MORPHOMETRIC INTERPRETATION OF THE NORTHWEST AND SOUTHEAST SLOPES OF TENERIFE, CANARY-ISLANDS

Both the northwest and southeast slopes of Tenerife, Canary Islands, o we their morphology to catastrophic sediment failures. An area of 4100 km(2) and a volume of about 2362 km(3) were involved in the failure. A 100- to 600-m-high scarp on the upper slope separates the sediment f ailures in the Orotova and Iced de los Vines Valleys on the northwest coast from those on the slope. A similar (700 m high) scarp also separ ates the failures on the southeast slope from the failure in Guimar Va lley on land. The sediment failure off Las Bandas Del Sur volcanic fan does not have any land counterparts and was the result of the failure of the front (1700 m high) of this depocenter; two generations of deb ris flows are mappable off this depocenter. We infer that the slopes o ff Orotova, Iced, and Guimar represent the front of the debris avalanc he and/or creep deposits that were created during the formation of the valleys. Downslope from the debris avalanche fronts are irregular sur faced masses extending to the base of the slope. The front may define the contact between the more dense deposits onshore and upper slope an d the more fluid deposits on the lower slope, Incised on the debris av alanche on the northwest lower slope are three channeled debris flows grading seaward into turbidites. Only one of these channels occurs on the southeast slope. The breakaway surface of these sediment failures was the front of the debris avalanches and/or creep. We ascribe the fa ilure of this front mainly to its rapid buildup, although groundwater sapping also may have contributed to its failure. On the southeast slo pe, movement along the northeast trending fault between Gran Canaria a nd Tenerife also may have been a contributing factor to the failure of the front. The debris flow deposits triggered by the failure of the s ediment front on the northwest slope are characterized by ridges forme d either by pressure between flows moving at different velocities or b y scouring; at least one volcanic edifice occurs within the deposit. A lthough the avalanche and associated debris flow surfaces on the north west slope appear pristine, being only partially covered by lava flow from a volcano in one of the channels, those on the southeast slope ar e partially buried by postfailure volcanics and detrital sediments. At the distal end of the slope failure masses, there are extensive fans, On the southeast slope these depocenters were reworked into a sedimen t drift field of northeast trending ridges by the southerly flowing No rth Atlantic Deep Water. On the surfaces of the fans off the northwest slope, there are exotic blocks transported downslope from their origi nal positions either by riding on the surface of the highly dense debr is avalanche or by being transported within the avalanche itself.