As North America began to split from Pangaea about 180 Ma ago, concurrent rifting separated Eurasian and African plates. A network of spreading ridges, subduction zones, and transform faults bounded the plates. Collapse of these features as Africa closed on Europe produced the complicated tectonic patterns that mark the alpine region. During the Cretaceous, Iberia was emplaced along the Betic fault zone and the Pyrenees. These form the broad arc that makes up the Alps proper.
Structures strongly control the alignment of the main valleys.
For example, longitudinal valleys are located along the strike of weaker rocks, along nappe boundaries, in tectonic grabens, or along the axes of breached anticlines. Transverse valleys, which cut across gross structures and rock types, are influenced by faults, old flextures, and axial depressions. These valleys have been widened and deepened by glacial erosion. The ground and aerial photographs and space image below provide a broader perspective on the structural and physiographic character of the Alps. A typical flowage fold within the Pleising nappe in Austria appears in Figure T-25.2 .