A lava tube is a natural conduit 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.
|Thurston (Nahuku) lava tube near summit caldera of
Kilauea Volcano in Hawaii Volcanoes National Park. Credit: Hawaii
Volcanoes National Park
Lava tubes can be as small as about a meter (3 ft.) across or as large as
a railway tunnel.
AND PLANETARY SCIENCE