III.

The Alpine System

Structurally, the Alpine mountain system is divided into the Western and Eastern Alps by a furrow that leads from the Rhine Valley in northern Switzerland, across Splügen Pass to Lake Como in northern Italy. The Western Alps average about 1,000 m (3,300 ft) higher, and are narrower and more rugged than the Eastern Alps. The highest peak of the Alps, Mont Blanc (4,810 m/15,781 ft), is on the French-Italian border. Among the principal ranges are the Maritime, Ligurian, Cottian, and Graian Alps in France and Italy and the Bernese, Glarus, and Pennine (or Valais) Alps in Switzerland. The Jura Mountains are a north-western extension of the French Alps. From Lake Geneva the Alpine ranges curve north-east and become more widely separated, attaining a width of 250 km (155 mi) in the centre of the arc. The ranges of the Eastern Alps diverge, finally plunging to the Danubian Basin near Vienna. Well-known mountain chains of the Eastern Alps are the Bavarian Alps, Algäuer Alps, Hohe Tauern, and Niedere Tauern in the north and the Dolomite and Carnic Alps in the south.

Summit regions above 3,000 m (9,800 ft) are glaciated. Peaks and crests, however, rise above the ice, displaying jagged shapes (toothlike horns, needles, and knife-edged ridges). About 2 per cent of the total area of the Alps is covered by ice. The longest valley glacier, the Aletsch Glacier in the Bernese Alps, is 18 km (11 mi) long.

Broad and deep longitudinal valleys, which hold the courses of the upper Rhône, upper Rhine, Inn, Salzach, Mur, and Drava (Drau) rivers, separate the structural units of the Alps, and contain the main settlements and the principal arteries for traffic. Deeply incised, transverse tributary valleys lead up to the pass regions. Passes at elevations above 2,000 m (6,600 ft) are blocked with snow during the winter months; these include the Mount Cenis, Great St Bernard, Simplon, and St Gotthard passes. Brenner Pass, at 1,370 m (4,495 ft), and Reschen Pass, at 1,508 m (4,948 ft), provide the easiest crossings. Engineering feats, such as tunnelling of the higher passes for roads and railways, have lessened the barrier effect of the Alps.