Great Blue Hole

The Great Blue Hole at Lighthouse Reef

A feature attraction of Diving in Belize, Especially for divers with a appreciation of geographical phenomena, is the opportunity to explore the famed Blue Hole. Part of the Lighthouse Reef System, it lies approximately 60 miles off the mainland out of Belize City. It is one of the most astounding dive sites to be found anywhere on earth, right in the center of Lighthouse Reef is a large, almost perfectly circular hole approximately one quarter of a mile (.4 km) across. Inside this hole the water is 480 feet (145 m) deep and it is the depth of water which gives the deep blue color that causes such structures throughout the world to be known as “blue holes.”

Like a giant pupil in a sea of turquoise, The Blue Hole is a perfectly circular limestone sinkhole more than 300 feet across and 412 feet deep. The array of bizarre stalactites and limestone formations which mould its walls seem to become more intricate and intense the deeper one dives. Near to The Blue Hole, one of Belize’s largest protected areas, Half Moon Caye Natural Monument, encompasses 10,000 acres of the atoll and 15 square miles of surrounding waters.

The diameter of the circular reef area stretches for about 1,000 feet and provides an ideal habitat for corals to attach and flourish. The coral actually breaks the surface in many sections at low tide. Except for two narrow channels, the reef surrounds the hole. The hole itself is the opening to a system of caves and passageway that penetrate this undersea mountain. In various places, massive limestone stalactites hang down from what was once the ceiling of air-filled caves before the end of the last Ice Age. When the ice melted the sea level rose, flooding the caves.

The temperature in the Blue Hole at 130ft is about 76F with hardly any change throughout the year at that depth.

For all the practical purposes the over 400-foot depth makes the Blue Hole a bottomless pit. The walls are sheer from the surface until a depth of approximately 110 feet where you will begin to encounter stalactite formtions which actually angle back, allowing you to dive underneath monstrous overhangs. Hovering amongst the stalactites, you can’t help but feel humbled by the knowledge that the massive formation before you once stood high and dry above the surface of the sea eons ago. The feeling is enhanced by the dizzying effect of nitrogen breathed at depths. The water is motionless and the visibility often approaches 200 feet as you break a very noticeable thermocline. 

In the deeper waters of the Blue Hole itself, you might see a curious blacktip tiger or hammerhead shark, but on most dives you won’t see anyone except your dive buddy. Little light reaches the depths of the Hole and water does not circulate freely. As a result, the deeper areas inside the Blue Hole don’t have the profusion of life associated with most drop-offs. But as you venture into the shallows around the rim of the Blue Hole to off-gas after your dive, you will discover a wonderful area filled with life.

Pederson’s cleaning shrimp are everywhere inhabiting the ringed and knobby anemones. With the frantic waving of their antennae, these shrimp invite you, along with passing fishes, to be cleaned. Neon gobies also advertise their cleaning setvices from the various coral heads. Angelfish, butterflyfish hamnlets and small groupers are also commonly seen. Elkhorn coral grows to the surface and purple seafans, resplendent of their rich hues, sweep at the calm surface waters. If you look up, you will double your pleasure as you catch the reflections of sea fans in the aquamarine mirror of the calm water.

Dive boats leave very early in the morning – most guides bring sweet buns for those who can’t find any place to eat in the early moring hours. Bring your own coffee, however.

One can get mildly narked in back-set caves 150′ down in clear, still water, filled with 25 to 50 foot long stalactites.

Guides pole the group and chum in sharks on a majority vote. Bull, Reef and Hammer Head sharks found here, that look enormous, even from behind the protection of a handy stalagmite.

A rare – wonderful dive. However this is truly a techical category decompression dive, not recommended for newbys or resort dive qualified divers. (The bottom of Blue Hole is over 400 feet down and the wall slopes back, such that one must have absolute buoyancy control rather than to depend on something to grasp if starting to plummet while descending. Likewise – ballooning is equally deadly to ones health when coming up from 150 plus feet and requires excellent buoyancy control. Decompression times are around 10 to 15 minutes at 20 feet.). The best dive guides anchor a spare tank and regulator at your 20 foot deco spot, usually at the permanent mooring anchor located around the rim of the Blue Hole, which your boat moors too.

The Blue Hole is a must when in Ambergris, some people liken it to a religous experience. For the less experienced, if you are concerned about the dive, talk with the dive masters or the people in the shops before going. The dive masters stay with you and look after you the entire dive, which is not that long to begin with, about 30 minutes. The rim of the hole starts about 30-35 feet, just a rock wall until you get down to the stalagtites. The snorkling around the perimeter is fabulous. Lots of color, crystal clear water, some of my best pictures are from there in about 6 ft. of water. The full day trip also has other dives at Lighthouse Reef usually about 70-80′ -beautiful walls that start at 30′ and go down forever.

For anyone who wants to dive into the geologic past, exploring the Blue Hole is guaranteed to be a rewarding experience. 

The site was proposed as a National Reserve by a FA0 (1978) and has subsequently been recommended for designation by the CZMU and as a Conservation Management Area by Wilson (1995). It is possible designation as a Natural Monument will be forthcoming in 1996, under the National Parks System Act.

There is no boundary defined as yet, but Blue Hole covers approximately 1.2 acres.

The Half Moon Caye National Monument 

Almost all the divers who visit Belize are keen to add this splendid dive site to their list of conquests. When they understand what the hole is and how it was formed, it makes the dive all the more exciting. The Blue Hole is a “karst- eroded sinkhole.” It was once a cave at the center of an underground tunnel complex whose ceiling collapsed. Some of the tunnels are thought to be linked right through to the mainland, though this has never been conclusively proved. The mainland itself has many water-filled sinkholes that are connected to caves and tunnels.

At some time many millions of years ago, two distinct events occurred. First, there was a major earthquake and this probably caused the cave ceiling to collapse forming the sinkhole. The upheaval, however, had the effect of tilting Lighthouse Reef to an angle of around 12 degrees. All along the walls of this former cavern are overhangs and ledges, housing pleistocene stalactites, stalagmites and columns.

Some of the stalactites now hang at an angle, yet we know they cannot develop at any angle other than perfectly perpendicular. In addition, there are those stalactites which were formed after the earthquake and others which were formed both before and after that cataclysmic event-the top of the stalactite being at an angle and the bottom being perpendicular.

At that time the sea levels were much lower than today and the second major event was to change all this. At the end of the Great Ice Age the glaciers melted and sea levels throughout the world rose considerably. This process occurred in stages. Evidence for this are the shelves and ledges, carved into the limestone by the sea, which run the complete interior circumference of the Blue Hole at various depths. The first of these ledges is found between 150 and 165 feet (45-50 m) and is best visited on the south side. The base of the ledge is perfectly flat and cuts back into the rock some 15 to 20 feet (5-6 m). This creates an ever-narrowing cavern until the roof reaches the floor right at the back. Here in the V- shaped ledges, cut into solid limestone, are stalactites, stalagmites and columns (where stalactites and stalagmites have joined) which do not exist in the shallower waters of the Blue Hole.

There is very little marine life in the hole, and the walls are of bare rock largeiy due to the scarcity of direct sunlight on the walls, but this hardly matters. Occasionally a lone hammerhead shark is seen, but the general lack of fish, and therefore food, suggests that the creature was simply passing through. The only other fish I have seen were four pompano, but other species have been seen, especially on the south side. Lemon and blacktip sharks, and horse-eyed jacks are spotted with some regularity.

Diving the Blue Hole is not for beginners, although anyone can complete a shallow dive and claim to have dived this marvelous wonder of nature. The deeper one dives into the Blue Hole, the clearer the water and the more breathtaking the scenery. But diving deeper than sport diving depths is for specialists only and cave diving requires even more training and equipment. This type of diving is not generally available in Belize, but a few groups have visited the Blue Hole in order to explore the tunnels and caves which extend from within. On the western side at a depth of 230 feet (70 m), there is an entrance through a narrow tunnel into a large cavern. In total darkness the stalactites, stalagmites and columns exist in an undisturbed world. The floor is covered with a’very fine silt which billows into great clouds with the slightest movement from a passing diver. In the farthest corner, another narrow tunnel leads upwards into a second cavern and then another leads finally to a third cavern. Here are the skeletal remains of turtles which found their way in but never found their way out. This is the very danger which faces a diver. Now at a depth of only 100 feet (30 m) he must find his way back by the same route down to 230 feet (70 m) before he can commence his surfacing and decompression schedule. if he, his buddy or even a turtle have stirred up the silt, the chances are he will never find his way out again. For those qualified cave divers, this is a very rewarding dive.

The Great Blue Hole is not marked on Admiralty Charts-the task of a survey ship is to map that portion of reef which represents a danger to shipping. The hole is found almost exactly in the center of the reef on a course of 3300 from Harrier Wreck. An entire diving trip to Belize is worth the effort and expense for this single dive.

Contrary to rumors, although Cousteau did explore the depths of the Blue Hole with his minisubmersibles in the 60’s, he did not lose his son Philippe here, he died elsewhere in a helicopter accident. Neither did Cousteau randomly use explosives to destroy the patch reefs while navigating the “Calypso” in the Blue Hole. He did selectively remove, by limited blasting, a very small area to enable the “Calypso” to reach the Blue Hole.

Several divers have lost their lives in the Blue Hole for various reasons, and as usual, caution is the rule and divers should be fully aware of safety as cave diving rules will apply when they enter the stalagtite-stalagmite area.

Traditionally, before the 1960’s, the Blue Hole, because of its awesomeness, was a place very much respected and feared by all who saw it. Lighthouse Reef, an atoll approximately 25 miles long and 10 to 12 miles wide, has a typical enclosed lagoon. The depths in this lagoon vary from 5 to 25 ft., and in it there are many scattered coral formations known as “patch reefs”. In the northeastern section of this otherwise shallow lagoon a mariner will come across this indigo blue apparent abyss. Up to the 60’s old timers would claim that this hole was bottomless. Because such a blue hole was so striking against a background of tranquil pastel greens of the shallow atoll lagoon, one may be reminded poetically of Homer’s accounts in the “Odyssey” of the whirlpool “Charybdis” that gave one a choice of two dangers. IN THE BLUE HOLE THERE ARE NO WHIRLPOOL LIKE CURRENTS, SO DIVERS NEED NOT FEAR THIS.

The Blue Hole is the result of the repeated collapses of a cave system formed during lower sea level stands. The reason that the hole is 475 deep instead of the shallower 390 foot depth is that this atoll is on a geological fault block that has been subsiding into the basin through geologic time.

First Blue Hole Diving Expedition
In the early 60’s, Al Giddings, noted underwater cinematographer and pioneer, first dove in the Blue Hole. Al Giddings chartered a boat called “The Geek” (a 40 ft. U.S. Navy surplus Captain’s “Gig”). “The Geek” was owned by an ex-U.S. Navy frogman, Richard “Dick” Moore, who started one of the earliest SCUBA diving businesses in Cuba in 1959. Because at the political climate in Cuba, “Dick” moved to the coast of Yucatan and participated in diving the shipwreck off Matanceros. This was a Spanish galleon apparently coming from the Old World to the New World as mentioned in the prior shipwreck section as “Nuestra Senora de los Milagros” and was carrying trade items to deliver to the New World. A vessel like this probably would not be carrying large amounts of gold and silver, but “Dick” expressed that some of the divers found about 9 lbs of gold leaf. “Dick”, the first real underwater SCUBA diving pioneer in Belize, subsequently moved to Ambergris Caye and bought some property in the Bacalar Chico area. Subsequently “Dick” sold his property and moved to southern Belize off Punta Gorda, to an island called Frenchman’s or Peter’s Caye, and continued his diving explorations in southern Belize. When he died, his request was to be buried on his island, and his request was granted.

One of the early articles in the 60’s in “Skin Diver” Magazine, written by Al Giddings, describes his explorations in the Blue Hole at that time, wherein he first describes the stalagtites and stalagmite formations. The first serious underwater documentary on the reefs of Belize was filmed by Al Giddings. This documentary was called “The Painted Reefs of British Honduras”. The second serious underwater documentation, which included 35mm footage of the Blue Hole was sponsored by the Canadian Film Board, 1965 or 1966 (about).

The senior author (RLW) had the privilege of participating in this expedition as a marine biologist. Several dives were made to the 200 ft level. The sport of SCUBA diving and underwater photography were beginning to come of age.

Along Comes Jacques Cousteau
Jacques Cousteau thoroughly explored the Blue Hole in the late 60’s and released one of his television documentaries about blue holes, including those in the Bahamas. He sounded its depths and recovered one of the fallen stalagtites-stalagmites at the bottom of the approximately 475 ft deep hole.

Blue Hole Monster Appears?

In the late 60’s or early 70’s, a diving expedition from Caye Caulker claimed that they had witnessed, while SCUBA diving, the very apparition of a genuine SEA SERPENT. This beast reportedly had red eyes, apparently as long as 20 ft.? semi-transparent and eel-like in shape, The dorsal and pectoral fins were apparently extremely long and flowing, and reportedly created some apprehension in the minds of the divers. On the basis of their descriptions, the only fish that would fit this description, would have been the ribbonfish or oarfish (Family Cepolidae), however, the oarfish is an open water, pelagic fish, and its presence in the Blue Hole would have been very unlikely.

Recently, in the last 10 years, many divers have safely visited and dived the Blue Hole. As far as the “monster” is concerned, Out Island Divers, along with other local dive boats, have for several years, been leading weekly expeditions from Ambergris Caye to the Blue Hole and have made hundreds of dives. The only recent “monsters” seen while SCUBA diving were themselves.

Biology of the Blue Hole

Once you pass the 60 ft. level, there is not much coral to see. At depths of 80-90 ft. the Blue Hole may appear somewhat sterile. One will not see the large sponges or large coral formations, that one will see at the same depth at the main reef drop off. One may see large jacks (fish), maybe a large shark or two, or groupers. The Blue Hole is not spectacular for its biology, but acre for its total mind absorbing awesomeness. At depths 120 to 155 ft. deep, one must realize that 10,000 to 11,000 years ago this was a land cave. Man was probably still a hunter-gatherer and possibly a cave dweller (although he probably never lived in this particular cave).



Some of the largest lobsters found in Belize are on the main atoll reef at Lighthouse. The reef at Lighthouse is very wide, well developed and is more massive when compared to the main barrier reef in northern Belize. In the very shallow water pools and caves in the middle of the atoll reef, some of these very red lobsters are 4 ft. long from the tips of their antennae to their tail.

At one time in the early 70’s the senior author, RLW, observed what may be termed a “conch walk” at Lighthouse. In the Thalassia-sand flats in between the patch reefs, hundreds of conch in depths of 20 to 25′, spaced about 11 apart, were seen at dusk moving in a southwesterly direction. RLW reoriented many towards the north, but upon release, the conch immediately resumed a southwesterly path. These were all adult conch with thick lip development.

Incredible new exploration of the Great Blue Hole. The Cambrian Foundation successfully completed a study of the Blue Hole and its cave systems with high resolution video and the latest diving equipment. An unknown cave system called the Abyss by local fishermen was explored to a new Belizean underwater cave depth record of 485 FSW.

Leave a Comment