Geomorphological Indication of the Regime of Neotectonic Movements

The regime of neotectonic movements shows up most vividly in the land‐sea contact zone where unique topographic elements—river deltas—are formed. The volume of river drift is one of the key factors of delta formation. The drift is represented by drawn, suspended, and dissolved substances deposited at river mouths as the water flow velocity decreases. According to the laws of hydrophysics, all large rivers form deltas at the mouth, the dimensions of which are comparable to the volume of alluvium drift. It is common knowledge that few rivers form classic lobate deltas. These are the Mississippi on the American continent; the Niger and Nile in Africa; the Rhine, Danube, and Po in Europe; the Indus, Ganges, Yangtze, Red (Songka), Mekong, and Irrawaddy in Asia; and the Volga, Lena, and Selenga in Russia. For comparison purposes, it should be noted that rivers such as the Amazon, Congo, Orinoco, Yenisei, Ob, and Amur, among others, lack analogous landforms despite the tremendous volumes of material evacuated to the oceans, and, in the best case, their river valleys end in vast coastal plains [1]. It may be inferred that deltas are developed in older rivers, which have carried a great volume of sediments to the mouth over the period of their existence. In the Northern Hemisphere, the age of a river network depends on the Last Glaciation, which affected significantly the formation of it. Although the Ob, Yenisei, and Lena are of postglacial age, nevertheless, their mouth endings are of different shapes. Of particular significance is the structure of the underwater part of the mouth seashore. At a high steepness of adjacent slopes, the alluvial material fails to accumulate and sinks into the depths to form open mouths [2].