Fig.3 a) Cartoon of the 'coffee can' submergence mass balance device. The device consists of a low-stretch, stainless steel wire attached to a metal anchor (initially a coffee can, hence the name) that is heated and placed into the drilling hole drilled in firn. The anchor is melted with the bottom of the ice and freezes in. The wire is stretched tight and guided by a stainless steel tube. The tube is held in place using plywood that was buried ~40cm into the snow to avoid melt around the darker wood surface. The top end of the wire has a loop and permanent marker, the tracking point (modified after Hamilton and Whillans 2000). b) picture of coffee can device deployed at Victoria Lower Glacier.