Geologically, the Alps were formed during the Oligocene and Miocene epochs as a result of the pressure exerted on the Tethyan geosyncline as its Mesozoic and Cenozoic strata were squeezed against the stable Eurasian landmass by the northward-moving African landmass. The squeezing action formed great recumbent folds (nappes) that rose out of the sea and pushed northward, often breaking and sliding one over the other to form gigantic thrust faults. Crystalline rocks, which are exposed in the higher central regions, are the rocks forming Mont Blanc, the Matterhorn, and high peaks in the Pennine Alps and Hohe Tauern; limestone and other sedimentary rocks are predominant (but not continuously present) in the generally lower ranges to the north and south. Mont Blanc (15,771 ft/4,807 m) is the highest peak.
Permanently snowcapped peaks rise above the snowline—located between 8,000 ft and 10,000 ft (2,440–3,050 m)—and glaciers (the longest being Aletsch glacier) form the headwaters of many Alpine rivers. Glaciation (see glacier) was more extensive during the Pleistocene epoch and carved a distinctive mountain landscape—characterized as alpine—of arêtes, cirques, matterhorns, U-shaped and hanging valleys, and long moraine-blocked lakes (such as Garda, Como, and Maggiore in the south and Zürich, Geneva, Thun, and Brienz in the north).
The Alps were the first mountain system to be extensively studied by geologists, and many of the geologic terms associated with mountains and glaciers originated there. The term alps has been applied to mountain systems around the world that exhibit similar traits to the Alps of Europe.
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