MINE SINKHOLE IN SICILY: GEOMORPHOLOGIC AND ENVIRONMENT HAZARD | ||
| The Egyptian Journal of Environmental Change | ||
| Article 7, Volume 1, Issue 1, October 2009, Pages 34-43 PDF (281.85 K) | ||
| Document Type: Peer-reviewed articles | ||
| DOI: 10.21608/ejec.2009.96549 | ||
| Abstract | ||
| The most complete Messinian evaporitic successions present in the Mediterranean can be found in Sicily. They are known as “Gessoso Solfifera Formation” and they widely emerge on the surface in the Sicilian central basin, Geologically known as " Caltanissetta Basin ", extending in direction NE-SW for around 140 Km, with a width of around 80 Km. Inside this area there are the Sicilian salty formations. The salt in these layers is white coloured and normally has an average grade in NaCl superior to 98%, which is comparable to the best of such layers in the whole world. In some mines KCl salts are extracted. However, NaCl remains the mineral more abundant with stratigraphic thickness of several hundred meters. Given the remarkable mining importance of the products of the “Gessoso Solfifera Formation”, in the central-Southern Sicily, since ancient times, different mining centres for the extraction of potassic salts and/or of rock salt have been developed. The greatest of such mines falls into the provinces of Enna, Caltanissetta and Agrigento. Among the many existing mines in the Sicilian territory at the moment, only two are active. All the others are disused and abandoned, sometimes without any control. For this reason and for the great solubility of this salt, the most feared events in these sites are: sinkholes and environmental pollution linked to the extraction procedures of the mineral. The mining basin of Racalmuto, classified as one of the greatest in Sicily, is a solid example of the geomorphologic modifications of the territory linked with the presence of the mines that are now abandoned. In this area, both halite and sylvite were extracted and the whole mining layer, given its dimensions, was separated in three sectors: a Western (Mine of Racalmuto) a central, and an oriental (Mine of Montedoro). The mines, built on more levels than one, had the typical structure of a gallery; chambers and pillars. The alkaline chlorides as sodium chloride (NaCl) and potassium chloride (KCl), suffer processes of dissolution because of the circulating waters which infiltrate the subsoil. The salts solubilisation has created a weakening of the hollow vaults of the mining tunnels producing, in extreme cases, sudden and local collapses that have involved the topographical surface (sinkholes), including in some cases, road and housing structures. The sinkholes, occurring in these areas, are often situated in correspondence with the meeting points of the mining galleries. They have almost always sub-circular shapes and diameters varying in depth. At the moment, the mine of Racalmuto (Western sector of the basin) in the layer of sub-emerging rock salt, shows an abyss of approximately 200 m in width and 40 m in depth. The mine was disused and finally abandoned because of the elevated depths of cultivation reached. The sinkhole occurred suddenly, swallowing the whole headgear of the well with some neighbouring buildings. The mine of Montedoro rises in an area where the covering grounds are clays that found the roof of the salty layer. The mining collapse in this case is produced by the missed covering of the well that has allowed the infiltration of the rainy waters inside the mine, destabilizing also the surrounding territory. Finally, in the central sector of the basin of Racalmuto there is another mine, disused for many years, and has in surface a large number of sinkholes resulting in critical instability of the area. The dimensions of the greatest sinkhole are approximately of 100 m in width and of 200 m in depth. The sinkholes, currently individualized, can be found in anthropic areas with road infrastructures and residences, and in sites used by man for cultivation and/or pasture. In many cases they are reasons for damages to houses and the activities that develop in the near areas. For this reason, the need for an accurate evaluation of the risk caused by this phenomenon, and a correct management programme of the territory are born. | ||
| Keywords | ||
| sinkholes; mines; Gessoso Solfifera Formation; evaporite dissolution | ||
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