Environmental Engineering Reference
In-Depth Information
crests that reveal the work of these ancient ice sheets. No less than the glaciers, wa-
ter has helped shape the Pyrenees, and in many of the limestone massifs it is rain-
water and snowmelt that have eroded the rock into a network of cracks and fissures,
some of which penetrate to great depths and produce subterranean galleries and cav-
erns, as those of Pierre St Martin. Other fissures become ravines and gorges, like
those of the Basque country, or impressive canyons such as Anisclo and Escuain.
4.5.2 The Apennines
The Apennines extend down the entire Italian peninsula and are connected to the
northwestern Alps, forming a pronounced curve with the concavity facing the
Tyrrhenian Sea, and continuing beyond the Strait of Messina in the mountains
of northern Sicily. The chain is approximately 1200 km long, 30 to 150 km wide
and covers an area of some 150 000 km
2
. The slopes are asymmetric: those of the
Tyrrhenian side are usually longer and cut by longitudinal grooves interspersed with
tracks from the upper reaches of tributaries draining into the Tyrrhenian Sea; the
Adriatic side slopes down to the sea through a hilly region. Despite the morpho-
logical differences, the Apennine landscape finds its unity in the almost entirely
sedimentary nature of the underlying rocks. Landforms created by water erosion be-
come particularly evident in the clayey soils, where the valley flanks are cut by the
furrows of the gullies and by landslides. When the soil is saturated by water content,
movements of mass downstream are possible. The physical boundary between the
Apennines and the Alps is conventionally regarded as the hill of Cadibona (436 m)
near Savona. The geological boundary is marked by the Sestri-Voltaggio tectonic
line. The Apennines orogenic cycle is determined by the Alpine orogeny. The ex-
pansion related to the formation of the Tyrrhenian basin has affected the entire mar-
gin of the Tyrrhenian Apennines, creating large faults, Horst-type structures (tec-
tonic block up) and Graben (rift), and causing the rise of large amounts of magma
that gave rise to the complex magmatic provinces of Tuscany, Lazio and Campania.
The Northern Apennines are composed mostly of sandstone and marly rocks
that are easily eroded and have rounded shapes; there are abundant landslide
soils. The Central Apennines, forming the main backbone, consist mainly of lime-
stone. This different lithology and the general uplift confer specific traits to this part
of the Apennines: in particular a more pronounced roughness of the landscape and
the development of karst landforms. The highest peak of the Central Apennines is
the Gran Sasso (2912 m at the summit of Big Horn), marking the culmination of the
entire system and the seat of the only glacier in the Apennines.
The Southern Apennines splits into isolated forms, separated by deep basins
without regular alignment. The geological structure is not uniform: although there
are some limestone reliefs, as in the Central Apennines, there are also ancient crys-
talline rocks that are quite different from those making up the rest of the system.
The Pollino massif in the Appennino Lucano, which rises to 2267 m in the Serra
Dolcedorme, marks the southern end. Profoundly different from the rest of the
