The gypsum massif of Sorbas (Almeria, SE Spain) is composed of very pure selenite and hosts important karst features and large number of caves. From a geological point of view this area is located in the Tabernas-Sorbas Basin, a intramontane Neogene depression in the Betic Belt where Messinian evaporite deposition occurred on silty and clay outcrops. The structure is poorly-deformed tabular and stratification slightly inclined. The landscape stands about 400 metres out above sea level topographical elevated, NE-elongated platform with steep edges looking out on dry valleys. The gypsum beds gradually disappear N-towards under the most recent continental sediments. The karst surface counts dolines, different forms of karren, fields of tumuli. The surface drainage is essentially ephemeral and loser, due to the semi-arid climate (210 mm/year), where most of the rain contributions reach the karst aquifer quickly. It is hierarchical and dependent mainly from the tectonic control and, secondarily, by the geometry of the strata. The main cave system in the study area is the Cueva del Peral. The great importance of this cave is due to a steady underground flow that giving rise to the spring of Peral (410 m asl). The groundwater drainage is strongly related to geological and structural control. Inside the karst system, it follows the gypsum and marl contact with a large discharge variation as a function of precipitation. The low water discharge of this perennial karst spring seems guaranteed by condensation process. The aim of this research is to detect the underground drainage direction performing hydrogeological study. For this purpose a dye test has been carried out, injecting 1 kg of fluorescein in the Peral stream and monitoring both the main outlets of the karst massif (Los Molinos and La Fortuna springs) and drinking water treatment plant of Sorbas village. During charcoal captors collections, physical-chemical parameters of the water have also been recorded. After KOH ethanol extraction, charcoals have been analysed, by a Turner Designs Digital Fluorimeter (10-AU-000 model - Detection limits 0.01 ppb) equipped with quartz cuvette and UV bulb lamp. The negative results at the all monitoring points show that the underground water is forced to stream towards the aquifer without reaching any of the known springs. A deeper groundwater flowing into the lowest gypsum strata draining directly towards NW through speleologically inaccessible karst systems hypothized.
Study of underground drainage in the Peral Cave (Sorbas, Spain).
Laura Sanna
2013
Abstract
The gypsum massif of Sorbas (Almeria, SE Spain) is composed of very pure selenite and hosts important karst features and large number of caves. From a geological point of view this area is located in the Tabernas-Sorbas Basin, a intramontane Neogene depression in the Betic Belt where Messinian evaporite deposition occurred on silty and clay outcrops. The structure is poorly-deformed tabular and stratification slightly inclined. The landscape stands about 400 metres out above sea level topographical elevated, NE-elongated platform with steep edges looking out on dry valleys. The gypsum beds gradually disappear N-towards under the most recent continental sediments. The karst surface counts dolines, different forms of karren, fields of tumuli. The surface drainage is essentially ephemeral and loser, due to the semi-arid climate (210 mm/year), where most of the rain contributions reach the karst aquifer quickly. It is hierarchical and dependent mainly from the tectonic control and, secondarily, by the geometry of the strata. The main cave system in the study area is the Cueva del Peral. The great importance of this cave is due to a steady underground flow that giving rise to the spring of Peral (410 m asl). The groundwater drainage is strongly related to geological and structural control. Inside the karst system, it follows the gypsum and marl contact with a large discharge variation as a function of precipitation. The low water discharge of this perennial karst spring seems guaranteed by condensation process. The aim of this research is to detect the underground drainage direction performing hydrogeological study. For this purpose a dye test has been carried out, injecting 1 kg of fluorescein in the Peral stream and monitoring both the main outlets of the karst massif (Los Molinos and La Fortuna springs) and drinking water treatment plant of Sorbas village. During charcoal captors collections, physical-chemical parameters of the water have also been recorded. After KOH ethanol extraction, charcoals have been analysed, by a Turner Designs Digital Fluorimeter (10-AU-000 model - Detection limits 0.01 ppb) equipped with quartz cuvette and UV bulb lamp. The negative results at the all monitoring points show that the underground water is forced to stream towards the aquifer without reaching any of the known springs. A deeper groundwater flowing into the lowest gypsum strata draining directly towards NW through speleologically inaccessible karst systems hypothized.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
