Alps

the highest mountain system in Europe, situated in Italy, France, Switzerland, Austria, the Federal Republic of Germany, Yugoslavia, and Liechtenstein.

The Alps extend in a convex arc to the northwest from the Ligurian basin to the central Danubian plain and Vienna basin. The main flexure of the arc is found in the vicinity of the highest elevation in the Alps—Mont Blanc, 4,807 m. The length of the arc is approximately 1,200 km along its outer margin and 750 km along its inner margin. It is 50–60 km wide at the longitude of Turin and up to 240–260 km wide at the longitude of Verona. The area is approximately 220,000 sq km. The boundary with the Apennines passes through the Colle di Cadibona escarpment, the boundary with the Carpathians runs along the Danube River, and the boundary with the Dinaric uplands is the margin of the Lubljana basin.

Orography. Two large orographic provinces are distinguished: the Western Alps (French-Italian and Swiss) and the Eastern Alps, which are bounded by the Transylvanian fold zone, from Lake Constance to the Hinterrhein, the Splügen Pass, and Lake Como. The highest ranges in the Alps are the main chain, or crystalline, zones. Ranges of moderate height dominate the marginal limestone and flysch zones. The main chain drops precipitously to the Venetian plain in the Western Alps and is bounded by a belt of lower marginal ranges and sharply expressed foothills on the north and west. The main chain of the Western Alps consists of the Maritime and Cottian Alps, the Pelvoux, Graian, Savoy, Mont Blanc, Lepontine, Bernese, and Glarus massifs, as well as a marginal zone in France that includes the Calcareous Alps (the Vercors and other ranges) and the Swiss Pre-Alps. The Eastern Alps, in general, are lower and broader than the Western Alps. The main chain here consists of the ótztal Alps, the tztal Alps, the Zillertal Alps, and the Hohe and Niedere Tauern. The ranges of the main chain border on the Calcareous Alps on the north (including the Allgäu, Karwendel, Salzburg, and Austrian Calcareous Alps) as well as on the south (the Bergamasque, Dolomite, Carnian, and Julian Alps).

Many deep transfers and longitudinal valleys create comparatively accessible passes (see Table 1).

Geology and mineral resources. A series of arcuate tectonic zones enters into the extremely complex geology of the Alps; these zones are made up of a variety of rocks ranging in age from Precambrian to Recent. Precambrian crystalline rocks constitute the controlling fold systems; these rocks include gneisses, micaceous slates, and less intensely metamorphose Upper Proterozoic and possibly Lower Paleozoic quartz-phillite slates, which are cut by Hercynian granites and basic intrusives.

The complex of rocks that covers the crystalline basement of the Alps includes a variety of sequences in which phillitic slates, graywacke sandstones and limestones of Lower Paleozoic, Molasse, Upper Paleozoic, and Mesozoic sericite-chlorite slates and limestones—which belong to the Great Mesozoic and Neocene flysch and molasse—fill the prealpide foredeep. Glacial deposits which may be assigned to the four complexes corresponding to the four glacial periods of the Alps—Günz, Mindel, Rissian, and Würm—are typical of the Recent deposits in the Alps.

The most important abyssal fault—the “seam”—runs for 600 km from east to west, from Maribor in Yugoslavia through Insubri to Ivrea, and divides the southern flank of the Alps from the central zone accompanied by granitoid intrusives. The central and most complex zone extends as an arc over the entire length of the Alps from Graz on the northeast to the Genoa bay on the southwest. Two complexes of rock play a controlling role in its structure: the crystalline basement complex and the Mesozoic micaceous shale complex, initially deposited in the Tethys geosyn-cline. Folding accompanied by thrusting of the so-called Pennine nappes brought about a thrusting of crystalline slates from the main fault zone northward over the micaceous shales. Both complexes were then thrust over similar sequences of rocks (the so-called autochthonous massifs). An extremely complex multilevel thrust sheet and nappe structure came into being; the structure of larger nappes was complicated by smaller nappes. Six main nappes have been identified in the most complex sections (Simplon-Ticino-Maggia); from the bottom, these are Antigorio, Lebendün, Monte Leone, St. Bernard, Monte Rosa, and Dent Blanche. The remains of eroded crystalline nappes may be seen in these peaks and in the Mischabel. Further to the east are the Adula and Tambo-Suretta nappes, and still further are a system of nappes made up of crystalline slates. Mesozoic micaceous shales may be observed in the northern portions of the Silvretta-Ötztal nappe, in the eroded “windows” of the upper Engadine—the upper reaches of the Inn River—and in the Tauern mountains.

A zone of crystalline (autochthonous) massifs is situated to the north of the central zone; these are the Mercantour in the Maritime Alps; the Pelvoux, Belledonne, and Mont Blanc peaks in the French Alps; and the Aar and St. Gotthard peaks in the Swiss Alps. They are partially covered by a blanket of Permian and Mesozoic rocks. The Paleozoic graywacke belt is a continuation of this zone in the Austrian Alps, east of the Rhine.

In the eastern Alps, north of this zone, there is a belt made up of Triassic and Jurassic limestones and dolomites. The limestones make up the system of East Alpine nappes, all of which have been thrust over the flysch zone from the south. (Some investigators feel that the East Alpine nappes were thrust into their present positions from the southern Alps.)

A flysch zone extends along the outer margins of the Alps. It is pinched in the eastern Alps because of the nappes; it widens in Switzerland, however, and extends intermittently to the Mediterranean Sea. It consists of intensely folded Cretaceous and Paleocene elastics. It has an especially complex structure in Switzerland, where it is complicated by the so-called Helvetide nappes, which include the rocks that enter into the cover of the autochthonous massifs (Aar and Mont Blanc), as well as thrust blocks transported from the central Alps. The Alpine foredeep, which is filled by Neocene molasse sequences, extends along the entire northern piedmont to Lake Geneva on the west.

The southern flank of the Alps, bordered by the main fault in the north, has a simpler structure. It is made up of undisturbed rocks dating from Triassic to Eocene; these are broken up into independent blocks by a system of faults. Extrusive and intrusive porphyries are also present.

Two phases are distinguished in the geologic history of the Alps. During the first (prealpide) phase, the crystalline basement, the Paleozoic rocks which cover the basement, and the granite intrusives, which cut the latter, developed. Basins that were filled with coal beds and variegated sediments of Carboniferous, Permian, and early Triassic sediments came into being at the end of this phase. The second (Alpide) phase can be divided into three cycles; the first of these is associated with development of the Pennine geosyncline, in which subsidence and sedimentation began at the end of Triassic time and continued until mid-Cretaceous time, when it was terminated by folding and thrusting of the Pennine nappe. The second cycle involved the development of flysch basins in the marginal and central portions of the Alps. The third cycle is associated with the Oligocene stage and involved the uplift of the Alps and folding within the flysch basins, the development of the marginal basins of the Pre-Alps, and their being filled with molasse deposits. The Helvetide nappes were overthrust and the granitoids were injected along the main fault during this period.

Magnetite, found in the Precambrian of the eastern Alps, is the most ancient mineral resource. Iron ores are associated with the Hercynian intrusives of the Austrian Alps (at Órtzberg); lead-zinc deposits are encountered in the Carnian Alps; and copper, lead, and zinc veins occur at In-subri. Coal beds are associated with carboniferous sediments in Briançon and elsewhere. The most important ore deposits of the Alps are associated with the micaceous shales of the Pennines, where there are many chalcopyrite bodies. Manganese and magnetite ore bodies are also found in the micaceous slates. Brown coal deposits are associated with the Neocene Alpide foredeep and some interior basins.

Terrain. The Alps were strongly degraded and eroded after the Alpide orogeny; they had assumed the character of mature mountains by Miocene time. The present elevation and character of the relief are associated, in the main, with very active vertical movements of blocks with respect to each other in Miocene, Neocene, and Recent times; the vertical displacements are estimated at between 1,000 and 5,000 m in various sections of the Alps. These movements involved considerable rejuvenation of erosion, reorganization of the drainage network, and complication of the morphology of elevations and depressions.

The most important factor in the Pleistocene development of relief was repeated glaciation, which affected the greater part of the Alps. The activity of great glaciers alternated with powerful interglacial stream erosion. The strongest action of ice affected the high French-Italian and Swiss Alps, where high elevations combined with abundant precipitation. Glaciation was weaker in the Eastern Alps, and the most southerly of the French Alps were not glaciated. In Alpine areas glaciation caused the development of strongly dissected topographic forms with many cirques, which descended to terraces; these are frequently cut by hanging valleys with waterfalls flowing over their lips. Valley glaciers are responsible for an enormous amount of erosion; such glaciers transport detrital material and deposit it at the feet of the mountains as terminal moraines. These moraines dam up the valleys over-deepened by glaciers at their convergence with the plains and promote the development of large piedmont lakes. Lithologic variations had a great influence on the development of the relief. Areas of limestone surrounded by crystalline rocks create steep ranges and massifs with sharp towering peaks and promote the various developments of karst. The relief on flysch and molasse deposits is gentler than it is on the peaks and sharp ridges.

Climate. Considerable atmospheric precipitation and sharp temperature variations, which depend upon elevation, exposure, and geographical location of various areas, are observed in the territories occupied by the European Alps. The decrease in air temperature with elevation is expressed more strongly during the summer (average, 0.6–0.7°C per 100 m) than in the winter (average, 0.3–0.5°C per 100 m); therefore, the summer temperature contrasts are sharper than the winter contrasts (see Table 2). The annual and monthly temperatures are highest on the southern slopes of the Maritime Alps. The annual 0°C isotherm passes at an elevation of approximately 2,000 m; the July 0°C isotherm lies at approximately 3,500 m.

The greatest precipitation is observed in the northern Pre-Alps in the front ranges of the main zone—between 1,500 and 2,300 mm annually, and 4,000 mm locally. The least precipitation (500–800 mm) is observed in the interior valleys and basins, where the climate possesses a number of continental features.

The precipitation maximum is attained during the summer months virtually everywhere. The proportion of solid precipitates increases with elevation to between 80 percent and 90 percent in the tiers above 2,000 m. The snow cover may attain a thickness of 7–8 m in some localities. Blizzards are frequent in the spring, particularly in areas under the influence of föhn winds. The snow line lies at 2,500 m in the moist outer ranges of the Alps and rises to 3,200 m in the drier interior ranges. The present glaciated area is 4,140 sq km (approximately 2 percent of the total area) of the mountain system; approximately 2,690 sq km of this lies in the Western Alps. The greatest concentrations of glaciers are at the Finsteraarhorn massif (484 sq km), Monte Rosa-Matterhorn (445 sq km), Mont Blanc (277 sq km), and Hohe Tauern (537 sq km). The longest glacier in the Alps is the Aletsch. The tongues of some glaciers descend to an altitude of 1,400 m to 1,100 m.

Rivers and lakes. The Alps are the most important hydro-graphic complex in Western Europe. The rivers that drain the Alps discharge into the North Sea—the Rhine, the Aar, and other tributaries; the Black Sea—tributaries of the Danube such as the Iller, Lech, Inn, Enns, and the upper Drava; the Adriatic—the Adige and the Po and its left tributaries; and the Ligurian Sea and the Gulf of Lyon—the Rhone and its eastern tributaries. The rivers have swift currents, high flow rates, and considerable discharge coefficients (between 70 percent and 85 percent); they are marked by highly regular flow variations in response to temperature changes. Melt waters from glaciers and snows, and rains to a lesser extent, are the main source of the water. The rivers fed by glaciers (the so-called alpine regimen) have maximum discharge during the summer and a very low minimum the rest of the time. The maximum flow in streams fed by melting snow occurs during the spring and the first half of the summer, while streams fed by rain attain maximum flow in the autumn and, in the Maritime Alps, also in the winter. A combination of a number of sources of water and flow regimens is characteristic of most major rivers. Weak profile development is the fundamental morphological feature of the river valleys, as well as a great number of notches in the valley; the notches mark the locations of waterfalls. The energy resources of the rivers are important. Lakes are an important controlling factor in stream flow. The largest group of small lakes is at high elevations. The large lakes—including Lake Geneva, the largest in the Alps (area, 581 sq km), and Thun, Brienz, Lucerne, Constance, Maggiore, Lugano, Como, and Garda—are associated with the piedmont belt.

Types of landscape. Five landscape tiers may be identified in the Alps. Their distribution is controlled by elevation. The forest environments occupy the greatest areas. The first and lowest tier embraces the foothills of the Alps and the slopes of the main ranges to elevations of 800 -900 m. The tier is influenced strongly by the adjacent extra-alpine areas and is a belt of relatively gentle hills and broad river valleys. The climate is warm-temperate and, in the south, warm. Beech and oak forests on brown mountain soils or rendzinas, in limestone areas, are the dominant vegetation. Pine and fir forests dominate the moist northern areas, while oak and pine associations with spots of grassland in the Central Danubian plain give the landscape a forest steppe aspect. Mediterranean features appear in the landscapes of the southern portions of the French and Italian Alps; the forests become less dense, and chestnut and, in places, pine become increasingly important. Xerophyllic shrubs are found. Brown and carbonate mountain soils develop. The lowest tier is the most developed of the Alps. The basic settlements, industries, and resorts, particularly on lake shores, are concentrated in the valleys. The economy is based on agriculture— corn, wheat, vegetables, grapes, and fruit—and in part on animal husbandry.

The second tier extends to elevations of 1,800 -1,900 m. The relief is more intensely dissected, the slopes of the ridges and valleys are steeper, and morainal deposits are widespread. The climate is temperate and cold-temperate, with abundant atmospheric moisture, a long snowy winter, and strong winds. The climate is drier in the interior valleys; there, temperature inversions are quite common. The tongues of major glaciers frequently descend into this tier. Blizzards are frequent, as are floods and landslides. Forests of oak, elm, and beech are dominant at elevations of 1,200 m; in moister areas at greater elevations, the dominant forests are dark conifers (fir), while the light conifers (pine, cedar, larch) occupy the drier areas. Brown forest soils are dominant with varying degrees of podzolization; rendzinas are observed, and the podzols are observed (primarily in the upper part of the tier). The forests have the greatest number and variety of animals in the Alps. The ungulates are represented by deer and boars, while the carnivores are represented by wolves, foxes, wildcats, skunks, martens, ermines, and weasels; occasionally brown bears and lynxes are encountered. The rodents include squirrels, hares, rabbits, dormice, and small mouse-like animals. The birds include crows, woodpeckers, tomtits, wood grouse, grouse, hazel grouse, bullfinches, and European nutcrackers.

Lumbering is a dominant economic activity in this tier. Livestock breeding is important to the north, and sheep herding is dominant in the limestone areas. The meadows have barley, oats, rye, root crops, and potatoes; the latter are cultivated even at elevations of 2,000 -2,400 m; wheat fields and gardens are found at lower levels of the tier.

The third (subalpine) tier rises to 2,200 -2,300 m and has intensely dissected relief, which was generated by glaciation and morainal weather. The climate is cold and snow abundant; but precipitation is less than in the lower tier, since the rainy season lasts only for the two or three months of the growing season, and the daily variations of temperatures are very great. A subalpine scrub growth (rhododendron, pillow cedars, and junipers) and perennials in the upland meadows constitute the vegetation. The soils belong to the upland meadow humus type. Chamois, mountain goats, marmots, and field mice are typical. The birds include Alpine jackdaws, Cornish cloughs, and wall creepers. The meadows may be used as basic summer pastures. There are no permanent pastures; but this tier, like the alpine tier, is an important tourist attraction and, because of the dry, sunny winter, a winter resort area.

The fourth (alpine) tier extends to the snow line and has a severe, cold climate coupled with prolonged sunlight, considerable nighttime temperature drop, and strong winds. The vegetation cover consists mainly of short alpine grasses and peat. Saxifrage is widespread, as are gentian, primroses, cyclamen, violets, asters, poppies, buttercups, and crocuses. The nutrient qualities of the pastures are poorer than in the subalpine tier. Rock slides, rock outcrops, and glaciers occupy much of the area.

The fifth (alpine) tier is encountered only in the highest central ranges and is characterized by a cold mountain climate and an environment which is a rocky, glacial, snow-covered waste. There is little organic matter.