Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

puzzles abound in the Catacombs; downstream,
Howards Hole and Cleopatras
Grave are outstanding examples.
Northeastern Part of Catacombs Caves
Downstream 250 ft from The Bathtub
the complexity of the Catacombs
tube system decreases noticeably. Most
of the short tubes filled with lava to their
roofs. The complex areas of high ceilings,
lava falls, and large roof collapses
give way to smaller tubes so filled with
lava that in many places they can be
traversed only by walking in a doubledup
position or by crawling on one's
belly.
From The Bathtub 1,100 ft downstream
to where the Catacombs tubes
become inaccessible, the lava was carried
forward through three nearly parallel
tubes with small vertical differences.
The direction of all three averages
N. 55° E. , except in the last 200ft, where
each turns sharply to the north. The
simplest of the three is the one on the
southeast.
The Southeastern Tube
The southeastern passage is the
downstream continuation of the tube at
the foot of the stair that gives access to
The Bathtub. Within the first 200 ft
downstream from The Bathtub, it sends
two branches north, each of which extends
only a few feet before feeding
down into the tube that crosses beneath
The Bathtub. It also receives one tributary,
the Dollar Passage, from the south.
The southeastern tube then continues
downstream in an overall N. 55° E.
direction for 650 ft without receiving a
tributary or creating a distributary.
Throughout this distance it is a fairly low
tube (from 2 to 6 ft in height), well
drained of lava fill in most places, but
pooled in others to heights requiring a
crawl. The roof, walls, and floor of the
tube are intact nearly everywhere. Excellent
examples of lavacicles and dripstone
abound. The floor varies from
normal to frothy (or cauliflower) pahoehoe.
At the downstream end of this stretch
the tube widens, subdivides around one
pillar, and then unites near two other
downstream pillars. The area near the
pillars underwent a partial roof unraveling
over 25 ft long. Its floor contains a
narrow trough 2-3 ft wide that begins 50
ft west of the southernmost pillar. It
begins as a lava gutter in the smooth
pahoehoe floor. It gradually deepens
downstream and 25 ft from its origin
dives below the surface of the pahoehoe.
From here it evidently continues as a
small tube-in-tube beneath the floor and
surfaces again (with collapsed top) 40ft
farther downstream. Another 20ft downstream
it is again lost beneath the pile of
collapse rubble west of the middle pillar.
What is probably the same gutter, but
with a different trend, emerges from
beneath the collapse pile between the two
northern pillars and dives steeply beneath
the east wall of the main tube
before becoming sealed with lava (map
3, pl. 1).
The Elephants Rump, named by J.D.
Howard, is a small downstream extension
of the northeasternmost pillar at
about waist height. It was smoothly
plastered over and rounded off by flowing
lava but to appreciate its similarity to
an elephant's rump does require a bit of
imagination.
Other features near these pillars, in
addition to the plunging tube, suggest
that the main tube feeds into a lower and
larger open tube downstream from the
pillars. Downstream from the cascade
both ceiling and walls of the tube are
irregular in height and trend. Heights of
6-10 ft are common, whereas much of
the tube upstream can be traversed only
by stooping or crawling. A remnant of an
adjacent tube, which contains a lava
pool, opens in the east wall of the tube
near the cascade, and many alcoves are
present on the sides of the tube. This
remnant tube also changes direction
from N. 70° E . toN. 15° E.
Travel within this irregular, highceilinged
passageway ends abruptly
some 400 ft downstream from the pillars
due to pooling of lava so close to the roof
that further access is nearly impossible.
Two Northeastern Tubes
Running roughly parallel with the
passage just described are two lava tubes
intertwining horizontally but mostly separated
vertically from one another. The
southeastern tube is never more than 100
ft southeast from one of these tubes, and
in places may approach so closely that
the wall between is not more than 10 ft
thick. The rough parallelism of these
three tubes exists through a length of
over 1 ,000 ft, and then all three bend
northerly and become inaccessible due to
lava filling. The features of two northeastern
tubes are more diverse than the
southeastern tube.
Area near Howards Hole
Howards Hole is an oval-shaped vertical
collapse pit 8 ft deep, which connects
the two northeastern tubes where
they cross each other. Unlike at The
Bathtub Drain, collapse at Howards Hole
was sudden, violent, and delivered much
molten lava into the lower tube immediately
after collapse. At the time of
collapse the tube upstream from the top
of Howards Hole was filled to the roof
with lava. Downstream and immediately
above Howards Hole, the ceiling rises
into a cupola with a shelf of ponded lava
just below the cupola ceiling. Within the
cupola the molten fill had cooled enough
to develop a fairly thick crust across its
surface. Solidification had also progressed
inward from the walls and floor
of the tube. A sudden collapse ofthe tube
floor where it crossed over the highest
point in the underlying tube produced an
opening (Howards Hole), which immediately
drained the ponded lava of the
upper tube and cupola into the tube
below. A large part of the solidified crust
of the ponded lava broke into large pasty
blocks, many of which lodged in the
upper margins of Howards Hole. Many
more dropped through the hole and were
rafted downstream. Some blocks that
stuck on the upstream side of Howards
Hole created a low dam, which formed a
small puddle of lava in the upper tube just
upstream from the hole. For the next 40
ft downstream, however, much of the
solidified upper crust survived the collapse
and was left hanging as a spearhead-shaped
balcony 5-8 ft above the
irregular floor. The floor near Howards
Hole is irregular due to accumulation of
28 Selected Caves and lava-Tube Systems, lava Beds National Monument, California