Abaco Life Magazine

Abaco Life, An Island Magazine


Archive for July, 2004

Blue Holes

07 12th, 2004

I was guiding a kayaking trip with a family from Canada, and their little boy kept politely asking me when we would arrive at our destination. His impatience was more wild curiousity than the result of being tired of paddling. Our destination was a blue hole, nestled in the cluster of islands that form the Snake Cay estuary south of Marsh Harbour.
“Just what is a blue hole?” the boy probed.

“You’ll know it when you see it,” I answered, letting the suspense build. We were kayaking in less than three feet of water over vast beds of turtle grass. Soon he pointed to a brilliant circle of turquoise and azure water up ahead. As we paddled across the 20-foot breadth of it, water welled up from below with the incoming tide. This was the blue hole that “Cave Diver” Fred Davis had named the “Fire Hydrant” because, when he tried to swim through one of its tunnels against the tide, he had to claw the walls: the sea current blasted through like a hydrant. Blue Holes of Abaco

With a fresh-water lens on the surface, and heavier, salt water beneath, these blue holes are connected underground to the sea and its tidal changes. They are lit near their openings, but mostly dark inside. Created as a result of the Bahamas’ special geologic history, the holes provide a home for some of our most mysterious creatures, and hide some of Abaco’s most interesting natural history.

When it comes to politics and economics, the Bahamas is often lumped together with the Caribbean. Geologically, though, these “isles of perpetual June,” as colonists referred to this archipelago, as well as the neighboring Turks and Caicos, differ from the Caribbean because sedimentation created them, rather than the volcanic upheavals that shaped other islands in the Greater and Lesser Antilles. This explains why our islands are so low lying, with the highest point being just 206 feet on Cat Island, while others in the Caribbean are hilly, if not mountainous.

When the continents separated on tectonic plates millions of years ago, the young Atlantic Ocean forming between the Americas and Africa was initially a shallow sea in which algae, mollusks, and coral grew and died, accumulating masses of calcium carbonate. As the ocean deepened, this sedimentary accretion kept pace, at a rate of one inch every millennium, and today the calcium carbonate buildup averages 3.5 miles deep, according to geologists. Thus, The Bahamas emerged. Whenever the sea level dropped during ice ages, the calcium carbonate was exposed to air and fresh water from rain, causing a chemical reaction that hardened it into limestone rock.

Limestone is soluble, susceptible to fresh water, as is evident by the potholes that deepen on our roads every time it rains. Fresh water percolating through the rock, over the ages, created features like caves, banana holes, and blue holes, both submerged and inland. As marine ecologist Dr. Stephen Thompson explained last January at the first Abaco Science Alliance Conference, a blue hole is “an old drowned cave system with a deep vertical entrance, terraced by earlier sea levels…a natural aquarium.” Bahamians sometimes refer to them as ocean holes or boiling holes; Floridians call them sinkholes; in Mexico they are known as cenotes or “big wells.” It is commonly said that if we were to cut the Bahama Islands in half, they would look like Swiss cheese because of all these holes.

No one knows exactly how many blue holes there are in Abaco. Ron Pagliaro, owner and guide of the ecotourism business Abaco Outback, guesses there are 50 blue holes in the Abaco chain. “They’re finding more all the time in the pine forest,” Pagliaro says. The Bight of Old Robinson, a unique tidal creek and proposed Marine Protected Area near Little Harbour, has more than a dozen blue holes within its shallow waters and mangroves. Abaconian Tim Higgs, who has been exploring Abaco’s blue holes for the past year, says there are eight “unknown” blue holes at Crossing Rocks alone.

A dive instructor and co-owner of Abaco Dive Adventures, Higgs has lately been “laying line” in the Dark River Boiling Hole, located in the middle of an inland lake that locals sometimes call “Cherokee River,” near Casuarina Point and Bahama Palm Shores. Just weeks ago, he and Fred Davis, (a.k.a. “Kalik” or “Caveman” Fred), a Marsh Harbour fixture and retired NASA employee, found what may be a new sponge species about 1,000 feet back in the darkness of this hole. Higgs described it as white, about the size of a beach ball, and shaped like cauliflower. An Exuma diver has discovered what he thinks is the same sponge in a blue hole there and is sending samples and photographs to experts for identification. The adventure of cave exploration, curiosity and an appreciation of unique finds like this unusual invertebrate are what appeal to Higgs about blue hole dives. “It’s also nice to be able to show people what it looks like through photographs and video,” he says.

In “Dan’s Cave” so called after spelunker Dan Wiltfang,who first explored this inland hole just south of Bahama Palm Shores – the remains of a crocodile have been found. These salt-water reptiles populated the Bahamas until the 19th century. when they were presumably hunted into extinction. Other than vague written accounts, little proof is available of the Bahamian crocodile and what species it might have been, so the blue hole find is a significant scientific event.

Similarly and in the same blue hole, divers have discovered an unidentified turtle. It is tantalizing to conjecture that this could be the remains of a long-extinct West Indian tortoise, a Pleistocene, three-legged, forest-dwelling creature, that has not been recorded on Abaco, but whose remains have been found on New Providence and Andros. Higgs says there is a pine tree upside-down in the Treasure Cay blue hole that he guesses is 70 feet tall, with a trunk he can’t get his arms around. He expects this well-preserved giant may be helpful in ongoing research of Abaco’s environmental history, as told from tree rings.

For Higgs, perhaps the most compelling aspect of exploring blue holes is entering their “Karst terrain,” a rarefied world of geological formations. During above-water periods, rainwater ran through the calcium carbonate ceilings and walls of these caves, forming stalagmites and stalactites. Higgs says Dan’s Cave is “highly decorated” and especially beautiful. “When you shine a light on it, the ceiling of the second room looks like icicles.” Speleo-thems, or “ribbon stalactites,” have formed smooth, white carbon flows down the sides of walls. In this room, dubbed by divers as the “Crystal Palace,” the speleothems have crystalized to look like glass. Some stalactites connecting the ceiling to the floor are 40 feet tall and just one inch thick. “They were created when the cave was dry and are extremely fragile,” Higgs says. In the bottom of some caves, he sees the cracked clay from its above-water days. “In the Saw Mill Sink, past Crossing Rocks, the clay is red and formations are white, so it’s very attractive.” The Lost Reel hole has gray clay in its caves, which pass under the road between Snake Cay and the Big Bird chicken farm.

Some blue holes are habitats for a myriad of bizarre creatures, such as blind cave fish (Lucifuga spelacotes), otherwise known as brotulids. Naturalist David Campbell calls brotulids “interglacial relics,” because they stem from a deep ocean species that scientists guess became trapped inland during the sea’s ice age recession. In order to survive, brotulids had to adapt to fresh water, and given the dim lighting in their new home, their eyes became expendable. Higgs describes those he has seen as six-to-eight inches long, ranging in color from whitish-pink to dark purple. They have eye sockets lacking eyeballs, but “with black specks inside.” Other novelties are remipedes, which look much like centipedes, having lots of legs, except these insects are white, eat shrimp, and can swim.

Over the years, Cave Diver Fred has been mapping these holes and getting a picture of where they lead underground. He has put in 16,000 feet of line so far at the Dark River Boiling Hole and still has three leads going. Higgs says they hope one of these will connect to a neighboring blue hole half a mile away. Some tunnels crisscross, above or under each other. Blue hole cave diving is a growing sport, particularly in Mexico, where in one cave, divers have laid 600,000 feet of line, connecting 70 different openings, some to the ocean. “Cave diving is different; you’re in an overhead environment,” Higgs says, describing as example the Abaco cave feature “Sidemount Passage,” where divers have to wear their tanks on their sides to be able to fit through a low ceiling. “People either really like cave diving or don’t want to have anything to do with it. It takes a lot of training. I’ve got 10,000 open water dives, but I was extremely humbled when I took the cave certification course.”

The risk factor in cave diving increases because of darkness, having to find one’s way back out, and sometimes poor visibility due to stirred up silt. Some holes have a red hydrogen sulfide layer, where the fresh and salt waters meet, that only offers about six inches of visibility and completely blocks all light below it. Add to that the fact that most blue holes in the Bahamas are around 100 to 150 feet deep. A diver from Mexico descended 296 feet in the hour-glass shaped hole near Big Bird farm and said he could still see the opening at the top.

The closer the hole to the sea, the more dangerous it generally is, because the water siphons with an outgoing tide. Higgs points out that their flows do not necessarily concur with Marsh Harbour tide charts. “You really have to know what you’re doing.” He notes that one must always have an extra full tank, an extra light, and a rope. He does not take anyone cave diving who is not cave certified.

Dr. Thompson, who researches marine ecology at Oregon State University, has been surveying fish species found in 24 blue holes of Robinson and Spencer’s bights since 1986. These estuary blue holes have been home to at least 48 coral reef fish, some not common on open reefs. Unfortunately, upon returning to these sites, he has found them to be heavily impacted from various human-related activities like chlorine bleaching, spear- fishing, SCUBA diving, and careless anchoring. He said two blue holes had been “irreversibly changed.” Divers’ fins break coral and lift silt off the bottom, which then settles in the pores of coral species and smothers them. When the corals die, the reef fish dependent on them disappear. “Biodiversity is decreasing,” Thompson said. He recommends installing moorings at blue holes with boat access and limiting boat speeds in these bights. He suggests policymakers should encourage low-impact activities, such as kayaking and snorkeling (without fins), around blue holes, and discourage fishing and SCUBA diving.

Given their fragile nature, Higgs is contemplating proposals to preserve certain blue holes, such as Dan’s Cave, so that they don’t get accidentally damaged by inexperienced divers or used as garbage dumps, as is already the case at blue holes on Fire Road and at Blackwood.

For most of us, blue holes are one of those beautiful but dangerous wonders of nature – similar to, say, moray eels – that are best observed from the surface. Higgs summed it up: “It’s nice to know they’re there.”


©  Jim Kerr, Abaco Life Magazine
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