Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

tation that this tube system was fed from
Modoc Crater, another vent for the basalt
of Mammoth Crater.
Some other features shown on map
19, plate 6, are Eagle Nest Butte, which
is a deeply eroded cinder cone older than
the Mammoth Crater lava, and a small
part of the Callahan flow of blocky lava.
This young flow is almost free of vegetation
and it was erupted from the base of
Cinder Butte, a cinder cone in an isolated
area near the southwest corner of the
monument (see fig. 4).
Geology of the Heppe Caves
The Heppe Caves are remnants of a
large lava tube, originally 25-30 ft wide
and 15-25 ft high. Nearly all primary
features have been lost by slow collapse
of the roof and walls. Behind the places
where blocks of dripstone lining have
fallen, one can see edges of the flow
units. These units are separated by sporadic
accumulations of bombs and ash;
most units are less than 3 ft thick, and
many have ropy pahoehoe tops. These
flow units dip to the north, away from
Mammoth Crater. Less well defined
flow units with only sparse accumulation
of pyroclastic material between them are
present higher on the walls, especially in
the scenic cliffs that ring the top of the
collapse pit separating the two Heppe
Caves.
In the Upper Heppe Cave floor, a
permanent mass of ice probably fills the
interstices between the collapse blocks.
When we mapped the cave in late May of
1976, the topmost edges of this ice mass
could be seen in spaces between the
fallen blocks around the edges of the
water pool and also all along the floor of
the alcove that extends into the east side
of the cave (map 19, pl. 6). The lobes of
ice between the blocks had sharp crests,
similar to seracs on the surface of a
glacier. In September 1977, no ice was
visible and the pool was dry, whereas
during 1985 to 1988 the ice block and
pool were present.
Lower Heppe Cave is so defaced by
collapse blocks that no original features
remain in place. Nevertheless, it is evident
that a collapse of an upper tube into
a lower tube dropped both ceiling and
floor 20ft. Thus, the upper tube did not
continue downstream but must have ended
in a semicircular wall, as did the upper
tube in Skull Cave (map 12, pl. 4). An
oval collapse pit (labeled "East Collapse"
on map 19, pl. 6), with a hydraulic
rampart of loose blocks piled on its
northern lip, ends Lower Heppe Cave.
On the east side of this collapse pit, a
remnant of the lava tube plunges beneath
a narrow natural bridge, Heppe Bridge.
Beyond this bridge the line of collapsed
trenches continues around the south and
east sides of Red Butte, but they are
small with only a few caves open to the
surface until the Natural Bridge area at
the southwest end of Cave Loop Road
(map 5, pl. 2). It is apparent, however,
that large tubes were required to transmit
the lava to the caves along Cave Loop
Road and then eastward through Post
Office Cave (map 15, pl. 5). Sections of
these large tubes are filled with lava or
ice where they have not been destroyed
by collapse.
Heppe Chimney
Heppe Chimney is an agglutinate or
spatter cone. Such cones are built of
pasty bombs that spattered out of a vent
and welded into a coherent conical mass
enclosing the orifice. In addition a sticky
spillover of lava emerged at the northeast
base of this cone and spread to the
northeast for 20 ft before it solidified.
The connection (if any) of the Heppe
Chimney with the adjacent Heppe tube is
obscured by talus. It seems likely, however,
that the Heppe Chimney is a rootless
volcano-that is, it was built
through a skylight on the roof of an active
lava tube, not as part of a dike arising
from a deep magmatic source. However,
dikes trending north-south appear in both
the north and the south walls of Mammoth
Crater, and it is possible that the
Heppe Chimney may lie above a northern
extension of one of these dikes.
Mammoth Crater
Mammoth Crater (fig. 4 and map 19,
pl. 6) is a funnel-shaped pit slightly more
than 0. 25 mi in diameter and 340 ft deep.
Eighty percent of its steeply sloping
walls are mantled with talus. A cliff of
thin flow units forms the southwest wall
just below the crest, and these flows also
continue eastward to form a broad sloping
shelf, which lies well beneath the
crest along the southeast wall of the
crater. In a notch on the south wall
several small vertical basalt dikes cut
through the cliff of lava flows. On the
south slope of the Mammoth shield is a
large spatter rampart 660 ft long and
50-100ft high, which obviously marks
the southward continuation of the dikes.
The rampart contains two elongate spatter
cones with deep clefts on their ends,
above the position of the underlying
dikes.
On the opposite (north) slope of the
Mammoth shield are two large, shallow
talus-covered depressions that resemble
the pit craters of Hawaii. Such craters are
generally attributed to subsidence of
crater walls into underlying dikes of
molten magma. These depressions, however,
may be only wide collapse trenches
over shallow lava tubes that surmount the
line of dikes. In any case it is apparent
that large lava tubes transmitted great
quantities of lava northward beneath the
two craters, and then into three systems
of lava tubes. As they leave Mammoth
Crater the feeder tubes surmount, or
possibly lie partly within, the northward
extension of the plexus of dikes on the
north wall of Mammoth Crater.
Two examples of filled lava tubes
surmounting basalt dikes can actually be
seen, despite partial masking by loose
talus blocks, on the north wall of Mammoth
Crater (map 19, pl. 6). That the
higher and westernmost tube of this
overlapping pair shows many thick concentric
shells of lava indicates it was
filled and drained numerous times. The
massive, coarser grained texture of lower
and older tube filling indicates that lava
ponded within it for a long time prior to
solidification. Both are oriented northsouth
and extended beneath the nearby
pit craters on the north slope of the
Mammoth shield. Note on the map that
a lava gutter nicks the margin of Mammoth
Crater above the deeper and older
lava tube. A later blanket of tuff and lava
prevents tracing the gutter beyond the
crater rim.
92 Selected Caves and lava-Tube Systems, lava Beds National Monument, California