Page 159 - (DK) Ocean - The Definitive Visual Guide

CORAL REEFS 157

Like all atolls, it is bounded by a produced a complex of air-filled caves HUMAN IMPACT
ringlike outer structure of coral and tunnels in the limestone. At some
formations, many of which break the point, the ceiling of one of the caves DIVING THE GREAT BLUE HOLE
surface. These form a natural barrier collapsed, producing what is now the
against the sea and surround a lagoon, entrance to the Blue Hole. Later, as sea The Great Blue Hole is one of
which sits on top of a mass of level rose, the cave complex flooded, the world’s most exciting dive
limestone. The lagoon is relatively deep and it is now accessible only by sites. It is not recommended for
but contains numerous patch reefs adventurous scuba divers. the fainthearted (as sharks are
along with six small, sandy, low-lying Elsewhere, the atoll boasts large commonly encountered) or for
islands, or cays (one containing a dive areas of mostly healthy reef, although novice divers (because perfect
center). At its center is Lighthouse some were affected by coral bleaching buoyancy control is needed).
Reef’s most remarkable feature—a in 2010. As well as patch reefs within At 125 ft (38 m) depth, an array of
large, almost circular sinkhole in the the atoll, around its margins are many impressive ancient stalactites can
limestone, known as the Great Blue coral-encrusted walls (dropoffs) that be seen hanging from the slanting
Hole. Approximately 410 ft (125 m) descend to depths of several hundred walls of the hole. The entrance to
deep, this feature formed some 18,000 yards. Lighthouse Reef exhibits a a system of caves and tunnels lies
years ago during the last ice age, when biological diversity typical of the a few yards farther down.
much of Lighthouse Reef was above region; it is home to some 200 fish
sea level. At that time, freshwater erosion species and 60 species of stony corals.

GREAT BLUE HOLE OCEAN ENVIRONMENTS
The water in this sinkhole extends to
a depth of 410 ft (125 m), producing the
deep blue color after which it is named.