Grey Glacier ends in a wall of blue ice six kilometres wide and thirty metres tall, standing in a lake full of its own wreckage, in Torres del Paine in Chilean Patagonia. Most of what it sheds, it sheds out of sight. A terrace of ice runs forward under the water from the visible cliff, as much as a hundred metres out, because the lake's warmer surface layer eats the wall back fastest near the top. That submerged ledge wants to float, and when the lift under it wins, the ice tears loose from below. The blue is not the sky, either. Snow starts out full of air bubbles that scatter every colour and look white. Under the weight of the ice field those bubbles are pressed out, and the dense ice left absorbs the red end of the light and sends back blue. The oldest, most compressed ice glows deepest.
The catamaran crosses silt-clouded water, weaving between icebergs drifted down from the front, and holds position a few hundred metres off the three-tongued wall, close enough that you hear the ice groan and crack. In a kayak you work lower and closer, at water level among the grounded bergs. With crampons, helmet and harness you can walk on the glacier itself, after a short zodiac ride past Nunatak island. A guide picks the line between crevasses and seracs, and the route ducks into meltwater tunnels and blue caves that only open on the ice's surface. Above the beach, Mirador Grey gives you glacier, bergs and Paine peaks in one sweep, and the wind up there rarely lets up. That wind runs the schedule and cancels boats and ice days without warning. Grey is not even the largest glacier here: nearly fifty pour off the same Southern Patagonian Ice Field. In March 2019 two flat-topped slabs of about six hectares broke away within a fortnight. And on some days nothing falls at all. A slab that has been under the water the whole time simply arrives at the surface, rolling up in front of the wall.