elevation. The major aim thus was to quantify shoreline deformation by remote sensing and high-resolution field measurements, accompanied by dating of associated marker horizons. Special emphasis was given on events and mechanisms responsible for basin closure and changes in fluvial connectivity of the lake system, recorded in the stratigraphy and geomorphology of the western lake outlet. The main objectives have been divided into two subprojects: (1) Lake level history and link to connectivity and potential outburst floods and (2) local and regional shoreline deformation. Together with my cooperators, we found that (1) one or several catastrophic floods occurred through the Boam gorge in the late Pleistocene. A temporal succession of Issyk Kul’s lake-level drop and boulder deposition at the outlet supports a link between both. Palaeoflood modeling, however, shows that catastrophic lake outbursts unconnected to Issyk Kul could have also produced the necessary peak discharges for moving the boulders at the gorge exit. Although the overall geomorphic and sedimentary evidence around Issyk Kul records some of the largest catastrophic outburst floods in the Tien Shan mountains, if not Central Asia, direct links to documented lake-level changes of Issyk Kul remain elusive. (2) The surface of lake Issyk Kul does not reflect a flat geoid/equipotential plane, perhaps from the strong gravity gradient between the shore and the adjacent high-relief mountains. This issue directly influences our regional, i.e. basin-wide, shoreline correlation because it incorporates a non-linear error of a few tens of centimeters. We look, however, for subtle tectonic signals, i.e. local or regional deviations from a mean elevation for a given shoreline in a similar order. We still work on the best solution and plan to finalize the analysis within the first half of 2017.
Publications
- 2017. Late Pleistocene outburst floods from Issyk Kul, Kyrgyzstan?, Earth Surface Processes and Landforms
Swenja Rosenwinkel, Angela Landgraf, Oliver Korup, Wolfgang Schwanghart, Friedrich Volkmer, Atyrgul Dzhumabaeva, Silke Merchel, Georg Rugel, Frank Preusser
(See online at https://doi.org/10.1002/esp.4109)
