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

Collapse of the flanks of the Pliocene Roque Nublo stratocone on Gran Canaria lead to large debris avalanches that traveled far beyond the coastline with velocities that may have exceeded 100 m/s. The deposits comprised at least 14 km3 of debris and covered an area of about 180 km2 in the southern half of the island. The debris-filled deep canyons are largely exhumed at present. Incomplete disintegration, poor fluidization and a good preservation of megablocks are thought to be mainly due to the confinement of the debris avalanche within deep canyons. The rheological behavior of lithologic domains varies with their size, internal strength and relative position within the deposit. The deformation structures indicate that distinct components flowed whereas others slid throughout the transport in a relatively dense mode. The following factors are believed to have been important in generating the Roque Nublo debris avalanche deposit: (1) unusual abundance of pyroclastic flow and other volcaniclastic deposits making up the upper Roque Nublo cone; (2) highly asymmetric basement beneath the cone with a very high southern ridge and a steep erosional southern slope leading to major instabilities; (3) intrusion of dikes and cryptodomes as well as hydrothermal alteration in the crater area further weakening the volcano.