Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

where it opens into the north end of the
collapse trench that lies just northeast of
the parking lot. At the opposite upstream
(southwest) end of the collapse trench is
the natural bridge that supports the road
to Merrill Ice Cave.
Downstream from the base of the
stairway, a trail and in some places a
boardwalk provide easy access over the
hummocky piles of collapse rubble littering
the cave floor. A narrow bench on
the southwest wall of the tube records
shallow ponding of lava during a late
episode of withdrawal. Some collapse
blocks appear to have been derived from
tube-in-tubes, which may have only partly
filled the main tube before their
drainage and eventual collapse.
At a point 160 ft downstream from
the stairway, a 16-ft ladder extends down
through a small hole in the floor of the
entrance level to the edge of an ice pond
on the lower level. The entrance level
extends downstream only another 40 ft
beyond the top of the ladder, and it is this
short section that reveals much information
about the origin of the entrance
level. In this downstream section, the
level is blocked by successive shells of
lava accreted to the walls. Each shell is
a record of one episode of filling and
partial draining. Each molten flood deposited
a layer of lava plaster upon the
tube's walls, roof, and floor as its edges
chilled against the colder rock encasing
it; then, the still-molten lava beneath the
thin coating drained away before completely
solidifying.
At this downstream end the tube
plunges and is constricted to a fraction of
its upstream size. A smaller opening
once drained lava from the entrance level
to an underlying tube. Nevertheless,
during each episode of maximum volcanic
activity the tube would fill completely
with lava, and as the eruption
waned, the molten interior drained slowly
through the opening and left a layer of
lava plaster behind. Successive layers
thus accreted until, as seen today, the
opening is too small to crawl into. Since
cessation of volcanism many of the
accreted layers have loosened and partially
peeled away from the roof and
walls. Peeling layers are also well exposed
at the upstream end of this level
where the wall of the collapse trench
slices across the lava tube to reveal
telescoped shells of dripstone and lavacicles.
Figure 44. Ross Chimneys in north-central Lava Beds National Monument are similar to poorly exposed Tickner Chimneys,
outside monument. Spatter vents formed by accumulation of hot lava spatter blown into air from an erupting fissure. Hammer
on middle chimney for scale.
54 Selected Caves and Lava-Tube Systems, Lava Beds National Monument, California