Geomorphological structure and neotectonics of the Lena delta

Abstract

New data about geomorphological structure and neotectonic movements of the Lena Delta is presented. Thet are based on results of the Russian-German expeditions Lena-2013, Lena-2014, Lena-2015 and Lena-2018 and include geomorphological profiling with high quality satellite instruments and a number of radiocarbon dates on the Sobo-Sise, Kurungnakh, Jangylakh-Sis and Khardang-Sise islands. These islands consist of the Late Pleistocene Ice Complex (IC) remnants eroded by river and sea, and the first terrace of the Delta, which adjoins the remnants. The first terrace started to form 8,000 years ago in the western part of the Delta and was finally formed in the last millennium in the eastern part of the Delta. From the previous works, it is known that the western part of the Delta is higher than the eastern part. In our work, we explain it by the eneven movements of the Earth’s crust in this region. The aim of the paper is to study the quantitative characteristics of the tectonic movements in the Lena River Delta. For this purpose we present the geomorphological schemes and descriptions of the islands mentioned and compare the terraces heights in the different parts of the Delta. In the Late Pleistocene, according to the heights of the IC remnants, the western part of the Delta rose 1 mm per year faster than its eastern part. In the Holocene the speed difference increased to approximately 2 mm per year, which is shown by the terrace surface’s altitude. The amplitude between the western and eastern parts of this surface is about 4 m. Finally, according to 60-years observation period of the water level in the Laptev Sea, the modern speed difference of the western and eastern parts movement in the Lena Delta is 2 mm per year. As a result, we can observe changes in the main flow direction in the Delta channels from the Olenekskaya branch at the beginning of Holocene to the Bykovskaya branch today.