Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

caliche, they may show a silver or paleblue
sheen when wet. This phenomenon
is the source of the names ''Silver Cave"
and "Blue Grotto."
In some areas (notably in parts of
Catacombs, Labyrinth, and Valentine
Caves) the caliche is pale buff or tan to
chocolate brown instead of white because
of a higher content of clay, soil
humic acids, hydrous iron oxide stains
washed in with the calcium carbonate,
and the growth of "lava-tube slime"
(bacteria and primitive fungi) on the
moist walls. Water droplets on this fungi-rich
caliche may glow like polished
gold when a light is played upon them
(fig. 18). This "false gold" is sometimes
visible in wet areas of Mushpot Cave and
is beautifully displayed on the moist roof
and walls of Golden Dome, Hopkins
Chocolate, and Valentine Caves.
Another uncommon but interesting
secondary effect, visible in near-surface
caves with wet floors, is a flickering
greenish glow along the floor, which
appears to change color and intensity as
light is played upon it. This is phosphorescence
derived from the decay of animal
droppings on the cave floor, and it is
occasionally seen in wet parts of Valentine
Cave.
Lava Brook Cave
The entrance into Lava Brook Cave
(map 1, pl. 1), like Mushpot's, appears
to have been a skylight when the lava
tube was active. The hole is so small that
the two steep stairs built into it-one
leading downstream, the other upstream-obscure
the walls; however,
some dripstone is visible and extends to
the surface.
Three Junction Area
For the first 50 ft downstream from
the entrance stair, Lava Brook is a small
lava tube that is about 8 ft wide, 5-6 ft
high, and cluttered with collapse blocks.
It then makes an abrupt turn to the right
(southeast). Its gradient steepens, and it
throws off two small distributary tubes
from its left side. The first one, located
exactly at the bend, is a small crossover
tube that leads to the entrance of East
Labyrinth Cave (see map 1, pl. 1).
This crossover tube leaves Lava
Brook by dropping abruptly in a 5-ft lava
fall. The tube is so narrow and low that
it requires stooping or crawling for much
of its 125-ft length. In places it is so
cluttered with collapse blocks that, except
for another lava fall about midcourse,
there is nothing to see except
collapse features.
The second small distributary heads
in the same direction from a point 10 ft
farther down the Lava Brook tube. It also
immediately drops in a 3-ft lava cascade.
Ceiling heights are only 3-4 feet, but the
tube is free of collapse blocks and displays
fine examples of lavacicles, dripstone,
and pahoehoe. After crawling for
32ft, you will find this direction blocked
by lava up to the roof, but the pahoehoe
stream that formed the floor actually
turns sharply to the left (north), drops
abruptly 3-4 ft below its upstream floor,
and resumes its course to the northeast.
Further access is denied only a few feet
beyond the northeast turn by the lava that
rose to within 6 in. of the roof. By
plotting this point on the maps we found
that this tube is the upstream continuation
of the tiny tube up which we had
Figure 17. White caliche deposit along
crack in wall of Post Office Cave (see fig.
4 and map 15, pl. 5). This cave deposit
was formed by evaporation of percolating
surface water carrying calcium carbonate.
Figure 18. False gold cave deposits on wall of Golden Dome Cave (see fig. 14 and
map 2, pl. 1). Deposit consists of thin coating of fungi-rich caliche. Field of view
is 6 ft across.
Lava-Tube Caves of the Headquarters Area 15