The propagation and emplacement mechanisms of the Tenteniguada volcanic debris avalanche (Gran Canaria): Field evidence for brittle fault-accommodated spreading

Abstract

The Tenteniguada volcanic debris avalanche deposit is located on the east of the island of Gran Canaria, Spain. Its internal structure is composed of a complex assemblage of extensional features and shearing structures including normal faults, horst and graben, brittle/ductile boudinage and clastic dike injections. Examination of these features in the field and evaluation of their distribution have allowed the generation of a new conceptual model for the transport and emplacement of this debris avalanche, and potentially others. In the majority of the deposit, the degree of disaggregation is low, with large portions of the original edifice preserved, although displaced by brittle deformation. Greater disaggregation is observed deeper and in the more distal section of the deposit. The findings suggest that the propagation of the volcanic debris avalanche was most likely facilitated by the normal fault-accommodated spreading and extension of the mass, with the majority of stress focused in fault zones. The greater disaggregation exhibited in the deeper and the more distal part of the deposit is likely to be due to greater stress accommodation from fault convergence and momentum transfer respectively. The abundance of competent lava lithologies and scarcity of weaker material that could be easily disaggregated is the most likely reason Tenteniguada did not fully evolve from a slide to a granular flow, and therefore generated a deposit which bears resemblance to non-volcanic blockslide deposits. Therefore, lithological properties are potentially a vital factor for the propagation mechanisms, distribution of stress and consequently the evolution of a debris avalanche from the initial collapse to its emplacement. The present study highlights the importance of dedicated field examinations of sedimentological, morphological, and structural features for providing constraints for models of debris avalanche propagation mechanisms and the factors dictating them.