Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

"pull outs" where the dripping plaster of
this final coat sagged down or peeled
away from the wall (fig. 11). Behind the
pull out another layer of dripstone is
exposed on the wall. Examine the crosssection
edge of a large lava tube sliced by
a major breakdown, and you will probably
see layer after layer of accretionary
lava plaster called linings welded together
in the cross section of the tube. Every
accretionary layer represents a separate
volcanic surge followed by a period of
quiescence. Most accretionary layers, as
can be seen by their tight welding,
resulted from small-scale fluctuations in
the amount of magma coursing through
the tube.
Instructive examples of the transitory
skins that form on moving basalt lava are
present in many of the 3-ft-high benches
that border the walls of large-diameter
(30-60 ft) cave passages such as in Craig
and Valentine. In places where a falling
roof block has sliced such a bench,
vertical inward-sagging thin layers of
basalt can be seen beneath the final
coating of lava plaster covering the
bench. Some of these layers exhibit torn,
crumpled, and pulled-out edges, all of
which indicate that their extensions were
sheared off and distorted by the pull of
the lava flowing beside them (fig. 12). A
thin plastic layer of congealing basalt
cannot remain arched over a cave of large
dimensions, but it can be preserved in
small tube-in-tubes, such as those in the
Garden Bridges area. Generally, such
skins of congealing lava are continuously
rafted forward and simultaneously sag,
shear, and pull loose along the walls of
the cave. The result of these processes is
precisely what can be seen within the
broken benches of Valentine and Crystal
Caves.
Exploring the Caves
For safety or conservation reasons
certain caves may be closed to the public
or have restricted access. As of April
1990, only Mushpot Cave is lighted, and
two of the caves described in detail have
restricted access: Crystal and Fern
Caves. Always check in at the Visitor
Center for information regarding cave
access as well as safety and exploration
guidelines before entering any cave in
the monument.
Time did not permit preparation of
geologic maps for all caves in the monument.
We did, however, explore a large
number of the known caves. Most caves
in the wilderness area of the monument
were rejected for mapping, not only
because of their remoteness, but because
most of the deep tubes have collapsed
and only small remnants oflittle geologic
interest remain. However, Craig Cave
and Craig Temple, accessible only by an
11-mi drive over rough, unpaved roads
or a 3-mi hike across rugged terrain,
were mapped because of this lava tube's
geologic importance and large size. Fortunately,
the group of caves whose easily
accessible entrances lie adjacent to Cave
Loop Road (maps 1-7, pis. 1 and 2)
provide excellent examples of nearly all
features typical of lava-tube caves.
Cave Names
Nearly all caves and many other
geographic features within Lava Beds
National Monument were named by J.D.
Howard, an early settler and guide whose
chief avocation became the discovery,
naming, and measuring of the caves. He
also assisted in the building of wagon
roads so others could visit these natural
Figure 11. Lava dripstone and " pull out" in wall of Mushpot Cave (see fig. 14 and
map 1, pl. 1). Dark area in center is a pull out where pasty red-hot dripstone
sloughed off the wall and oozed downward. Pencil for scale.
Figure 12. Broken, partly collapsed Ia a
bench on wall of Crystal Cave (see fig.
14 and map 18, pl. 6) .
8 Selected Caves and lava-Tube Systems, lava Beds National Monument, California