The first attempt to compile maps of future multi-pattern coastal evolution under the possible accelerated sea level rise during the 21st century is presented. General tendencies in coastal evolution are predicted after the separation of dominant processes into passive inundation, reformation of accumulative coasts, sea cliff recession, etc. In addition to sketch survey map of the whole coastal USSR scaled 1:4000000, a case study map of the Sea of Azov is compiled. Palaeogeographical analogous method is used as additional one for the latter map. Preliminary quantitative estimates of shoreline migration for certain coastal segments are also presented. Natural coastal «risk zones» for different types of coastal development are mapped.
The World Ocean level fluctuates incessantly under the influence of both hydro- and geocratic factors. Studies of the Holocene coastlines position as well as modeling experiments indicate that the Ocean level rise due to melting of the Pleistocene ice sheets was different in various parts of the Ocean. The post-glacial transgression is supposed to have reached its maximum about 5 to 6 key BP. A latitudinal analysis of the Ocean level changes during the last 6 thousand years provides evidences of symmetrical changes of the water surface with respect to the equator. The observations bring us to a conclusion that the Ocean level changes are influenced by variations of the EaM rotation rate and by the position of its axis.
The morpholithogenetic line is based on multi-discipline studies of the relief' s morphology, of the composition of the material the relief is built of, the material' s movements and the energy required for the relief formation. It is necessary to distinguish between morpholithogenesis and morphopetrogenesis. The lithological-minetalogical analysis of loose sediments is considered with a view to assessment of the relief's dynamics and genesis. The authors stress the fact that sedimentary sequences always retain «memory» of different morphogenetic phases. Problems are discussed how the results of dynamic geomorphology can be applied to ecological purposes.
Дискуссии
Fluvial process on watersheds is controlled with a system of shallow hollows which form a dense network. They cover practically all the surface including the water-divide zone, which becomes but nominal under the conditions. Two qualitative levels of the fluvial process are distinguished, those are diffused and linear (concentrated). They are delimited by a distinct boundary which may change its position in lime: it moves towards the water-divide at the stage of ascending topographic evolution and towards valleys at the descending stage. The switch from one trend to another is due to a number of factors which account together for a complicated and controversial evolution of all the landforms and their elements.
Научные сообщения
Conditions are determined under which straight, meandering, braided and anastomosing channels develop. Roles of channel-forming discharge, valley bed slope and other factors are considered which control channel process. The new method of channel analysis is described; it permits to forecast channel pattern transformation as a result of changing hydrological regime.
A scheme of early stages of the valley network formation is developed and substantiated for the marginal area of the last ice sheet. Principal Pleistocene cycles of alluviation are identified in the southern Baltic region, and different types of the river bed profiles are distinguished. Fluvial terraces and sediments are described. River valleys are subdivided into three groups: glacial-stadial, glacial stadial-phasial and glacial-phasial ones. If the valley network development is elucidated in the Southern Baltic and adjacent areas, it will help to understand trends in the valleys formation in other regions of the Northern Hemisphere.
A latitudinal hollow between the Vyatka and Kama upper reaches (where the rivers take opposite direction, near the city of Kirsa) is proved to be paleovalley, presumable of the Pliocene age. During the Early and Middle Pleistocene the water flow was directed southwestward, from Kama to Vyatka. No flow existed during the Late Pleistocene and the Holocene. The drainage network transformation took place at the Middle/Late Pleistocene boundary, probably due to the valley division into two parts by a lobe of the Dnieper ice sheet, though neotectonic factors could contribute to the process.
Field studies and morphometric works provided data on the fluvial systems structure at four different times: 1172, 1885, 1925 and 1955. Changes in number and length of rivers of different order are assessed as well as the river network density. Transformation of fluvial systems parameters is estimated using coefficients which reveal trends in the drainage network changes due to silting and drying of individual streams, and changes in the streams order since 1772 to 1955; quantitative characteristics of the process have been obtained. Main causes of changes in the structure and ecological state of fluvial systems are suggested.
The paper discusses the ancient agriculture impact on gullies' density and soil loss within the limits of the former Olvia agricultural region. Differences are indicated between the fluvial landforms in the areas of old and recent cultivation. Some aspects are discussed of interaction between the soil formation and erosion processes.
Annular structures identified from space photos are revealed in the drainage pattern and in the distribution of bogs and various types of relief and landforms (of glacial, lacustrine, fluvial and eolian origin). Structures of the 2nd to 4th order appeared to be most distinct in relief, while larger structures are distinguishable only locally and by fragments. Some differences in the geomorphic manifestation of annular structures are found related to the age of topography.
The paper presents the Cenozoic history of the Southern Kara shelf topography. The region is a peripheral part of the West Siberian Plate submerged under the sea level. The principal morphostructures are relics of the Southern Kara arch, Baidaratsk foredeep and Eastern Novaya Zemlya graben. Some structural-denudational levels are identified E0 have been formed during regressive epochs of the Late Oligocene, Late Miocene, Late Pliocene - Eopleistocene, late Middle Pleistocene and Pleistocene - Holocene boundary. The submarine erosional-depositional levels were formed during transgressive epochs of the Early to Middle Miocene, Pliocene, Early to Middle Pleistocene, Late Pleistocene and Holocene.
As a result of long-term geological and geomorphological studies three groups of the present-day relief-forming processes have been distinguished, namely: A - natural, unaffected, B - natural, affected by human activity, and C - man-induced ones, the author's attention being focused on the latter. Space images data used along with field observations permitted to develop a classification of the man-induced processes and to define keys to their identification on the space images with a view to mapping.
Some special features of morphostructure and morphosculpture are discussed which are typical of the shelf's edge, that is of the transitional zone from the continental shelf to the continental slope. Morphometrical data on the shelf's edge depth are summarized from many regions of the ocean and used as a basis of the edges' classification, various edges distribution is assessed on shelves differing in morphostructure. Some features of the edge's mesorelief are discussed; they are considered to be morphosculptural characteristics of the ocean floor zone under consideration. The most distinct in morphostructure are edges of the so-called glacial shelves, while edges of oceanic shelves differ essentially from those of internal seas on the morphosculpture.
О геоморфологическом строении южной части Мавритано-Сенегальской впадины (территория Республики Гвинея-Бисау)
Рецензии
Крупный вклад в изучение экзодинамики Байкальского рифта - монография Б.П. Агафонова «Экзодинамика Байкальской рифтовой зоны» (Новосибирск: Наука, 1990. 176 с.)
Первая монография о самоорганизации геоморфологических систем - монография А.В. Позднякова, И.Г. Черванева «Самоорганизация в развитии форм рельефа» (М.: Наука. 1990. 24 с.)
ISSN 2949-1797 (Online)
