Rivers in the North of Yakutia: what Determines the Destruction of the Frozen Banks

Northern Yakutia is characterized by continuous permafrost with a thickness of 300–400 m or more with temperatures from –6 to –10°C. The occurrence of permafrost affects the rates of thermal erosion and thermal abrasion of river banks. Many investigators believe that permafrost inhibits fluvial erosion, while others think it has an enhancing effect. Our investigations along the lower reaches of the Indigirka, Adycha, and Kolyma rivers have shown that the effect of permafrost varies depending on site specific conditions. The highest rate of thermal erosion (60 m/year) was observed in the Lower Indigirka region. This was promoted by the high ice content of the yedoma deposits, the presence of a talik beneath the channel, as well as the great water depths and strong currents. Bank recession along the meandering Adycha River, the Yana River tributary, occurs at rates of less than 1 m/year. The low rates of bank erosion can be explained by the low thickness of loose deposits (up to 3–5 m), which lay on the channel pebbles and generally remains above the low- and medium-water levels. Also, the coastal cliff deposits consisting of silty sand with a massive cryostructure and thin ice veins turned to be relatively resistant to erosion.

permafrost, river, coast, thermal erosion, thermoabrasion, thermokarst, coastal plain, yedoma upland, ice veins, cryogenic texture