Coupled fluid and solid evolution in analogue volcanic vents

Abstract

Volcanic eruptions emit rock particulates and gases at high speed and pressure, which change the shape of the surrounding rock. Simplified analytical solutions, field studies, and numerical models suggest that this process plays an important role in the behavior and hazards associated with explosive volcanic eruptions. Here we present results from a newly developed laboratory-scale apparatus designed to study this coupled process. The experiments used compressed air jets expanding into the laboratory through fabricated rock analogue material, which evolves through time during the experiment. The compressed air was injected at approximately 2.5 times atmospheric pressure. We fabricated rock analogues from sand and steel powder samples with a three-dimensional printing process. We studied the fluid development using phase-locked particle image velocimetry, while simultaneously observing the solid development via a video camera. We found that the fluid response was much more rapid than that of the solid, permitting a quasi-steady approximation. In most cases, the solid vent flared out rapidly, increasing its diameter by 20 to 100%. After the initial expansion, the vent and flow field achieved a near-steady condition for a long duration. The new expanded vent shapes permitted lower vent exit pressures and larger jet radii. In one experiment, after an initial vent shape development and establishment of steady flow behavior, rock failure occurred a second time, resulting in a new exit diameter and new steady state. This second failure was not precipitated by changes in the nozzle flow condition, and it radically changed the downstream flow dynamics. This experiment suggests that the brittle nature of volcanic host rock enables sudden vent expansion in the middle of an eruption without requiring a change in the conduit flow.

Volcanic tremor and plume height hysteresis from Pavlof Volcano, Alaska

“…In stage 3, tremor amplitudes continue to decline, likely because the crater has sufficiently widened such that the erupting jet is no longer strongly coupled to the vent walls, thereby leading to a different relationship between tremor and plume height. Our proposed vent evolution is consistent with laboratory experiments of vent erosion, which show a rapid widening followed by stabilization and occasional sudden expansion (28). …”

The dynamics of volcanic jets: Temporal evolution of particles exit velocity from shock‐tube experiments

“…The following four different geometries are applied: a nozzle with converging walls ( α = −5°) and area ratio A 2 / A 1 = 0.67, a cylinder where A 2 = A 1 , a funnel with diverging walls ( α = 15°) and area ratio A 2 / A 1 = 2.36, and a funnel with diverging walls ( α = 30°) and area ratio A 2 / A 1 = 4.All of them are made from stainless steel and have a constant height (77 mm) and internal diameter (28 mm). Vent shape does not change during the experiments (not erodible), differently to other studies [ Solovitz et al ., ]. The setups (1, 1b, 2, and 3 in Figure b and Table ) differ in the distance of the sample surface from the vent before decompression, and the particle load. Setups 1 and 3 have identical particle load, but different sample surface location.…”

“…All of them are made from stainless steel and have a constant height (77 mm) and internal diameter (28 mm). Vent shape does not change during the experiments (not erodible), differently to other studies [ Solovitz et al ., ].…”

Characterising vent and crater shape changes at Stromboli: implications for risk areas

“…Changes in eruption characteristics may be influenced by observable topographic changes of active vents (shape, size, depth, open/closed, rim height) [e.g. Capponi et al 2016;Cole et al 2015;Jessop et al 2016;Solovitz et al 2014;Suzuki et al 2020].…”