An ice cave is any type of natural cave (most commonly lava tubes or limestone caves) that contains significant amounts of perennial (year-round) ice. At least a portion of the cave must have a temperature below 0 °C (32 °F) all year round, and water must have traveled into the cave’s cold zone. Terminology This type of cave was first formally described by Englishman Edwin Swift Balch in 1900, who suggested the French term glacieres should be used for them, even though the term ice cave was then, as now, commonly used to refer to caves simply containing year-round ice. Among speleologists, ice cave is the proper English term. A cavity formed within ice (as in a glacier) is properly called a glacier cave. Types Ice caves occur as static ice caves, such as Durmitor Ice Cave, and dynamic or cyclical ice caves, such as Eisriesenwelt. Temperature mechanisms In most of the world, bedrock caves are thermally insulated from the surface and so commonly assume a near-constant temperature approximating the annual average temperature at the surface. In some cold environments, such as that surrounding Mount Erebus, average surface (and thus cave) temperatures are below freezing, and with surface water available in summer, ice caves are possible and are sometimes overlain by fumarolic ice towers. However, many ice caves exist in temperate climates, due to mechanisms that result in cave temperatures being colder than average surface temperatures where they formed. Cold traps: Certain cave configurations allow seasonal convection to import cold air from the surface in winter, but not warm air in summer. A typical example is an underground chamber located below a single entrance. In winter, cold dense air settles into the cave, displacing any warmer air which rises and exits the cave. In summer, the cold cave air remains in place as the relatively warm surface air is lighter and cannot enter. The cave will only exchange air when the surface air is cooler than the cave air. Some cold traps may ensnare surface snow and shade it from the summer sun’s rays, which may further contribute to the colder cave temperature. Permafrost: Even temperate environments can include pockets of bedrock that are below freezing year round, a condition called permafrost. For example, winter wind and an absence of snow cover may allow freezing deep enough to be protected from summer thaw, particularly in light-colored rock that does not