Environmental Engineering Reference
In-Depth Information
high; they are classified as Mollisols; the high content of organic matter reduces the
volume of soil penetrated by plant roots.
4.4.7 Landscapes on moraines
On the moraines at the foot of the mountains soils are common but variable in
character. In the most ancient and evolved cases, the Alfisols are stable, sometimes
desaturated in depth, with processes of acidification and leaching causing the evo-
lution of Ultisols. In the youngest moraines or where there is ongoing erosion, the
soils have reached a degree of evolution (Alfisols and Inceptisols). A good example
is located in Serra Ivrea in northern Italy. Dating back to the Quaternary this is the
largest glacial moraine of its kind in Europe.
4.5 Northern Mediterranean mountain landscapes:
from the Pyrenees to the Hellenids
4.5.1 Pyrenees
The Pyrenees are divided into three longitudinal sections: the Western or the At-
lantic Pyrenees, from the Bay of Biscay to the Pic d'Anie; the Central Pyrenees,
from the Pic d'Anie to Col du Puymorens; and the Eastern or Catalan Pyrenees,
from the Col du Puymorens to the Gulf of Lion in the Mediterranean sea. The Cen-
tral Pyrenees include the highest summits of the chain: Pic de Nethou (3404 m) in
the crest of Maladeta, Mont Posets (3375 m), and Monte Perdido, or Mont Voyager
(3355 m).
Approximately 30-40 million years ago the same earth movements that created
the Alps pushed up the Hercynian mountain mass submerged and covered by Sec-
ondary Era deposits. During this mountain-building era, the comparatively pliable
sedimentary beds folded, whereas the much older and more rigid platform broke
up, with hot springs bursting through the fracture lines.
The Axial Zone of the Pyrenean range is characterized by sharply defined ridges
and bold peaks where a number of granitic extrusions have thrust through the more
easily eroded primary sediments. However, limestone and schists of a particularly
resistant type are also found among some of the highest summits; Monte Perdido
is a good example, being Western Europe's highest limestone mountain. Nearby,
the Cirque de Gavarnie (also limestone) reveals huge platforms of horizontal strata
stacked one upon the other. The Pic du Midi d'Ossau owes its distinctive shape to
an extrusion of volcanic rock. Glaciers of the Quaternary Ice Age (10 000 years
ago) did much to give the range some of its most dramatic and appealing features.
Although this glacial cover has almost completely disappeared today, there remain
countless hanging valleys, more than 1000 tarns, cirques, sharp peaks and ragged
