Atoll

Atoll            Continuous or broken circular formation of coral reef and low coral islands surrounding a central lagoon. Historical Background: It was the enormously productive mind of Charles Darwin that created the modern theory of coral atoll formation. Evolution of birds and fish and assorted other creepy, crawly creatures wasn’t the only thing Charles was thinking about during the voyage of the H.M.S. Beagle when between November 1835 and April 1836 the crew visited Tuamotu Archipelago in the south central Pacific and Cocos Keeling Island in the eastern Indian Ocean. Those halcyon days of exploration and discovery were made famous in his book, The Structure and Distribution of Coral Reefs, which was first published in 1842 as Part One of the Geology of the Voyage of the Beagle. In that volume Darwin suggested a single theory for the formation of lagoon-islands, atolls, and coral reefs, a theory whose power resonates to this day.

By the early 1800s, well before Darwin left merry old England for tropical parts then all but unknown to the general public and even to the cognoscenti, various scientific investigators had stumbled onto the fact that corals were animals that grew only in shallow seawater. Almost immediately atolls became an exciting mystery of the tropical oceans. Facts then in evidence: Coral reefs and the algae that cemented the individual animals/skeletons together only grew in shallow water, in the upper 300 feet or so of tropical oceans where light penetrates. Observations: Atolls, which were coral islands that were found in the tropics, consisted of living rings of coral built on huge piles of dead coral that extended deep below the surface, often far below 1,000 feet. Paradox: How were atolls found in deep water if coral could only grow in shallow water?

By the time Darwin bumbled along in the ineptly named Beagle, no one had been able to explain the apparent contradiction. He was the first scientist to sift through the data, make pertinent observations, identify the relevant pieces, and put them together in a logical order that could withstand the test of time and scientific criticism. His elegant solution to the mystery was perhaps the major geological contribution from his voyage round the world in the Beagle.

After collecting numerous geological samples and puzzling over the unseemly jumble of facts that refused at first to make sense, Darwin created the following scenario. Over the course of time an undersea volcano began building itself by depositing one layer of lava after another, adding more and even more lava until a land mass eventually pushed itself above high tide. Almost immediately living organisms (including coral) began pioneering the shallow waters and the shores of the new land mass. Over time, the volcano became dormant and began sinking slowly (Author’s Note: All you good geoscientists better be thinking sea-floor spreading and mid-oceanic ridges or you better hustle back to Accounting 101 or Computer Language 240 as quickly as your legs can carry you).

As the volcanic island sank, the older coral died, in part because it found itself in water too deep for it to survive. But new coral immediately began growing on top their dead mates. Before long, the sinking island was decorated by a vertical and circular necklace of coral with a lagoon that separated it from its host volcanic island. Eventually, the island sank under the sea (from more sea-floor spreading) and all that was left was the coral atoll, with a shallow lagoon in the middle. Thank you, Charles Darwin, for a brilliant piece of geoscience reasoning.

Real World Examples: Palmyra Atoll is a circular string of 54 small, heavily vegetated islets in the Pacific Ocean formed by the growth of coral on the rim of a submerged volcano. Palmyra is the last intact marine wilderness in the U.S. tropics. It is uninhabited by humans and remains largely unaltered by human settlement or use of nearby areas. The pristine waters around the Atoll harbor feature five times as many coral species as the Florida Keys and its shores offer one of the few nesting areas for seabirds within 450,000 square miles. The Nature Conservancy bought the Atoll to preserve Palmyra’s biological diversity. In January 2001, the U.S. Fish and Wildlife Service extended further protection when it designated the coral reef habitat surrounding Palmyra Atoll as a National Wildlife Refuge. In terms of physical dimensions, the world’s largest atolls are found in the Maldive Islands, a string of 1,196 islands with 26 distinct coral atolls in the Indian Ocean.

More Real World Examples: Much closer to home and far less expensive to reach than any of the south Pacific hot spots, Lighthouse Reef off the shores of Belize is largely uninhabited and, with over 40 world-class dive sites, magnificent coral reefs, and over 200 species of fish, constitutes one of the premiere destinations in the Caribbean for those determined to explore undersea treasures. Approximately 55 miles east of Belize City, the atoll is 28 miles long and ranges from two to six miles in width. Six small islands make up the Reef, which has an underwater marine trail and a number of marine parks, including the world famous Blue Hole popularized by Jacques Cousteau, and the Halfmoon Caye National Monument, The Blue Hole, which is located near the center of the atoll, was originally a cave whose roof collapsed about 10,000 years ago as the land receded into the sea. An almost a perfectly circular structure, the Blue Hole is 1,000 feet in diameter and about 400 feet deep. Don’t worry about getting bored since Lighthouse Reef is not the only great diving opportunity; the reefs of Belize have long been known as the richest in the Caribbean. So if you visit, be prepared to see many wonderful things that you can’t even imagine in Peoria.

Author’s Rant: Here’s another, not so fun example of real life kicking powerless people in the teeth. The native people of Bikini Atoll, Enewetak Atoll, Uterik Atoll, and Rongelap Atoll in the Marshall Islands were displaced after WWII by the American government so their islands could be used for 67 nuclear and hydrogen bomb tests, with a total yield of 108,496 kilotons; those tests were conducted from 1946 to 1958. Many of the native peoples were exposed to high levels of radiation by the nuclear blasts. As a horrific example, the Bravo Test in February 1954 was at that time the single most powerful hydrogen bomb (15 megatons) ever detonated by the United States. It vaporized four small islands and scattered radioactive debris over nearly 50,000 square miles, including many inhabited islands. The total megatonnage was equal to exploding slightly more than 1.5 Hiroshima-size atomic bombs each day for twelve years. In January 2005, the Bush Administration unilaterally decided to discontinue providing medical tests for the Marshall Islanders to determine their radiation and health levels. Those medical tests had been mandated in 1980 by the U.S. Congress. If that’s how America treats poor, powerless people like the Marshall Islanders and that doesn’t make your blood boil I don’t know what will. Another Author’s Note: The word atoll comes from the Dhivehi word, atolu. Dhivehi is the Indo-Aryan language of the Maldive Islands. The first recorded use of the word in English was in 1625.