Deterioration Processes on Prehistoric Rock Art Induced by Mining Activity (Arenaza Cave, N Spain)

Arenaza Cave is located in Vizcaya (N Spain) and contains important Palaeolithic rock art representations. This cave belongs to an active karstic system developed on Lower Cretaceous limestones, mainly consisting of micrites and biomicrites with abundant pyrite moulds. The paintings are made directly on the host rock or on thin stalagmitic calcite crusts. Cretaceous limestones in this area contain important iron ore deposits, which have been mined by subsurface and surface-mining methods since the beginning of the 20th century. Mining activities have induced significant changes in the karstic drainage pattern and in the endo and exokarstic morphologies of the Arenaza karstic system, directly affecting the state of conservation of the prehistoric paintings. Thus, in addition to natural process of deterioration, the enlargement of the limestone fissure system as a result of blasting-induced vibrations seems to be the responsible for changes in the rates of water-rock interactions and of the formation of botryoidal gypsum concretions on the rock surface. The final result is the activation and acceleration of detachment processes and the increase of irreversible deterioration processes in the cave.