engleski

The instability phenomena along the coasts of the Kvarner area (NE Adriatic Sea)

The Kvarner area is a semienclosed part of the Adriatic Sea located between the Istrian Peninsula and the Vinodol–Velebit coast. The island chains Cres–Lošinj and Krk–Rab–Pag divide it into the Rijeka Bay, the Kvarner, Kvarnerić and the Velebit–Vinodol Channel. The wave heights in the channel part of the northern Adriatic Sea are smaller than in the western open zone due to relatively short wind fetch. Hence the strongest northeastern wind Bura (or Bora) does not generate the highest waves. On the other hand, on the western open coast of Cres and Lošinj islands, the stormy southeastern wind Jugo (or Scirocco) can generate waves higher than 6 m. In the terrestrial part of the Kvarner area Cretaceous carbonate sedimentary rocks (limestone, dolomites and carbonate breccia), Paleogene limestone (foraminiferal limestone) and Paleogene siliciclastic rocks (marls and flysch) are present. Carbonate rocks prevail, whereas siliciclastic outcrops are restricted. Pleistocene and Holocene deposits partly cover this bedrock substrate. Intensive morphogenetic processes caused by tectonical movements and rapid sea-level changes, as well as climatic changes, caused the present shape of the Kvarner area. Slow sea-level rise during the last 6, 000 years created conditions for more intensive marine erosion. Marine abrasion caused by wave impact is not very pronounced due to its sheltered position and coastal geological settings in the Kvarner area. In places where the rock mass is tectonically crushed or/and karstified, wave notches and cliffs evolve. The destructive impact of waves is more pronounced in coasts formed in siliciclastic rocks, even in sheltered zones, where wave energy is low. There, a different effect of wave erosion is observed. Cliffs are formed in more resistant sandstones, whereas mass movements, earth flows and rockfalls are common in less resistant marls. Gentle inclined carbonate rocky coasts are generally stable, without visible mass movements. Against that, different types of mass movements are common on very steep and subvertical coastal parts. These morphodynamic processes are clearly visible along the north and northeastern coasts of the Cres Island, southeastern coast of the Plavnik Island and north and southwestern coast of the Krk Island. Similar types of instabilities have been found near very steep northeastern coasts of the Rab, Prvić, St Grgur and Goli islands. These phenomena are also visible along the western coast of the Rijeka Bay: between the Plomin Bay and the Mošćenička Draga valley, in the northeastern part of the Bakar Bay and sporadically along other steep coasts. Active scree and rockfall prevail on rocky scarps. Somewhere, the traces of planar or wedge failures are visible. The rests of dormant debris flows are situated in several dry karstic valleys. Remarkable phenomenon is a combination of tectonic subsidence and huge rocky slide on the eastern coast of the Rijeka Bay. The destructive impact of waves is more pronounced in the coasts formed in siliciclastic rocks. Slope and marine erosion prevail, but somewhere different types of landslide are found. Active or dormant slide are visible in the southeastern coast of the St. Marko Island, near the Jadranovo settlement (northeastern coast of the Vinodol-Velebit channel) in the Murvenica cove (northeastern coast of the Krk Island) and near Stara Baška settlement (southwestern coast of the Krk Island). Instability phenomena along the coasts of The Kvarner area are a part of very complex morphodynamic processes which include sea level change and seismotectonic activity.

karst; flysch; marine erosion

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