Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

the older Schonchin Butte lava flow.
Kirk Whites, Beaconlight, Skull, and
Frozen River Caves are located along
this tube system. The line of trenches
(map 20, pl. 6) extends north for another
6 mi and then turns east. Many distributaries
fan out toward former Tule Lake
(fig. 1), although one major tube may
continue east and then north to Fern
Cave.
The large lava field built by flows
from this major lava tube is older than the
one built from the feeder tubes in the
Cave Loop Road area. Roof collapse
ruined far more of the underground
passages along this lava tube than along
the Cave Loop Road lava tubes. The
large collapse trenches and pits that
resulted are spectacular features of the
landscape when viewed from an airplane,
but on the ground most are invisible
until you approach their rims.
Between the collapse trenches are
natural bridges and short caves that
reveal parts ofthe underground lava-tube
system. Most such caves, however, are
disappointing to the student of underground
"lava plumbing" because they
have been greatly defaced by the unraveling
of rock from their walls and roof,
a process that continues today. Overhead
are many loosened blocks held precariously
against the side of a neighboring
loose block. Along the walls are slides of
loose talus. The floors of such caves are
difficult to traverse because blocks of all
sizes clutter their floors and may shift
under your weight when you step on
them.
Kirk Whites and Beaconlight Caves
are typical of the many short caves that
lie along this line of collapse trenches.
We chose to study them because they are
near the paved road through the monument.
Caves along this line between
Merrill Ice Cave and Skull Cave include
Castle, Kirk Whites, The Igloo, Beaconlight,
Symbol Bridge, and Irish Bridge.
Caves downstream from Skull are Ship
Cavern, White Lace, Big Painted, Peninsula
Bridge, Frozen River, and Captain
Jacks Ice Cave. Most of these are shown
on map 20, plate 6-a reconnaissance
map of the collapse trenches from Skull
Cave to the Three Bridges area.
Kirk Whites Cave
Kirk Whites Cave (map 11, pl. 4),
named by J.D. Howard, has a large
entrance room 185 ft long, 60-70 ft
wide, and 20ft high. Enter the cavern on
the trail built in the 1930's by the Civilian
Conservation Corps and note that the
original roof and walls have been obliterated
throughout the cave by slow unraveling
from rockfalls. The floor, except
for a small space at its upper end, is
completely covered with thick piles of
collapse debris including many very
large blocks. Details of the massive lava
flow in which the cave developed can be
seen in places along the wall of the
cavern, but they are better displayed on
the northwest wall of the collapse trench.
Near its upstream end the cavern
tapers to a width of 35 ft, and then nearly
the full width of its floor falls away into
a lower tube, the Mouseoleum. Remnants
of the pahoehoe lava that formed
the true floor of the original lava tube are
left as overhanging ledges around parts
of the rim of this collapse pit. Two small
holes through the pahoehoe floor at the
northwest comer of the entrance cavern
provide a relatively easy entry into the
lower tube; however, there is little to see.
Upstream and downstream it is completely
closed by collapse blocks that
have fallen from the walls or been
dumped through its roof, and only a
small room 45 ft in diameter, which is
one-half to two-thirds filled with collapse
blocks, remains. In the few places
where a true wall of the lower tube is
exposed, dripstone forms a thin coating
over red volcanic breccia instead of the
basalt flow that enclosed the upper cavern.
Underneath the overhanging ledges
that partly ring the top of this room, the
nearly horizontal contact between this
red breccia and the overlying flow is
visible in places. It was the collapse of
this unstable red breccia inward through
the walls of the lower tube that destroyed
the tube's continuity upstream.
The Igloo
Of greater geologic interest, although
smaller than Kirk Whites Cave, is
The Igloo, which lies at the opposite
(southeast) end of the collapse trench that
also provides the entrance to Kirk Whites
Cave (map 11, pl. 4). This 40-ft-long
cave is shaped like an elongate dome.
The highest point on the ceiling ( 11 ft) is
at the cave's center; from here, the roof
rounds down rapidly in all directions.
Well-preserved lavacicles and dripstone
line the surface of this dome. You enter
the cave through a small opening where
collapse debris spilled onto the floor of
the cave. Downstream from the toe of
this slide the floor is a jam of jostled
pahoehoe blocks produced by the lava's
attempt to drag its already solidified crust
beneath the sloping roof of the cave at the
downstream end. Undoubtedly, the do m­
al shape and its walls of congealed
dripstone suggested the name "The Igloo."
The Igloo may have formed as a short
distributary tube from the upper part of
the main lava tube, or it may be a cupola
in the main tube with its floor having
formed by the crusting-over of a balcony
fill of lava in the main tube. It is
impossible to decide between these alternatives
because there is no access to
the continuation of the tube either upstream
or downstream.
Beaconlight Cave
Beaconlight Cave (map 11, pl. 3) is
large in girth but only 340 ft long. It
consists of two chambers: an entrance
cavern 150 ft long, 50 ft wide, and as
much as 35 ft high; and a larger chamber
downstream, the Silver Clouds Cavern,
which is 190 ft long and in places more
than 50 ft high. Silver Clouds Cavern
appears offset about 55 ft to the right
(southeast) from the entrance cavern. A
short arch 30 ft across connects the
present roof of the two caverns above a
high talus pile.
From the large alcove in the south
comer of the Silver Clouds Cavern, a
10-ft-wide break in the floor spills a steep
slide of collapse rubble into a lower tube
12 ft below. This deeper tube is 20 ft
wide and 8 ft high; it trends almost due
east for about 30 ft, and it has retained
outstanding examples of pahoehoe floor,
58 Selected Caves and Lava-Tube Systems, Lava Beds National Monument, California