Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

surface lava tube ranging from 20 to 30
ft wide. It is also wetter than the upper
parts of the cave. The latest lava flow
formed a gently sloping floor of pahoehoe
with the lava fill gradually increasing
downstream. Pahoehoe ropes also
tend to be more spiny and broken farther
down the tube. Approximately 160 ft
downstream from the entrance pit a
section of jammed floor blocks marks the
start of a section of intact roof called The
Silver Lining after the reflections from
water droplets on its surface. Debris
from roof falls is scattered along the floor
and rises in several large collapse
mounds. A particularly large pile of
roof-collapse debris almost closes the
tube in the area where the tube changes
direction from northeast to east. Entrance
to the final 250 ft of the cave
requires negotiating a very tight, wet
crawl way. In this final segment a tubein-tube
exposed in the cave roof above
another floor jam of blocks can be
explored for 35 ft. Farther downstream a
small side tube surrounds a pillar on the
north wall of the cave; a few feet beyond
this pillar access is denied by a roof
collapse. Although the collapse prevents
a crawl to the surface, it is apparent that
the surface is not far above because warm
air can be felt descending into the cave
and small animals make their homes
here.
Tickner Chimneys
The Tickner Chimneys (map 9 inset,
pl. 3) were not studied in detail. Most of
them surmount the fissures through
which the basalt of Valentine Cave was
erupted. Additional spatter vents lie farther
south along the same trend and are
not shown on the map. The chimneys are
small agglutinate cones, most of which
are less than 5 ft high. They formed
where clots of molten lava fountained
and accumulated along the fissure. A few
chimneys rise from smaller fissures parallel
to the main one. Some chimneys are
connected underground by short lava
tubes, which trend along the course of
the fissure. Surface features in the vent
area also include many lava gutters and
spillover lava lobes. Many of the small
agglutinate cones have miniature spillout
lava lobes and tiny surface lava tubes
radiating from them. Unfortunately a
thick coating of pumice and an almost
impenetrable thicket of mountain mahogany
prevents close inspection of
many of these small-scale features.
Therefore we prepared only a reconnaissance
map of the vent area, at a different
scale from the map of the caves. The
visitor interested in acquiring a knowledge
of this kind of vent area is better
advised to visit the excellently exposed
Ross Chimneys (fig. 44) in the monument.
Merrill Ice Cave, Bearpaw Cave,
and Nearby Collapse Trenches
A line of large collapse trenches
begins along the east base of the large
cinder and agglutinate cone named Bearpaw
Butte, 2 mi north of Mammoth
Crater. From there, this line of collapse
trenches can be traced east and north
around the Schonchin Butte flow for
about 10 mi. The collapse trenches were
formed by the collapse of roofs in a
system of two to three or more lava tubes
stacked above one another. These tubes
served as feeder conduits through which
molten lava escaped from a former lava
lake fed by Mammoth Crater (map 19,
pl. 6). This lava built a plain downstream
covering approximately 50 square miles
to the north and northeast of Bearpaw
Butte. The lava dispersed through the
Bearpaw tubes, surrounded Schonchin
Butte, and spread northward to the
shores of Tule Lake. The lava lake that
spawned the Bearpaw tubes eventually
drained to a lower level through a lava
tube that burrowed through loose cinders
around the base of Red Butte and then
contributed to the lava-tube system of the
Cave Loop Road area.
Most of the surface collapse trenches
that currently mark the position of feeder
tubes in the Bearpaw-Skull system range
from 50 to 1 ,500 ft long. Partly destroyed
relics of lava tubes survive between
the collapse trenches as caves,
natural bridges, and tubes blocked with
congealed lava. Two of these caves, a
natural bridge, and three large collapse
trenches are shown on map 10, plate 4.
Merrill Ice Cave is accessible by a
paved road leading to a parking lot, and
then by trails and stairs to the cave's two
levels. Bearpaw Cave is also easily
accessible, although not by developed
trails. Its entrance is the mouth of a huge
domed cavern at the upstream (south)
end of the large collapse trench over
which the paved road crosses via a
natural bridge.
According to National Park Service
records, the names "Bearpaw Cave" and
"Bearpaw Butte" are derived from the
activities of pioneer trapper Tom
Durham, who killed a bear and nailed its
severed paws to a juniper tree above the
entrance of the cave. Merrill Ice Cave
whose deeper, ice-bearing level was
discovered later was named "Bearpaw
Cave" at first, but in 1938 the Park
Service changed the name to "Merrill Ice
Cave" in honor of Charles Henry Merrill
whose land was donated to the monument
(National Park Service, unpub.
data, 1965).
Merrill Ice Cave consists of two
superposed lava tubes. The entrance
level is accessible for a distance of 290
ft. The lower ice level is 360 ft long;
about one-third of its floor area is occupied
by pools of ice or by collapse rubble
cemented with ice. The only entrance to
the ice level is by a steel ladder placed
through a hole a few feet in diameter in
the floor of the entrance level. On the
map the ice level is offset from its true
position to avoid confusion with the lines
and lettering of the entrance level.
Bearpaw Cave is accessible for 300ft
upstream from its high-domed entrance.
The cavern at its mouth is 60 ft high and
35-50 ft wide. The upper section of the
cave is much smaller and is nearly closed
at its south end by large blocks of
collapse rubble.
Merrill Ice Cave, Entrance Level
From the north side of the parking lot
a trail leads northeast 250 ft to a stairway
(fig. 45) placed against the west wall of
a 20-ft-diameter hole in the roof of a lava
tube, which constitutes the entrance level
of Merrill Ice Cave. From the foot of the
stair the tube extends upstream 85 ft to
Merrill Ice Cave, Bearpaw Cave, and Nearby Collapse Trenches 53