Observing Greenland from a helicopter, the main problem is one of comprehending scale. I have thought we were skimming low over the waves of a fjord, before noticing the tiny shadow of a seabird far below and realising what I suspected were floating shards of ice were in fact icebergs the size of office blocks. I have thought we were hovering high in the sky over a featureless icy plane below, before bumping down gently onto ice only a few metres below us.
Crevasses – cracks in the surface of glaciers – are the epitome of this baffling range of scales. Formed by stresses at the surface, their direction and size tell us how the ice sheet is flowing towards the ocean. Inland, far away from the fast-flowing glaciers that discharge hundreds of gigatonnes of icebergs a year into fjords, crevasses can be tiny cracks only millimetres wide.
