The Calabrian fiumara streams

Sorriso-Valvo M, TERRANOVA O, 2006, The Calabrian fiumara streams, Zeitschrift für Geomorphologie. Supplementband 143 (2006): 109–125.,

Calabria is the southernmost part of the Italian peninsula. Its climate is Mediterranean with arid conditions along spots of the Ionian coast and montane modifications. Its morphology is dominateci by tectonics, with mountains and valleys corresponding to uplifted blocks and intervening grabens, respectively. Most of the streams in Calabria are fiumara torrents with very steep slopes and riverbeds; the latter are usually flat, braided and wide, covered with coarse-grained alluvium. Alternating predominance of debris production by mass-movement and erosion on slopes, and of the transport capacity of fiumara torrents, gives rise to their typical strong aggradation/degradation cycles which may last from years to centuries. Factors of fiumara generation are essentially four_ geodynamics, lithology of the drainage basins, climate and human pressure. Geodynamics, in particular tectonic uplift, is the generator of relief energy keeping the morphogenetic processes at a high magnitude and in a relatively stationary condition since the end of the Early Quaternary. Occasionally, earthquakes act as landslide trigger events. Widespread diffusion of lithic rocks is the origin of coarse-grained alluvium. Aggressive clima te with intense storms and high variability is the cause of widespread mass-movement reactivation. Human pressure acting either directly on riverbed stocks, or indirectly on climate changes, may strongly influence the degradation/ aggradation regime of fiumara torrents that, in turn, is reflected in the beach aggradation/degradation regime. Hypsometric curves of fiumara basins are predominantly concave, even though departures from this form are numerous; the average value of the hypsometric integrai, however, indicates equilibrium conditions. This may explain why riverbeds of fiumara, though presenting aggradation/degradation cycles, are essentially stationary forms since a t least the Holocene. The drainage network is characterised by a high number of anomalous branches. The hydraulic regime of fiumara is typically torrential as regards surface runoff, but a relatively regular ground-water flux in the alluvial bed is a common feature. In comparison to other Mediterranean ephemeral streams, Calabrian fiumara streams are characterised by an extremely high rate of mass-movement on the slopes, by a high solid/liquid discharge average rate, by the scarcity of evidences of discontinuous gullying to accommodate for stages of reduction in solid/liquid discharge rate, and by the neat prevalence of fiumara torrents on the Ionian side of Calabria, due to the geologica! and climatic peculiarities of this side of the peninsula ..

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