Fire on snow: building a platform

Snow is frozen water with a lot of air in between. Beneath a fire it melts, and the meltwater collects exactly where the embers lie. Water cools the embers strongly because it absorbs a lot of heat as it evaporates. At the same time, the fire sinks into the hollow it melts for itself and gets less air down there.

A platform separates fire and snow. Thick logs take a long time to burn through and keep the embers and fuel above the snow. The meltwater underneath drains away without reaching the fire. Over time the platform logs burn too – so you have to replace them in good time.

First choose the site: an open spot with no snow-laden branches above, sheltered from wind if possible and at a safe distance from your shelter. Then check the depth of the snow. If there is only a little, clear it down to the ground. If it is deep, tramp it down firmly so the platform does not sink.

For the platform, lay thick logs close together, with a second layer crosswise on top if needed. The thicker and denser the logs, the longer they last. Stones work too, but only dry ones. Wet stones or stones from streams and lakes can crack when heated.

Then build your fire on the platform as usual. Watch how the platform burns down and add new logs underneath or alongside in good time, before the fire sags through. Plan extra wood for this – in snowy landscapes, fuel wood is often scarce.

The heat of the fire rises and can make snow on branches slide. A load of snow can put out the fire and hit people. So only make a fire in an open spot. Fire on the ice of lakes, ponds or rivers is off-limits, because the heat weakens the ice from above – and ice is often thinner than it looks anyway.

Fires, embers and stoves never belong in a snow cave, igloo, tent or other enclosed space. Carbon monoxide can build up there – invisible, odourless and potentially fatal. Keep a distance from the snow shelter outdoors too, so that smoke does not drift in and the heat does not damage it.

If you use the fire to melt snow for drinking water: water from snow is not automatically clean. Boil it before drinking and follow official advice on water treatment. Also check the local rules before every fire – they apply in winter too.

A fire platform makes sense on a winter bivouac, on snow or icy ground on land, and anywhere you need warmth or want to melt snow. It costs extra time, energy and wood – which is a lot in the cold.

So the order is: first secure your body heat with clothing, insulation from the ground and shelter from wind. Only then invest energy in a fire. Military survival manuals recommend a base of wood or stones on snow and wet ground; in winter, however, fire should never be the only source of warmth. Where wood is scarce, a stove may be the better choice.