Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

Cave and Ship Cavern. Farther northeast
is a somewhat larger elongate collapse
that is the entrance to White Lace Cave,
named by Howard from the open filigree
of white caliche decorating nearly all of
this cave's roof and walls. Within this
cave, a steep connector slants down to
the north into a lower tube.
Southwest of White Lace Cave the
line of collapse features turns to the
northeast. Downstream another 600 ft is
an oval sag basin with walls that slope
gently toward its center. In places,
cracks and small faults rift the basin's
margins. Occupying the central part of
this shallow basin is a "cork" bounded by
a ring fracture . It appears to be part of the
roof of a lava tube, which was uplifted
slightly when molten lava was present
and then stuck in its present position
when the lava in the tube lowered and the
sag basin formed .
Just beyond the northeast edge of this
sag basin is a deep collapse trench-the
trace of a large lava tube whose roof has
collapsed. At the northeast end of the
trench one can enter a cave, which
continues the tube to the northeast. Thin
flow units are well exposed on the upper
walls of the collapse trench. A spillover
surface flow escaped from the northeast
end of this collapse and flowed east in a
channel 8 ft deep at the point where it
joins the northeast end of the breakdown.
This lava spillover is the first evidence
that an obstruction, probably a roof
collapse, occurred somewhere downstream
while molten lava was flowing
through the tube. The obstruction forced
lava to back up behind it, as recorded by
several features. Downstream 440 ft and
across Lyons Road is a tiny skylight out
of which three small overspills of lava
emerged, flowed several tens of feet, and
then solidified. Farther downstream 200
ft is another shallow depression with
overs pills of lava on its east side. Nearly
50 ft farther is the upstream end of an
unusual-shaped large collapse trench
with hydraulic block ramparts (fig. 46)
rising to heights of 10-15 ft along its
southeast margin. This large roughly "C"
shaped breakdown probably marks a site
where a major lava tube was temporarily
blocked by roof collapse and then reopened
by magma forcing a detour
around one side of the collapse. As the
molten lava backed up behind the collapse,
it raised and tilted a segment of the
tube's roof high enough to shed a wall of
talus blocks, which form the hydraulic
rampart (map 20, pl. 6) along its southeast
margin. The backed-up lava also
produced the spillover tubes and lobes
from the skylight and trenches upstream.
When flow of lava in the tube was
resumed, either by forming a bypass
around the obstruction or by entraining
and bulldozing the collapsed blocks, the
raised parts of the tube's roof lowered;
thus, the direction of tilt of the roof
blocks that previously had shed the ram-
Figure 70. Aerial view southwest showing snowcapped Mount Shasta in hazy distance. Schonchin Butte and its block lava
flow showing in foreground as dark area near center of Lava Beds National Monument. Elongate dark patches south and east
of Schonchin Butte flow are collapse trenches formed along Merrill Ice-Skull Cave lava tube, which formed in basalt of
Mammoth Crater that flowed around the preexisting Schonchin Butte flow.
Collapse Trenches Between Skull Cave and Three Bridges Area 97