Geological and geomechanical models of the pre-landslide volcanic edifice of Güيmar and La Orotava mega-landslides (Tenerife)

The geological and geomechanical characterizations of the volcanic rock mass succession affected by the Güímar and La Orotava mega-landslides (Tenerife, Canary Island) are presented here for the first time. The estimated subaerial volume of rocks mobilized by each of these landslides is in the range of 30–50 km3, one of the largest known in the world. Field data, gallery surveys and borehole drilling have allowed the main types of materials and their structural arrangement to be identified. Based on these information a geological model of the pre-landslide volcanic edifice is proposed. A palaeo-morphological reconstruction has been produced and possible slope angles and heights of the pre-landslide volcanic edifice are presented. Five main lithological units have been identified in the emerged part of the edifice, three of them forming the flanks and two forming the structural axis of the island. On the flanks, lava flows predominate with different degrees of alteration and proportion of dikes increasing near the structural axis. The predominant materials on the structural axis are pyroclastic deposits, lava flows and dikes. In the submarine edifice four main lithological units have been distinguished, formed by hyaloclastites, pillow-lavas, dikes and gravitational deposits (slope and basin facies). The geomechanical characterization of these materials has been obtained from field data, boreholes, laboratory tests and literature review. The geological and geomechanical models obtained provide the fundamental basis for the explanation of the instability processes that generated the Güímar and La Orotava mega-landslides.