On the genesis of some bottom and coastal features in the Eastern Gulf of Finland |
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Authors: | I O Leont’ev D V Ryabchuk A Yu Sergeev L L Sukhacheva |
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Institution: | (1) A.P.Karpinsky Russian Research Geological Institute (VSEGEI), Sredny pr., St.Petersburg, 199106, Russia |
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Abstract: | An investigation undertaken recently by the Division of Regional Geoecology and Marine Geology of the Karpinsky All-Russian
Research Geological Institute in the coastal zones of the Eastern Gulf of Finland allowed finding some specific relief forms
of both near-shore bottom topography and shoreline shape. First of all, among the most interesting objects, the sand ridges
on the surface of submarine terrace (between Repino locality and Cape Lautaranta) should be mentioned. These ridges are elongated
at an angle to the shoreline and are located beyond the limits of wave action. The other interesting morphological type is
represented by longshore sand waves up to some hundreds of meters long and some tens of meters wide near the Bol’shaya Izhora
locality. Longshore sand waves move along the southern coast of the gulf, this causing alteration of erosion and accretion
zones and leading to formation and degradation of the sand spits. Shore-face-connected ridges are believed to develop under
the action of drift currents generated during the passage of deep west cyclones. It is shown that the ridge turned toward
the current gives rise to a convergence of the cross-shore flows over the crest and provokes a shift of the maximum velocity
toward the front side of the structure. Associated changes in sediment discharges result in accumulation and growth of the
ridge. The origin of wavelike features in the shoreline contour (longshore sand waves) is due to a very oblique wave approach
caused by predominance of the west winds blowing along the axis of the gulf. Under these conditions a small perturbation of
the shoreline contour is shown to manifest a trend to increase with time. |
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