Volcanic debris avalanche transport and emplacement at Chimpa volcano (Central Puna, Argentina): Insights from morphology, grain-size and clast surficial textures

Abstract

Understanding the flow dynamics in debris avalanches is an important tool to advance the knowledge about lateral failures of volcanoes, a fundamental step towards an accurate risk assessment and mitigation in volcanic areas. We describe the morphological, grain-size, and clast surficial textures of the Casana volcanic debris avalanche deposit emplaced by the sector collapse of Chimpa volcano (Central Puna, Argentina). We focused our analysis on the volcanic debris avalanche deposit, characterized by ridges, reduction in downflow matrix grainsize, jigsaw-cracked blocks in the whole extent of the deposit, collision superficial textures in grains (fractures, percussion marks, and voids). Sedimentological and textural analysis show a progressive disintegration and fracturing of the larger particles with greater distance in a dry, granular flow with minimal internal deformation during propagation. Casana avalanche behaved like a rigid body in the proximal area and as a granular flow in the medial and distal reach. Block sliding mechanisms generated the toreva block in the proximal region whereas granular flow produced the debris avalanche deposits. This is an example of how different mechanisms can interact during debris avalanche emplacement, which are strictly related to the cause of the volcano instability, the lithology and the degree of alteration of the source mass, and its interaction with paleotopography. Although the geological risk of the proposed study area is low, the study of Casana VDAD is important to understand similar processes in other volcanoes providing constraints to hazard assessment.