Franz Josef is one of the few glaciers on Earth that slides out of high alpine snow almost into rainforest. It comes down the western side of New Zealand's Southern Alps to a face a few hundred metres above the sea, low enough that tree ferns grow within sight of the ice. It also moves fast. Near the face the ice creeps about half a metre a day and the steep icefall above it travels several metres, and during one storm researchers watched that speed almost double within the hour, as rain worked under the glacier and lubricated its bed. Between 1983 and 1999, while glaciers almost everywhere were shrinking, this one advanced 1,420 metres. Since 2008 it has pulled back about a kilometre and a half, and it now stops some three kilometres short of where it stood a century ago.
That retreat closed the way in. A free track still runs from the car park along the Waiho riverbed, through rainforest and past waterfalls, to a viewpoint below the terminal face. But the ice sits further off each year, and most of what you walk is bare scoured rock the glacier covered within living memory. Getting onto it means flying. A helicopter lifts you over the icefall and sets down on the upper glacier, and from there you go roped to a guide through a shifting maze of crevasses, seracs and meltwater channels, with the forest and the coast a long way below. A harder day puts an ice axe in each hand and crampons on your boots for a sheer blue wall, which takes no previous experience to begin. Low cloud grounds the flights altogether, and the most reliable flying comes with the cold, clear high pressure of winter. Deep in the glacier, meltwater bores tunnels and caves where the compressed ice glows electric blue, and a guide picks a route into one whenever it is stable. It is never quite the same room twice. The walls shift and refreeze from one week to the next.