Structure and emplacement of the Pliocene Roque Nublo debris avalanche deposit, Gran Canaria, Spain

Collapse of the flanks of the Pliocene Rogue Nublo stratocone on Gran Canar ia lead to large debris avalanches that traveled far beyond the coastline w ith velocities that may have exceeded 100 m/s. The deposits comprised at le ast 14 km(3) of debris and covered an area of about 180 km(2) in the southe rn half of the island. The debris-filled deep canyons are largely exhumed a t present. Incomplete disintrgration, poor fluidization and a good preserva tion of megablocks an thought to be mainly due to the confinement of the de bris avalanche within deep canyons. The rheological behavior of lithologic domains varies with their size, internal strength and relative position wit hin the deposit. The deformation structures indicate that distinct componen ts flowed whereas others slid throughout the transport in a relatively dens e mode. The following factors are believed to have been important in genera ting the Rogue Nublo debris avalanche deposit: (I) unusual abundance of pyr oclastic flow and other volcaniclastic deposits making up the upper Rogue N ublo cone; (2) highly asymmetric basement beneath the cone with a very high southern ridge and a steep erosional southern slope leading to major insta bilities; (3) intrusion of dikes and cryptodomes as well as hydrothermal al teration in the crater area further weakening the volcano. (C) 1999 Elsevie r Science B.V. All rights reserved.