Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

level of the tube. The southern entrance
of Stinking Cave shows approximately
how much the cave passage has collapsed
laterally. The main tube is a fairly
uniform 9ft wide until it approaches the
Stinking Cave collapse, where it flares to
a width of 39 ft. Many thin linings of lava
can be seen in the alcoves just inside the
entrance arch; progressive collapse of
these shells resulted in the very wide
entrance arch.
Labyrinth Cave System
The line of collapse trenches (or
breakdowns) along which Indian Well
and Sentinel Cave lie intersects the Cave
Loop Road area (fig. 14) at Natural
Bridge and continues northeast past Ovis
Cave for 2,100 ft. There, the tube that
collapsed to form the collapse trenches
divides into two major distributaries.
Looking downstream, the one on the
right appears to be the larger of the two.
It extends northeast and is marked by an
almost continuous line of collapse
trenches for 1,250 ft. Farther northeast,
a few large segments of its roof survive
along a continuing line of trenches.
Sentinel Cave, which consists of at least
three partially collapsed feeder tubes
stacked one on top of another, is a
roofed-over section of this distributary
system. Indian Well is the next cave that
interrupts the line of breakdowns to the
northeast.
The left and smaller distributary
(which divides into the Labyrinth Cave
system) takes off on a more northerly
course. Unlike the Sentinel distributary,
additional distributaries diverge from it.
By the time this northern line of collapse
trenches, natural bridges, and partly collapsed
caves reaches the northern end of
the Garden Bridges area 900 ft downstream
from its junction with the Sentinel
distributary, it has subdivided into six
major distributaries. Most of these
branches, however, maintain connections
with their neighbors through secondary
distributaries and crossovers (see
fig. 14 and map 2, pl. 1).
Nearly all this network of lava tubes
lies close to the surface and many roof
collapse openings provide additional entrances.
To the early explorers who
lacked maps, these interconnected but
outward-fanning underground passages
seemed a complicated maze, although in
reality they form an orderly distributary
pattern. It is not surprising that the name
"Labyrinth Caves" appears in the notes
of J.D. Howard, who explored and
measured the length of many Labyrinth
passages between 1918 and 1933. Some
of the Labyrinth System caves, however,
were known to Native Americans and
early settlers long before Howard's
work. E.L. Hopkins explored Chocolate
Cave in 1892 and named it for the
chocolate-colored "mud," which coats
roof and walls of parts of this cave during
the period of snowmelt or after heavy
rains. Other names in common use for
parts of this system are Blue Grotto,
Garden Bridges, Golden Dome, Hopkins
Chocolate Cave (also called Hopkins
Chocolate Cup), and Thunderbolt. Lava
Brook, Mushpot, and Arch are the Labyrinth
tubes that reach farthest northeast
before filling with lava. These names and
the features to which they apply are
shown on figure 14 and maps 1 and 2 (pl.
1). The Garden Bridges is an area of
collapse trenches and natural bridges
from which the Hopkins Chocolate Cave
and Golden Dome Distributaries split
and fan out to the north. The true
Labyrinth area lies east of Garden Bridges
where the name Labyrinth is used in
a more restricted sense for the maze of
interconnected tubes on different levels.
Finally, two very long distributaries
(Thunderbolt and Labyrinth), which carried
a small part of the reunited lava flood
northeast into the Mushpot-Lava Brook­
Arch Cave area, complete the Labyrinth
distributary system.
The divergence of the main Labyrinth
feeder into six large branches lies
within an area only 650 ft long and 150
ft wide. From here the tubes fan out to the
north and northeast (fig. 14). The tube in
Arch Cave that is filled with lava (see
northeast part of map 1, pl. 1) can be
traced south and southwest through the
Thunderbolt Distributary (map 2, pl. 1)
and into the Labyrinth, a distance of
more than 3, 800 ft. Most tubes of the
Labyrinth, however, are inaccessible
due to lava filling and collapse over short
distances.
Garden Bridges Area
The name "Garden Bridges" (map 2,
pl. 1) is applied to the region characterized
by many large oval breakdowns
separated by natural bridges, within
which the original Labyrinth parent tube
subdivided into six main tubes and several
minor ones (fig. 21). During the time
since lava drained from these tubes, the
weak roof above most of the junctions, as
well as above wide parts of the tubes, has
collapsed. The result is many large oval
collapse pits between short stretches of
lava tube forming natural bridges. At the
ends of some collapse pits, debris has
piled up to ground level. Between such
pits natural bridges probably exist, but
entrance to them is blocked by talus.
Many, however, are open; a climb over
a loose pile of talus will generally reveal
an entrance to a short section of lava
tube.
Geologically, most of these short
sections show only a few primary features
because their floors are littered with
collapse blocks, and their roofs are
scarred in places where blocks have
fallen out.
To a biologist, however, the Garden
Bridges area is of much more interest.
The small caves under natural bridges,
the loose piles of talus blocks, and the
countless nooks and crannies in the cave
roof and walls provide refuge for many
mammals. Birds are abundant, and there
is a greater variety of insects and arachnids
here than in most areas of the
monument. Lizards and snakes, too, are
attracted to this area by the abundance of
food.
Botanists, too, will find a wide variety
of plant life. The large range of
temperature and humidity, from the cool
moist air of the caves to the burning heat
and desiccation on top of the lava bridges,
produces microclimates to which a
surprising variety of plants has adapted.
Access to the Garden Bridges is from
a parking lot off the Cave Loop Road,
with signs marked for both Garden
Bridges and Hopkins Chocolate Cave.
The trail from the parking lot forks: the
left (north) fork goes to a stairway that
leads into Hopkins Chocolate lava tube;
the right (south) branch continues on the
20 Selected Caves and Lava-Tube Systems, Lava Beds National Monument, California