Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

stream from the bottom of the pit. The
small pile of collapse debris on the floor
of this pit accounts for less than 3 percent
of the missing parts removed from the
basalt units seen on the pit's walls.
Evidently, the missing materials were
rafted down the tube. This deep vertical
pit is very similar to one located east of
Post Office Cave along the same line of
collapse trenches. We named this pit
Duffys Old Still Well because in prohibition
days a still was concealed beneath
the overhang produced by the egress tube
at the north comer of the well. This pit
has been shown as "Duffys Well" on old
maps of the area.
Prohibition Cave
Southwest 100 ft from Duffys Old
Still Well is the upstream continuation of
the collapse trench. At the trench's
downstream end is a small preserved
segment of lava tube. Two small entrances
lead down into Prohibition Cave
through collapse rubble. Virtually no
interior surfaces remain in the cave's
single chamber because the walls and
ceiling have unraveled extensively and
covered the floor with collapse rubble.
Collapse blocks prevent any travel beyond
the first 35 ft down the tube toward
the small cave at Duffys Old Still Well.
Prohibition Cave is a continuation of the
main tube that extends both upstream and
downstream from Duffys Old Still Well,
and its name is derived from the dashed
hopes of explorers to find an easier way
into Duffys Old Still Well.
Hercules Leg and Juniper Caves
The Hercules Leg and Juniper Caves
(map 6, pl. 2) constitute an interconnected
system of near-surface lava tubes and
irregular short passages. Altogether they
contain 4, 810 ft of passage if one counts
the deviations around the many pillars,
short blind tubes, and alcoves. The two
major entrances to this cave system were
discovered and named by J.D. Howard
in 1918.
The entrance to Hercules Leg Cave is
adjacent to Cave Loop Road. It is marked
by a sign and parking area. The entrance
to Juniper Cave, the downstream continuation
of Hercules Leg Cave, is
reached by a trail leading east from the
Juniper parking area.
The near-surface nature of the Hercules
Leg-Juniper Cave system can be
seen in the shallow surface breakdowns
in the caves. At most breakdowns the
roof of the cave is less than 10 ft thick.
Collapse blocks clutter the floors of
many underground passages, and approximately
a quarter of the floor of the
caves is completely covered with fallen
blocks. Because this slow unraveling of
the roof is still in process, parts of these
passages must be considered dangerous.
The Hercules Leg Cave is undoubtedly
a distributary from the large feeder
tubes that once conveyed molten lava
from Mammoth Crater to Natural Bridge
and then on through Ovis and Sentinel
Caves to Indian Well and beyond. The
collapse trench closest to the upstream
end of Hercules Leg Cave is the one
between Ovis Bridge and Ovis Cave (see
map 5, pl. 2, Natural Bridge area). No
direct connection between this taluswalled
trench and the head of Hercules
Leg Cave is visible in the field; however,
an underground connection seems likely
because the head of this tube is less than
100 ft from the wall of the trench, and the
upper part of the Hercules Leg tube lies
beneath a surface lobe of lava that
spreads eastward from this area.
The actual visible underground
source of the lava that once poured
through Hercules Leg Cave can be
reached by a traverse of 235 ft upstream
(west) from the entrance. Here, at the
head of this low tube, upwelling lava
formed a mound as it rose from below.
This mound is the top of a connector to
a lower lava-filled tube, which must have
split off from the feeder tubes to the west.
An unusual feature of Hercules Leg
and Juniper Caves is four abrupt rightangle
turns of the main lava tube (map 6,
pl. 2). The lava flowed first to the east for
500-700 ft, then turned north for about
the same distance then repeated this
pattern. A complicated melange of pillars,
short dead-end passages, and alcoves
generally formed at the abrupt
bends.
Features Near Entrance
The entrance to Hercules Leg Cave is
a halfdome-like opening, which appears
to have been a large gas blister developed
under a thin-roofed part of the lava-filled
tube. The north wall of this blister, plus
a part of the tube roof upstream from it,
has fallen in and left a pile of rubble in
the opening. The main trail leads underground
(left) into the downstream part of
the tube.
A second and little-used trail takes
off over the pile of collapse rubble and
heads upstream (right). At the farthest
upstream point along this part of the
Hercules Leg tube, the source of the
upwelling lava can be seen. Also, numerous
pillars, lava cascades, and rafted
blocks are present on the pahoehoe floor
of this segment. There is much evidence
that molten lava once filled this section
to the roof. High-lava marks are common
on the tube walls and on the plastered
sides of the pillars. Lava cascades accentuated
the flow around pillars, especially
near the downstream ends.
By following the main trail downstream
from the entrance, one can observe
many interesting features on the
way to the Barrel Skylight collapse nearly
550ft downstream. For the first 150ft
the lava was confined to one relatively
straight and high tube, but over the next
350 ft the tube splits up into an intricate
network consisting of an intact west
branch and segmented east branch with
crossovers and numerous irregular connections.
This part of the Hercules Leg
Cave displays the pattern of parallel
tubes with crossovers as seen in the
Catacombs system, but here it is not as
well developed. The similarity is closer
if we restore the connection that evidently
formerly existed between the collapse
area at the Birdshead Lava Pool (map 6,
pl. 2) and the two lava tubes 50 ft farther
east. If this restoration is made, we can
visualize three parallel tubes dumping
lava over small cascades into one medium-sized
tube draining the collected lava
of all three to the north past Barrel
Skylight. Downstream 160ft from Barrel
Skylight the tube makes its first
right-angle bend. A floor jam of
stretched and tilted pahoehoe blocks
Hercules Leg and Juniper Caves 37