It's difficult to forget standing in front of a glacier that is advancing towards you, towering ice pillars constantly cracking as they inch forward. The motion is too slow to see in real time, but obvious from one day to the next. One of us (Harold) experienced this during fieldwork in 2012 at Nathorstbreen on the Arctic archipelago of Svalbard, which was moving forwards more than 10 metres per day. Encounters like this are rare. Most of the world's glaciers are retreating rapidly as the