Great Blue Hole is a large submarine sinkhole off the coast of Belize

The Great Blue Hole is a world-class destination for recreational scuba divers attracted by the opportunity to dive in crystal-clear waters and see myriad species of marine life including tropical fish and spectacular coral formations.

The marine life in these areas includes nurse sharks, giant groupers, and several types of reef sharks such as the Caribbean reef shark and the Blacktip shark. Dive excursions to the Great Blue Hole are full-day trips, that usually consist of one dive in the Blue Hole and two additional dives in nearby reefs. 
The Great Blue Hole is a large underwater sinkhole off the coast of Belize. It lies near the center of Lighthouse Reef, a small atoll 100 kilometres (62 mi) from the mainland of Belize City.

The hole is circular in shape, over 300 metres (984 ft.) across and 125 metres (410 ft.) deep. The world’s largest natural formation of its kind, the Great Blue Hole is part of the larger Barrier Reef Reserve System, a World Heritage Site of the United Nations Educational, Scientific and Cultural Organization (UNESCO).
Glyn Collinson, a NASA scientist who recently dived the Great Blue Hole described it thus:

“It was the deepest, deep blue hole imaginable; A chasm that fell away deep into the deep, dark blue. It had been forged out of solid rock as caverns, hundreds of thousands of years ago during the last ice age. For eons, water filtered through the rock and into these great stone cathedrals, breeding multicolored stalactites and stalagmites. Then, one by one they collapsed in on each other, creating a chasm four hundred feet deep. As Earth’s swollen polar ice-caps receded, the warm Caribbean ocean swept in to fill the chasm with boiling white hands, the last rays of sunlight struck the chasm’s floor. Then, as the limestone broke down, it began to rain tiny fragments of rock, which slowly began to fill the great Blue Hole.”

“Alright,” the dive master said, jolting me back to reality. “Welcome to the Blue Hole. This one is real deep, starting with a drop off from forty feet that goes right the way down to the bottom past 400 feet.” The man held up a detailed custom drawn map of the site and pointed as he talked. “We will go down fast to one hundred and thirty feet where stalactites come down from this overhang. We will stay there for a maximum of twelve minutes, starting from the time that the first pair gets there. We all need to keep together and watch each other. To make sure that you all keep an eye on your depth, the dive pair who goes the deepest will buy a round of drinks for everyone back at the Island.” ‘Great’, I thought, ‘so much for pushing our depth limits.’
Noted SCUBA diver, writer and photographer Rick Frehsee wrote the following account of his research on the Great Blue Hole:

Origin of the Belize Atolls

“Lighthouse Reef, Glover’s Reef and the Turneffe Islands are all distinct anomalies in the Caribbean. Nothing else in the Western Hemisphere resembles a true coral atoll, except perhaps Chinchorro Reef, off Mexico’s southern Yucatan Peninsula (just above the Belize atolls). According to geologists they are even more unusual in that the origin of their formation does not seem to mirror the atolls of the Pacific Ocean, where rings of coral are better known.

“The ancient processes contributing to Belize atoll development may have begun as many as 70 million years ago and the atolls did not develop around subsiding volcanoes. Instead, they originated atop giant fault blocks; limestone covered ridges that settled in steps, providing a series of offshore platforms for coral growth. After the last ice age, with the slow rise of sea level, coral growth continued upward, creating the precipitous outer walls and the shallow inside lagoon that typifies these distinct formations. Many drop-offs surrounding the Belize atolls are thousands of feet deep, while depths in the shallow lagoons average 10 to 30 feet.”

Recent History: Belize Atolls and Great Blue Hole First Explored By Jacques Cousteau

“The sense of isolation and remoteness that accompanies a visit to the atolls, belies a rich history. Although only archaeological traces remain, it appears the ancient Maya inhabited at least a few of the atoll islands for more than 1,000 years. The recorded history of the atolls begins in the early 16th century with the arrival of the Europeans. From 1528 to 1532 Spanish explorers researched and and charted the coastline and offshore reefs of Belize and the Yucatan.

“Original names known to the indigenous inhabitants or given by the first Spanish explorers are now obscured. The only names that have survived are published on charts discovered decades after their making. It appears that Turneffe used to be called Terre Nef; Lighthouse Reef, Quattro Cayas (four cayes) or Eastern Reef; and Glover’s Reef, Longorif. The present names evolved with English discovery and occupation in the 1750s. Glover’s Reef was named for the English pirate John Glover, who used this particular atoll as a hideout. Lighthouse Reef was renamed after a navigational light was permanently established on Half Moon Caye.”

In 1836 the famous biologist-evolutionist Charles Darwin paid homage to these remarkable formations when he said the Belize atolls and the Belize Barrier Reef constitute “..the richest and most remarkable coral reefs in the entire western Caribbean.”

In the mid 1970s Jacques Cousteau’s Calypso made its famous investigation of the Great Blue Hole and the Belize atolls, which corresponds to the arrival of dive travel to the region.

Blue Hole Experience from Captain Ray Auxillou

Wide angle view Great Blue Hole in Belize courtesy a Private Island.

Canadian-Belizean diver Captain Ray says: “I was one of those early arrivals from the scientific and sport diving community, accompanying the Cousteau divers into the Blue Hole and participating in one of the first dive travel ventures along the Belize River.

“Because of the relative isolation, our atolls have remained nearly as pristine as I remember them 30 years ago. As a result of today’s relatively easy travel, this sense of remoteness and the quality of the underwater environment is even more extraordinary. With only a few exceptions, I can visit any above or underwater site in the Belize atolls and the scene appears unaltered.”

On-shore caves of similar formation, as large collapsed sinkholes, are well known in Belize, and in the Yucatan Peninsula, where they are known as “cenotes”.

Video – Diving The Great Blue Hole

The Other Blue Hole

Belize has another, lesser known Blue Hole. This is an inland sinkhole located 12 miles south of the City Of Belmopan in the very center of the country. Yes, it is locally known simply as the Blue Hole. Its location right on the Hummingbird Highway makes this natural swimming pool an attraction for locals and tourists. The inland Blue Hole is within the St. Herman’s Cave system and is administered as a national park, Parking facilities are available and the Blue Hole is accessible by a short flight of stairs that take you down approximately 30 feet into the very cool freshwater pool.

The inland Belize Blue Hole off the Hummingbird Highway

The Inland Blue Hole is sinkhole formed by the collapse of an underground river channel. The exposed section of the underground Cave’s Branch River tributary can be viewed for about 150 feet before it disappears again beneath the surface.

Located just off the Hummingbird Highway, the inland Blue Hole steps lead to a 30 foot deep pool, for which the park is named. The cool, turquoise waters, surrounded by dense rain forest, overhung with mosses, vines and ferns are the perfect spot for a cool and relaxing dip.

Facilities are limited to park rangers during working hours and you can enjoy an exhilarating soak in year-round cool water in perennial shade of rainforest and hills that shield the visitor from the tropical sun. The pool is fed by the Cave’s Branch River and disappears underground around a small sandy beach. A nature walk and St. Herman’s Cave are nearby as is the Belize Cave’s Branch River. This is easily accessible a short 15 minute walk or a 5 minute drive across the highway into the area of Ian Anderson’s jungle lodge. The river in this area is spectacular and is accessible to the general public during working hours.
Belize.com Managing Editor Manolo Romero is a frequent visitor to the area and writes:
“The drive is about 5 minutes headed south on the Hummingbird Highway – a very short distance on your left after departing the Blue Hole. This is through a narrow jungle trail with overlapping rainforest. You turn off on your left unto the Ian Anderson’s parking lot that overlooks the Caves Branch River to the front, and the lodge to your right.

“If you arrive an hour before lunch or supper, you can report to the lodge and request food and beverage service and this will be arranged. The lodge management is very accommodating to “drop in” visitors provided they request service in advance.

“If you are not a guest, feel free to park your vehicle and descend into the river which is sweet and clean water. Throughout most of the year the river is clear, low and safe even for those not experienced in swimming rivers but do check with your guide before taking a dip.
“There are some stones on the approach so river sandals may be useful. I find that the river has two distinct temperatures. The area adjacent the parking area is just below body temperature and sunny. The area on the opposite bank is cool and full of shade and privacy and the howler monkeys are not as inquisitive – draw your own conclusions!”

St. Herman’s Cave

St .Herman’s Cave is located about 450 meters off the Hummingbird Highway in the neighborhood of the inland Blue Hole. The information center and parking are located just off the highway.

St. Herman’s cave in Belize

The largest of the three known entrances to St. Herman’s Cave sits in a sinkhole 180 feet wide narrowing to a 60-foot wide entrance.

Concrete steps over stone steps once cut by the Maya make for easy access for visitors.
A trail with markers is provided within the cave. It is about a half mile through to the first exit.
Once inside, visitors can scale large boulders and navigate through the water course, while admiring stunning cave formations.

After exploring the cave, you can hike through a 2 mile interpretive trail.