No 4 (2019)

Mountains are topographic features caused by erosion after vertical uplift or ‘mountain building’. Mountain building is often confused with ‘orogeny’, which today means the formation of structures in fold belts. The common assumption that folding and mountain building go together is generally untrue. Many mountains occur in unfolded rocks, granites and volcanic rocks, so there is no direct association of folding and mountain building. In those places where mountains are underlain by folded rocks the folding pre-dates planation and uplift. The age of mountains is therefore not the age of the last folding (if any) but the age of vertical uplift. Since mountains are not restricted to folded rocks, lateral compression is not required to explain the uplift.

A compilation of times of uplift of mountains around the world shows that a major phase of tectonic uplift started about 6 Ma, and much uplift occurred in the last 2 Ma. This period is known as the Neotectonic Period. It is a global phenomenon including mountains on passive continental margins, and those in deep continental interiors. Several hypotheses of mountain building have problems with this timing. Some fail by being only able to make mountains out of folded rock at continental margins. Many translate the vertical uplift into lateral compression, but vertical uplift alone can create mountains.

The Neotectonic Period has important implications for geomorphology, climate and global tectonics. In geomorphology it does not fit into conventional theories of geomorphology such as Davisian or King cycles of erosion. Neotectonic uplift might initiate several cycles of erosion, but most planation surfaces are much older than the Neotectonic Period. The increasing relief associated with Neotectonic uplift affected rates of erosion and sedimentation, and also late Cenozoic climate.

The Neotectonic Period does not fit within plate tectonics theory, in which mountains are explained as a result of compression at active margins: mountains in other locations are said to have been caused by the same process but further back in time. This is disproved by the young age of uplift of mountains in intercontinental and passive margin positions. Subduction is supposed to have been continuous for hundreds of millions of years, so fails to explain the world-wide uplifts in just a few million years.

Geomorphologists should be guided by their own findings, and refrain from theory-driven hypotheses of plate collision or landscape evolution.

The main focus of the article is the significance of the geomorphological method for the reconstruction of paleogeographic events that took place in the Late Pleistocene and Holocene. The specific data obtained as a result of applying this method are given. A reasonable curve of the Caspian Sea level fluctuations in the Holocene was compiled. A “risk zone” has been defined, within which the level of the Caspian Sea will fluctuate in the future, under modern physics-geographical conditions, which is fundamental importance when planning any economic measures in the coastal zone. Predictions were made and later justified of the Caspian Sea level fluctuations in the 20^th–early 21^st centuries. The climatic nature of the Caspian transgressions was confirmed. Obtained were new data on the evolution of the shores of the Caspian Sea under rising level conditions, which can be used when forecasting the development of the shores of other seas in the conditions of the present-day rise of the World Ocean level.

Central part of Narva bay is characterized by accretive coast, which is formed due to the presence of significant volumes of sand deposits. In the paper, the current state of coastal relief was analyzed and the forecast of its evolution under the prevailing wave climate was performed. The problem of the equilibrium of the coastal morphosystem for a given sediment budget and the probable trend of relative sea level was considered. Morphodynamic forecast for the period of the next decades was justified for designing the crossing of the coastal zone by the main pipeline route. Increasing of the role of accumulation processes from the south to the north has been identified through the field survey and analysis of satellite images, and has been shown by the nature of the beach relief and the underwater coastal slope. The calculation of the longshore sediment drift revealed the existence of a convergence zone for two differently directed sediment flows. Convergence of the sediment flows leads to accumulation of sand deposits at the rate of 19.0 m³ per one running meter per year. Estimates of the sediment budget resulted in the estimation of the accumulation rate at 8 m³ per one running meter per year in the coastal zone of area of the pipeline route. Sand accumulation leads to coastal accretion at the rate of 1 m per year. The obtained results lead to the conclusion on the stability of the coast in the coming decades unless the change of the sources of sand sediments and tendencies of its transport.

The bottom topography of the studied area of the South China Sea is characterized by an uneven distribution of depths, their sharp variations and the presence of a large number of seamounts. As a result of the research conducted, bathymetric profiles, a bathymetric map and a scheme of Faye anomalies were compiled. Geomorphological zoning was conducted. Sections of bottom distinguished by morphology were identified: 1) weakly dissected slope, steep (angles up to 15°) in the upper part and more gentle (5–7°) to the bottom of the deep-water step, 2) slope eroded by fluvial processes, 3) stepped slope, 4) chains of mountains and flat-topped hills, 5) accumulative bottom of the deep-water plain. It was established that the gravitational field as a whole reflects the complex structure of the bottom, and the local forms of the underwater relief are expressed in Faye anomalies. For elevations, zones of positive anomalies of Faye are marked, and sections of canyon-like valleys were mapped by an intense negative anomaly of the gravitational field to -60 mGal. In the process of endogenous evolution of the region, the relief became more complex. The primary endogenous continental slope was almost everywhere transformed by exogenous processes. Within the shelf, the filling of the basin led to the unification of all its projections into a single raised base. A significant role in the formation of the modern relief was played by large-scale repeated sea regressions, as a result of which the formation of the sedimentary cover was interrupted by periods of its erosion with the formation of planation surfaces. The Late Pleistocene peak of the regression (16–18 thousand years BP), which caused the complete drainage of the shelf areas of the region, caused the erosion of the shelf and the movement of coarse clastic material through submarine canyons and valleys.

The article is devoted to a detailed morphogenetic analysis of erosion topography of the right Volga river bank (Volgograd region, Russia). The estimation of the factors in the development of erosion processes: lithological, geomorphological, climatic, biotic. It is established that the general trends of the development and the propagation of gully systems depend on the zonal conditions, and their specificity — from structural-lithological and geomorphological features of the area. The actual basis for the work, based on data from field observations, interpretation of satellite imagery, morphometric processing of topographic maps. The obtained results were used for compiling maps, morphometric characteristics of the relief and zoning of the right bank of the Volgograd city according to the intensity of erosion processes. It was established that the studied area is among the most erosion-affected territories in the European part of Russia with the average erosion density of the network from 0.1–0.3 up to 3–4 km/km². Comparison of factors determining the intensity of the evolution and morphology of gully systems led to the conclusion that modern intensification of erosion is the result of economic activities.

Examples of relief studies by seven prominent Russian soil scientists, representatives of the Dokuchaev school, are presenterd. Geomorphological issues, ideas and concepts in the works of soil scientists of the XX century. showed their high professional interest in geomorphology. The beginning of the geomorphological research of Russian soil scientists was laid by the great Russian researcher V. V. Dokuchaev. Geomorphological views of V. V. Dokuchaev were ahead of the V. M. Davis' concept of the geographic cycle. Soil-geomorphological studies of S. S. Neustruev partially supplemented the concept of V. M. Davis. B. B. Polynov proved the necessity of attracting geomorphological methods and techniques when conducting soil studies, used geomorphological principles in the deduction of the three laws of the distribution of weathering crusts. I. P. Gerasimov created the theory of morphostructure and morphosculpture, introduced the idea of three macrocycles in the history of the formation of the Earth's landscapes. All the researchers cited in the article conducted detailed complex studies using geodesy methods. Scientists were able to identify a large array of new geomorphological data from the classification of microrelief to the adjustment of the main laws of geomorphology. The main feature of the scientific activity of Russian soil scientists-geomorphologists was the Dokuchaev school that gave rise to all them. It was from the Dokuchaev's principles and approaches that the mentioned scientists started and developed and passed to their students and followers. The well known Russian soil scientist and geomorphologist I. P. Gerasimov completed the century-long period of the geomorphological studies by soil scientists started by V. V. Dokuchaev.