The calm surface of the Caribbean Sea off the island of Andros slowly starts to rotate, whirlpools form and at their centre gaping dark blue holes begin to gulp water. For centuries, a Bahamian legend of a sinister, mythical creature called the Lusca has been woven around this strange phenomenon. Seen from the air, the low-lying island of Andros in the Bahamas is a fissured mass of inlets, channels, islets and coral shallows. Here and there, dappled patches of inky blue divert the eye from the brilliant turquoise hue of the lagoon. These are the blue holes, the notorious ‘doors’ to a subterranean maze of flooded cave systems interwoven with passages and galleries that by twists and turns lead to small chambers, immense canyons and cathedral-like vaults.
At each high tide, as the water rises inside the barrier reef that embraces the coast of Andros, the blue holes begin the performances that has earned them their fearful reputation. They start to slowly rotate, gulping water ever more rapaciously so that the inflowing currents create whirlpools which draw into their vortex – and thence to watery oblivion – anything that floats, from plant debris to small fishing boats. As the tide recedes, a powerful reverse action takes place and the holes spew out great mushrooms of water. Local people attribute this dramatic sequence to a mythical creature, the Lusca that is reputed to dwell in the blue holes. Half shark, half octopus, the Lusca supposedly uses its long tentacles to drag food into its deep lair then disgorges remain when sated. Small wonder that Bahamian fishermen, some of whom have lost ancestors to the raging maelstroms of these deceptively calm waters, continue to treat the blue holes with circumspection.
Andros is the largest of the Bahamian islands. Some 100 miles (160km) long and 40 miles (65km) across at its widest point, the island sits on the marine plateau of the Great Bahama Bank. It is lapped on three sides by warm, shallow seas, but a channel of deep water known as the Tongue of the Ocean curls past the length off its eastern shore. In places along the wall of this abyss, colourful coral shallows suddenly give way to dark blue depths. These deep openings in the limestone on the margin of the island are the mysterious blue holes. Their equivalents on land are circular black lakes in wooded parts of the islands.
About 50 blue holes have been recorded in the interior of Andros and in the shallows offshore, with more still to be counted. Relatively few have been investigated; moreover, it is only in the past two or three decades that the very existence of the holes has been explained. The first serious modern explorer of the area, the Canadian driver and photographer Dr. George Benjamin, in the 1960s made aerial surveys to chart the caves. Then, equipped with an aqualung and underwater cameras, he dived to probe their secrets. His discoveries provided geologists with the information they needed to begin at last to unravel the mystery surrounding the holes.
The Bahamas are part of a chain of limestone platforms, or banks, which began to form around 130 million years ago. Over the last 2 million years, successive ice ages the sea level to fall. In the warmer periods the ice melted and the sea level rose accordingly. At the peak of the last ice age, around 20,000 years ago, sea levels were as much as 400ft (120m) lower than they are today. This meant that underwater caves – carved out of the limestone over millions of years by a corrosive mixture of fresh water and sea water – were drained. No longer buoyed by water, their ceilings started to collapse.
In many cave roofs a dome developed upwards and in some places broke through the earth’s surface, forming an open shaft. When sea levels rose again, the shafts filled with water and created the blue holes. Today, at high tide, sea levels around Andros rise above the groundwater levels of the island’s water table. The pressure of the sea forces water into the holes, creating their strong characteristic whirlpools, and groundwater levels rise slightly. As the tide recedes and pressure of the sea water drops, the ground water pushes the sea water down, causing it to well out of the blue holes in great domes. The myth of the Lusca has its origins in these strong reversing currents.
Surprisingly, a wealth of creatures has adapted to life in this seemingly hostile environment; indeed, explorers have likened some of the caves to underwater zoos. Nurse sharks rest motionless on sandy floors; crayfish inhabit rock crevices; sky-blue and lavender sponges drift eerily through the indigo depths; and at certain levels the water is alive with tiny crustaceans and swimming worms. Ne of the most curious species of all is the Lucifuga, a blind cavefish with a pale, colourless body.
More dramatic still was the discovery, In 1991, of human bones and skulls at an island diving site known as Sanctuary Blue Hole or Belize Blue Hole. These remains have been attributed to the Lucayan people (an Arawak-speaking tribe which inhabited the Caribbean at the time of Columbus) who probably used the holes as burial grounds.
The prospect of being trapped in the holes discourages many divers, and there is still danger involved in exploring them. Even with the most modern safety equipment divers never venture into the blue holes alone: anyone attempting to do so at high tide would be sucked in like a cork down a drain, sustaining the legend of the Lusca.