LAVA FLOW TRAIL
STOP 6
Lava
tubes |
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| A
lava tube with a partially collapsed roof at Kilauea in Hawaii.
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 Hidden beneath the thick lava crust lie caves called
lava tubes. Lava tubes are remnants of the Bonito Lava Flow’s plumbing
system. These pipes first form while the lava is actively streaming downhill.
The scorching, runny basalt lava cools and hardens quickest on the surface
of the flow where it contacts air. The first solid rock forms plate-like
sheets that are swept along like rafts on this swiftly-flowing stream
of lava. As the surface continues to cool the plates will pile up and
fuse together to form a kind of crusty roof over the gushing lava river
below. The solid roof insulates the still-molten lava below from the cooling
effects of the air. The long, straight tubes may extend miles from the
vent where the lava emerges, emptying their molten contents far downstream.
Eventually the vent exhausts its lava supply or simply becomes
plugged up. Lava already in the tube drains out at the down stream end,
leaving an empty lava tube behind. Sometimes part of the thin, crusty
roof collapses, and an entrance to the tube opens up as it did here at
Sunset Crater.
If the lava is not able to drain completely, lava within the tube
solidifies to form a flat floor. The last drips of molten rock often form
lava
'stalactites' to decorate the drained tube. |
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|
 Inside
the ice cave
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This lava tube is unusual because ice is
found inside it year-round. Ice is rarely found year round in large lava
tubes because large tubes generally have good air circulation that eventually
melts any ice that accumulates there during the Winter. The lava tube
you see here has a very narrow interior compared to other lava tubes.
During the winter months, ice forms from water seeping through the porous,
fractured basalt. Cold, heavy air settles into the lava tube, allowing
the ice to form thick deposits along the walls and floor. Although much
of the ice melts each year, basalt is such an effective insulator that
some ice remains in the cave even through the summer months. |
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