Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

which grades into a steep rubble slope.
The trail negotiates this steep slope by
stairs, which end on a platform built on
the floor next to the pool basin for which
the cave was named. The floor of this
ephemeral pool is a smooth oval saucer
20ft long and 15ft wide. It is white from
the caliche efflorescence precipitated by
evaporating water. This deposit of calcium
carbonate, along with clay washed
down into this spot during the spring
snowmelt, gives the bottom of the basin
enough of an impermeable seal to hold
water through part of the summer season.
The pool occupies only a small part
of this deep central depression, which
continues 60ft farther south to where the
floor rises abruptly in a steep rubble
slope. How could this deep depression
form at the bottom of a higher lava tube
that transmitted molten lava to the north?
Part of the answer becomes clear when
we examine the pool basin in more
detail. On the east, north, and on part of
the northwestern margins of the pool is a
rock lip overhanging the surface of the
pool but no more than 4 ft above the
bottom (see heavy dashed line on map 1,
pl. 1). Apparently this is the roof of a
second large tube, at a lower level. The
deep depression in the central part of the
upper tube was caused by its floor giving
way and tumbling piecemeal through the
roof of the tube below.
When did this collapse happen? Evidence
is equivocal, but at least a part of
the collapse occurred while the lower
tube was filled or nearly filled with
flowing lava. Many of the collapse
blocks, and all of them in the immediate
area of the present water pool, apparently
were carried down the tube by this
flowing lava. Supporting evidence is that
the caliche and clay which helped form
the basin of the water pool were not
deposited on an irregular heap of large
fallen blocks, but they were instead
deposited on a relatively flat surface. The
lateral extent of this flat surface and the
lavacicle roof above it can be investigated
by poking a long rod between roof and
floor. In several places a 15-ft stadia rod
can be extended all of its length. This
must mean that the lower tube is now
filled almost to its roof. The blocks,
which poured through this hole in the
roof when the collapse occurred, did not
jam but were transported down the lower
tube. They were later enveloped by the
ponding lava, which nearly filled the
tube when it cooled. Such relations are
not unusual in lava-tube caves. Clearer
Figure 20. Much of original wall lining has collapsed but some remains on wall of
Indian Well Cave (see fig. 14 and map 1, pl. 1).
evidence of such transport can be seen in
Post Office, Catacombs, Valentine, Berthas
Cupboard, and many other lava-tube
caves.
The trail ends at the foot of the stairs,
but the remaining 150 ft of accessible
cave to the south is easily traversed if one
does not mind climbing over large jumbled
blocks. High on the west wall in this
part of the cave are remnants of a balcony
that runs along most of the wall, buried
by slides near the middle and the south
end.
At the south end of the cave the floor
rises higher and higher until it ends in a
clutter of huge blocks not far below the
surface of the ground. A small dug-open
crawlway serves as an egress out into the
collapse fill at the north end of the Doc
Yock-Stinking Cave breakdown.
In summary, Indian Well Cave is a
300-ft-long remnant of a part of two
superposed large feeder tubes. Only the
upper tube can be traversed. It has been
so modified by rockfalls from its roof,
slides through its west wall, and the
collapse of 60 ft of its floor into the lower
tube that almost nothing but collapse
features are visible. A little of the intact
roof of the lower cave can be seen in an
overhang just above the floor of the water
pool in the deepest part of the cave.
Doc Y ock Cave is a continuation of
the upper level of Indian Well Cave. As
in Indian Well, the cave has undergone
massive collapse with most of the resulting
breakdown falling into the lower tube
levels. A short intact segment of tube
complete with several rafted blocks and
a pahoehoe floor is present at the upper
southern end of the cave. Judging from
this intact segment of Doc Yock Cave,
the original tube was 21 ft wide and
probably in excess of 17 ft high.
Stinking Cave is a further extension
of the Indian Well-Doc Yock Cave tube.
In cross section the 128-ft-long cave is
shaped like a tall rectangular canyon,
with little collapse except at the ends.
The northern end lies partly underneath
Dock Y ock Cave and probably represents
a middle level in the tube system.
It is closed by the deep collapse of the
tube at the southern end of Indian Well.
A short lower segment of passage just
inside the entrance may represent a lower
Lava-Tube Caves of the Headquarters Area 19