Общетеоретические статьи
Terraces of the mountain rivers are an important source of mineral products and paleogeographic information. To reveal the terraces and give their precise description the genetic approach is suggested. According to such an approach the cycle terraces are the remnants of equilibrious bottom of the river valley. Knowing the regularities of the bottom structure helps to distinguish their important morphologic elements spreading to terraces - the surface of the former high floodplain and over-talweg step or the bed. They both represent intermediate and ending equilibrious profiles of the corresponding erosion cycle and have horizontal cross-sections. Usually they are buried under deposits on the terraces but their connections with certain lithofacies allow to determine their position in the geologic sections. Realization of the genetic approach is expensive but it should paid off due to resulting possibility of the higher accuracy of the river valley development reconstruction.
The mechanism of the islands and island clusters movements is suggested. The velocity field and circulating flows usually lead to washing of their upper part and to formation of spits in their tails which result in the island's displacement. If the sediment run-off exceeds carrying capacity of the river, then backwater due to the island existence causes accumulation at the upper part of the island and its regressive displacement. Symmetrically braided river bed expresses directional development of the bed deformation (the sediment accumulation and the bottom level rising). Regressive displacement often is manifested in the formation of midstream sandbank upstream the island due to water surface inclination. The backwater appears at some distance from the head of the island and the flow is directed to the one or another braid during different phases of a regime. These flow are carrying sediments out from under the ridge, determine the midstream sandbank stabilization, and prevent its coming onto the island. Localities of the island's regressive movement were determined: in the periphery of the bed, in the zones of backwater upstream the confluence, before the valley bottom narrowing, downstream the local sources of sediments influx. Conditions of island stabilization depend on the meanders formation in the braids circumflexing the island, geomorphologic limitations (transition from the wide flood-plain to incised river-bed, constraints by bedrock coast promontories), transition from the braided bed to the wandering or relatively rectilinear not braided one. The meander bars and midstream sandbanks consecutive coming on to the point of braiding from the upstream reach is also significant.
Экологическая и прикладная геоморфология
The presence of the frozen grounds on the coasts including the barrier lagoon ones, thermo-abrasion observed on some sites, the presence of shore ice and icings lasting up to the end of May, allow to consider the shores of the north-western and eastern Sakhalin as subarctic type. It was determined that during last 50 years more than 15 км 2 of accumulated plain was lost as a result of shore erosion only in the north and south-east of Sakhalin Island. The spatial structure of erosion has existed in its general outline since the 1930s. Since 1940 the extension of eroded shores has enlarged nearly two times. The spatial rhythms of erosion with wave length about 30 and 60 km determine the main regularities of shore erosion pattern. The formation of non-uniformity of beach structure and accordingly the irregular distribution of its wave- decreasing properties along the shore were considered. On the seashore of Sakhalin more than thirty sites were found, where quasi-rhythmic forms of shore relief were observed. But all the deformations of underwater relief were observed only in the frames of rated close depth. The special attention was devoted to the changes of wave-suppression characteristics of the beach during beach deposits freezing and under the open sea influence. The freezing of the 40-50 cm of the upper parts of shore profile and decrease of wave-suppression characteristics (mainly drainage and roughness), caused by this, occurred during this period before the formation of the shore ice and icings (1.5-2 months). According to the observations the height of swash zone increases by 30-45%. The calculations showed that the height of wave run-up for bank slope of storm bar may increase owing to freezing by 2-2.5 times.
Urbanization, industrial, agricultural and recreational land development actively transform landscapes in the Astrakhan region. First of all, the processes of land development affect the relief of the area, and properties of rocks and unconsolidated sediments (physical-mechanical, chemical, toxicological, microbiological, radiological etc.). Environmentally hazardous changes in geomorphological conditions in the region are associated with deflation, suffosion, landslides, wave erosion and water erosion, pollution of soil, pasture and recreational digression of the landscape. Changes of geomorphological conditions take place due to natural, anthropogenic, mixed effects, including techno- and biogenic processes. Special concern is paid to transformation caused by the influence of wind and water flows, as well as the “new factor” - organized but mostly disordered activity of different kinds of tourists. Thus, erosion threatening area reaches 2031 10 3 hectares, and deflation affects 29% of these areas. The annual number of tourists reaches 1.8 million people, most of which are spontaneous tourists. At one of the test sites on the beach of Volga-Akhtuba floodplain annual weight of waste from such activity amounted to 94 kg/hectare, and the amount of the people on the beach reaches up to 50 per 10 m along the shore. Damage can be reduced by a scientifically grounded environmental management.
An assessment of the sediment spatial redistribution on two facing slopes of the site Gracheva hollow (Kursk region) was fulfilled. Soil-morphologic method, magnetic tracers, radiocesium dating, LISEM, and physical- statistical empirical model were used. By the complex of field methods related to different time intervals (150, 140 and 21 y.) regularities associated mainly with the influence of slope morphology on the sediment runoff and redeposition were obtained. On the dispersing convex slope all field methods showed wave-like alternation of the accumulation and wash-out, which manifests in and is augmented by the microrelief elements. According to the three field methods the value of the intra-slope accumulation ranges from 11% to 79% of the total dislodged material value; the mean value reaches 35% (with the use the erosion models calculations). On the straight convex slopes zones of alternation were not observed; accumulation close to slope bottom, revealed by soil-morphologic method and magnetic tracers, is connected with the changes of the low boundary of ploughing during agricultural exploitation. The calculated rates of sediment redeposition obtained with the erosion model LISEM helped to evaluate with sufficient validity the total wash out from the slope and to determine zones of sediment redestribution along the strike of the slope. The physical-statistical model also describes well the peculiarities of this process but gives less values of intra-slope accumulation than LISEM.
Научные сообщения
The aeolian-accumulative complex Sarykum is the biggest in Russia and one of the highest isolated sandy landforms in Eurasia with total area over 2500 ha. It is the whole system of sandy knolls and dunes, ridge sands located in the NE Caucasus foothill within the Terek-Sulak plain, 16-17 km towards NW of the Makhachkala City seaport (Republic of Daghestan, Russia). The origination and age of the sands, of which Sarykum massif has been formed, are still a big mystery. The existing hypotheses of the Sarykum sands genesis from those that considered the Sarykum as a relic phenomenon of the vast Central Asia deserts, widely stretched along the Caspian lowland, to aeolian versions explaining the origin by wind transportation from the Central Asia’s sandy deserts (namely the Karakums) across the Caspian Sea, or by weathering of indigenous sandstones composing the Foothill Daghestan and/or the loose pebble-clay- sandy deposits of high marine terraces of the Caspian Sea) are described and critically evaluated in the paper. Also the critical assessment to coastal-marine and relatively exotic volcanogenic versions is made. However, despite the different scientific validity of most of these hypotheses, none of them cannot convincingly answer the simple question: why did it happen here on the banks of the Shura-Ozen’ River, at the site of the river’s exit from the Foothill Daghestan to the Caspian lowland? The author puts forward its own version of the sands genesis: originally, prior to their partial aeolian transformation, the Sarykum sands were the deltaic deposits of the Shura-Ozen’ River. The denudation area which supplied the sand material to the delta was the river basin upstream from the Kapchugay gorge of the Narat Tube ridge. According to one of the possible scenarios the sandy accumulation occurred in one of the stages of Late Pleistocene glaciation (presumably during the high Caspian transgression - the Early Khvalyn’ marine palaeobasin, around 30-20 ka BP) under favorable conditions for intensive periglacial denudation of the sandstones of the ridge and deltaic sandy sedimentation. According to another version of the hypothesis the Sarykum sands are deltaic formation of the Late Khazar (Caspian) transgression epoch (around 120-75 ka BP).
The existence of the relict spillway connecting Age Vitim basin with the Nercha river valley in the Pleistocene Ice is reasoned. The spillway was formed by the runoff from the ice-dam lake in the Vitim River valley over the continental divide. Ice-dam reservoirs were formed in the Taz, Muruktinsk, and Sartan glacial epochs with the levels of 900, 880, and 860 m respectively. Formation of the terraces of the Vitim with the relative heights up to 50 m, 10-12 m, and 6-7 m took place in the Shirtinskoye, Kazantsevskoye, and Karghinskoye interglacials respectively. Runoff from dam lake into the Nercha valley increased its catchment area from 27 600 km 2 to 201 600 km 2. Multiple increase of the runoff resulted in the development of new longitudinal profiles of the river valley and in the formation of the erosion terraces during each glaciation. Sedimentation analysis, chronological, and palynological methods were used.
Mapping and regional analysis of the “geomorphological tension” were made for the territory of the central fragment of the continental margin mountain system of the Andes (latitude between 5°S - 19°S). We determine the geomorphological tension as a susceptibility of the territory to the development of catastrophic processes. According to the regional level of generalization tension was evaluated in ordinal scores. Assessment was based on the analysis of seismicity, amount of precipitation, the depth of the relief dissection, and the spectrum of the dominant geomorphic processes. On the base of the results of mapping on the scale of 1:8 million it was determined that zone of maximum geomorphological tension is situated at the Western megaslope of the Peruvian Andes between latitudes 9 °S and 13°30'S and in the band width of 100 km from the Pacific coast. Its value here reaches 15-16 scores due to natural causes. The tension on the Eastern megaslope of the Andes ranges from 9 to 12 points, except for some areas where it rises to 13-14, and for the Altiplano where it decrease to 6-10 points. An important feature of the study area is the asymmetric distribution of geomorphological processes and the geomorphological tension, which differ significantly at the oceanic and the inland slopes of the mountain range. Comparison of data obtained for the two segments (NW and SE) of the circum pacific mountain belt allows to conclude about the existence of its geomorphological tension general regularities. The areas of potential catastrophic processes are located near the margin of the continent in either case.
Conditions and factors of a sediments granulometric differentiation on the beaches and intertidal zones of the test site of the White Sea beach are under consideration. Trends and results of transformation of sediments granulometric structure have been analyzed in the view of changes in the nature and direction of morpholithodynamic processes. Vectors of lithological changes and morphodynamic processes are closely associated. It is shown that the degree of transformation of sediments granulometric structure does not depend on the extent of morphometric changes and is more noticeable in dynamically stable areas of the coastal zone, where conditions for the influx of sediments of different origin and fractional composition exist.
История науки
И.Н. Гладцин был талантливым геоморфологом первой генерации российских геоморфологов, прекрасным организатором науки, воспитателем могучих отечественных ученых: И.П. Герасимова, К.К. Маркова, С.С. Шульца и др. Проводил полевые исследования в Забайкалье, на Кольском полуострове и Крыму, в его научной жизни преобладали региональные работы. Основные темы его геолого-геоморфологических исследований: курумы, каменные многоугольники, динамика и происхождение соленых забайкальских озер, строение и происхождение красноцветных отложений Крыма. И.Н. Гладцин – автор первой монографии-учебника «Рельеф СССР».
Юбилеи
Друзья, коллеги, товарищи, ученики и последователи поздравляют с юбилеем Виктора Андреевича Брылёва – доктора географических наук, геоморфолога, сотрудника Волгоградского государственного социально-педагогического университета.
Потери науки
На 91 году жизни скончалась Елизавета Яковлевна Ранцман – одна из старейших сотрудниц Института географии РАН, известный российский геоморфолог, доктор географических наук.
ISSN 2949-1797 (Online)