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The Aspromonte Massif, literally “Wild Mountain”, shows a very rugged and uneven topography due to a dense alternation of V-shaped valleys and interfluves. Three broad sets of geomorphic processes are principally responsible for landscape modelling and for carving the wide variety of landforms occurring in Aspromonte: tectonic uplift, river dissection and slope processes. These geomorphic processes, combined with weathering processes and contrasting rock erodibility, make Aspromonte one of the most landslide-prone areas in the Mediterranean basin, and the local river network a large in-channel sediment storage to be conveyed to the sea.

On 15 February 2010, as a result of intense and long-lasting rainfalls, a large landslide affected a wide area near the town of Maierato (Calabria, Italy). The studies conducted – including (i) aerial photo interpretation, (ii) geological and geomorphological field investigations, (iii) interpretations of lithology and stratigraphy from borehole data, and (iv) observation of videos filmed during the main diastrophic phases of the landslide and of antecedent Google Street View® images – allowed researchers to reconstruct the geological and tectonic setting of the slope and the internal structure of the landslide with the estimation of the depth of the sliding surface, the triggering mechanisms and its evolution. The analysis of the prelandslide event setting demonstrates that this mass movement is the reactivation of a preexisting landslide of alleged seismic origin, remaining at an incipient stage. The Maierato landslide occurred on a gentle slope made of late Miocene to Plio-Pleistocene clastic and evaporitic sedimentary rocks. The main basal failure surface that developed on the hemipelagic marls has a maximum depth of 50 m. The volume of the landslide is ~ 5 million cubic meters. The type of landslide movement is a complex one, consisting of a very rapid slide of rock and earth and of flow of debris and earth. The landslide clearly shows three major types of failure mechanisms: the first type is described as a rapidly moving rotational slide where back-tilted blocks of sediment are preserved; the second type includes a very rapidly moving translational slide of large rock blocks; the third type includes sudden, extremely rapid flow-slides where the slide material is disaggregated while flowing downward along a gentle slope. The slide is a compound one, with a retrogressive evolution and transformation into earth and debris flow during the failure. After the triggering of the landslide, and as a result of the relevant displacement, an important portion of the lower evaporitic unit ( Calcare di Base Formation), close to the failure surface, collapsed, thereby undergoing a quick change of its mechanical behavior that became similar to that of a viscous fluid. During the landslide evolution, large rocky blocks consisting of Miocene evaporitic limestones, Pliocene silty clays, and sands were rafted, without severe disturbance, on the destructurated and fluidized limestone. The intense destructuration and the presence of water transformed the limestone (in the lower parts of the unit) into a viscous material that was squeezed out of the landslide mass through the jags between the several rafted rocky blocks and along the natural levees of flow tongue. This event is a rather frequent combination of mass movements made complicated and spectacular by the fluidization of the weak limestone that imparted great dynamics to the movements. Such fluidization is an infrequent phenomenon especially in this geological context.

Deeply weathered plutonic rocks occur widely in the Sila Massif, Calabria, southern Italy. Three representative weathering profiles developed on the hilltops indicate that sand represents more than 50% by weight throughout most of the weathering profile, and silt- and clay-size fractions are also well represented, filling the interstices among corestones. Both sand, and finer fractions of grus, and soil horizons, are thought to be derived from a combination of granular disintegration and chemical decomposition, developed on relatively flat terrains of the Sila massif. These slopes are now experiencing transport-limited morphodynamics, under a montane-modified Mediterranean climate. The depth of the weathered layers, that have suffered little erosional truncation, typically exceed 15 m, and may reach 50–60 m or more. Major isolated or grouped exfoliation boulders are the most common minor landform feature developed on the Sila massif granite. Boulders have developed as a result of spheroidal weathering and by removal of the sandy-textured granite. The Schmidt hammer (SH) test on boulders and corestones, suggests three distinctive degree of weathering (from moderately to completely weathered rock), and that biotite content is the major controlling factor of the granite mechanical behaviour. Understanding of the dynamics of this weathering system is crucial to the interpretation of the complex suite of variables that control landscape evolution of granitoid terrains.

Source rock lithology and immediate modifying processes, such as chemical weathering and mechanical erosion, are primary controls on fluvial sediment supply. Sand composition and Chemical Index of Alteration (CIA) of parent rocks, soil and fluvial sand of the Savuto River watershed, Calabria (Italy), were used to evaluate the modifications of source rocks through different sections of the basin, characterized by different geomorphic processes, in a sub-humid Mediterranean climate. The headwaters, with gentle topography, produce a coarse-grained sediment load derived from deeply weathered gneiss, having sand of quartzofeldspathic composition, compositionally very different from in situ degraded bedrock. Maximum estimated CIA values suggest that source rock has been affected significantly by weathering, and it testifies to a climatic threshold on the destruction of the bedrock. The mid-course has steeper slopes and a deeply incised valley; bedrock consists of mica-schist and phyllite with a very thin regolith, which provides large cobble to very coarse sand sediments to the main channel. Slope instability, with an areal incidence of over 40 per cent, largely supplies detritus to the main channel. Sand-sized detritus of soil and fluvial sand is lithic. Estimated CIA value testifies to a significant weathering of the bedrock too, even if in this part of the drainage basin steeper slopes allow erosion to exceed chemical weathering. The lower course has a braided pattern and sediment load is coarse to medium–fine grained. The river cuts across Palaeozoic crystalline rocks and Miocene siliciclastic deposits. Sand-sized detritus, contributed from these rocks and homogenized by transport processes, has been found in the quartzolithic distal samples. Field and laboratory evidence indicates that landscape development was the result of extensive weathering during the last postglacial temperature maximum in the headwaters, and of mass-failure and fluvial erosional processes in the mid- and low course. Copyright © 2000 John Wiley & Sons, Ltd.

Deep-seated mass-movements of different types affect the Pizzotto–Greci slope in northwest Calabria, Italy. The slope is carved out of phyllitic rocks capped by gneissic layers. Its geological structure is extremely complicated by tectonic structures that pervasively cross the slope transversely and downslope. A large-scale gravitational deformation of sackung type affects the slope. On the upslope side a debris-flow source area feeds a large fan constructed by recurrent debris-flow deposits. Aggradation is consequently occurring along the stream at the base of the slope. In order to define the internal structure of the slope for a stability slope model, geological, geostructural, geomorphological, historical and dendrogeomorphologic studies, as well as direct geotechnical logs and indirect geophysical investigations have been carried out over a two-year project financed by the EC Environment Programme. The main aspects of the geological and geomorphological studies and some preliminary geotechnical data are presented here, along with a conceptual model aimed at describing the relationships between the mass-movements on the slope and the construction/destruction stages of the fan at the base of the slope. The model is based on the assumption that aggradation has a stabilising effect on the slope, thus debris-flow activity is reduced and, consequently, destruction of the fan occurs, bringing the slope again towards unstable conditions. The reactivation of mass-movement, however, leads to the reconstruction of the fan and the buttressing effect at the base of the slope is restored. Thus, the process is cyclic and self-regulating.

Alluvial fans are widespread throughout Calabria, but only a minority display evidence of current activity. In order to understand if and to what extent fan types and their morphology are dependent on the physical environment, including characteristics and processes of the depositional site and drainage basin, we performed a series of discriminant analyses. These analyses used as classification factors the presence or absence of fill in the feeder channel, conditions of confinement by host terrain, the dominant depositional process (debris-flow or sheetflood); and morphometric attributes of fans and drainage basins as the discriminant function variables. in general, fan slope, area and width-length ratio, and, for basins, Melton's ruggedness number and source ratio, were the most useful variables for classification. Best results were obtained by discriminating the types of fan deposits and the presence versus absence of fill in the feeder channel, if the feeder source is singular. Fan morphology is controlled by constructional processes and is tightly linked to basin morphology. On the other hand, fan and basin morphology are also strongly dependent on the rock mechanical characteristics, with hard rocks imparting to the basin a high ruggedness and to fans a high gradient. Larger fans, however, are those where sheetflooding predominates. Results of discriminant analysis based on fan and basin variables are much more significant than those based on fan variables only. This means that the differences between characteristics of fan-and-basin systems are better defined than those between characteristics of fans only. (C) 1998 Elsevier Science B.V. All rights reserved.

Geomorphic and structural studies have been carried out on the headwaters of Vallone Colella Torrent, in an area intensely affected by mass-movement phenomena on the Aspromonte massif of southern Italy. Rock types outcropping in the area are mostly gneiss and granitoids, with subordinate presence of metarenites, phyllites, and biotite schists; all lithologies experienced low-grade metamorphism, as indicated by petrographic analysis. Structural surveys, performed at macroscopic and mesoscopic scale, allowed recognition of several sets of discontinuities related to different deformation events. The upper reaches of Vallone Colella Torrent present a large, active landslide zone, the debris materials of which feed the debris flows along the drainage system towards the main valley. Mass-movement phenomena are both shallow and deep-seated; the latter are limited to a sector of the study area, while shallow processes are present throughout the landslide zone. Some considerations of the relationship between tectonics and mass movement are presented, with particular reference to the presence of a large-scale downthrown wedge (bounded by structural surfaces on both sides of the valley), located in the same area affected by deep-seated phenomena.

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 a variety of 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. 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 structures of all orientations, but they also make steep scarps in the small alluvial fans and in sediments of the coastal plain. Locally, some of the scarps are buried by recent debris flow deposits. Incipient young rivers utilized the weaknesses along the major faults and cracks as avenues of erosion. Smaller streams and gullies generally flowed westward downflank of the north-trending horst and incised, thereby, deep, V-shaped canyons; some of them have captured older, SW-flowing canyons. Locally, they were guided in other directions where they encountered faults or tectonic fractures. The rocks present a varied resistance to erosion, depending upon the degree of cementation by groundwater salts, upon the orientation of the foliation, and upon the rocks themselves. Thus, mica schist with a relatively flat foliation forms nearly vertical sea cliffs, but the sea cliffs are more gentle where the foliation is steep or dips towards the sea. Therefore, downslope movements are facilitated by seaward slip on foliation, schistosity, bedding and fault surfaces, and are evinced especially by large and deep pre-Holocene landslides (Sackung) in phyllite having areal dimensions up to 2 Km2. Other downslope processes include surficial creep and soil slip, particularly of highly fractured phyllite and schist, block sliding and rock falls.

A graphical and statistical treatment of data taken from a sample of 40 rock avalanches selected mainly from the literature enables us to distinguish three ways in which the local morphology controls the shape and motion of such landslides. The three different situations are characterized as follows: (1) channeling of the debris mass, (2) unobstructed spreading of the debris mass, and (3) right-angle or almost right-angle impact against an opposite slope. Mobility of rock avalanches decreases going from situation 1 to situation 3. As presumably local morphology exerts its action ("geomorphic control") by influencing the rate of dissipation of the total mechanical energy involved in the process, the three cases are respectively defined as low-energy-, moderate-energy-, and high-energy-dissipative. As secondary results, we find the following. (1) By using the properties of the ratio of "excessive travel distance" to "travel distance," the Hsu (1975) runout-prediction model can be modified so as to avoid the difficult problem of estimating the landslide volume prior to failure. (2) If landslide volume and type of geomorphic control can be preliminarily estimated, then a maximum possible runout can also be computed corresponding to each of the three classes of geomorphic control.