THE ORIGIN OF CERTAIN WIDE VALLEYS IN THE CANARY-ISLANDS

The present work addresses a long-term controversy concerning the origin of Orotava Valley, one of the most peculiar valleys in the Island of Tenerife (The Canary Islands, Spain). This valley is characterized by its great width, its flat floors gently inclined towards the sea, its parallel and almost vertical lateral slopes, and its equally steep but irregular valley-head, where there are recent volcanic cones, the source of the lava flows that have covered the valley floor. Several different theories were formulated since the last century for the formation of Orotava Valley. Examination of other wide, volcanic valleys and gorges in Tenerife, whose origin may be similar to Orotava Valley, indicate an alternation of erosion/volcanism. Analysis of the key features of Orotava Valley itself leads to formulation of an hypothesis which could be applicable to numerous volcanic areas. Such valleys are developed as volcanic valleys undergo lateral expansion due to repeated alternations of processes: initial erosion of the gorges by streams. the burial of the gorges by lava flows, and the inversion of the relief by erosion at the base of valley walls. The continued occurrence of this mechanism causes the side walls of the valley to retreat progressively giving a configuration similar to that of Orotava Valley.