mass falls in the Wachau-Danube Valley (Bohemian Massif

Fig. 3 Rock-mass fall near the town of Dürnstein (view towards SSE, photo: Müllegger, August 2009).
Contrary to many alpine rock-mass falls in uninhabited areas (cf. Weidinger and Vortisch 2005) these two
events in abandoned quarries caused major damage and still endanger transport infrastructure, which thus
made geo-scientific investigations and protective measures necessary. Aim of this paper is to comment on
geomorphological and geotechnical causes of these rockslides/rock-mass falls.
Study area
Geomorphic overview
40 m
Between Passau and Krems, the Danube River runs along the southern edge of the Bohemian Massif, most of
which is overlaid by Tertiary and Quaternary sediments. The exposed edge of the hilly fault residual plateau
takes the form of a 500-600 m high piedmont stairway. Where higher mountain ridges reach the plateau’s
margin, the river cuts down into the granites and gneisses of the crystalline basement, and carves out
transverse valleys, such as the Wachau-Danube Valley (Kohl 1966). The morphogenesis of this river section was
last analysed by Nagl and Verginis (1987), whose research focused on the palaeogeographic development of
the catchment area. They suppose that the valley between Melk and Spitz (cf. Figs 1 and 4)was drained by the
Enns River during the Tertiary, while the Danube River at that time run further north. In consequence of Late
Tertiary tectonic processes the Danube River was captured by the Wachau-Enns River.
The geomorphological appearance is characterised by the fact that the orientation of the river bed follows two
conjugated major tectonic lineaments, striking approximately NE-SW and NW-SE. Wide basin and terraced
landscapes are therefore non-existent in contrast to adjacent areas with Tertiary and Quaternary cover
sediments. The tectonically fragmented and weakened rock mass along fault structures caused accelerated
river erosion forming V-shaped valleys with relatively steep rock slopes and triggering large rockslides during
the Oligocene. Matura (1983 and 1989) mapped a fossil slide mass deposited in the Wachau-Danube Valley
near the village of Weißenkirchen (Fig. 4). He also interprets deposits of gneiss boulders in Weißenkirchen as
rockslide sediments of the same age.
In the present day, the rock slopes of the Bohemian Massif are usually considered to be stable. Gattinger (1980)
assumes that mass movements are of minor relevance to the Bohemian Massif, owing to its relatively small
relief ratio, and are limited to single rockfalls or local slope ruptures.
3
Dürnstein
Danube river