Water-Melt Chutes/Tunnels

When temperatures warm, water melts below the snow surface and flows in river-like patterns downhill. As the water flows, a tunnel of air forms and melts the snow from underneath. On steep slopes, and in areas with deep gullies, larger chutes/tunnels may form. Much like a crevasse, these chutes/tunnels may not be evident on the snow surface, though sometimes the snow appears thinner or is of a different color. You may also hear water flowing underneath as you near a chute/tunnel area. Also like a crevasse, if the tunnel is large enough, a climber can fall through the weakened snow surface and be buried and/or swept by the water under the snow down the tunnel. A fall into the tunnel on a steep slope can also precipitate backfill of snow from above into the tunnel as the melting, weakened snow surface moves to stabilize itself.

The steepest section on the route. John Platt Photo

Slope where a water-melt tunnel could form. John Platt Photo

Water-melt tunnels can be large permanent features below established glaciers and year-round snowfields, or short-lived, more shallow features on seasonal snowfields. Accidents and fatalities from falling into water-melt chutes/tunnels are rare, though these melt features are common. However, risk a chute/tunnel posses to a climber is related to a multitude of factors including: the steepness of the slope, the thickness of the snowpack, the terrain below the snow, the amount of melting occurring, whether a tunnel already exists or is forming, and if a chute/tunnel is large enough and close enough to the surface to collapse and fall into.

In 1987 a climber died on Mount Borah in an accident involving an uncontrolled self-arrest, combined with falling into a water-melt tunnel, and being buried by an avalanche he triggered. It’s important to assess your terrain for the potential of water-melt tunnels before selecting your descent path.