Environmental Engineering Reference
In-Depth Information
The chains of the Pyrenees to the west and the Dinaric Alps and Hellenids to the
east are the natural setting that overlooks the Mediterranean Basin, which includes
the territories that, due to culture and geographical location, display similarities
with western Asia and North Africa. Though belonging from the same orogenic
events, the geomorphological evolution of Mediterranean mountain ranges was also
strongly conditioned by the climate and its recent changes in the Quaternary (see
Chapter 2).
It is customary to distinguish between the structural morphology, which depends
on the curvature of the Earth's crust, and the glacial morphology and karst related
to landslides. The first trend is manifested by the almost straight valleys and ridge
lines, due to profound changes (faults and tectonic lines), while the layers of over-
lapping thrust belt do not usually present a clear morphological correspondence.
The glacial morphology is demonstrated by the U-shaped valleys, with cirques,
amphitheatres and glacial dorsal moraines (see Chapter 3). Lithology plays an im-
portant role in shaping mountain landscapes. Crystalline rocks (granite, gneiss, etc.)
are resistant to erosion and are associated with prominent structures. Soft sedimen-
tary schists and flysch have high erodibility and are prone to landslides, but pro-
duce good-quality soils. Resistant limestones, in contrast, result in soaring cliffs.
On mountain foothills there are sandstone formations, resulting from the accumu-
lation of material eroded by rivers and glaciers, which are mostly associated with
soft landscapes.
4.3 Geological setting
Mountains dominate much of the Mediterranean area and are visible to travellers
on land and sea alike. The Mediterranean Basin was shaped by the ancient collision
between the northward-moving African-Arabian continent and the stable Eurasian
continent. As Africa-Arabia moved north, it closed the former Palaeo-Tethys
Ocean, which formerly separated Eurasia from the ancient supercontinent of Gond-
wana, of which Africa was a part. During the Permian along the eastern margin
of Gondwana began the opening of the Neo-Tethys Ocean and the subduction of
the Palaeo-Tethys Ocean. The collision of continents pushed up a vast system of
mountains, extending from the Pyrenees in Spain to the Zagros Mountains in
Iran. This episode of mountain building, known as the Alpine Orogeny, occurred
mostly during the Oligocene (34 to 23 mya) and Miocene (23 to 5.3 mya) epochs.
The Neotethys became larger during these collisions and associated folding and
subduction. Tectonics and climate are the primary external processes governing
mountain landscape evolution. Tectonic uplift creates elevated terrain and provides
increased potential energy to the agents of erosion, such as fluvial systems (Quigley
et al.,
2007), which are the source of most of the sediments and waters shaping and
feeding lowland and coastal areas.
During the Quaternary period five major Pleistocene ice ages have occurred:
Donau, Gunz, Mindel, Riss and Wurm, named according to the moraine of the
