The Tricky Energy Budget of Freezing Soil: A Thermodynamic Framework for Understanding Phase Changes

Freezing soil presents unique challenges in understanding the coupled mass and energy dynamics within the Earth’s critical zone. This paper presents a comprehensive thermodynamic framework for analyzing phase transitions in soil-water-ice systems. We present a unified treatment based on non-equilibrium
thermodynamics, where temperature, pressure, and chemical potential act as primary driving forces. The framework accounts for freezing point depression through mechanisms including the Gibbs-Thomson effect, solute presence, ice nucleation, and surface interactions. We demonstrate how upscaling from pore-
scale thermodynamics to the Darcy scale introduces theoretical challenges in determining phase transformation rates and flux laws. The sequential freezing process, governed by water energetic states in different pore sizes, creates complex interplay between capillary forces and phase changes essential for modeling

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This paper is an evolution of the talk given last summer at PanAm Unsat 2025 conference that you can find here. Official, preprint will be soon available. Temporary preprint available here.