Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

dead-end passages on different vertical
levels. This part of the tube system is
truly a labyrinth, and the visitor who
wants to explore it is advised to carry the
accompanying map and keep track of his
or her exact whereabouts by observing
the map at each tube junction. The
easiest approach to this interesting area is
through the Blue Grotto entrance, but do
not take the left (north) fork, which drops
over a 4-ft scarp into the head of the
crossover tube leading to the Blue Grotto.
Instead, continue northeast down the
main distributary tube. This northeasttrending
tube runs in a relatively straight
line with no embellishments except a
former skylight and some lava benches
along the walls until it reaches a largescale
breakdown. The trail partly avoids
this breakdown by entering a small bypass
tube on the left (west). It then enters
a maze of intersecting and branching
passages that offers a wide choice of
where to go and what to see. This maze
is the heart of the Labyrinth-a place of
blind alleys, numerous lava falls and
cascades with lava pools between, hanging
balconies and side tubes, and a wide
variety of narrow benches and pillars .
Most of the tubes within this maze
contain excellent lavacicles and dripstone
walls, and many are embellished
with the lace-like tracery of caliche,
clay, and iron oxides deposited by rainwater,
which seeped through the roof and
precipitated on roof and walls. The floor
features range from smooth to slightly
ropy pahoehoe on the lava pools to large
frothy pahoehoe ropes in tubes of moderate
gradient. Rare spiny aa surfaces are
present below some rapids and lava falls.
The roofs of many larger tubes, especially
at tube junctions, have been
scarred by roof collapse and in a few
places by breakdowns to the surface.
Most of the more interesting features are
shown on map 2, plate 1. Note the
position of stairs or ladders constructed
by the National Park Service to assist you
over lava falls and other obstacles, and to
help you get from one place of interest to
another. Nearly all features typical of
lava tubes are contained within this
compact but diverse area.
This complex network of intertwining
tubes appears to suddenly become
more orderly approximately 1 ,050 ft
downstream from the Blue Grotto trail
entrance. Here the anastomosing pattern
virtually ceases and the tubes recombine
into two major outlets-the Thunderbolt
and Labyrinth Distributaries.
Thunderbolt and Labyrinth
Distributaries
The western Thunderbolt Distributary
(map 2, pl. 1) is monotonous compared
to the wild jumble from which it
emerged upstream. It has high ceilings
and is easy to traverse. Large parts of its
interior are intact and preserve a good
display of lavacicles, dripstone, and pahoehoe
floors.
The eastern Labyrinth Distributary
(map 2, pl. 1) is larger, but it is littered
with far more collapse breccia. Beyond
the Popcorn Chamber, the passage turns
north, bends sharply northeast again and
promptly subdivides, and finally reunites
in a complicated fashion around a cluster
of five pillars. An array of lava benches
clings to the tube walls and to parts of the
pillars. These benches record fluctuating
levels of lava, some of which persisted
long enough for considerable solidification
before final withdrawal to the level
of the present cave floor. Withdrawal
must have been abrupt and complete, as
indicated by steep 1- to 5-ft-high benches
and narrow balconies that remain.
The Labyrinth Distributary lies close
to the surface, and numerous roof collapses
are found along it. Two major
breakdowns reach the surface, and much
of the tube floor is littered by blocks that
fell from the roof and walls.
Beyond the Labyrinth area, both the
Thunderbolt and the Labyrinth Distributaries
bend left and trend almost due
north (map 2, pl. 1). Although the course
of each is sinuous in detail, they maintain
a northerly direction for more than 1, 100
ft. Then, 200 ft southwest of the Thunderbolt
entrance both assume an approximate
N. 45° E. direction. Whereas upstream
from the Thunderbolt entrance
the two distributaries unite in a single
tube, below this entrance about 180 ft
they split into the Lava Brook, East
Labyrinth, and Mushpot Caves shown on
map 1, plate 1.
Catacombs Cave
Catacombs Cave (map 3, pl. 1) is
popular among monument visitors; J.D.
Howard was the first to record notes on
exploration of this complicated and interesting
network of underground passages.
Visitors who are unable or unwilling
to venture far underground can
find excellent lavacicles and dripstone
exposed on the ceiling and walls of
several branching passages within 200ft
of its entrance. These features, plus a
floor of ropy pahoehoe, are nicely displayed
in the small dead-end tube called
The Bedroom, which is easily reached by
a 150 ft traverse that takes two left turns
and then two right turns from the entrance.
Those who wish to spend more
time underground and observe a wide
variety of lava-tube features will enjoy
the area around The Bathtub. It is
reached by an easy traverse of nearly 720
ft down the main passage, where a short
flight of stairs leads up to The Bathtub.
Adventurous persons who enjoy long
crawls over rough-surfaced pahoehoe
(fig. 24), while simultaneously trying to
avoid the thrust of sharp lavacicles into
their backs, will find their mettle tested
by a long underground trip to Cleopatras
Grave (fig. 13) via Howards Hole.
And finally, people interested in the
hydraulics of a complicated near-surface
lava-tube system will find the pattern of
tubes, complicated breakdowns, lava
falls, drains, and cascades near The
Bathtub to be particularly interesting.
Similar features, as well as balconies and
rafted blocks, are found farther downstream
near Howards Hole.
The overall length of the accessible
area of the Catacombs system is 2,000 ft
but rarely is it as wide as 250 ft. Yet,
because of the abrupt turns, the interconnected
passages, small complicated
cascades, lava falls, interchanges that
join passages together at different levels,
and the numerous short distributaries that
are nearly filled with lava, the total
length of accessible passage is more than
7,500 ft. This very complicated system
of irregularly branching tubes of different
sizes, lengths, and trends (see map 3,
pl. 1) makes Howard's name, the "Catacombs,"
particularly apt.
24 Selected Caves and Lava-Tube Systems, Lava Beds National Monument, California