Abstract

Despite the numerous geological and geophysical studies performed in Las Cañadas Caldera (LCC; Tenerife) its origin is still controversial between two different hypothesis: 1) a nested collapse caldera formed by three different vertical collapses; and 2) one or several lateral landslides. We have critically analyzed the implications of the existing hypothesis, looking for evidences which allow discarding any of them. We have gathered in a 3D GIS the existing geological information from water galleries and boreholes drilling LCC and Icod valley together with off- and on-shore geological, volcanological and geophysical data. This allows us to obtain a coherent surface of Icod landslide breccia deposits, although data from LCC are still insufficient to discard any hypothesis base on the breccia geometry. Other data from LCC, such as Montaña Majua borehole, allows making estimations of the geometry of the proposed calderas. For Guajara caldera case (6.5 km diameter) a 1500 meters minimum depth is obtained, resulting in a theoretical volume of around 50 km3. Applying typical density values for magma and pyroclastics, this represent an emitted volume of around 250 km3 of pyroclastics (pumice + ignimbrite). Since the Granadilla eruption, the proposed Guajara caldera forming event, has produced a maximum estimated volume of 25 km3 of pumice (including offshore estimations), the emitted ignimbrites should have a total volume of more than 200 km3, which seems highly improbable due to the estimated 5 km3 volume of onshore ignimbrites. Therefore, our results cast further important doubts about an origin related to vertical magmatic collapses for LCC, the most widely cited hypothesis at present. In our opinion existing data do not allow discarding the lateral avalanche origin for LCC but show some questions still open about the geometry of the Icod landslide and therefore additional geological and geophysical data of the area are necessary.