Dissolution processes on the gypsum surfaces
The process of karstification - the formation of caves and related surface features - arises from the gradual dissolution and erosion of the rock; in our case, gypsum. But how fast does gypsum dissolve in nature? How long does it take to form a large gypsum cave?
In order to answer these questions, various monitoring stations were installed in the vicinity of the Cueva del Agua, which allowed the scale of this dissolution process to be assessed. Some unexpected data resulted. It was shown that the rates of dissolution and erosion on the ground surface of the gypsum karst were several times greater than the rate within the caves. The average lowering of the gypsum ground surface is 30 cm every 1000 years, while the galleries of the cavities "grow" by some 10 cm in width every 1000 years.
This difference is due to the fact that rainwater, which is very aggressive at first, becomes saturated with gypsum within the first few metres of its subterranean journey, thereby losing much of its aggressive potential. Only during periods of very high rainfall, when infiltration is tremendously rapid, does dissolution in the interior of the cavity become really significant. So karstification in a semiarid climate like that of Sorbas can be considered as a sporadic process, with marked peaks and troughs through time. For this reason, the Sorbas Caves form and grow only during periods of torrential rainfall.
Dissolution processes on the gypsum surfaces