||Location and tectonic setting of the study area
between Paola and Amantea in Calabria, Italy
ABSTRACT - The geomorphology of the central Coastal
Range, a north-south trending horst along the west coast of northern Calabria,
is governed largely by major faults, fault scarps, and the distribution
of principal rock types, as well as by various slope processes operative
in a Mediterranean climate. Segments of the major rivers and streams have
three principal orientations parallel to major faults in the study area:
Northwest right-oblique slip faults (oldest); E-W oblique-slip faults;
NE left-oblique slip faults; and north-south right oblique normal faults
(youngest), all of which cut pre-Tertiary metamorphic rocks, Mesozoic
limestone, Miocene molasse and calcarenite. The type of rock exposed at
the surface depends on the pattern of separation of the stratigraphic
succession across east-west faults (Fig. 1).
||Figure 1. Basement rocks in the study
area represent a stack of nappes consisting of Late Paleozoic and
Mesozoic metamorphic rocks emplaced in mid-Miocene time (upper diagram)
and displaced by east-west striking faults (lower diagram). The nappe
sequence is overlain non-comformably by Neogene sedimentary rocks.
The two diagrammatic cross sections are parallel to the N-S coastline.
The youngest, least metamorphosed, and structurally weakest rocks
are at the base of the sequence. The colored bar in the lower diagram
indicates those parts of the sequence that are presently exposed along
the seacoast flank of the Catena Costiera.
Small, underfit alluvial fans, composed chiefly of locally derived debris
flow detritus, are present at the mouths of large, west-flowing canyons,
some of which reach eastward to the crest of the mountain range. Not only
do the north-south normal faults displace rocks and structure of all orientations,
but they also make steep scarps in the small alluvial fans and in sediments
of the coastal plain. Recent debris flow deposits locally bury some of
the fault scarps.
Incipient young rivers utilized the weaknesses along the major faults
and cracks as avenues of erosion. Smaller streams and gullies generally
flowed westward or down flank of the north-trending horst and thereby
incised deep, V-shaped canyons; some of which have captured older SW-flowing
canyons. Locally they were guided in other directions where they encountered
faults or tectonic fractures (Fig. 2).
||Figure 2. Schematic fault and drainage
patterns. The sinuous lines on the left-hand sides of each diagram
represent the coast line. Relative age of faults: black (oldest),
blue, green, orange (youngest).
The rocks present varied resistance to erosion, depending on the degree
of cementation by groundwater salts, on the orientation of the foliation,
and on the rock types. Thus mica schist with a relatively flat foliation
forms nearly vertical sea cliffs, but the sea cliffs have a gentler slope
where the foliation is steep or dips toward the sea. Therefore, downslope
movements are facilitated by seaward slip on foliation, schistosity, bedding,
and fault surfaces, and they are especially evinced by large and deep
pre-Holocene landslides (Sackung) in phyllite up to 2 km2.
Other downslope processes include surface creep and soil slip, particularly
in highly fractured phyllite and schist, block sliding and rock falls.
These downslope movements are just one of several geologic
hazards in the study area.
Main Conclusions from this Study
Slope Process: Landslides
slip on foliation, bedding, low angle faults
high-grade metamorphic rocks make resistant cliffs
slaty and phyllitic rocks are highly prone to landslides.
Determinant of Rock Distribution:
of four sets of faults bringing rocks of variable resistance
to the range front.
of Landslides: >40,000
sea level was 100 m lower – now the major slides have
stabilized with their toes buttressed by recent marine deposits.