Lava Beds National Monument in California has amazing geological features that incorporate over 700 caves formed by intense volcanic and geological activity. One of the most interesting features of the Monument are the ice caves which are present in several of the lava tubes at the site. The ice in these caves is perennial and never melts, so despite being summer on the surface, the ice is still presence in the caves below the ground. This begs the question of how these ice caves were actually formed.
In order to understand the formation of the ice caves, it is important to first understand the formation of the lava tubes that are present at the site and at many other volcanic sites around the world. The tubes are the reason for large numbers of caves at the site and the reason why ice has become a permanent feature of some of the them. Lava tubes are often a feature of basaltic lava eruptions. There are several different methods of lava tube formation but basically it results from low viscosity lava that flows very easily. The lava will flow across a surface and the other portion of the flow will began cooling and solidifying. As it cools, the lava underneath it will continue to flow because it is still hot and the solidifying outer layer actually serves to insulate the lava underneath. As the flow continues, it will grow larger as the outer layer is pushed outwards by more lava pushing through. Eventually the lava flow will cease and, unless the lava flow stagnates and is left inside the solidified outer later, most or even all of the lava will leave the tube. The empty tube may be covered by later lava flows or even expanded if another flow enters the tube.
The result is the formation of one or even multiple lava tubes that can stretch for only a few feet or perhaps even miles. Sometimes the tubes are hard to get to because they are buried but sometimes they can be accessed because of a collapse that has occurred along its length. The tubes are a very interesting feature of an eruption and not found everywhere that eruptions occur.
The tubes at Lava Beds are unique in that many of them have their own controlled climates. Typically, the cold air that enters the caves will not leave because of the fact that hot air rises, so many of the tubes are quite cold. As one proceeds deeper into the layers of tubes, the temperature can sometimes plummet until it is below freezing. Despite being over eighty degrees on the surface, the temperature may vary little in the below ground tubes and stay at or below freezing.
The ice caves have formed as the result of water that has trickled from the surface through the other caves and lava tubes and has reached the colder tubes. Once there it is frozen by the cold temperatures in the tubes. The water forms many different structures in the lava tubes as it drips in from the ceiling an eventually freezes. In Skull Caves, the entire floor of the lowest level of the cave system is a sheet of solid ice. In other areas of the lava tubes, the perennial ice is present and has formed beautiful ice sculptures and stalactites as well as stalagmites that have been there and will continue to be added on for years.