Crust (geology) the crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity. The crust of the Earth is of two distinctive types: Because both continental and oceanic crust are less dense than the mantle below, both types of crust "float" on the mantle. This is isostasy, and it's also one of the reasons continental crust is higher than oceanic: continental is less dense and so "floats" higher. As a result, water pools in above the oceanic crust, forming the oceans. The temperature of the crust increases with
Geology of the Alps mountain ranges: the Apennines to the southwest, the Dinarides to the southeast and the Carpathians to the northeast. In the east the Alps are bounded by the Viennese Basin and the Pannonian Basin, where east–west stretching of the crust takes place. The Alps have a complex geology, but the general structure is the same as for other mountain ranges formed by continental collision. The Alps are often divided into Eastern, Central and Western Alps, even though the boundaries between these subdivisions are rather arbitrary. The division between the Eastern and Central Alps is approximately the line between St. Margrethen, Chur