THE SHORELINE MORPHOLOGY OF THE QUATERNARY LAKE CHUJA-KURAY, ALTAI MOUNTAINS, SOUTH-CENTRAL SIBERIA

A temporal series of large lake(s) formed in the Quaternary within the Chuja-Kuray Basin of the Altai Mountains in Siberia due to glacier dams blocking the drainage. Variations in the drainage through and over the ice, coupled with variation in meltwater supply and evaporation at the lake surface, ensured rapid and repeated lake level fluctuations. Consequently, the margins of the basins exhibit multiple and often complex palaeo-shorelines. Several processes control the development of shorelines. The main factors are: wind-wave regime, water level fluctuations, sediment supply, geology, tectonics, and the local geomorphological history of the basin. The shorelines are on bedrock, moraine, river terraces and fans which formed in earlier periods and which were active or morphologically stable when the shorelines developed. As water level rose, or fell, shorelines were inundated or abandoned. In the first case the shorelines could be preserved, albeit with morphological modification, by processes acting below the wave base. Abandoned shorelines could be modified by sub-aerial processes but were preserved. Pre-existing shorelines were cut into by later shoreline development. Shoreline building is determined by the fetch and the direction of the prevailing winds. The NW-SE extension ensured (during periods of maximum lake level) a fetch of 70 km in the Chuja and 30 km for the Kuray Basins. North-Easterly winds dominated and were funneled to the SE by basin topography, developing NE wave trains. Dominate wind direction is confirmed by strong strandlines on the W, SW and SE sides of the basin, where longshore drift was N to S. For high-stand lakes, the glaciers terminated as floating ice which calved. Ice-berg evidence are groups of drop stones. These are large (>8m) with well defined glacial striae. Abrasion, abrasion-accumulative and accumulative shorelines have been identified. Of these the latter are impressive and often complex, including spits, tombolas and barrier-beaches enclosing ‘lagoons’. Length of individual barriers are up to several kilometers, whilst heights vary from 5 to 8 meters with widths of 30 to 40 meters. The beaches consist of sands and gravels and the internal structure was locally revealed through excavation and GPR survey.