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Every year, and in many countries worldwide, wildfires cause significant damage and economic losses due to both the direct effects of the fires and the subsequent accelerated runoff, erosion, and debris flow. Wildfires can have profound effects on the hydrologic response of watersheds by changing the infiltration characteristics and erodibility of the soil, which leads to decreased rainfall infiltration, significantly increased overland flow and runoff in channels, and movement of soil. Debris-flow activity is among the most destructive consequences of these changes, often causing extensive damage to human infrastructure. Data from the Mediterranean area and Western United States of America help identify the primary processes that result in debris flows in recently burned areas. Two primary processes for the initiation of fire-related debris flows have been so far identified: (1) runoff-dominated erosion by surface overland flow; and (2) infiltration-triggered failure and mobilization of a discrete landslide mass. The first process is frequently documented immediately post-fire and leads to the generation of debris flows through progressive bulking of storm runoff with sediment eroded from the hillslopes and channels. As sediment is incorporated into water, runoff can convert to debris flow. The conversion to debris flow may be observed at a position within a drainage network that appears to be controlled by threshold values of upslope contributing area and its gradient. At these locations, sufficient eroded material has been incorporated, relative to the volume of contributing surface runoff, to generate debris flows. Debris flows have also been generated from burned basins in response to increased runoff by water cascading over a steep, bedrock cliff, and incorporating material from readily erodible colluvium or channel bed. Post-fire debris flows have also been generated by infiltration-triggered landslide failures which then mobilize into debris flows. However, only 12% of documented cases exhibited this process. When they do occur, the landslide failures range in thickness from a few tens of centimeters to more than 6 m, and generally involve the soil and colluvium-mantled hillslopes. Surficial landslide failures in burned areas most frequently occur in response to prolonged periods of storm rainfall, or prolonged rainfall in combination with rapid snowmelt or rain-on-snow events. © 2011 Springer Science+Business Media B.V

Salento, the southern portion of Apulia region (SE Italy), is a narrow and elongated peninsula in carbonate rocks, with prevailing low coastlines, locally interrupted by high rock cliffs. The long stretches of low coasts are marked by typical karst landforms consisting of collapse sinkholes. As observed in many other karst coastal settings worldwide, development of sinkholes may be particularly severe along the coasts, where both natural and anthropogenic processes contribute to accelerate the dissolution of carbonate rocks and subsidence processes, even influencing the coastline evolution. Following a previous study, where the main features of sinkholes at Torre Castiglione (Taranto province) were investigated and described, and a preliminary susceptibility map produced, at the light of updated data and elaborations in the present paper we perform a detailed morphometric analysis on the sample of identified sinkholes. The main morphometric parameters generally used for sinkhole characterization have been considered in this study: shape of the sinkhole, azimuth and length of maximum and minimum axes, depth, elongation ratio, and distance from the shorelines. Each of them is described, both as individual parameter and in conjunction with the others, in the attempt to identify the main factors controlling development of sinkholes in the area, and their evolution as well. With regard to this latter aspect, beside simple morphometry of the sample of sinkholes at Torre Castiglione, we also focused our attention on the likely relationships existing between distribution and shape of the sinkholes and the tectonic discontinuities. To investigate the matter, a three-stage analysis has been carried out in this study by means of: field measurements of the fractures bounding the sinkholes, field measurement of the long axes azimuth of the elongated sinkholes, comparison of the previously described sets with the strikes of the main regional geological structures. The obtained results show, in addition to the coincidence of the main regional discontinuity systems with the major axis of elongated sinkholes, a clear control exerted by development and evolution of the sinkholes on the formation of coastal inlets and bays. Eventually, the approach here presented may be applied in other karst coastal sinkhole-prone areas, to gain new knowledge on the genesis and evolution of coastal sinkholes, and to properly evaluate the hazard they pose to the anthropogenic environment. © 2013 Springer-Verlag Berlin Heidelberg

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