Geography of the Alps
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The Alps cover a large area. This article describes the delimitation of the Alps as a whole and of subdivisions of the range, follows the course of the main chain of the Alps and discusses the lakes and glaciers found in the region.
The Alps form a large mountain range dominating Central Europe, including parts of Italy, France, Switzerland, Liechtenstein, Austria, Slovenia, Germany and possibly Hungary (if one includes the Günser Gebirge or the Ödenburger Gebirge in the Alps). In some areas, such as the edge of the Po Basin, the edge of the range is unambiguous, but where the Alps border on other mountainous or hilly regions, the border may be harder to place. These neighbouring ranges include the Apennines, the Massif Central, the Jura, the Black Forest, the Böhmerwald, the Carpathians, and the mountains of the Balkan Peninsula.
The River Rhône forms a clear boundary between the tectonically-formed Alps from the largely volcanically-formed Massif Central. Working upstream, the River Rhône turns to the east near Lyon, and forms part of the boundary between the Alps and the Jura that ends at Lake Geneva. An area of flat ground reaches from there to Lake Neuchâtel, continuing the border, with the Jura to the north-west and the Alps to the south east. From Lake Neuchâtel to its confluence with the River Rhine, the Aar forms the border.
The Black Forest is separated from the Alps by the River Rhine and Lake Constance, but exact delimitation is difficult in southern Germany, where the land gently slopes up to meet the mountains (known in German as the Schwäbisch-Bayerisches Alpenvorland, the "Swabian-Bavarian pre-Alps").
In Austria, the Danube runs to the north of the Alps, separating it from the majority of the Böhmerwald, although some small areas, such as the Dunkelsteiner Wald south of the Wachau, belong geologically to the Böhmerwald despite being south of the Danube. The Wienerwald near Vienna forms the north-eastern corner of the Alps, and here the Danube passes at its closest to the Alps (see Viennese Basin). 
East of Vienna, only the Marchfeld, a 30-km wide flood plain separates the easternmost Alps from the Lesser Carpathians. After Vienna, the Pannonian Basin, a large area of steppe, meets the edge of the Alps, clearly delimiting the eastern limit of the Alps.
The south-easternmost extension of the Alps is to be found in Slovenia, including Pohorje, the Kamnik Alps and the Julian Alps (the last being shared with Italy). The town of Idrija may be taken as marking the dividing line between the Alps to the north and the Karst plateau to the south, which then leads on to the mountains of the Balkan Peninsula.
The remainder of the southern edge of the Alps is clearly delimited by the basin of the River Po.
This delimitation of the Alps is, however, largely subjective and open to argument. In particular, some people restrict the use of the term "Alps" to the higher mountains in the centre of the range, relegating the surrounding hills and mountains to the status of "pre-Alps" or foothills. This can sometimes lead to conflicting definitions, such as Mont Ventoux being considered to lie outside the Alps (there are no comparably sized mountains around it, and it is at a considerable distance from the main chain of the Alps).
It is also not possible to define the Alps geologically, since the same orogenous events that created the Alps also created neighbouring ranges such as the Carpathians. See also Geology of the Alps. The Alps are a distinct physiographic province of the larger Alpine System physiographic division, but the Alps are composed of three distinct physiographic sections, the Eastern, Western and Southern Alps physiographic sections.
While smaller groups within the Alps may be easily defined by the passes on either side, defining larger units can be problematic. A traditional divide exists between the Western Alps and the Eastern Alps, which uses the Splügen Pass (Italian: Passo dello Spluga) on the Swiss-Italian border, together with the Rhine to the north and Lake Como in the south as the defining features. While the Splügen Pass is neither the lowest nor the most important pass in the Alps, it is approximately halfway along the main chain, and makes a convenient boundary.
- Flysch zone (up from the Vienna Woods to the Bregenz Forest. The Swiss Jura do not geographically belong to the Alps;
- Northern Limestone Alps, peaks up to 3000 m;
- Central Eastern Alps (Austria, Swiss), peaks up to 4050 m;
- Southern Limestone Alps, peaks up to 3500 m.
However, the geologic subdivision, based on tectonics, suggests a different system:
- The Helvetic system in the north (including the Jura mountains),
- the Penninic system: mainly Central Alps (Engadine and "Tauern window") and Flysch Alps,
- the Austroalpine system: Northern Limestone Alps, Graywacke-Schist zone, Central Crystalline,
- the Southern Alps (Southern Limestone Alps and other chains south of the Periadriatic Seam)
- south of a huge geologic fault ("alpine-dinaric seam") parts of the Dinarides.
The Western Alps are commonly subdivided into the following:
- Ligurian Alps (from Savona to Colle di Tenda)
- Maritime Alps (from Colle di Tenda to Colle della Maddalena)
- Cottian Alps (from Colle de la Maddalena to Montgenevre Pass)
- Dauphiné Alps (from Col du Mont Genevre to Col du Mont Cenis)
- Graian Alps (from Col du Mont Cenis to the Little Saint Bernard Pass)
- Chablais Alps (from Lake Geneva to the Col des Montets)
- Pennine Alps (from the Little St. Bernard Pass to the Simplon Pass)
- Lepontine Alps (from Simplon Pass to Splügen Pass)
- Bernese Alps (north of the Rhône to the Grimsel Pass)
- Urner Alps (from Grimsel Pass to the Reuss river)
- Glarus Alps (north-east of Oberalp Pass)
- Appenzell Alps (north of Sargans)
Within the Eastern Alps, the most widely used subdivision is the Alpine Club's 1984 classification, which divides the region into about seventy small areas.
The "main chain of the Alps" follows the watershed from the Mediterranean to the Wienerwald, passing over many of the highest and most famous peaks in the Alps. The most important passes and peaks which it crosses are given below (mountains are indented, passes unindented). From the Colle di Cadibona to Col de Tende it runs westwards, before turning to the north-west and then, near the Colle de la Maddalena, to the north. Upon reaching the Swiss border, the line of the main chain heads approximately east-north-east, a heading it follows until its end near Vienna.
- Colle di Cadibona (Italy, 435 m)
- Colle di Tenda / Col de Tende (France / Italy, 1908 m)
- Colle della Maddalena / Col du Larche (France / Italy, 1994 m)
- Monte Viso (France / Italy, 3841 m)
- Col de Montgenèvre (France / Italy, 1854 m)
- Col de Fréjus (France / Italy, 2537 m)
- Col du Mont Cenis (France / Italy, 2084 m)
- Aiguille de la Grande Sassière (France / Italy, 3748 m)
- Little St Bernard Pass (France / Italy, 2157 m)
- Great St. Bernard Pass (Switzerland / Italy, 2469 m)
- Simplon Pass (Switzerland, 2005 m)
- Blinnenhorn (Switzerland / Italy, 3374 m)
- Saint Gotthard Pass (Switzerland, 2044 m)
- Rheinwaldhorn (Switzerland, 3402 m)
- Splügen Pass / Passo dello Spluga (Switzerland / Italy, 2113 m)
- Maloja Pass (Switzerland, 1809 m)
- Piz Bernina (Switzerland / Italy, 4049 m)
- Fuorn Pass (Switzerland, 2419 m)
- Piz Sesvenna (Switzerland / Italy, 3205 m)
- Reschen Pass (Austria / Italy, 1504 m)
- Weißkugel (Austria / Italy, 3738 m)
- Timmelsjoch / Passo del Rombo (Austria / Italy, 2491 m)
- Brenner Pass (Austria / Italy, 1371 m)
- Hochtor (Austria, 2575 m)
- Ankogel (Austria, 3246 m)
- Radstädter Tauern (Austria, 1739 m)
- Hochgolling (Austria, 2863 m)
- Schober Pass (Austria, 849 m)
- Hochschwab (Austria, 2277 m)
- Gerichtsberg (Austria, 581 m)
- Danube, 160 m
Some of the highest peaks in the Alps, however, fall to one side or other of the main chain. These include:
- Barre des Écrins (France, 4102 m, highest point in the Dauphiné Alps)
- Gran Paradiso (Italy, 4061 m, highest point in the Graian Alps)
- Finsteraarhorn (Switzerland, 4274 m, highest point of the Berner Oberland)
- Jungfrau (Switzerland, 4158 m, Berner Oberland)
- Ortler / Cima Ortles (Italy, 3905 m)
- Marmolada (Italy, 3343 m, highest point in the Dolomites)
- Tödi (Switzerland, 3614 m, highest point of the Glarus Alps)
- Triglav (Slovenia, 2863 m, highest point in the Julian Alps).
For more detailed lists of passes, please see the articles about individual areas of the Alps.
Several glaciers are located in the Alps, the longest of which is the Aletsch Glacier in the Bernese Alps. They may be found in all of the higher groups of mountains from the Dauphiné Alps in France to the Hohe Tauern in central Austria, and the main ascent routes on many of the highest mountains pass over glaciers.
Very few large lakes are found within the body of the Alps, but a number are situated around the edge, particularly in areas formerly covered by glacier tongues. These include Lago Maggiore, Lake Como and Lake Garda on the southern side of the Alps in Italy, and the lakes of Switzerland, southern Germany and the Austrian Salzkammergut in the north.
- Rhine: Aare, Reuss, posterior Rhine;
- Rhone: Durance, Drôme, Isère;
- Danube: Sava, Drava, Mur, Enns, Inn;
- Po: Oglio, Adda, Ticino, Dora Baltea.
The triple watershed Rhine-Rhone-Po is south of Furka Pass near the summit of the Witenwasserenstock, at ; the triple watershed Rhine-Po-Danube is at Lunghin Pass, Grisons ( , 2645 m); the triple watershed Po-Danube-Adige is at the Swiss-Italian border, near the summit of Monte Forcola south of Val Müstair, at .