arXiv subjects

Alain Burgisser

Publications and source records attributed to Alain Burgisser.

2 recordsLinked to original sources

arXiv2026

A transient depth-averaged lava flow model with a Herschel-Bulkley rheology accounting for three phases

This study presents a three-phase suspension lava flow model with a Herschel-Bulkley rheology. The suspension contains crystals and gas bubbles, and two closures for the evolution of the crystal volume fraction are considered. The first closure minimizes the complexity of the system by treating crystal fraction as a transported quantity subject to relaxation towards an equilibrium state. This closure avoids a parametrization of the many heat transfer mechanisms a lava flow is subjected to. The other closure is on the lava temperature considering four heat transfer mechanisms and a prescribed temperature--crystallinity relationship. We deduce from this system and solve numerically a one-dimensional depth-averaged model. A comparison with a pre-existing model based on real lava flow data suggests that the prediction of flow parameters done with the multi-parametric evolution of temperature yields more accurate results than those obtained with the other closure. The transient nature of our model correctly predicts that confined lava traveling down an irregular steep slope yields a series of cascading fill-then-breakout lumps that causes the overall flow to be pulsatory. These pulses dominate the local dynamics and preclude a strict steady state to be reached. Theoretically, taking gas bubbles into account is best done with a general rheological relationship valid at any capillary number. In the conditions explored herein, bubbles modulate viscosity within a factor 2 with a shear thinning behavior, decelerating slow flows and accelerating fast flows. When a simplified rheology treating bubbles as hard spheres was used, the only dynamic parameter affected was bulk viscosity.

math.AP↗

arXiv2024

Numerical simulations of the latest caldera-forming eruption of Okmok volcano, Alaska

The 2050 14C yBP caldera-forming eruption of Okmok volcano, Alaska, had a global atmospheric impact. The associated global climate cooling was driven by the amount of sulfur injected into the stratosphere during the climactic phase of the eruption. This phase was dominated by pyroclastic density currents, which have complex emplacement dynamics precluding direct estimates of the sulfur stratospheric load. We simulated the dynamics of the climactic phase with the two-phase flow model MFIX-TFM under axisymmetric conditions with several combinations of mass eruption rate, jet water content, vent size, particle size and density, topography, and emission duration. Results suggest that a steady mass eruption rate of 1.2-3.9e11 kg/s is consistent with field observations. Minimal stratospheric injections occur during emission as most of the volcanic gas is injected into the stratosphere by the buoyant liftoff of dilute parts of the currents at the end of the eruption. Overall, 58-64 wt percent of the total amount of gas emitted reaches the stratosphere. Combined with petrological estimates of the degassed S, our results suggest that the eruption injected 11 to 20 Tg S into the stratosphere, consistent with the subsequent climate response and Greenland ice sheet deposition. Our results also show that the combination of the source Richardson number and the mass eruption rate is able to characterize the buoyant-collapse transition at Okmok. We extended this result to 141 runs from 10 published numerical studies of eruptive jets and found that this regime diagram is able to capture the first-order layout of the buoyant-collapse transition in all studies except one. An existing multivariate criterion yields the best predictions of this regime transition.

physics.geo-ph↗