An Ice Cave is a cave which contains ice, not a cave formed inside ice those are called Glacier Caves. Ice caves are also called Glacieres or freezing caverns.
Ice caves may be caves of any type, karst caves, primary caves like lava tubes or tectonic caves. What they have in common is the fact, that there is ice inside the cave. The ice is formed by dripping water and the low temperature of the cave itself. The resulting ice structure look like stalactites and stalagmites, like ice lakes or glaciers.
But it is not that easy: If the cave temperature is below zero, why did the water not freeze inside the rock? The temperature of the rock must be above 0°C, the cave air below zero. And if this is the case, why ist the cave not completely filled with ice? There must be a change, and a period of ice accumulation is followed by a period of melting ice. There are two different ways how this works:
1. cold trap or ice cellar type: the shape of the cave works as a trap for cold air
Very often, an ice cave has a special shape, a high entrance and no exit at the bottom. The entrance allows cold air, which is heavier than warm air, to flow down into the cave. So the cave temperature gets colder than the temperature of the rocks. In summer the cold air stays inside the cave because of its higher specific weight. It is the same principle used in supermarket refrigerators to keep the cold inside.
2. dynamic ice caves: outside air blows through the cave
This kind of ice caves works by outside air streaming through the cave and bringing the outside temperature into the cave. Those caves are generally through caves, caves with at least two entrances. The average long term temperature outside is also the temperature of the rocks and normally that of the cave. It must be above 0°C, otherwise the rock is below zero and water freezes in the cracks and blocks them. As a result there would be no water and thus no ice inside the cave. Then there must be cold and warm seasons. During winter cold air blows through the cave and dripping water from the warmer rocks freezes inside the cave and the ice grows. During summer warm air blows through the cave and the ice melts. If more ice grows than melts, the cave fills slowly with ice until it is blocked and the cold air does not blow through the cave any more. Otherwise the ice grows during winter, but melts completely during summer and there is some time without any ice.
Ice caves are very cold, always below 0°C, the paths are often hard to walk on. It is normally not possible to build concrete paths in the areas with ice, as the ice moves every year and tends to destroy anything in its way. The paths across the ice are often rebuild every year using wooden planks and ropes. Ice caves often have no electric light, as the same problems with moving ice apply to electric installations. Visitors are equipped with headlamps or carbide lamps, the guide additionally use magnesia ribbon, which produces a very bright light when it burns down.
It is essential to wear warm clothes and good shoes. The cave is not suitable for people with health problems.