Strategies for a planned bivy in alpine terrain: choosing the right site, insulating against ground cold, and preventing fatal hypothermia in a storm.
When is a night outdoors planned, and when are you forced into one? The honest answer: the line between a calculated bivy and a life-saving emergency bivy is blurry — which is exactly why you need to be ready for both. A planned bivy comes into play when a long, demanding tour can't be finished in a single day.
At altitude, nighttime brings real danger — especially combined with wet conditions and wind — through hypothermia and frostbite. The culprit is often the wind chill effect: wind strips heat from your skin through evaporation and convection much faster than the raw air temperature suggests — so it feels noticeably colder than the thermometer reads, and your body chills accordingly faster. You need to read the terrain to avoid traps when choosing a site, and know how to use your body and emergency gear as efficiently as possible.
Look for level, dry ground — ideally rock or scree rather than sensitive vegetation. Consistently avoid hollows and depressions: during a thunderstorm, they flood in a flash. In winter or spring this matters even more — a dip in the snow can fill in from wind-driven drift so fast that suffocation becomes a real risk.
Scan the wall above you for falling ice, rockfall, and spindrift (fast-moving loose snow) — these can turn into a real problem overnight. On glaciers, always probe the spot first, or you might end up sleeping on a hidden crevasse bridge.
Use boulders as a natural barrier, or build your own wall from stones, branches, or snow. If your site is exposed — say, on a narrow ridge — rig a handrail rope that everyone clips into with their harness; you sleep belayed. If a thunderstorm threatens: leave summits and ridges immediately, no debate.
Direct contact with cold rock or ice pulls heat out of your body through conduction — faster than you'd think. Without a sleeping pad, improvise: coiled rope, empty backpack, branches if you have to — anything laid flat beneath you. That's the crucial buffer against deadly ground cold.
Put on every layer following the layering principle. Pack yourselves together in one bivy bag — close body contact and rubbing each other warm multiplies your combined heat output. Keep your head warm, since that's where you lose the most heat. Light, repeated muscle tension keeps circulation going and helps prevent frostbite in your fingers and toes.
During a major weather collapse, you often can't retreat under your own power — then it's about holding out until help arrives. The best strategy is still prevention: if a marked cold front is forecast, skip ambitious long tours or glacier crossings, since these fronts arrive reliably. Always ventilate your bivy bag — otherwise condensation builds up, and in winter especially, CO2 can accumulate.
The DAV's national training team recommends the "emergency blanket hood" against hypothermia in an emergency bivy: thread the foil up your back between your base layer and second layer, fold the top end snugly over the back of your head like a hood, run the bottom end between your legs, and tuck it into your waistband. That way it sits right against your body and won't blow away, even in a storm.
Without insulation from the ground, you can chill dangerously within a few hours, even if the air temperature isn't extreme — conduction through rock or ice pulls heat away far faster than cold air alone. Improvised insulation from a rope or backpack is mandatory, not optional.
If a marked cold front or serious thunderstorm risk is forecast, skip long, ambitious tours with a planned bivy. Cold fronts arrive reliably — the risk of ending up in an unprepared emergency bivy just isn't worth it.
Never seal it completely — a small gap for airflow is enough. Without ventilation, moisture from your breath and sweat builds up inside, and in winter the risk of CO2 buildup rises too.
You share body heat like two heat sources in one room instead of two separate ones. The shared bag retains warmth that would otherwise be lost individually — often the difference between an uncomfortable night and a dangerous one.
Wind strips heat from your skin through evaporation and air movement much faster than the raw air temperature suggests. A wind-sheltered site and a windproof hardshell are therefore at least as important during a bivy as warm insulation layers.
Tour Leadership & Group Psychology