Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

crawled 180 ft from the Mushpot tube.
Access is blocked for less than 20 ft
between them.
Twin Pillars-Sleeping Beauty Area
Returning to the main Lava Brook
tube and continuing downstream, we
come to two small pillars, with a nest of
intersecting benches and lava tubes
around them. To understand this complicated
area, carry the map and refer to
it constantly while examining this part of
the cave. The first feature to note downstream
is a lava bench, 2ft high, which
begins on the left (north) wall 12 ft
downstream from the head of the tiny
tube described previously that leads from
the Mushpot tube. Beyond this bench the
left wall of the tube turns due east,
whereas the opposite wall diverges
southeast. The main lava channel follows
the southeast trend and is bounded
on its north side by the lava bench. The
gradient steepens, and as the channel
deepens the bench of its left side subdivides
into two benches; the lower bench
ultimately rose 4-5 ft above the floor of
the tube downstream. Because of the
divergence in direction of the tube's
walls, the benches soon widen to a
maximum of 18 ft. At the point of
divergence, twin pillars connect both
benches with the roof of the cave. The
higher bench is attached to the north side
of the smaller (northern) pillar, and the
lower bench clings to the southwest side
of the larger pillar. Between the two
pillars is a deep cleft. An early rush of
molten but viscous magma, which
formed the higher bench named "Sleeping
Beautys bier," rose in a standing
wave 2 ft high and stuck in the upstream
end of this cleft. It thus protected the
deep cleft from further invasions of
molten lava while the benches and channel
were built. Moreover, a small tributary
from the north was also spilling lava
into the main Lava Brook tube just at the
downstream edge of the pillars. As the
lava from this tributary decreased in
volume it carried away what may have
been molten or sticky continuations of
the benches downstream from the pillars.
The same kind of action was probably
occurring on the edges of the Lava Brook
channel simultaneously. The lava from
this tributary appears to have been fed
from a tube-in-tube (now filled in), but
the last lava emitted cascaded in a curving
steep-gradient gutter, which today
resembles a ramp making a left turn to
join a freeway on a lower level. A further
complication is that a much larger tributary
joins the Lava Brook tube from the
opposite (south) side at the same point.
The pahoehoe floor of this tributary tube
is at the level of the lower bench, so its
mouth hangs 3 ft above the Lava Brook
channel. The exact order in which these
different benches, gutters, and channels
were built is perplexing, but the order of
their final abandonment by liquid lava
can be worked out. Lava stopped flowing
from the south tributary first, then from
the main Lava Brook tube, and the final
driblet down the tube was out of the
curving lava gutter that drained the north
tributary.
Mushpot-Lava Brook Floor jam
Continue down from the Twin Pillars
through the main Lava Brook tube on a
traverse that runs slightly north of east
for 110 ft to where a big tributary
intersects this tube from the south. Along
the first 80ft of this traverse, Lava Brook
is an ordinary clean tube exposing good
lavacicles, dripstone, and a spiny pahoehoe
floor. Two long remnants of the 3-ft
bench cling to its south wall. About 80ft
below the Twin Pillars the roof of the
cave begins to lower, and the lava on the
floor pooled and broke up into blocks,
which were heaved up in a semisolid
state and deformed against one another.
Another 5-10 ft farther, these broken and
distorted blocks were raised in two giant
steps by molten lava, and finally a little
farther downstream the heaved blocks
were rebroken and jammed tight against
the roof. This is the opposite side of the
lava jam just upstream from the Mush pot
bubble. Access between the two caves is
barred by the lava jam over a distance of
approximately 30 ft (see map 1, pl. 1).
Curiously, no clear evidence was seen
that molten lava backed up high enough
to fill the tube behind this dam. Apparently
the floor jam did not form until the
final stages of lava occupancy. The last
of the molten lava trickled between the
floor jam blocks and formed both the
Mushpot bubble and the small lobe of
yellowish lava that extends downstream
from it.
South Tributary
On returning to the Lava Brook
entrance, a side trip to the head of the
south tributary is worthwhile, although
for about half its length you will have to
walk in a stooped position and crawl over
the last few feet.
As previously noted, a step up a 2- to
3-ft scarp is required to enter this tube.
One can then continue upstream in a
particularly clean cave with a well-exposed
ropy pahoehoe floor. At 120 ft the
source of the lava that built this floor is
evident. It is a thin flow that debouches
from a gutter down the middle of the
tube, leaving benches of older lava on
either side. In another 60 ft the entire
tube appears to end bluntly in a rock
wall, beneath which the gutter disappears
as a tube-in-tube. However, there
is a narrow opening along the right
(north) side of the cave, and by climbing
up over a 5-ft lava fall, one can squeeze
through and find that the tube opens up
to its full width upstream at a level 5-7
ft higher. A small linear breakdown in
the floor indicates that the gutter we
followed to the lava fall continues beneath
the higher level as a tube-in-tube.
This upper tube is only 40ft long. It ends
in a wall from which several large blocks
have tumbled, revealing an unusually
clear example of a tube that had been
open at one time but that is now completely
plugged with lava. The tube
received a tributary from the south, 10ft
downstream from this wall. Solidified
lava chokes this tributary nearly to the
roof, but by crawling into it and poking
a stadia rod out as far as it would go, the
shape outlined on the map was obtained.
The direction of flow was noted from the
pahoehoe ropes.
Lava Brook Cave Upstream from Entrance
The upstream part of Lava Brook
Cave is an ordinary tube with a steeper
gradient than most other tubes. Upstream
16 Selected Caves and Lava-Tube Systems, Lava Beds National Monument, California