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Lava cave
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A lava cave is any cave formed in volcanic rock, although in typical usage it is reserved for caves formed by volcanic processes, which are more properly termed volcanic caves. Sea caves, and other sorts of erosional and crevice caves, may be formed in volcanic rocks, but are unrelated to volcanic processes and typically form long after the volcanic rock was emplaced.
e are numerous types of lava caves, the most common and most extensive being lava tubes.
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A lava cave is any cave formed in volcanic rock, although in typical usage it is reserved for caves formed by volcanic processes, which are more properly termed volcanic caves. Sea caves, and other sorts of erosional and crevice caves, may be formed in volcanic rocks, but are unrelated to volcanic processes and typically form long after the volcanic rock was emplaced.
Types
There are numerous types of lava caves, the most common and most extensive being lava tubes. But not all lava caves are lava tubes. Other types of lava caves include the following classifications:
- Volcanic rift or fissure caves, which form along volcanic rift zones and eruptive fissures, or in fractures associated with volcanic activity. These are tectonic in formation, caused by “stress in lava during and after solidification.” They may also be the site of fissure eruptions, and the walls covered with spatter. Notable rift caves include Crystal Ice Cave, formed in Idaho’s Great Rift (and now part of Craters of the Moon National Monument and Preserve). Caves in the Great Rift are known up to 800 feet deep.
- Inflationary caves tend to be small chambers which form when lava under pressure pushes up surface rock from below and then drains back down. One surface expression of this is the tumulus, a fractured hillock of lava which is often hollow. In some cases volcanic gases may exert pressure on solid or semi-solid lava and form what is basically a bubble of thin rock. Rarely, the latter may be big enough to qualify as a cave.
- Lava mold caves, which form when lava flows around trees or even large dead animals. The engulfed material eventually burns or decays away, but ends up leaving a hollow space with the original shape. These aren’t usually very large but can get somewhat complex where groups of fallen logs were touching, and may then form caves that go in several directions where the resulting voids intersect. Such caves are known from Washington (USA), near Ape Cave, and from most notably from Japan in the Yoshida-tanai area. Elephant mold caves are known from the Nyiragongo volcano in Africa, and one in the shape of a Tertiary-age Rhinoceros is known from Blue Lake, Washington (USA).
- Open vertical volcanic conduits are voids open to the surface which remain after magma has erupted. They tend to be narrower near the top and bell out below, requiring a roped descent for exploration. The deepest known example is Thrinukagigur in Iceland at 204m deep.
- Pit craters form when magma that doesn’t quite reach the surface drains to form a void, and the ground above it slumps. These huge open-air pits with their sheer walls are analogous to some of the large shafts formed by solution, and typically require a roped descent for exploration. While most have no extension beyond the visible floor, others may have entrances into adjacent (now empty) magma chambers, such as was seen when the crater of Mauna Ulu in Hawai`i Volcanoes National Park was explored by a team of Swiss cavers. In Na One, a pit crater on Hualalai Volcano in Hawaii, a narrow opening at the bottom of an 130m-deep pit crater leads into an open vertical volcanic conduit, with a total depth of 268 m.
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