Spontaneous reheating of crystallizing lava

Alan G Whittington,Alexander Sehlke

doi:10.1130/g49148.1

Alan G Whittington, Alexander Sehlke

Open Access

https://doi.org/10.1130/g49148.1

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Abstract

Abstract We show that recalescence, or spontaneous reheating of a cooling material due to rapid release of latent heat, can occur during disequilibrium crystallization of depolymerized Mg-rich melts. This can only happen at fast cooling rates, where the melt becomes undercooled by tens to hundreds of degrees before crystallization begins. Using a forward-looking infrared (FLIR) camera, we documented recalescence in pyroxene (Fe, Mg)SiO3 and komatiite lavas that initially cooled at 25–50 °C s–1. Local heating at the crystallization front exceeds 150 °C for the pyroxene and 10 °C for komatiite and lasts for several seconds as the crystallization front migrates through. We determined the latent heat release by differential scanning calorimetry to be 440 J g–1 for pyroxene and 275 J g–1 for komatiite with a brief power output of ∼100 W g–1 or ∼300 MW m–3. Recalescence may be a widespread process in the solar system, particularly in lava fountains, and cooling histories of mafic pyroclasts should not be assumed a priori to be monotonic.

Highlights

Molten materials, from magma oceans to lava droplets, crystallize when they are cooled at slow to moderate rates (Fig. 1A, path 1)
We investigated crystallization using differential scanning calorimetry (DSC) to demonstrate that recalescence occurs in melt quantities that are smaller by orders of magnitude and to quantify the heat flows involved
Our observations of temperature differences of up to ∼100 °C on a millimeter scale (Fig. 2) suggest that thermal imaging of basaltic lava flows using hand-held or tripod-mounted forward-looking infrared (FLIR) cameras needs to be conducted with millimeter-scale spatial resolution to assess true temperature fluctuations

Summary

Introduction

From magma oceans to lava droplets, crystallize when they are cooled at slow to moderate rates (Fig. 1A, path 1). Latent heat released during crystallization typically slows, but does not halt, monotonic cooling. Molten materials can become supercooled, i.e., they can exist below their liquidus without immediately crystallizing. These supercooled liquids can undergo rapid disequilibrium crystallization at temperatures far below those of the liquidus but still above those of the glass transition (Fig, 1A, path 3; Kirkpatrick, 1975). If latent heat is released faster than it can be removed by radiation or conduction, the material can spontaneously heat up through a phenomenon known as recalescence (Fig. 1A, path 2; Fig. 1B). At the highest cooling rates, the liquid will quench to glass, which retains the amorphous structure of the liquid but lacks its mobility (Fig. 1A, path 4)

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