Kazumura Cave is a lava tube on the island of Hawaii. The cave formed between four and six centuries ago, when a vent on the east side of Kilauea Caldera erupted, sending lava down the northeast flank of the volcano. As these lava flows advanced, they cooled from the outside in. This produced a hard crust around the flow, which protected the lava from cooling too quickly. (Hawaiian lavas erupt at approximately 2165°F (1185°C). The air and ground temperature is therefore cold to lava.) In time, this protective crust thickened and confined the flow to an oval or rounded conduit referred to as a lava tube.
Lava tubes which are active for long periods of time, can be enlarged by lava flowing through the tube. Lava is a very abrasive fluid which can erode the surround rock. Given enough time and favorable conditions, this erosion can form canyons and lava falls. Erosion can also expose gaps in the existing bedrock. Lava injected into these gaps sometimes remains molten, and later drains back into the tube to form lava straws or runs.
If during an eruption, a hole develops in the ceiling of a lava tube, that hole is called a skylight. Skylights allow heat to escape while admitting cold air. Any time the lava level in the tube drops, cold air entering a skylight can chill the surface of the flow causing a second crust to form. This produces what is known as a tube in tube. Cold air can also crack hot rock, allowing sections of the tube walls and ceiling to collapse, producing breakdown.
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A dropping lava level also allows lava sticking to the ceiling to sag and form lavacicles, (a feature similar in appearance to a stalactite). As the lava level drops further, the tube begins to drain and cool. The last bit of lava flowing over a fall has cooled to a puttylike consistency and begins to pile up on itself. This forms an irregular column called a dribble spire. At the base of a fall, a thick crust forms on the plunge pool surface, and then sags as lava drains from beneath. The last tubes in tube, also begin to collapse without lava to support their weight.
It can take years for a lava tube to cool sufficiently to support life. As many cave creatures are dependant upon plants for their food, it is likely the cave is not fully colonized until after these plants have become established on the surface above.
Kazumura Cave is just one of several lava tubes that formed in that eruption, but it is by far the most important. As the worlds longest known continuous lava tube, Kazumura is a national treasure that is virtually unknown to all. Geologically speaking, Kazumura has been called a master lava tube. Nearly every type of feature found in a lava tube can be found in this cave.
