The Drava basin: Geological and geomorphological setting

Abstract

The Drava catchment comprises three major geological units of the Eastern Alps and their southeastern foreland: 1. the Austroalpine Nappe System (with a small portion of the High Tauern Window), 2. the Southalpine Nappe System (with the eastern Dolomites) and 3. the southwestern margin of the Pannonian (Carpathian) Basin. Mountain building in the Alps started in the Cretaceous driven by lithospheric plate movements: the northward drift of the African plate and its microplates. The plate tectonic evolution was also controlled by the opening and closure of two oceans: from the Triassic to the Middle Jurassic the Neotethys extended from the east to the west; the Piemont-Penninic Ocean existed from the Middle Jurassic to the Late Cretaceous and evolved parallel with the opening up of the Atlantic Ocean. The principal tectonic units of the upper Drava catchment are divided by the marked Peri-Adriatic Lineament system. Although with lower intensity than in the Western and Central Alps, the orogeny still goes on today on the eastern end of the mountain arc. Huge horizontal displacements of blocks are observed in the form of strike-slip faults, which control the overall drainage pattern (e.g., in the Gail Valley). According to age, the rocks of the Eastern Alps range from metamorphosed Paleozoics (e.g. in the Tauern Window, Austria) to the late Holocene alluvia of the Lower Drava Valley (e.g. at the Kopački rit in Croatia). Rock variability is also great with regard to resistance to erosion. The most spectacular landforms are the high-mountain glacial and karst assemblages, the dolomite cliffs and pinnacles, earth pyramids, deep ravines, marked landslide features, narrow gorges with waterfalls, and caves in limestone. There are overdeveloped cutoff meanders and undercut bluffs in the lowland section.