Spontaneous reheating of crystallizing lava

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 calo-rimetry 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.