Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

collapse blocks overrun by lava. Most of
these blocks are large chunks from fallen
parts of the balcony.
Balconies Near Crossover Between Tubes
The collapse at Howards Hole may
have triggered further collapses and
abrupt changes downstream. Downstream
from Howards Hole the upper
tube drained out to the northeast and has
a normal pahoehoe floor locally embellished
with stretched-out pahoehoe
lobes. However, evidence that this tube
was once filled to the top is seen in
numerous small remnants of balconies
near the roof.
Downstream 200 ft from Howards
Hole a prominent balcony occupies an
area extending 45 ft upstream and 25 ft
downstream from a tiny crossover connecting
this tube with a lower level. The
same sequence of events as at Howards
Hole seems to have operated here: ponding
in the upper tube nearly to its roof,
partial solidification, and then sudden
draining through the crossover into the
lower tube.
Downstream from this crossover
both the upper and lower tube show signs
of a later ponding. The lava dumped into
the lower tube from Howards Hole and
the crossover was quickly carried away,
and the lower tube was drained beyond
the large pillar 20 ft downstream from the
crossover. A short distance from here,
however, the lava began to pond, and 90
ft downstream from the crossover it
ponded to the roof and thus ended further
access within this tube.
Relations in the upper tube are superficially
similar. Downstream from the
crossover, the tube drained and the floor
composed of rafted blocks in frothy
pahoehoe formed. Downstream 40 ft
pooling began where the tube turns
abruptly north, and 135 ft beyond the
crossover, the tube is filled to its ceiling.
Second Crossover and
Area Near Cleopatras Grave
The upper tube system mentioned in
the previous section is not accessible. On
the right wall of the tube, 85 ft downstream
from the crossover and 50 ft
upstream from its filled end, is what
appears to be a second crossover. It is
entered by climbing over a 4-ft-high sill
on the east wall of the tube and then
traversing down the crossover tube 40 ft
to the east to reach a large pool 50 ft
across, ponded very close to the roof.
Another tube appears to enter this pool
very close to the mouth of the crossover.
It could well be the continuation of the
lower tube, which pooled to the roof only
50ft upstream (map 3, pl. 1) . From this
tube a sticky lobe of pahoehoe was
exuded onto the surface on the large lava
pool. It can be traced 45 ft to where it
merges into the larger lava pool. Both
masses of lava were molten, or pasty, at
the time they came together.
At the tip of a V -shaped irregularity
in the wall of this large pool, two tubes
take off downstream. One, headed north,
with only 1 ft of clearance, is filled to the
roof with lava just downstream. The
other, headed in the normal downstream
direction, has 3-4ft of clearance allowing
entrance to another 400 ft of branching
tubes and lava pools.
This final downstream section is
complicated. Downstream 80ft from its
exit out of the large lava pool, the tube
widens into a small lava pond. This pond
is a drainage divide, because one tube
actually heads back to the southwest-in
exactly the opposite floor direction from
the rest of the tubes in this system. After
flowing for 45 ft, lava in this tube
tumbled over a 4-ft cascade into an oval
pool 18 ft long and 11 ft wide. The west
wall of this pool is within a few feet of
the large pool described previously but is
at a lower level (map 3, pl. 1). From this
oval pool a small tube, ponded almost to
its roof, appears to exit south but instead
may be backflow from the oval pool.
The second, longer tube from the
drainage divide takes the more consistent
northeastern course. Downstream 15 ft
from the divide its lava flowed over a
cascade and into a wider area where it
subdivided and rejoined around three
pillars. There is evidence here of two
large roof collapses that were smoothed
over and partly carried away by the
moving lava. Rafted blocks are abundant
in the pahoehoe floor; they dot its surface
for another 100ft until a floor jam closes
the tube.
One large rafted block, located a few
feet south of the middle pillar, is of
special interest. Its exposed surface is
rounded and smoothed (fig. 13)-it
floated with its upper surface rising a few
inches above the molten flood. The
surrounding lava festooned its edges
with two to four discontinuous pahoehoe
ropes that seem to set the block in a
frame. J.D. Howard found the exposed
rafted block surface with its pahoehoe
frame strikingly similar to an Egyptian
sarcophagus in shape. Therefore, when
he explored this part of the tube in 1914,
he named the block Cleopatras Grave.
Ovis Cave and Paradise Alleys
Map 4, plate 2, of Ovis Cave and
Paradise Alleys, overlaps map 3, plate 1
in the Catacombs Basin area and extends
map 3 to the southwest. Paradise Alleys
are the upstream continuation of the
Catacombs lava-tube system beyond the
lava lake that filled the Catacombs Basin.
The near-surface Paradise Alleys
lava tubes were fed from the large tube
of which Ovis Cave and Ovis Bridge are
uncollapsed remnants. A large distributary
from this feeder once ran northeast
just upstream from the head of Ovis Cave
but is now represented only by a broad
shallow collapse basin that extends N.
65° E. for 125 ft. From the north wall of
this collapsed distributary, three nearsurface
lava tubes extend north. Another
eastward-extending lava tube joins them
from just under the roof of the south end
of Ovis Cave. Beyond Ovis Cave these
tubes trend northeastward and form the
network of passages that makes up the
Paradise Alleys (see maps 4 and 5, pl. 2).
Ovis Cave and Paradise Alleys are
difficult to traverse because of partial
roof collapse. This collapse has obliterated
most of the ceiling features except in
some of the smaller tubes of Paradise
Alleys. For the student of lava-tube
hydraulics, this area furnishes a fascinating
look at the anatomy of a major
feeder tube and its distributaries.
Ovis Cave and Paradise Alleys 29