Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

surface collapse and only one comer of
the cascade is exposed (map 2, pl. 1,
lower left corner). Downstream from the
base of the lava cascade a floor jam of
pahoehoe blocks spreads across the tube
just upstream from the entrance stairway.
Downstream from the entrance the
tube widens greatly and spreads around
two large pillars near its southeast wall.
At the point where these lava streams
reunite farther downstream another small
oval collapse breaks through to the surface.
Still farther downstream about 45
ft, the tube again forks . The right (northeast)
branch is the continuation of the
main tube; the smaller (north) branch,
the Chiroptera Crossover, was left hanging
4 ft above the main tube's floor when
both tubes drained. The north branch is
a crossover to the Blue Grotto. At some
time in its history the upper Blue Grotto
tube broke through its floor into the
crossover, leaving a hole 6ft deep. The
Blue Grotto derives its name from the
pale-powder-blue to blue-gray color of
its roof in a particular light. A thin
coating of a mixture of caliche and clay
left by rainwater, which seeps through
the roof of the cave and evaporates, is the
cause of this color.
One can climb out of the Blue Grotto
tube through a surface collapse and
continue along the surface via the Garden
Bridges trail. Small tubes and lava blisters
just below the surface are common to
the north and west of this part of the
Garden Bridges area; a few are large
enough to show on the map. From the
entrance to Hopkins Chocolate Cave,
additional partly collapsed near-surface
lava tubes and blisters are visible at the
ground surface to the north and northeast.
Hopkins Chocolate Cave
This cave (map 2, pl. 1) , discovered
by E.L. Hopkins in 1892, is reached by
a fork from the same trail that services
the Garden Bridges area. E.L. Hopkins
is credited with discovering the cave in
1892, although it may have been known
previously to Native Americans. On
some National Park Service maps the
cave is designated as "Hopkins' Chocolate
Cup." The name comes from the
chocolate to yellow-brown mud , which
drips through parts of the roof of the cave
during the wet season.
The cave is entered by a stairway
placed in a small circular roof collapse at
the northwest end of the Garden Bridges
area. At the base of the stairway the lava
tube drops off to the northwest with a
high downstream gradient, over lava
cascades and falls, and joins a larger tube
380 ft downstream. Upstream from the
entrance the tributary tube cannot be
followed underground because of collapse
pits at the north end of the Garden
Bridges area. However, the distribution
of these pits (see map 2, pl. 1) demonstrates
that this tube and the tube that
leads to Golden Dome are separate
branches of one larger tube exposed only
as a few natural bridges upstream from
their junction. The point at which the
Hopkins Chocolate tributary diverges
from the Golden Dome tube is 150 ft
upstream from the Hopkins Chocolate
Cave entrance.
The relation of the large tube segment
into which the tube containing the
Hopkins Chocolate Cave debouches as a
tributary to the rest of the Labyrinth Cave
system is equivocal. This segment,
called Hopkins Chocolate Cave Distributary
on the accompanying map, extends
approximately 650ft to the north. Downstream
it is filled with lava; upstream it
is demolished by a surface collapse at a
point only 120 ft northwest of the nearsurface
lava chamber that contains the
tube-in-tube previously described as a
geologic curiosity in the Garden Bridges
area. Very likely there was an underground
tube connection between these
two points, although now it may be filled
with lava. A collapse near this area could
have blocked the flowing lava and
dammed it to the roof of the large tube
that contains the tube-in-tube. The small
surface lava tubes and blisters that
abound in this area probably broke out
through cracks in the collapsing roof.
Downstream from the inferred collapse,
the Hopkins Chocolate Cave Distributary
would have drained to where it could
be replenished by lava from its tributary
that contains the Hopkins Chocolate
Cave entrance. The entrance tube is
considered a crossover from the Golden
Dome Cave Distributary into the Hopkins
Chocolate Cave Distributary. Hopkins
Chocolate Cave is a remnant of the
northwestemmost large tube of all those
in the Labyrinth system. Although we
strongly favor this scenario, it has not
been verified by leveling along floors
throughout the Labyrinth distributaries.
Whatever the exact relations, the
Hopkins Chocolate Cave Distributary
has features of interest that are easily
reached from the Hopkins Chocolate
Cave entrance. In its lower part, downstream
from the crossover (tributary)
junction, wet patches on the roof and
walls show excellent examples of the
golden lava-tube slime for which Golden
Dome Cave was named.
In the middle section of the Hopkins
Chocolate Cave Distributary, the tube
detours around one large and one small
pillar. A floor jam of pahoehoe blocks is
present above a constriction of the tube
at the west tip of the upstream pillar. On
the opposite side of this pillar the last
trickle of lava ends in a lobe with a thin
steep front.
The best development of the pale
chocolate-colored mud is in the crossover,
on and around the benches and
small rounded pillar 17 5 ft downstream
from the entrance.
Golden Dome Cave
Golden Dome is the name given to
the arched roof of a large lava pool at the
north end of the accessible part of the
Golden Dome Cave Distributary (fig. 23
and map 2, pl. 1). The downstream end
of this dome has collapsed and partly
buried the pillar that helps to support the
remainder of the dome. This collapse
effectively blocks exploration of the tube
farther downstream, but judging from
the size of the tube and the width of the
pools along it, only a small part of the
total tube length is now exposed to view.
The Golden Dome generally has a
small amount of water dripping from, or
evaporating on , its ceiling. The water
droplets on the roof glisten with a golden
luster, as internal reflection within the
drops enhances the golden brown color
22 Selected Caves and Lava-Tube Systems, Lava Beds National Monument, California