The 70 ka ‘Perote Pumice’ inter-caldera dacite-rhyolite Plinian eruption of Los Humeros Volcanic Complex, Mexico: Lithostratigraphy, hazards, and eruption dynamics

Abstract

Volcanic calderas span diverse eruptive styles, magnitudes, and intensities, comprising effusive/explosive activity often wrapped in between catastrophic caldera-forming episodes. During the inter-caldera stages, frequent Plinian eruptions, fueled by chemically varied magmas, pose significant hazards. The basaltic-rhyolitic Los Humeros Volcanic Complex (LHVC), Mexico's widest active caldera system, typifies such dynamics. The 70 ka Perote Pumice (PP), the largest eruption during LHVC's inter-caldera period (164–69 ka), marks a critical phase of high-intensity volcanic activity following the main caldera-collapse (164 ka). Here, we integrate lithostratigraphic mapping (52 locations) with geochemical and microtextural analyses to reconstruct the PP eruption source parameters, hazards, and dynamics. Our findings indicate that the PP deposits, comprising 13 layers (8 fallout and 5 pyroclastic density currents) reflect progression from dacite unsteady plumes and outgassed lava-plug bursts to a sustained gas-rich rhyolite-driven Plinian column, culminating in column-collapse due to waning gas and magma supply. This catastrophic VEI-6 eruption produced 30–40 km-high columns, 4.73 ± 0.18 km³ DRE, and maximum 9 × 10⁸ ± 0.9 kg s⁻¹, depositing pumice from proximal (∼1360 km²) to distal offshore areas (max. 200 km from the source to the Gulf of Mexico). The geochemical and microtextural data suggest that both dacite and rhyolite magmas mingled, were rapidly decompressed, and fragmented, yielding pervasive banded pumice. The refined stratigraphy, eruption parameters, and dynamics underscore PP as a benchmark for high-intensity inter-caldera volcanism. Considering LHVC's potential for future silicic activity, a PP-scale event would threaten two-million people within 140 km east and southeast of the caldera.