Undercooled water in basaltic regoliths and implications for fluidized bebris flows on Mars

Experiments on the freezing of water in wet, sand-sized “basaltic” substrates confirmed that substantial degrees of undercooling can be achieved under conditions applicable to Mars when the substrate particles are relatively poor nucleators of ice (i.e., igneous minerals). This physical undercooling is independent of (but would be enhanced by) freezing-point depressions caused by soluble salts. Using differential scanning calorimetry, undercooling was studied in a carbon dioxide atmosphere as a function of soil particle size (silt- and sand-sized intervals), water/soil mass ratio (range of 0.1–1), and cooling rate (range of 0.5–10°K/min). Results for a clay-poor, glacial-outwash soil from Mauna Kea, Hawaii (with negligible salt content), showed that degree of undercooling is approximately independent of both soil particle size and water/soil mass ratio but varies with cooling rate. Undercoolings of 6–9°K were achieved for the Mauna Kea soil and undercoolings of 10–13°K were achieved for powdered whole-rock samples of peridotite, basalt, and a shergottite meteorite. Initial melting of the same icy materials occurred at temperatures that were 1–3°K lower than for melting of pure bulk ice. Undercooling of water below 273°K in debris flows composed of relatively unweathered “basaltic” sand on Mars should be expected to support fluid flow over greater distances than might otherwise be expected. Likewise, incipient melting and remobilization of the same icy debris might occur at temperatures below 273°K.