The growth of ice stalagmites obtained by the solidification of impacting droplets on a cooled substrate ($-50^{ \circ}$C to $-140^{ \circ}$C) is investigated experimentally. It is shown that for any combination of substrate temperature and drop discharge, there is a critical height above which unfrozen water accumulates at the stalagmite's tip, drips and develops into fingers that give a star-shape to the stalagmite. Both the vertical growth and the radial growth of the stalagmite are discussed through the Stefan problem and mass scaling arguments respectively. Finally, a phase diagram that presents the stalagmite aspect ratio in function of the main control parameters is proposed.
Categories: physics.flu-dyn