How are mountains formed? Objective Students will learn how tectonic forces form mountains and valleys. They will also learn to distinguish between compressional and extensional forces. Background There are two types of tectonic forces that can create mountains and valleys: compressional and extensional. At a convergent boundary, or compressional environment, two continents collide and rock layers undergo buckling and folding. The buckles and folds form mountains and valleys. In rock, the buckles can fracture and slide on top of each other. In this situation the rock behaves in a brittle fashi Duration: 60 Minutes.