Instability phenomena in the evaporite karst of Calabria, Southern Italy

Instability phenomena in the Upper Miocene to Pleistocene deposits of the evaporite karst in the Crotone Basin (Calabria, southern Italy), are described in this article. Calabria is worldwide known as one of the most landslide-prone areas in the Mediterranean basin. Different types of slope movements affect the outcropping rocks in the region, due to the combined action of a number of causal factors, either predisposing (abundance of weathered materials, rugged topography, high relief energy, and active tectonic uplift), or triggering (heavy rainfall, moderate to strong seismic shocks, and anthropogenic action). In a karst area, such as that dealt with here, further instability is related to development of sinkholes, subsidence phenomena, and the presence of karst caves: the area includes several renowned caves as the system Grave Grubbo - Vallone Cùfalo (the second longest Italian gypsum cave, with a length over 2,800 m). Observed slope movements belong to diff erent typologies, with the greater impact on the anthropogenic environment deriving from rockfalls above the main communication routes. A less dramatic but very subtle type of instability is represented by sinkholes, a very common karst landform in evaporite rocks. Many caves have their entrance at the base of large sinkholes or in their proximity. Th e effects from gravitational and erosional processes are described in the article also through direct observations within the underground system, which pattern is controlled by a combination of tectonics and breakdown mechanisms. Th e low resistance of evaporites, locally increased by prevailing clays in the stratigraphy, determines high frequency of fallen blocks. The comparison between the landforms and deposits observed at the surface and underground pointed out to the difficulty in directly linking what is observed at the ground with the processes acting within the karst system. This has obvious consequences in terms of civil protection, due to the lack of premonitory signs at the ground surface, or to difficulties in observing, and correctly evaluating, such signals.