Onset of glacier tables

Abstract

A glacier table consists of a rock supported by a slender column of ice. These structures form naturally on glaciers through differential melting of the ice. In this paper, we investigate the onset of their formation by reproducing glacier tables at a smaller scale, using model materials in a controlled environment. We show that in the lab the melting process of an ice block in air is controlled by both the infrared radiations form the environment and by the natural convection of air. Using cylindrical caps made of materials of various thermal conductivities, one can initially observe either the formation of a table standing on an ice foot, or the sinking of the cap into the ice block. A onedimension model shows that the differential ice ablation rate is controlled by the thermal conduction through the cap leading to a competition between two effects: a geometrical amplification of the heat flux on the one hand, and a heat flux reduction due to the higher temperature of the cap compared to that of the ice. Our model captures the transition between the two regimes and identifies a dimensionless number which control the onset of the formation in its early stages.