ИСТИНА

Ice gouging is destructive mechanical impact of ice on the underlying ground surface associated with ice cover dynamics, ice hummocking (ridging) and formation of grounded hummocks (stamukhas) under the influence of hydrometeorological factors and coastal topography. Climate change and anthropogenic influence can cause changes in conditions of ice scour formation. Shallow freezing seas and big lakes are most vulnerable to such changes. Studying of the ice scours’ parameters has a great economic and fundamental importance. In the present study, results of the first investigations of recently discovered ancient ice gouging forms on the exposed bottom of the Aral Sea are presented. Using remote sensing data interpretation, we measured the parameters of ice-gouging topography of different morphology at the former Aral Sea bottom. The ice scours range from 2 to 50 m wide (10-12 m on the average) and from 200 m to several km long (0,5-1 km on the average). They mostly concentrate at former depths from 15 to 25 m in relation to the 53-m base elevation, at which the lake level was situated when the shallowing started. Estimating the exact position of the zone with the most intense ice effect on the bottom of the disappearing Aral Sea still remains a challenge. However, we found out that in similar conditions of the Caspian Sea with its fluctuating level, the most intense ice gouging occurs at depths of 2-5 m. Based on this finding and on the known position of the lowering Aral Sea shoreline in time, we estimated the formation time for separate scours. It was revealed that the majority of ice scours formed on the Aral Sea bottom from 1980 to 1997, as this giant lake was drying up. Ice scours cover up to 100 % of former Aral Sea bottom confirming the presence of intensive ice gouging in shallow freezing seas and lakes and its intensification due to water level fluctuation.