Alps - geography.

Alps - geography. I INTRODUCTION Alps, great mountain system of south central Europe, forming an arc some 1200 km (750 mi) long from the Gulf of Genoa to the Danube River at Vienna. The Alps are the highest and most densely settled mountain belt of Europe, occupying an area of about 200,000 sq km (about 80,000 sq mi) and inhabited by some 20 million people. The valleys of the Alps are areas of year-round settlement; the flatter upland tracts comprise pastures and seasonally inhabited settlements, and the zone above the timberline serves as pasture and for recreation. Important economic activities include tourism, dairy farming, forestry, the production of hydroelectric power, and the extraction of salt and iron ore. With its important pass routes between central and southern Europe, the Alps have been an area of transit trade since ancient times. II GEOLOGIC STRUCTURE AND FORMATION The Alps are a complex fold-mountain system. Sedimentary deposits of vast thickness, mainly limestone and dolomite, were laid down in the ancestral Tethys Sea during the Triassic and Jurassic periods. Subsequently, enormous pressure generated by a collision between the African and Eurasian plates (see Plate Tectonics) thrust these rock strata upward and northward to form recumbent folds (nappes), which in the process of movement were detached from their roots. The four glaciations of the Quaternary period (beginning about 2.5 million years ago) were of great importance in the sculpturing of the Alps. Vast ice masses moved through the valleys, transforming them into deep troughs with steep walls; the overflow of ice across the mountain divides shaped the passes. Glacial deposits in the form of moraines dammed the streams and rivers and produced the region's many lakes, the two largest of which are Lake Geneva and Bodensee (Lake of Constance). 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 1000 m (about 3300 ft) higher and are narrower and more rugged than the Eastern Alps. The highest peak of the Alps, Mont Blanc (4807 m/15,771 ft), is on the Franco-Italian border. Among the principal ranges are the Maritime, Ligurian, Cottian, and Alpes Grées in France and Italy and the Bernese, Glarus, and Pennine (or Valais) Alps in Switzerland. The Jura Mountains are a northwestern outlier of the French Alps. From Lake Geneva the Alpine ranges curve northeast and become more widely separated, attaining a width of 250 km (155 mi) in the center of the arc. The ranges of the Eastern Alps diverge, finally to plunge to the Danubian Basin near Vienna. Well-known mountain chains of the Eastern Alps are the Bavarian Alps, Allgäu Alps, Hohe Tauern, and Niedere Tauern in the north and the Dolomite and Carnic Alps in the south. Summit regions above 3000 m (about 9800 ft) are glaciated. Peaks and crests, however, rise above the ice, displaying jagged shapes (toothlike horns, needles, and knife-edged ridges). About 2% 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 2000 m (about 6600 ft) are blocked with snow during the winter months; these include the Mont Cenis, Great Saint Bernard, Simplon, and Saint Gotthard passes. Brenner Pass, at 1,371 m (4,497 ft), and Reschen Pass, at 1508 m (4948 ft), provide the easiest crossings. Engineering feats, such as tunneling of the higher passes for highways and railroads, have lessened the barrier effect of the Alps. IV THE PHYSICAL ENVIRONMENT The Alps receive high precipitation on the windward (N) side, amounting to about 3000 mm (about 120 in) annually. This precipitation sustains the forests, and the runoff feeds several of the large rivers of Western Europe, such as the Rhine, Rhône, and Po rivers and the tributaries of the Danube (Inn and Drau rivers). Elevation and exposure to maritime air masses and to the sun's rays are the prime variables influencing vegetation. Oak, hornbeam, and pine trees dominate the warm foothill zones, and sheltered valleys opening onto the Upper Italian Lakes abound with subtropical vegetation. A region of beech forests encompasses the cooler zone and grades at higher elevations into the fir and spruce belt. Mountain maple, spruce, and larch extend to the timberline. Above 1800 m (about 5900 ft) is the treeless zone, a realm of Alpine tundra and Alpine flora that extends to the permanent snow line and includes rhododendron, edelweiss, rock flora, sedges, rowan, creeping pine, and dwarf shrubs. This is a strikingly colorful zone during the short summer growing season of three to four months. Alpine fauna occupies the solitary heights below the snow line. The dominant species are the ibex, chamois, woodchuck, snow grouse, snow mouse, and Alpine daw. Contributed By: Elsa T. Schmidt Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.