Times of the Islands Summer 2016

green pages newsletter of the department of environment & maritime affairs
water of the freshwater lens
by diffuse flow to the coast is
unable to conduct water efficiently.
Tubular cave conduits
develop, much like water pipes,
to carry the flow. These tubes
can be quite large, up to 10
m (33 ft) or more in diameter.
They can become large enough
that their roofs become unstable
at certain locations, and
collapse occurs. This collapse
can work its way upward until
it breaches the surface of the
bank. When sea level rises at the
end of a glaciation, these collapses
become flooded to form
blue holes. Cave divers can go
into these blue holes, and sometimes
are able to enter the large,
horizontal caves that developed
during a lower sea level.
The map above depicts a flank margin cave at Blue Horizon Resort in Middle Caicos. The cave has a
cultural feature, the stairway, which is included on the map, along with symbols that help describe
When sea level was higher what the cave contains. The cave has been breached by modern wave erosion and is on its way to
being overprinted by marine processes.
than today during the last interglacial,
the TCI was a collection of islands much smaller contain mineral displays, the most common being those
than today, as only the eolian calcarenite dune ridges made of the mineral calcite, such as stalactites that hang
were above sea level. In such small islands, diffuse flow from the ceiling, and stalagmites that rise up from the
easily carries the water of the lens to the island margin, ground, as well as slopes of calcite called flowstone. A
and only flank margin caves develop. Even Conch Bar variety of exotic minerals can also be found. Stalagmites
Cave, with its huge length, is only a series of connected are especially important, as they grow from drip water in
chambers that run along the edge of the ridge enclosing thin layers, and their interior looks much like the growth
the cave; it is not a conduit cave system.
rings found in the trunk of a tree. These layers can be
These flank margin caves form without entrances; dated, and their isotopes examined, to study how climate
years later, erosion of the hillside, or collapse of the roof, changed in the past.
may create an entrance. Conch Bar Cave has both types of Along the coasts of the TCI, especially the Crossing
entrances. Indian Cave on Middle Caicos is highly altered Place Trail of Middle Caicos, a number of flank margin
by collapse and the roof remains as a series of arches. caves have been exposed by wave erosion of the high
There may be flank margin caves still intact inside hillsides
today in a completely natural state, unentered by present an interesting problem, as sea cliffs are exactly
dune ridges. The caves are present in sea cliffs, and
humans or bats.
where one would expect to find sea caves produced by
the mechanical energy of waves and not by dissolving the
What do TCI’s caves tell us?
rock.
First, the mere existence of the caves tells us that sea One useful line of evidence is where the cave exists
level was once higher. They allow geology to be seen from above the tide level, above the intertidal notch. Such a
the inside, which includes the nature of the rock, and cave could not form by wave energy under current conditions.
These caves also contain eroded how that rock has been altered through time. The caves
stalagmites,
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