The Final Freezing of Spongy Ice: Hailstone Collection Techniques and Interpretations of Structures

Small volumes of spongy ice were produced by nucleating supercooled water in balloons at temperatures from −3 to −10C. The original freezing structure is faithfully preserved by quenching the spongy ice in a dry ice-alcohol mixture, and this method is suggested as an important collection technique for freshly fallen hailstones. With slower final freezing rates, recrystallization takes place, consisting of either grain growth only, or of nucleation and growth of new grains. Free growth of ice in water at or above −10C is probably not accompanied by spontaneous nucleation of new crystals in these experiments; reports to the contrary may be a result of primary recrystallization, which does occur at normal rates of final freezing.