## 2 Geological Settings  
The Danube area in the zone of Fruska Gora Mountain was considered (Figure 2). Given the presence of many types of lithogenic rocks and the emphasized tectonic relationships between them, Fruska Gora has a complex geological structure [1; 12], especially when compared with the surrounding terrains. The serpentinites are the oldest. They are products of altered gabbro-peridotites, which are of the Paleozoic age. Apart from serpentinite, other Paleozoic rocks are also present: phyllites, schists, mica, chlorite, and amphib. The direction of the schist is, generally speaking, east-west, while the dip is toward the south. On the surface, they appear in the central parts of the mountain. On the north side, the main belt of Paleozoic formations is generally limited by sediments of the upper Cretaceous. In the far western part, it is limited by Miocene sediments and Quaternary sediments in the south. Contact surfaces between serpentinite and Paleozoic schists are tectonic by nature. Figure 1: Locations of unstable slopes along the Danube. The Mesozoic is represented by rocks of the Triassic, Jurassic, and Cretaceous ages. The rocks of the Triassic age (T) are conglomerates, followed by a series of purple and yellow sandstone, purple, gray, and yellow clay shales, and clayey sandstones, as well as limestones. The upper Cretaceous (K) is represented by basal conglomerates and breccias, coarse-grained sandstones, gray shales, and marks, which alternate with sandstones and conglomerates, limestones, and limy marks. Miocene sediments are fully developed. The lower Miocene is represented by basal conglomerates, breccias, and various sandstones. The middle Miocene consists of conglomerates, sandstones, sandy marks, tufo-sands, and clayey limestones. The upper Miocene consists of conglomerates, sandstones, sands, clays, limestone, marl, and marl clays. Sands and sandy clays dominate the Pliocene, while gravels and lignite are less common. The deeper facies consist of marks and marl clays. The middle Pliocene is represented by multicolored clays. Sands and gravels are present to a much lower extent. The upper Pliocene consists of yellowish sands, brownish sands, silts, and clays (Figure 2). Deep landslides along the Danube were formed in these Pliocene clays and sands. These sediments are slightly inclined toward the Danube at an angle of about 5\({}^{\circ}\). The main causes of the landslides' occurrence are sloping layers of clay and sand toward the Danube, groundwater in sands, erosion of the right river bank, thin layers of soft carbon clays, and altered Pliocene sediments by surface influences. In the Quaternary (Q), sediments on land and in the aquatic environment were deposited. The oldest is the complex of sediments often named as \"Srem series\" in the scientific literature. It is located below the surface loess. Lithologically observed, they are highly heterogeneous and consist of irregularly alternating clays, sands, and gravels. Loess builds relatively large areas on the northern and especially the southern slopes of Fruska Gora. Morphologically speaking, loess builds the so-called Fruska Gora loess plateau, and the tongue forms inflection zones between Fruska Gora streams. Loess within the inflection zones between streams is narrow and, in some places, extremely thick. For example, at the location of the Cardak water reservoir, its thickness is 23 m. These loess-built inflection zones start from a level of about 400 m and descend to the loess plateaus. The loess plateau encircles Fruska Gora on all sides. Its average elevation is 120-140 m. The loess zone is of variable width. It is the smallest in the north, whereas in the south, loess builds much larger areas all the way down to the lowest Fruska Gora foot, on the Sid-Ruma-Stara Pazova line. The loess contains fossil soil horizons (Laskarev--four fossil soil horizons in Zemun [13]; Gorjanovic-Kramberger--four fossil soil horizons in Srem [14]; Markovic-Marjanovic--eight fossil soil horizons in Slankamen [15]).