The Brandstatt landslide is located at the northern slope of the Lampelsberg in the municipality of Gresten, district of Scheibbs, Province of Lower Austria. The mainly as grass- and pastureland used area displays surficial wavy deformation patterns as well as numerous bulges and hollows (Gottschling 2001). The slope gradient ranges from 15° to 20° (Office of the Lower Austrian provincial government 1970). According to previous studies (e.g., Schweigl 2012), the slope instability affects an area of approximately 20 hectares. Considering displacement rates ranging from 1.5 to 8 cm/yr and an estimated shear surface located at a depth of ~20 m (Schweigl 2012), the landslide can be defined as a deep-seated, slow-moving earth slide system (acc. Prinz 1997, Varnes 1978).

The area is characterized by a complex geological setting, consisting of formations of the Grestener Klippenzone (Lias to Paleocene) and the Inner-Alpine Molasse (Oligocene) (Lotter & Jochum 2010). The middle and upper parts of the studied slope are made up of a mixture of sandstone blocks and deeply weathered, soft clay slates of the Grestener Klippenzone (Lotter & Jochum 2010, Office of the Lower Austrian provincial government 1970). The lower part is dominated by clastic and carbonate sedimentary rocks of the tertiary inner-Alpine Molasse (Oligocene), especially dark-grey marls, yellowish sandstones, and grey limestone sands (Gottschling 2001, Lotter & Jochum 2010). These formations are covered by thick layers of heavily weathered, loamy material (Office of the Lower Austrian provincial government 1970, Gottschling 2001).

The study site and the surrounding hillside areas have been known to be unstable for decades (Lotter & Jochum 2010). First surface movements were documented in the 1960s, after which the agricultural district authority rehabilitated the landslide area by installing deep drainage stone ribs (Office of the Lower Austrian provincial government 1970). The area was further drained in 1982/83. However, further reactivations of the surficial displacements were evidenced after intense precipitation events in 1985 and 2001. Both events led to a stepped sinking of the terrain up to 30 cm deep (Hinteregger 1985, Gottschling 2001). Consequently, additional deep drainages were installed in the slip area Gottschling 2001).

The high susceptibility to sliding of certain rocks in the Grestener Klippenzone, especially rocks from the Gresten strata and the Buntmergel series, in connection with the existing relief, has been recognized to be the principal cause of mass movements in the area. These rocks are particularly sensitive to the infiltration of water and therefore very sensitive to weathering (ibid). Consequently, with an increasing degree of weathering, the stability of the rocks is partially reduced, given a reduction in the carbonate content (ibid). Moreover, increased infiltration of water after heavy precipitation events can lead to an increase in pore water pressure and a further reduction in stability, leading to the progressive evolution of the landslide (ibid).

_{Fig. 1: Field work impressions. © R. Kanta. 2022.}

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