— Vertical sided, water-filled holes in the glacier, like this one, are quite common. I think this is because water is densest at above freezing (4 degrees C), so when a pool forms and the air is warmer than freezing, the surface water sinks to the bottom and melts the ice there before rising up again to be warmed again by the air. It's a convection process, but in reverse from what we usually see.
Read more about our Life on Ice expedition.
