Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

arrangement in wintertime only so as
not to damage the fragile ice formations.
Other caves that usually contain
much smaller amounts of frost
and ice are Skull, Merrill Ice, Captain
Jacks Ice, Frozen River, Caldwell
Ice, and Upper Ice Cave.
4. People interested in early Indian cultures
will find the best displays of
pictographs in Fern Cave. Other
good localities are among the breakdowns
between Skull and Merrill Ice
Caves, especially near Symbol
Bridge. Petroglyphs are well exposed
in both Juniper Cave and in a
separate and protected area of the
monument at Prisoners Rock (fig.
15), northeast of the main area of the
monument and 2.5 mi southwest of
the town of Newell.
5. Those interested in the microclimate
adaptations of plants will find the
Garden Bridges, easily reached from
Cave Loop Road, a rewarding area.
The breakdowns and numerous short
cave remnants within a small area
provide variations from moist cool
air at cave entrances to the dry
sun-baked roof tops over caves. Examine
the Natural Bridge area as
well. Fern cave is named for the large
population of ferns (rare in this desert
region) that cover its entrance
mound. The greenhouse-like atmosphere
of this cave is in stark contrast
with the dry air above ground. Fern
Cave is kept locked, but tours can be
arranged by contacting National Park
Service personnel at the Visitor Center.
Each cave description herein should
be read with the respective map unfolded
beside it because most of the text material
is tied directly to the map.
orientation at a new station is controlled
by backsight to the former station. Position
of the walls is obtained and plotted
directly on the planetable sheet: an assistant
walks beside the steel tape, carrying
a lightweight stadia rod to measure
the distance (horizontally at right angles
to the tape) of all points where the wall
of the cave changes direction. At each of
these points he calls out the distance on
the tape, and then the distance to the
wall, to the person operating the planetable,
who immediately scales off and
plots this point on the planetable sheet.
After both walls have been drawn, the
positions of geologic features-such as
balconies, skylights, breakdowns, rafted
blocks, collapse piles-are plotted, using
the stadia rod to measure their outlines
with reference to the tape. The
height of the ceiling above floor is
determined at selected points with the
stadia rod held vertically or if the roof is
too low, with a folding rule. The heights
of benches, balconies, lava cascades,
and other salient features are obtained
and plotted on the planetable sheet. Thus
a rough draft of the map is prepared
continuously as the traverse is extended.
Before a traverse of more than a few
hundred yards was completed, we nearly
always encountered passages too small
for the planetable to be leveled on its
tripod, or we had to extend the traverse
through crawlholes along the side or roof
of a cave. In such situations we used
cloth tape and a Brunton compass (a
compass with attached clinometer to
measure angles) to extend the traverse
until the planetable-alidade work could
be resumed. At first we were concerned
about the magnetic errors that might arise
from using a Brunton in such close
proximity to basalt lava. To our surprise,
repeated checks showed that large magnetic
deviations are not a problem in
caves but are common when a Brunton is
used on top of a prominent basalt outcrop.
Apparently, this discrepancy is
caused by lightning strikes on a surface
outcrop of basalt that produce magnetic
changes great enough to strongly affect
the needle of a Brunton.
Acknowledgments
A project to map selected lava-tube
caves within Lava Beds National Monument
was initiated by Paul F. Haertel,
former Superintendent of the monument,
in 1974. At Haertel's request, Aaron
Preparation of the Maps
Planetable and alidade traverses were
made in mapping the larger lava tubes,
and a description of the procedure follows.
A station is occupied, and a sight
through the ali dade is taken on a miner's
lamp or flashlight placed at the next
station. Distance between stations is
measured with a stretched steel tape, and
Figure 15. View northeast across Tule Lake to The Peninsula and Prisoners Rock
where the Petroglyphs section of Lava Beds National Monument is located.
Photograph taken from near Hospital Rock, in northeastern part of monument.
Acknowledgments 11