Phase Change Caves


Caves that are caused by a phase change of a substance involved. A phase change is the transition of a substance from one state of matter to another.

An obvious process of cave formation is the removal by a liquid, usually water, either in solid but comminuted form or in dissolved form. But what if the material itself changes its phase, for example, ice melts and the "liquid ice" aka water, simply flows away? The change of phase, i.e. the physical state as a gas, liquid or solid, is temperature-dependent for all substances. Melting consumes energy (heat), freezing or solidification releases additional heat. There is both water and ice at 0 °C, one of the more interesting lessons in school physics.

And there are very many substances for which at least one phase change lies in the temperature interval that occurs at the Earth's surface and in the uppermost crust. And each of these phase changes has the potential to be a cave-forming process.

The phase change is also known as a phase transition. The following phase transitions can occur in our biosphere:

The formation of a cave through this process seems obvious: a solid becomes liquid and the liquid moves away, creating a cave. But there are other possibilities. A liquid moves, but its surface cools and becomes solid, the liquid inside flows out, and the crust forms a cave. This may seem a little far-fetched, but in fact, this is how lava tubes are formed and this is the second most common type of cave on Earth. It is also quite surprising that this type of cave formation occurs in both primary and secondary caves. The two examples are each from one of the two camps.

While lava tubes are widespread, glacial caves are much rarer. Other types of caves caused by this process are conceivable but at least very, very rare. For example, caves can form when the water around the cavity freezes, i.e. solidifies. Sublimation and resublimation are also conceivable, either of water on Earth or of carbon dioxide on other planets such as the moons of Saturn. So while the first two types of caves mentioned exist in relevant numbers on Earth, the others are rather exotic. However, this changes as soon as we look at cave formation on other planets.