In the morning we walk along an exposed wall of the Nef Glacier. A thirteen-story slab breaks away, tilts in slow motion, bursts into powder and bergs. How do you not feel fragile in this landscape?

On the ice, crampons crunch across a surface darkened by wind blown dust. The sound of meltwater emerges from deep below us, mumblings in the belly of the glacier. I peer down a hole where shadows within shadows lead into a blue Jules Verne landscape, journeying into the source of the Baker.

Oxygen-rich ice near the surface is white. Below it, baby blue falls into a saturated indigo so deep and rich it seems perilous. Becoming aware of the depths, I feel dizzy.

Every hole and crack emits a sound. Some places are whispers, and some rumble like a ship engine below deck. Unseen rivers roar and hiss as one of the largest ice caps in the world melts under our feet.

Jonathan Leidich, a local glacier expert whose knowledge comes from 15 years on the ice, takes us to a measurement station that he maintains in conjunction with CECS, Centro de Estudios Cientificos de Valdivia here in Chile. A PVC pipe sticks up from a hole. Leidich runs a tape measure, says that a month ago the surface of the glacier was six feet over our heads. That much has melted in 30 days across this entire expanse. Hearing this, I take in the scope around us, daggers and ridges of ice, holes shaped like giant's navels. Ice stretches as far as I can see, rising up through the teeth of mountains where the Patagonia Ice Cap spills through from the other side. I can feel it all melting. This is how the river starts.