In some cases, the ice directly changes into vapour state rather than changing into liquid and liquid to vapour. This is called sublimation.

It is a natural phenomenon. Examples of ice changing directly to vapour without changing to water are

• Snow, which is a particular type of ice crystal, can also transition directly into water vapour. On cold days it is not possible for snow to melt. Hence, snow will eventually sublime into the air as water vapour.
• Glaciers experience a particular form of sublimation