Morphodynamic classification of moraine cliffs of the Southern Baltic Sea coast

Cliff coasts constitute an important geoecosystem of the Southern Baltic coast. The varied geological structure, cliff morphology, and variable hydrometeorological conditions in the annual and multi-annual cycles result in the development of different types of relief, which determine the morphodynamic type of the cliffs. The changes in relief that occur over the annual and multi-annual cycle are good indicators of cliff coastal morphodynamics.

The variation in cliff relief is mainly determined by the lithology, resistance and structure of the sediments. Regardless of the geological structure, the most important factor determining cliff morphodynamics is the morphogenetic activity of the sea. In addition to storm surges, denudational processes associated with mass movements and washout play a very important role. Slopes composed of compact glacial till are mainly modelled by striprockfall and flow processes, while slopes dominated by sandy series are subject to dry ravel processes. In the case of cliffs with a more varied structure conditioning the occurrence of groundwater outflows, the dominant process shaping the relief is landsliding and flow processes. The above conditions, combined with seasonal weathering variability, determine the characteristic types of moraine cliff relief.

A long-term and systematic study of the cliff morphodynamics of Wolin Island and other cliff sections comprising the southern Baltic coast has provided the basis for presenting a morphodynamic classification of moraine cliffs.

The classification was based on two criteria: lithological and morphogenetic. While the lithological criterion takes into account the dominant type of sediment building the cliff slope (clayey, sandy, sandy-clay), the morphogenetic criterion takes into account the genetic type of forms shaping the cliff relief. Based on the criterion of morphogenetic typology, forms related to rockfall, flow, landslide and dry ravel should be distinguished. It should be pointed out that the type of landforms is strictly conditioned by the lithology of the cliff.

Taking into account the assumed classification criteria, the following types were distinguished: rockfall-flow, talus-landslide, rockfall-landslide and landslide-flow. The presented morphodynamic types, in connection with seasonal variability of weathering types, are subject to constant change. Depending on the prevailing hydrometeorological conditions, the presented cliff types may occur in different variants (rockfall, flow, landslide and talus).

In a time of ongoing climate change, the morphogenetic potential of all morphodynamic factors modelling cliff relief is projected to increase systematically. This situation suggests that all the proposed morphodynamic types will be modelled with increasing intensity in the future, and that the process of transition through the various stages of development will accelerate significantly.