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Morphology

Shelf (continental terrace)

The continental shelf is a natural continuation of the neighbouring land, remaining under the seawater after the last freeze (10 000 - 12 000 years ago). It represent very slightly inclined underwater terrace, including the zone between 0 and 100 m, in same places to the depth of 140 m. The Sea of Azov, and also the bays and the open firths of the northwestern coast belong to it. The width of this coastal shallow zone is quite variable in the different parts of the basin. The biggest area is occupied on the north by the line the Kaliakra Cape. Sevastopol , where the width reaches 200 km. Opposite the southern Cremean peninsular coast the shelf becomes narrower. On the east, however (in front of the Kretch) the shelf grows wider again in the shape of an underwater cape, protruding to the south in the sea, 60 km wide. It has complicated contours and not a big area near the southern coast. Here, the underwater cuts to the south similar to bays and cape jutting out to the north, mainly in some big rivers" mouths, make the continental terrace with quite complicated uneven contours. Near the Balkan Range and Strandja Mountain coast the shelf is well shaped and reaches 40 km width, and its incline to the east is below 1°. In its coastal area the underwater swells to the north-south destination, make the relief more complication. The short review of the continental shelf features shows, that it occupies much wider area in the northwestern, western and southwestern periphery of the Black Sea hollow, while near the Caucasus and Pontian coast it is quite narrow interrupted line. The studies of the shelf area, especially over the last years, found out that it is formed in parts of the neighbouring land with different geological structure and age. Near the North Doubroudja the shelf zone includes some structures of the old damaged Doubroudja massive. In the northwestern and western coastal parts the Black Sea water have covered some low parts of the Scit and Russian platform. All this and also the slight incline and the flat-plain relief make researchers conclude that the Black Sea shelf zone represents abrasive-accumulation platform - formed by offensive abrasive activity of the sea waves and exposed at the same time to uneven tectonic sinking.

Continental slope

Almost everywhere the shelf turns to the continental slope through sharp increasing sea bottom incline. There are three kinds of continental slopes in the Black Sea. The first one is steep, indented, located near the coast. Its incline reaches 20-30°. This kind of slope is typical for the Caucasus coast, Pontian coast on the east of the town of Ordu and between the town of Inebolu and Bosphorus, as well as the southeastern part of the Crimean peninsular. The second kind of slope has rectilinear contours and progressive transition to lowland bottom. The incline is 1-3°. Of the kind is the slope of the Strandja coast and the Kertch on the south. The third kind of slope has much more complicated contours. It includes the areas between the towns of Inebolu and Sinop. In the first are there are two wide terrace of with soft contours. Systems of underwater mountain ridges are parallel to these of the neighbouring land. Tha biggest ridge is 60-70 km apart from the coast and saperated by underwater mountains. New researches found that this slope usually slides. The considerable complication of the smooth relief of the shelf and the continental slope is caused by the underwater valleys and canyons found in many parts on the sea bottom. In some parts they are even outline on the small-sized maps. In most cases, these shapes have curved outlines with clearly expressed slopes and canyons in the shelf periphery on the continuation of the river valleys from the neighbouring land. There are different versions about the origin of the underwater valleys and canyons. Most researchers of the Black Sea share the viewpoint that they are parts of river valleys, which came under the sea bottom after the sea formation and the earth crust sinking.

Lowland bottom

It occupies the central parts of the Black Sea hollow. Its shape is oval, longer in the west-east direction. It occupies larger area in the eastern part of the basin, where it represents 1/3 of the total Black Sea area. The depth varies between 2100 and 2200 meters. The lowland bottom represents an underwater plain with perfectly smooth relief. The biggest depth is close to the Pontian coasts (maximum depth of 2245 m). It proves that the bottom itself has asymmetric occupation toward the north and south Black Sea coasts.

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