THE ORIGIN OF GIANT DUNES IN THE KURAY BASIN (SOUTHEASTERN GORNY ALTAI) BASED ON MORPHOMETRIC ANALYSIS AND GPR STUDIES; [О ПРОИСХОЖДЕНИИ ГРЯДОВОГО РЕЛЬЕФА КУРАЙСКОЙ КОТЛОВИНЫ (ЮГОВОСТОЧНЫЙ АЛТАЙ) В СВЕТЕ МОРФОМЕТРИЧЕСКИХ И ГЕОРАДАРНЫХ ИССЛЕДОВАНИЙ]

New data on the mechanism of giant dunes formation in the Kuray Basin of the Gorny Altai has been obtained in the Kuray dune field on the right bank of the Tjute River. We analyzed its morphology from remote sensing data (satellite images and UAV) and the internal structure of dunes with ground-penetrating radar. The morphometric indices: dune lengths and distribution of special points of the Kurai dune field were statistically compared with indices for dune landscapes of different genesis: cata-fluvial dune field near Lake Missoula (USA), ribbed moraine in southern Scandinavia, Baer knolls of Northern Pre-Caspian, Yenisei flood ridges, riverbed ridges of Tapi River, India, and erosion patterns of Loess plateau in China. In terms of the statistical distribution of morphometric parameters, the Kuray dune field is close to the dune fields formed by water streams and strikingly different from moraine and erosional landscapes. Their internal structure, which was determined by ground-penetrating radar data, is also typical of channel dunes on river beds: one or more oblique-layered strata with a dip in the stream flow direction are unambiguously identified in the cross-sections. The results obtained allow us to finally confirm ridge formation to be a result of a powerful water flow apparently formed by the descent of a subglacial lake occupying the Kuray Basin. New details of the dune formation mechanism have been established. The relationship between dunes' size, internal structure and the altitudinal position at the bottom of the basin, points to the dependence of their formation on the depth of the flow. At shallower depths (southern part of the Kuray dune field), small dunes composed of a single laminated package (one pulse of motion) were formed; at greater depths (the northern part), large ridges composed of several laminated packages (several pulses of motion) were formed. The height difference between the southern and northern periphery of the dune field is about 80 m. For the difference less than 80 m to be significant for the dune formation, the average flow depth should not have exceeded 200-300 m, i.e. dune formation occurred closer to the end of the lake descent. Our study for the first time establishes the presence of packages with the reverse direction of layering within large dunes in the northern part of filed. This fact indicates the possibility of reversible flow movement at the final stage of dune field formation. This indicates an increase in the instability of the current, the appearance of its rapid multidirectional pulsations at the last stage of lake drainage. © 2022 Russian Academy of Sciences. All rights reserved.