Geological risk assessment of the area surrounding Altamira Cave

Geological risk assessment of the area surrounding Altamira Cave: A proposed Natural Risk Index and Safety Factor for protection of prehistoric caves

Miguel A. Sánchez, Alberto Foyo, Carmen Tomillo, and Eneko Iriarte

Altamira Cave occurs in a carbonate sequence-dated as middle to upper Cenomanian, being characterized by tabular bedding. This sequence has been studied in detail and mapped in an attempt to delimit the beds in which the cave was formed. The cave forms part of a karstic complex developed in the Altamira Formation, which consists of eight stratigraphic units characterized by karstic forms and landslides as the main geomorphologic elements. The strong relationship between sinkholes and faults within the area was also revealed, with sinkholes of oval morphology aligned along the faults. Inside the cave, the subhorizontal bedding is intersected by subvertical joints, generating geometrical blocks prone to falling down. This is the main process of the present evolution of the cave in addition to the dissolution and precipitation of carbonates in local zones. We used this geological characterization as the basis for the definition of protection areas around prehistoric caves, applied in this article to the Altamira Cave. Landslides, water flow towards the cave, rock falls within cave and karstic features are the main geological risks affecting the karstic complex. Two semi-quantitative indexes were proposed, the Natural Risk Index (NRI) and Safety Factor (SF), with the main aim of determining the risk level in different zones of the study area. The information provided by geological studies as well as the results obtained using the proposed indexes allowed definition suitable protection areas around the cave.

Keywords: Geological risk; Protection areas; Prehistoric caves; Altamira Cave; Spain

Engineering Geology Volume 94, Issues 3-4, 2 November 2007, Pages 180-200

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