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From Curtains of Fire to Focused Flow: Experimental Insights into Conduit Evolution in Volcanic Fissures

Javiera Ruz-Ginouves 1 , James D.L. White 1, Rachael J.M. Baxter1

Abstract

Thermal feedback processes between dikes and crustal rocks influence magma transport, eruption dynamics and the longevity of volcanic conduits. In fissures, variations in width and crustal rock temperature can lead to conduits of focused flow that sustain eruptions, and domains of slower viscous flow that seal them. In modern eruptions this is seen as a shift from a curtain-of-fire behaviour, to focused eruptive sites that prevail and intensify. Better understanding why, how and when this transition occurs can yield improved risk reduction in an active eruption's early stages.  To do this, we perform experiments with an artificial fissure, where warm molten wax (25°C) is injected into a cold-sided slot (5°C) with a preset shape. The setup's flexibility allows adjustments to fissure shape, width and temperature, simulating conditions that affect wax solidification, flow diversion, and conduit or blockage formation. Upon initial ascent, a layer of insulating solid wax forms against the cold wall, and its accretion produces narrower, colder domains from which flow is diverted into wider, warmer active conduits. Moreover, wax flow responds quickly to geometric obstacles, where unstable trails of slow-flowing wax develop downflow (above the obstacle), shifting laterally and generally increasing in surface area through an experiment.  These experiments illustrate thermo-rheological processes in volcanic systems, where thermal mechanisms influence the development of stable conduits or blockages. The unstable viscous trails formed downflow of obstacles indicate instabilities generated in the laminar flow, and may play a role in the failure of fissure eruptions to regularly localize.