Download PDF - Speleogenesis

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NCKRI Special Paper No. 1
connecting feeders to outlets, reflecting rising flow
patterns and a considerable role of buoyancy effects
(upward-focused dissolution by buoyant currents – rising
limbs of free convection cells).
Rising wall channels (examples are on Plate 1) and
rising sets of ceiling cupolas are found immediately
adjacent to feeders, continued through ceiling half-tubes to
cupolas and domepits. Rising sets of ceiling cupolas or
series of upward-convex arches are also common for
passages or rooms connecting different stories in a cave
system (Plate 6, A through D).
Cupolas on the ceiling are commonly arranged in
linear series comprising a kind of channel (Plate 6, H, I
and K; Plate 7, B and C) but they can occur separately. In
many cases where bottom features are observable,
prominent cupolas or complex domes with numerous
cupolas match in the plan view to particular feeders or
groups of feeders at the floor, clearly suggesting a
convection origin of the ceiling features. This origin for
cupolas had been well recognized for hydrothermal caves
(Müller and Sarvary, 1977; Dubljansky V., 1980;
Lauritzen and Lundberg, 2000), but largely similar features
at all scales are common for other types of hypogenic
caves (sulfuric acid, “normal” limestone caves, caves in
gypsum). Many cupolas have guiding fractures at their
apexes but others show no such guidance. Cupolas alone
are not exclusive to hypogenic speleogenesis; they may
form in unconfined phreatic caves (reflecting the
confinement of water within a passage itself), but their
occurrence in a suite with other ceiling features as
described here is clearly indicative of hypogenic
speleogenesis and buoyant dissolution effects. Extensive
discussion of cupolas has been recently provided by
Osborne (2004).
Ceiling channels, also often called half-tubes, although
commonly interpreted as paragenetic features formed when
sediment fill directs phreatic dissolution upward, are very
typical for hypogenic caves that have never been filled
with sediment to the ceiling level. Instead, their
relationships with feeders (through rising wall channels),
and outlets in hypogenic caves, and rising patterns from
the former to the latter, clearly suggest an origin due to
buoyancy effects (Figure 19). In large passages or rooms
where multiple feeders are present, several ceiling
channels may braid in close proximity, leaving ceiling
pendants in between. Particularly good examples of such
pendants can be found in some gypsum caves in the
western Ukraine, in the USA at Carlsbad Cavern, New
Mexico, and in Caverns of Sonora, Texas. The vertical
relief between pendants and adjacent channels can be as
great as several meters, and such pendants are often well
prepared to break down when a cave is drained and
buoyant support is lost.
3) Outlet features. These are cupolas and domepits
(vertical tubes) that rise from the ceiling of passages and
rooms at a certain story and connect to the next upper
story, or ultimately to the discharge boundary - the bottom
of the overlying formation, a prominent bedding plane or
the land surface. The ultimate outlets serve as discharge
paths in a confined transverse system. Their ascending
formation is suggested by their smoothed, curving walls,
and by continuous morphology from connecting rising
ceiling/wall features (Plate 8, A, B and D; Plate 9-I). In
many caves, the bottom of the overlying aquifer bed
(“receiving unit”) is exposed at the outlet apex, sometimes
with a gaping contact suggesting outflow via the bedding
plane (Plate 10-A; see also Figure 9). Outlets that break
into the next upper cave story, or to the ultimate discharge
boundary are “successful” outlets, whereas blindterminated
cupolas can be regarded as “undeveloped”
outlets. Closely spaced individual outlets in passages lying
not far below the upper aquifer may merge to open the
upper contact through a broader area along a passage (Plate
9-A), the ultimate case being where the upper contact is
opened at the ceiling along the entire length of a passage
(Plate 9-B).
Individual outlets can vary greatly in size, from less
than a meter to many meters in cross-section and from less
than a meter to tens of meters in vertical extent. Complex
outlets from large systems may have composite
morphology and rise for tens of meters from the main cave
level (the entrance series of Lechuguilla Cave and the
Spirit World above the Big Room in Carlsbad Cavern are
good examples).
Plate 11 shows mega-outlets and gives an example of
the described morphologic suite of rising flow, derived
from the program presenting interactive 360 o panoramic
views of Lechuguilla Cave, NM, created by Four
Chambers Studio in collaboration with the US NPS. These
views, with their three-dimensional range, proved to be a
useful tool to study the cave morphology, enabling capture,
even with certain skewing, of broad panoramas showing
various morphologic components and their relationships.
Subaerial and other alternative possibilities for the
origin of wall and ceiling features
Some individual morphs that compose the abovedescribed
suite were previously interpreted in different
ways. See Ford and Williams (1989, 2007) and Lauritzen
and Lundberg (2000) for overviews of cave mesomorphology,
and Osborne (2004) for discussion of
cupolas.
Cupolas (ceiling pockets) commonly occur in
unconfined phreatic caves, reflecting the confinement of
water within a passage itself. Such cupolas normally have
simple forms and are not connected by ceiling half-tubes in