Emplacement mechanism of volcanic debris avalanche deposits: Insight from inter- and intrablock-matrix characterization at Quevar Volcanic complex, Argentina

Compound volcanoes are inherently unstable landforms prone to recurrent collapses driven by both internal and external factors, undergoing multiple failure -regrowth episodes during their evolution. While large-scale collapses dramatically reshape volcanic landscapes, small-volume events also play a key role in modifying volcanic morphology. The Quevar 1 deposit, located in the Quevar Volcanic Complex (Argentine Puna), represents a small-scale volcanic debris avalanche deposit (VDAD) formed by the gravitational collapse of an unaltered dacitic lava dome. This study combines digital elevation model (DEM) analysis, granulometry, and scanning electron microscopy to reconstruct the emplacement dynamics of Quevar 1. The deposit is monolithological, composed exclusively of Quevar Dacite, and displays features typical of a rock rotational slide evolving into a debris avalanche, including a curved main scarp, and abrupt confinement against paleotopography, consistent with a short-runout collapse likely triggered by post-eruptive seismic shaking. Grain-particle variations indicate shear-driven particle segregation. The axial zone has a smaller mean particle size, poorer sorting, higher matrix content, and the smallest maximum block size. Voids indicate high-velocity point-to-point impacts, possibly linked to higher axial velocities, with subtle scratches and fractures. The marginal zone is characterized by larger clasts and better sorting. In this area and in the basal region fractures, lips, striations, staircase geometry reflect lateral friction at the margins and base, indicating prolonged particle–particle interactions under a frictional-elastic regime and high stress. The Interblock matrix shows greater transport influence, whereas the intrablock matrix preserves confined shear and in situ fragmentation. The absence of hydrothermal alteration, pyroclastic deposits, and water-related facies, combined with morphological evidence, supports interpretation of Quevar 1 as a structurally controlled slope failure, dominated by gravitational forces. These findings underscore the diversity of failure mechanisms in composite volcanoes and emphasize the importance of tectonic triggers in generating small-scale VDADs. • Quevar 1 is a small-scale monolithic VDAD from unaltered dacitic dome collapse. • Quevar 1 is a rotational slide evolving to a debris avalanche with short runout. • Axial shear segregation with impact features and margin with frictional features. • Inter vs intrablock matrix microtextures reveal transport vs in situ fragmentation. • Tectonic trigger key for small VDADs in composite volcanoes.