Stop 1: landslide Kostanjek

The Kostanjek landslide is the largest landslide in the Republic of Croatia. It is a reactivated deep-seated translational landslide located in the urbanized area of the City of Zagreb at the base of the southwestern slopes of Medvednica Mt. (Fig. 4). The sliding surface is developed in Sarmatian laminated marl, characterized by alternation of very thin light and dark laminae known as varves (according to WEINHEIMER & BIONDI, 2003). Displaced mass above the Sarmatian sediments consist of Lower Pannonian clayey marls with thin limestone layers and Upper Pannonian massive clayey marls. The width of the displaced mass is 960 m, and the total length of the Kostanjek landslide is 1.26 km. The maximal depth of the sliding surface is 90 m, according to interpretation of ORTOLAN & PLESKO (1992). The total landslide area is approximately 1 km2, and the volume of the sliding mass is evaluated to be 32 × 106 m3 (STANIC & NONVEILLER, 1996). Since its activation in 1963, Kostanjek landslide has caused substantial damage to buildings and infrastructure in the residential (Fig. 5) and in industrial zones. The deep-seated landslide was caused by anthropogenic factors, mainly by excavations in a marl quarry placed in the toe part of the landslide (Fig. 6). Uncontrolled blasting during the 1960s and 1970s in the marl quarry and the limestone quarry, placed approximately 1 km to the north from the upper part of the landslide, were also important destabilizing factors. Surface deformations are mostly expressed as ductile deformations with rare opening of cracks, even at the landslide boundaries. Despite extremely slow to slow landslide movements for 52 years, the risk in the area of the Kostanjek landslide is very high for residential properties (approximately 300 single-family houses and infrastructure networks are placed on the moving landslide mass).