Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

Red Ice Room (fig. 63), which lies at the
extreme downstream end of the accessible
part of the lower level. The 35ft long
and 20 ft wide Red Ice Room is seldom
visited because it requires a crawl in ice
water beneath a 1-ft-high roof. This
crawlway is at the downstream base of
the large collapse pile, which descends to
the lower level. As previously noted, red
tuffs and breccias line the tube in this
passage. It is these walls of red pyroclastics
enhanced by draperies of icicles
and a varnish of clear ice that give color
to this room-not red ice, but clear
icicles and ice dripstone covering a pink
to red background. In addition to "pink"
icicles, this room contains a floor of
"pink" ice. Slides of coarse red rubble
that block the tube downstream are cemented
by and coated with transparent
ice as well.
(2) Ice Pools and Ice Mounds. Meltwater
pools that have frozen into ice are
rare in Crystal Cave, but large parts of
the cave floor are covered by ice mounds
and hummocky ice slopes. These are
built by drops of water and melted bits of
icicles and frost that fall from the roof
and walls. The ice slope below the
entrance of Crystal Cave is a large
mound that accumulated from rain and
snow blown in through the entrance. The
semicircular ice mound along the west
wall another 20 ft downstream is an
overgrown stalagmite formed by drip
from the roof. At the south end of the
lower level is the Blue Glacier Room, so
named because the large ice mound on its
floor is a murky powder blue. It is not
known whether admixed dust, algal
growth, or a finely cracked texture of the
ice is responsible for the scattering of
light that causes this color-it may be a
combination of all three.
(3) Ice-cemented Breccia. Collapse
breccia at the upstream and downstream
ends of the upper level are encased in ice ,
but because of the rock color here , the
results are less spectacular than the iceencased
breccias in the Red Ice Room.
As noted before, almost the entire floor
of the Overpass is a hummocky pile of
collapse blocks encased in ice, as are the
breccias adjacent to the Blue Glacier,
which block upstream continuation of
the lower level.
(4) Frost. Rivaling the draperies of
icicles in beauty are the rimes of pure
white hoarfrost that cover large parts of
Crystal Cave's walls and roof (fig. 64).
Hoarfrost is extensive near the larger
masses of permanent ice, especially in
Fantasy Passage, and can also be found
spreading outward from the large drapery
of icicles on the lower level. It grows
most abundantly on the one lava flow in
the wall that is more porous than the
others. Unlike the transparency of an
icicle display, hoarfrost forms pure white
rimes that appear to be opaque when
viewed at a distance. Closer inspection
shows that they are composed of intricately
interlocking frost crystals, some in
well-developed hexagonal plates or in
cleavage rhombs two inches or more
across. Others are lacy and interlocking
crystals of varying sizes. In fact, each
crystal is transparent or translucent, but
the lacy intertwining forms and abundant
cleavage cracks give frost rimes a whitish
luster (fig. 65) quite different from
the limpid transparency of ice stalagmites
and icicles .
Some of the frost crystals show evidence
of repeated, probably seasonal,
growth. Zonally arranged inclusions of
fine dust were deposited upon an irregularly
etched crystal, then covered by an
overgrowth of clear ice, which is in
optical continuity with the core crystal.
Several such zonal bands can be counted
within some of the larger hoarfrost crystals.
Very likely they record seasonal
Figure 63. Icicles, ice glaze, and ice crystals decorate wall of Red Ice Room in
Crystal Cave (see fig. 14 and map 18, pl. 6).
Figure 64. Hexagonal ice crystals as
much as 1 in. across present in winter
on walls of Fantasy Passage, Crystal
Cave (see fig. 14 and map 18, pl. 6).
90 Selected Caves and lava-Tube Systems, lava Beds National Monument, California