Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

circle the two large downstream pillars.
These benches are made of many sheets
only 1-3 in. thick that solidified as crusts
from the walls of the molten lava and
curled down (fig. 43) or broke off as the
lava changed in level. They have the
same origin but even better form than the
benches at the upper end of Tickner
Cave.
The last of the large pillars downstream
is canted at a slight angle to the
west wall. The tube on the northwest side
of it therefore narrows downstream
where a large floor jam piled up. It
consists not only of slabs from the floor,
but also of rafted blocks from the collapsed
tube-in-tubes upstream and some
debris from roof collapses. Downstream
from this last pillar the combined flow
narrows into one tube, which narrows
abruptly to 15-20 ft another 75ft farther,
only one-third of its upstream width. In
this narrow section the benches of
curled-lava plates change to higher and
broader balconies, with turned down
edges covered with dripstone. This tube
decreases to a width of only 12 ft with a
height of less than 5 ft. A very low
tube-in-tube occupies the center of the
passage for nearly 70ft; on either side the
floor consists of plates buckled by the
last lava flow into waves 1 ft high and 6
ft crest to crest. A lava boil 1 ft high and
12ft wide nearly closes off this passage
at the Gates of Dis. Beyond the Gates of
Dis, the tube suddenly broadens downstream
into a high-domed chamber 75ft
long, 40ft wide, and originally 27ft high
at the apex of the dome. This room has
shelf-like openings in its walls and at
several levels of the arched sides of the
dome. These are separations between
flow units that have been pulled apart.
Grotto-like clefts also break across flow
units and extend outward into the walls .
Two collapses to the surface are closely
associated with this dome: one is a small
cupola (11 ft in diameter) that demolished
part of the sloping roof of the
northwest part of the dome and left a
shelf of debris against the northwest
wall, and the other is a large irregular
collapse pit roughly 40 by 30 ft at the
surface with a floor that is at the same
level as the floor of the dome. This larger
collapse, which provides the main entrance
to Berthas Cupboard Cave, lies
only a few feet downstream from the
edge of the dome, but the connection
between them has such a low ceiling that
one must stoop to enter the dome. Also
like the dome, this collapse pit contains
several open separations between the
flow units exposed on its walls. It is these
shelf-like openings on the walls of this
pit, and the irregular grottos between
them, that prompted Howard to name the
cave Berthas Cupboard (see fig. 37 and
the sketch of this breakdown on map 9,
pl. 3.)
Within the dome, collapse fragments
dropping from these shelf-like separations
have built a ring of debris on the
floor of the cave near its walls. An
arcuate ring of tumbled debris, 5-15 ft
high, borders the west rim of the dome.
Many pieces dropped from the sloping
roof of the dome and from edges of flow
units in the dome's walls when the rock
was hot and plastic. They welded together
on impact. This arcuate ridge of
collapse debris is also responsible for the
low ceilings that must be negotiated
when leaving the dome in either direction.
A short natural bridge is present at
the southwest comer of this debris ring.
Downstream from the dome, Berthas
Cupboard Cave can be traversed for 650
ft before access is denied by partial lava
filling and roof collapse. This part of the
cave has a thick covering of collapse
debris compared with the upstream part
of Tickner Cave. It is a typical near-
Figure 42. Large pillar in Berthas Cupboard Cave (see fig. 4) is known as the
Mush room (see map 9, pl. 3).
Figure 43. Curled lining of Berthas Cupboard
Cave (see fig. 4 and map 9, pl. 3)
peeled away while still hot.
52 Selected Caves and Lava-Tube Systems, Lava Beds National Monument, California