One of the greatest nonpolar concentrations of glaciers in the world, the Juneau Icefield spans 90 miles of southeast Alaska. On a sunny August morning, I stand on its surface with a 22-year-old mountaineer named Tristan Amaral. He is with the Juneau Icefield Research Program, in which students (from high school to graduate programs) assist scientists in climate research. Every summer since 1946, members have traversed the icefield, contributing to the oldest continual study of a glacier in the Western Hemisphere. They have witnessed the effects of climate change firsthand: Snow is falling less predictably, and glaciers are retreating. I am in Alaska to photograph scientists measuring how a place as wild as the Juneau Icefield is changing because of human activity.

Tristan peels an orange — a bright spot of color in a gray, white, and blue landscape. In front of us is a crack in the surface of the glacier, an opening 3 feet wide and 20 feet long. I check the ropes tied to my harness, and Tristan lowers me over the edge. As I descend, the crevasse widens into a cavernous space. I realize that we had been standing on a cliff ledge made entirely of snow. I spin slowly beneath it. The walls are undulating blue ice. Hundreds of icicles dangle, with water dripping from the tip of each one.

After about 80 feet, I come to a large block of ice lodged between the walls. Its top is roughly flat. I stand on it and let my rope go slack. It feels stable: safe enough. I set up my tripod and take out my camera. On both sides, the crevasse branches off into dark angular tunnels.

All I hear is water splashing and a faint creaking. A glacier forms when snow accumulates over time, turns to ice, and begins to flow under the pressure of its own weight. As a glacier moves, the motion creates crevasses. I wonder if the creaking is the sound of ice shifting around me.

I wait for others to come down. After 15 minutes I shout up to Tristan. No one answers. Looking up, I notice that the sky, visible through the opening, has turned from blue to white. I shout again. Later, I will learn that no one answered because the temperature had suddenly dropped and a storm had blown in, covering the glacier in a thick fog. On the surface, everyone was struggling to set up a shelter from the wind.

In most places I have traveled, the impact of humans feels big. There is evidence of people everywhere. We build roads around almost all remaining wilderness, as if nature were a piece of art framed by us. But, waiting inside the crevasse, alone and uncertain of what is going on above me, I am small. Even the icicles are bigger than I am, and they’re ready to fall.