Aspects of weathering and landforms evolution on gypsum slopes and ridges of Sicily

Abstract

In Sicily, on the rocky outcrops of the gypsum, it is possible to recognize a weathering crust, which is often evidenced by a polygonal pattern and by some gypsum bubbles. The crust is the consequence of the phenomenon of expansion of the outer layer of the gypsum. The main forms of the crust are described as gypsum bubbles, pressure ridges, pressure humps, pans, pancakes, and steps. The evolution of the crust seems to be linked to a mass transfer by solution inside the outer gypsum layer and to the growth of crystals; these are controlled both by the seasonal cycle of the pore water and by single event cycles determined by rainfall episodes during the summer season. The dynamics of the crust also influence the evolution of larger forms such as the «mega bubbles», and the domelike hills, minimizing the influence of the pre-existing structural elements.