Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

through onto the tube floor below. Be
cause of the almost perfect preservation
of the cracked Boxing Glove Chamber
floor on the upper funnel walls, we
reason that The Bathtub Drain did not
open until late in the history of The
Bathtub after the floor and much of the
interior lava was solid or pasty. When
The Bathtub filled, most of the excess
lava escaped through two other exits: one
is the previously described small tube in
the east wall; and the other is over a
larger lava fall at the southwest end of
The Bathtub where the ladder is located.
This 8-ft lava fall dropped the lava into
a large tube whose level is 5-6 ft above
the floor of the tube under The Bathtub
Drain (see map 3, pl. 1).
Where did the lava come from that
entered The Bathtub and ponded within
it? Its source was one of the network of
tubes upstream to the southwest. The
map pattern shows that the source tube is
one of the several northeast-trending
distributaries common to the Catacombs
system. But where, exactly, is the upstream
continuation of the Bathtub tube?
Congealed lava at the southwest comer
of The Bathtub (just southwest of the Pin
Cushion, a large fallen block on the edge
of the Bathtub Drain funnel) exhibits
pahoehoe ropes indicating that this lava
was flowing into The Bathtub through an
almost completely filled tube. This tube
cannot be examined farther upstream
because of a clearance of only a few
inches between fill and roof, but the top
of this flow can be seen from the top of
two lava cascades that pour out of the
northwest wall of The Igloo, a tube that
contains the stairway (map 3, pl. 1). One
cascade is 15 ft and the other 50 ft
upstream from the base of the stairway.
Again, the clearance between ponded
lava and ceiling as observed from the top
of these cascades is in most places 1 ft or
less, but by probing around with a stadia
rod, we determined that the tube is at
least 8 ft and in some places more than
20ft wide. Perhaps at one time the tube
continued upstream to a junction (now
walled off) with the plexus of tubes 250
Figure 26. Protective fence prevents visitors from stumbling into The Bathtub Drain
(see map 3, pl. 1) formed when lava drained into lower level of Catacombs Cave
(see fig. 14).
ft or more upstream. The elevation here
is sufficient to have fed lava into The
Bathtub.
But there are other possibilities. Only
40 ft southwest of the foot of the stair,
access is almost blocked by a huge
cave-in of the roof (map 3, pl. 1). This
particular pile of collapsed blocks is
younger than the volcanism; the blocks
fell into an already drained tube. Moreover,
an earlier collapse at or near the
same spot when the lava tubes were
active could easily have blocked this tube
and raised the level of the lava upstream;
thus the direction of flow through the
present lava cascades on the northwest
wall was reversed, a process which
would cause a large flow into The Bathtub.
Later the collapse dam might have
been breached and removed to leave the
features we see today. Nor is this the only
place where a collapse would have
brought about this sequence of events. A
second large area of collapse breccia is in
this same tube, 140ft downstream from
the base of the ladder. That earlier
collapses may have occurred at these or
other nearby sites is clearly indicated by
the abundance of rafted blocks downstream.
Accumulations of collapse breccia
smoothed over by lava occur downstream
in both this tube and in the one
beneath The Bathtub Drain.
A close study of the many lava falls,
ponded lava tubes, and areas of both
pre-lava and post-lava collapse breccia
within 200ft of The Bathtub shows that
the general sequence of events outlined
for The Bathtub was partly duplicated in
many of the other nearby tubes. Most
show evidence of ponding and of synchronous
or later collapse into other
tubes that left balconies or other features
indicating an earlier ponding. Many
abrupt changes in trend or in elevation of
lava tubes are difficult to explain, except
by the shunting oflava from one tube into
another; the details that can be worked
out of such changes in the complex area
within 250ft of The Bathtub are a lesson
in lava hydraulics, but we can never
know the entire story. Much evidence is
not available because of ponding in many
lava tubes to their roof and by the
transport or impounding of collapse
breccias by further flow of lava. Such
Catacombs Cave 27