Gibraltar is composed of several different types of sedimentary rock. Fossiliferous limestone dating back from the Jurassic period, some 200 million years ago, forms the main structure of the Rock of Gibraltar (Rose & Rosenbaum 1991). Tectonic plate movements brought the continents of Europe and Africa closer together, therefore crumpling the mountain chains bordering the Mediterranean Sea. This produced an arc of mountain chains known as the 'Arc of Gibraltar' and is composed of the Betic Cordillera running along the mountain chain near Alicante, down through the Sierra Nevada and Sierra de los Filabres curving through the mountains on either side of the Strait and forming the southerly arc encompassing the Rif mountain chain of Morocco.
The uniqueness of the geology of the Rock of Gibraltar in relation to the surrounding countryside is a determining factor in the variety of flora that can be found here and signifies the importance Gibraltar has in contributing to the diversity of flora and fauna of the Strait area.
Over time, major changes in the relative sea level of the Mediterranean Sea have taken place. These changes were as a result of various factors including changes in the polar ice cap during the ice ages that have resulted in the formation of several raised beaches and wave-cut platforms, a feature that is unique in the region. These changes in sea level have also resulted in numerous caves being formed through the action of the sea and the erosion of the rock by groundwater flowing to the sea (Rose & Rosenbaum, 1991).
Caves have been forming for thousands of years, as weakly acidic ground water has flowed down the cracks and fissures of the fractured Gibraltar limestone, reacting with and dissolving the rock. This has resulted in numerous caves around Gibraltar, with some located below sea level and formed during the ice ages when the level of the sea around Gibraltar was much lower, or when the landmass rose above the level of the sea (Rose & Rosenbaum 1991).
Some of caves within the Nature Reserve show evidence of occupation by early man. Testimony of this can be found in the results of many excavations carried out by enthusiastic military personnel in the 19th century, which prompted some renowned archaeologists to visit and excavate some of our caves in the 20th century. Amongst these were Abbe Breuil, Dorothy Garrod and G. Waechter. The former two investigated the site of the Neanderthal skull at Forbes Quarry and also the Mousterian rock shelter at Devil’s Tower Cave. The latter accomplished a comprehensive excavation of Gorham’s Cave at Governor’s beach using the archaeological methods available at the time. No consideration was given to the caves located on the Upper Rock. This was possibly due to military restrictions in force during the two World Wars. These restrictions continued into the 1960s, during which time access was permitted to the local population only during daylight hours. It was during this period that the Gibraltar Cave Research Group was formed. This group had a major impact on the knowledge we now have at our disposal. One of the members of this group, George L. Palao, recorded in an unpublished map of 1966-68, over 107 caves, some of which have since been excavated and surveyed. Since then, other speleological enthusiasts have discovered a few more.
As the local competent authority, the Department of the Environment, on behalf of H.M. Government of Gibraltar, aims to minimise the threats to, and preserve, our unique caves. Within this website, we have highlighted some of those caves that are found in a natural state within the Upper Rock Nature Reserve, or have been discovered within main cave systems or in tunnels that can be accessed within the Reserve.
Perez, C.E. & Bensusan, K. (2005) The Upper Rock Nature Reserve, A Management and Action Plan. The Gibraltar Ornithological & Natural History Society. Gibraltar.