lava tube

^{ALASKA VOLCANO OBSERVATORY GLOSSARY}

A tunnel formed when the surface of a lava flow cools and solidifies while the still-molten interior flows through and drains away.

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^{GLOSSARY OF VOLCANIC TERMS}

A hollow region, commonly found within crystallized pahoehoe lava flows, which was filled with hot, flowing lava during a volcanic eruption. Lava tubes are formed when the top surface of a channelized lava flow crystallizes, and the magma flowing in the interior of the lava flow drains during and/or immediately following a volcanic eruption.

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^{USGS PHOTO GLOSSARY OF VOLCANIC TERMS}

Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow. Tubes form by the crusting over of lava channels and pahoehoe flows. A broad lava-flow field often consists of a main lava tube and a series of smaller tubes that supply lava to the front of one or more separate flows. When the supply of lava stops at the end of an eruption or lava is diverted elsewhere, lava in the tube system drains downslope and leaves partially empty conduits beneath the ground. Such drained tubes commonly exhibit "high-lava" marks on their walls, generally flat floors, and many lava stalactites that hang from the roof. Lava can also erode downward, deepening the tube and leaving empty space above the flowing lava.

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Photograph provided by Hawai`i Volcanoes National Park.

Thurston (Nahuku) lava tube, shown here, is near the summit caldera of Kilauea Volcano in Hawai`i Volcanoes National Park.