The phenomenon of karst. The big epigean karst form.

The rocks are subjected to a continuously action of modeling done by atmospheric agents. Especially water has an important role in the evolution of landscape, because exerts a mechanical action of erosion and a strong chemical action of dissolution for some types of rocks, such as gypsum. Water sculpts and models the rocks, seeps along the breaks digging them deeply; on the surface, it creates characteristics shapes and, in the underground, it give rise to extended systems of tunnels. This process is called “karst”.
The name “Karst” takes its origins from the pre-Indo-European “kar” that means “stone” and that is present in many languages of Europe and Middle Est. 

Dolines – In Sicilian dialect  they are called “zubbie”, they are the largest karst forms in the chalky rocks. They are closed basins, with a diameter ranging from a few meters to a kilometer, with a draining bottom that allows the infiltration of the rainwater in the underground. They can have different shape and origin; frequently, on the bottom, there is a sinkhole that give access to an underground cavity.

-Doline of subsidence       -doline of collapse       -doline of solution      – doline in the coverage    
 -asymmetric doline       -funnel-shaped doline.

Blind valleys – They are diffused in the chalky areas, they are valley with more or less steep slopes, wich end abruptly at a chalky wall where at the bottom there is a sinkhole; here the river’s water goes into the undersoil, flow in the undersoil and then re-emerges, even after many kilometers, through a resurgence.