Stress pinch points from glacial loading modulate magma ascent and storage in continental arcs.

Abstract

Growing evidence indicates that glacial cycles influence volcanic activity, yet the physical mechanisms linking glaciation to magmatic processes in continental arcs remain unclear. We integrate realistic ice and topographic loads with a dike model to evaluate how glaciation modulated magma ascent beneath Mocho-Choshuenco, Chile, during the Last Glacial Maximum (LGM). Ice loading generates a crustal stress "pinch point" that causes dikes rising from lower-crustal reservoirs to stall deeper than under ice-free conditions, effectively shutting off recharge to shallow magma reservoirs. This mechanism explains the ~2-3 km increase in magma storage depth and reduced eruption rates during the LGM without invoking changes in mantle melt supply or reservoir strength. Shutting off recharge also favors magma differentiation, setting the stage for more explosive silicic eruptions during deglaciation once recharge resumes. We identify a parsimonious explanation for glacially-driven shifts in magma composition, storage depth, and eruption rate at Mocho-Choshuenco and arc volcanoes worldwide.