Post-fire erosion response in a watershed mantled by volcaniclastic deposits, Sarno Mountains, Southern Italy

In this study we document a post-fire erosion response to a short-lived, intense rainstorm occurred on 6 September 2012 in the Sant'Angelo creek watershed, Sarno Mountains, Southern Italy. The rainstorm occurred one month after a wildfire that burned about 11 ha of the steep watershed (55 ha), almost entirely mantled by volcaniclastic deposits. The research was based on fieldwork and laboratory analysis addressed to the understanding of the geomorphic effects of the wildfire and their impact on erosional and depositional processes triggered by subsequent rainstorms. Field evidence indicates that a series of overland flows caused significant runoff and sediment yields along the hillslope and accumulation of hyperconcentrated flow deposits in a concrete channel occluded by a sealed culvert at the outlet of the watershed. The results of geomorphological and sedimentological analysis suggest that the occurrence of volcaniclastic covers mantling the slopes likely favored accelerated soil erosion, especially where vegetation and litter had been removed by the fire. Chemical analysis on sediment samples, revealed the occurrence of iron oxides that enhanced soil water repellency conditions over wide areas of the burned watershed compared to the unburned areas. Quantitative analysis of sediment budgets showed that the rainfall-induced erosion response at Sant'Angelo creek watershed resulted in a soil loss of 19.8-33.1 tons ha(-1) over bumed areas. Post-fire erosion response following severe rainstorms needs to be considered in the spectrum of natural hazards associated with the geomorphological evolution of mountainous landscapes mantled by volcaniclastic deposits.