Walker - 1967 - A geography of Italy

THE N ORTH ERN LOW LANDS
Apennines feeders have certainly helped to determine the course o f the main
artery. Above Piacenza the heavily charged Alpine tributaries pin the Po against
the Apennine margin; downstream the Alpine feeders, despite their greater discharge,
caimot compete with the enormous load o f the Apennine rivers. This
contrast owes much to the absence o f lakes in the courses o f the Apennine rivers
and the extremely erodible nature o f their catchment basins.
A notable feature o f the Po’s Alpine feeders is the tendency they exhibit to
turn eastwards in their lower coxurses. A possible explanation is that they were
diverted by the very heavy load o f silt brought down by the Po itself at a time
when its course was unconfined by levees; in much the same way the Adige is
stiU obhged to find an independent outlet to the sea to the north o f the modern
delta zone. It is perhaps significant that the easterly trend o f the tributaries becomes
more marked downstream from a point where the heavily charged Apennine
rivers begin to make their contribution to the Po.
It will already be apparent that the seeming uniformity of the plain masks a
great diversity o f relief, structure and hydrology. This diversity may not be
obvious to the casual observer but its influence on the pattern o f cultivation and
settlement is extremely important. In an attempt to simplify what is in fact very
complex, the following physiographical zones may be recognized (fig. 27):
I THE H ILL ZONE OF THE A LPIN E M ARGIN. This varies greatly in width, relief
and composition. T o the south o f lakes Maggiore, Lugano, Como, Iseo and
Garda, and where the Dora Riparia, Dora Baltea, Adige and Taghamento reach
the plain, this zone is mainly developed on morainic arcs. As far as it has been
possible to distinguish the contributions o f successive glacial phases, the Gunz
deposits are exposed only where the major rivers have incised themselves deeply.
The Mindel moraines, however, are extensively revealed and enclose within
their arcs the fresher debris o f the last two glacial phases. T he characteristic
terrain is usually one o f low irregular hills but occasionally more continuous arcs
and ridges are recognizable; the most obvious example is the Serra dTvrea. In
general the moraines are excessively permeable but in places, usually on the
older surfaces, a chemical alteration associated with leaching has produced a
clayey impermeable pan known as ferretto. The soils on the moraines are always
acid but this tendency is particularly marked on the ferretto where, under natural
conditions, the associated vegetation is a sterile heath (brughiere). In depressions
among the morainic debris, where the water table reaches the surface or where
glacial clays discourage seepage, peat bogs and lakes were a common feature o f
the post-glacial landscape; most o f the peat bogs (torbiere) have been drained but
a sprinkling of lakes survives within the Dora Baltea moraine (Viverone) and between
the Ticino and the Adda (Varese, Comabbio).
Elsewhere the hill country is developed on ‘sohd’ structures. In Lombardy and
Piedmont these usually take the form of isolated spms or down-faulted fragments
of the Alpine or Pre-Alpine margin (Saluzzo spur, Rocca di Cavour); in Veneto
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