Geomechanical behavior evolution of the blocks involved in the Arteara rock avalanche, Gran Canaria, Canary Islands, Spain

Abstract

Close to Arteara (The Canary Island), an Holocene rock avalanche comprises accumulation of large reddish blocks which cover the right side of the Fataga ravine. This course is entrenched into the Phonolitic Formation, which comprises an alternating sequence of lava flows and ignimbrites. The avalanche defines an elongated deposit of variable thickness. A low friction angle was deduced, which is related to the existence of a previous slope with an easily weathered rock favorable to the rolling of the blocks. The movement would have been a dry granular flow with a component of saltation at the head and of turbulent flow at the intermediate and distal areas. The deposit varies widely in size and is structured in bands of blocks with a polymodal distribution and low selection. The geomechanical properties of the rocks involved vary substantially in each block and along a longitudinal profile of the deposit. Schmidt Hammer rebound measured in 233 block shows a polymodal dispersion. Some facies have been differentiated in the blocks, not only by their appearance, but also by their rebound index (R). The different hardness reflects the differences in density and porosity in these rocks. The hardness zoning shows the differential weathering of the blocks, which depends on the lithological structure (anisotropy) and the turbulence of the granular flow, which determines the influence of abrasion and punching of the blocks. The rebound show a direct correlation with the bulk density and an inverse correlation with the distance to the source area.