Evolution of the north flank of Tenerife by recurrent giant landslides

Geomorphologic analysis of submarine and subaerial surface features using a combined topographic/bathymetric digital elevation model coupled with onsh ore geological and geophysical data constrain the age and geometry of giant landslides affecting the north flank of Tenerife. Shaded relief and contou r maps. and topographic profiles of the submarine north flank, permit the i dentification of two generations of post-shield landslides. Older landslide materials accumulated near the shore (<40-km) and comprise <similar to>700 km(3) of debris. Thickening towards a prominent axis suggests one major la ndslide deposit. Younger landslide materials accumulated 40-70 km offshore and comprise the products of three major landslides: the La Orotava landsli de complex, the iced landslide and the East Dorsal landslide complex, each with an onshore scar, a proximal submarine trough, and a distal deposit lob e. Estimated lobe volumes are 80, 80 and 100 km(3), respectively. The old p ost-shield landslide scar is an amphitheatre, 20-25 km wide, partly submari ne. now completely filled with younger materials. Age-width relationships f or Tenerife's coastal platform plus onshore geological constraints suggest an age of ca. 3 Ma for the old collapse. Young landslides are all less than 560 ka old. The La Orotava and Iced slides involved failures of slabs of s ubaerial Rank to form the subaerial La Orotava and Iced valleys. Offshore, they excavated troughs by sudden loading and basal erosion of older slide d ebris. The onshore East Dorsal slide also triggered secondary failure of ol der debris offshore. The slab-like geometry of young failures was controlle d by weak layers, deep drainage channels and flank truncation by marine ero sion. The (partly) submarine geometry of the older amphitheatre reflects th e absence of these features. Relatively low H/L ratios for the young slides are attributed to filling of the slope break at the base of the submarine edifice by old landslide materials, low aspect ratios of the failed slabs a nd channelling within troughs. Post-shield landslides on Tenerife correlate with major falls in sea level, reflecting increased rates of volcanism and coastal erosion. and reduced support for the Rank. Landslide head zones ha ve strongly influenced the pattern of volcanism on Tenerife, providing site s for major volcanic centres. (C) 2000 Elsevier Science B.V. All rights res erved.