| What they are | Cup-shaped hollows in the snow surface |
| Cause | Uneven melting under strong sun |
| Where | Spring/summer snowfields, altitude |
| Effect | Awkward, tiring travel |
Sun cups are bowl- or cup-shaped hollows that form in a snow surface from uneven melting under strong sun, creating a honeycomb-like dimpled texture. Common on spring and summer snowfields and at altitude, they range from small dimples to deep, awkward depressions that make walking and skiing tiring and uneven. They’re a fair-weather snow feature, not an avalanche concern.
Dimpled spring snow
A melt feature of the same warm conditions that make corn snow and form firn; awkward terrain for snowshoeing.
Frequently asked questions
What are sun cups?
Sun cups are shallow to deep, bowl-shaped depressions that develop in a snow surface when strong sunlight melts the snow unevenly. Small differences in melting amplify over time, leaving a honeycomb of cups and ridges. They're common on spring and summer snow, especially at altitude and on glaciers and snowfields.
Why do sun cups form?
They form through a positive feedback: once small hollows appear, they trap heat and reflected light and melt faster than the ridges between them, deepening over days of strong sun. Factors like clean versus dirty snow, dry air, and intense high-altitude sun influence how pronounced the cups become.
Are sun cups a problem for travelers?
They aren't an avalanche hazard, but they make travel awkward and tiring — the uneven, dimpled surface is hard to walk, ski, or climb across smoothly, and deep sun cups can be ankle-twisting. Mountaineers and skiers often plan around them, traveling when the snow is firmer or choosing smoother routes.
Sources
- Snow surface features — The Mountaineers
- Melt features — USGS