Exogenous processes such as weathering, erosion and sedimentation have an important impact on modelling the land surface and creating rock formations. The exogenous processes have formed stone rivers in Vitosha; screes in the Balkan Mountains, Rila and Pirin; earth pyramids in Melnik, Stob and Katina; landslides, mainly along the Danube banks and the northern Black Sea coast; fluvial terraces; aeolian forms, such as dunes; karst forms, including numerous caves, sinkholes, ponors, etc.