The Great Blue Hole

Rebecca Sparling

1The Seven Natural Wonders of the World include incredible places like Mount Everest, the Grand Canyon, and the Great Barrier Reef. These places are truly magnificent, but there are hundreds of amazing natural sites around the world worth exploring. One of the most breathtaking sites is the Great Blue Hole off the coast of the Central American country of Belize.

2Nearly sixty miles off the mainland, the hole sits in the center of a barrier reef system. The hole measures nearly 1,000 feet across and reaches a depth of more than 480 feet. Though not the deepest blue hole—that distinction belongs to Dean’s Blue Hole in the Bahamas—the Great Blue Hole is an almost perfect circle. This makes aerial views of the hole especially remarkable.

3The Great Blue Hole is the result of repeated collapses of an underwater cave system during the Ice Age. Scientists believe that an earthquake was responsible for the initial collapse of the cave’s ceiling. At its outer edge, the water is only a few feet deep at high tide. This makes the nearly 500-foot drop at the center even more striking. The drastic change in depth contributes to the hole’s appearance. Sunlight reflecting off the deeper water gives the hole a deep blue color.

4The poor water circulation inside most blue holes makes them anoxic. This means that oxygen levels are extremely low at certain depths. The unfavorable environment makes it difficult for marine plants and animals to survive, but large numbers of bacteria seem to flourish in these holes. Some divers claim to spot the occasional shark in the deeper parts of the hole where the water is much clearer. Explorers and scientists believe that a series of underwater tunnels might connect the hole to the mainland. The hazards of exploring such a network make this theory difficult to verify.

5In 1972, famed explorer Jacques Cousteau took his one-man submarine into the depths of the Great Blue Hole. Cousteau examined calcium deposits from inside the hole onboard the research vessel Calypso. The explorer traced a route in the hole that scuba divers still use today.

6The people of Belize believe that the Great Blue Hole should be added to the list of the world’s natural wonders. In 1996, the World Heritage Committee named the Great Blue Hole to the list of World Heritage Sites. This committee encourages the conservation of cultural and natural wonders across the globe. The country of Belize declared the hole a national monument in 1999. The Great Blue Hole is now one of the country’s top tourist attractions.
Question
Which best expresses the main idea of this passage?
Responses
A Scuba-diving is an extremely expensive and challenging hobby, but it also has many rewards.Scuba-diving is an extremely expensive and challenging hobby, but it also has many rewards.
B In 1972, famed explorer Jacques Cousteau took his one-man submarine into the depths of the Great Blue Hole.In 1972, famed explorer Jacques Cousteau took his one-man submarine into the depths of the Great Blue Hole.
C The Seven Natural Wonders of the World include incredible places like Mount Everest, the Grand Canyon, and the Great Barrier Reef.The Seven Natural Wonders of the World include incredible places like Mount Everest, the Grand Canyon, and the Great Barrier Reef.
D The Great Blue Hole off the coast of Belize is one of the most wondrous and scientifically interesting natural wonders of the world.The Great Blue Hole off the coast of Belize is one of the most wondrous and scientifically interesting natural wonders of the world.