Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by Tiffany Scofield
are three kinds of coral reefs found in the world. There are fringe reefs, a
barrier reefs and atolls. All three are from different ages of a volcano. Atolls
form when the volcano cannot keep up with the rising water level and it is worn
away by the tides. The water rises over the volcano and coral creating a ring of
There are atolls scattered throughout tropical waters in the Atlantic and Pacific Oceans. Kwajalein Atoll in the Marshall Islands is the biggest atoll in the world. Its lagoon area, in the middle of the islands, has an area of over 2,173 squared kilometers and ranks number one is both lagoon and land area size. It has 93 islands throughout the whole chain. The islands are built on top of the coral. When you look down on a atoll you can see the ring of coral but then islands is where sand has built on top of the coral creating islands. The sand is a mixture of broken fragments of quarts, coral, and shell.
Coral reefs are fragile structures that hold many arrays of life. Little organisms, polyps, attach to rocks and as they die they leave behind a limestone skeleton creating corals. The polyps pull is the calcium and carbonate ions out of the water so most coral is made of Aragonite or Calcite. Even though the coral is hard, it is alive. There are also soft corals. Soft corals are not sharp like the hard coral but still rough like leather. They create fan like shapes because of the polyps. The coral is very sensitive, by touching it, or changing water temperature, can interrupt the growth of the coral. Corals work along with certain algae. Corals produce a waste that the algae use and as they under go photosynthesis, it produces energy for the corals.
Courtesy of Jane Erekson
The coral reefs hold a home to many unique sea creatures. Most of the creatures live in the ocean. There are diverse species of plants and animals. Some species can be unique to each atoll. There is a wide array of fish, sharks, turtles, rays, dolphins, and crustaceans. These animals can live either in the lagoon or the out reef of the atolls. The animals are supported off the coral. Fish are found the most in coral reefs. They use the coral for food, protection and resting. The animals live together working from each other to create an ecosystem. Small animals like fish and shrimp will clean or feed off of larger animals like sharks. Then larger animals like sharks and dolphins will eat small fishes and crustaceans. Under the water is a new world. Coral reefs are always changing and adapting. They are perfect to explore scuba diving and snorkeling.
Atolls in History:
One of the worst
recorded nuclear bombs set off by the United States was in the Bikini Atoll. The
over all explosion was 1,000 times more times bigger than either of the bombs
set off in Hiroshima during World War II. The Bikini inhabitations were moved
“temporarily” from the atoll to uninhabited Rongerik Atoll and the United States
prepared for testing beginning with Operation Crossroads. The navy moved in
boats planes and testing equipment to the atoll to start testing. The first two
bombs set off were about the size of the bombs set off in Japan. On March 1,
1954, the bomb, Castle Bravo, was dropped expected to yield about five megatons
but yielded 15 megatons. The bomb left a mile crater on the island dropped and
vaporized everything on three total islands. The mushroom in a minute after the
explosion was over 47,000 feet tall by 7 miles wide and 10 minutes later reached
130,000 feet tall by 62 miles. The mushroom cloud could be seen from the
Kwajalein Atoll 250 miles away. After the explosion, scientists found a
flourishing coral community. They dived down into Bravo creator finding many
species of corals but the bomb had killed many of the species that had lived
Marshall Islands Atolls:
During World War II, the Japanese had hold of many atolls
in the Pacific Ocean. After the Japanese bombed Pearl Harbor, they brought the
United States into the war in the pacific. Many battles raged through the
Marshall Islands. The biggest battle was on Kwajalein Atoll, the center of the
Japanese hold. Fighting started January 31, 1944 and went to February 4, 1944. 8,400 Japanese died in the fight, mostly suicide bombers and about 500 Americans
died. During the last yea of the war holds half of the causalities during the
war in the Pacific. The Americans tried new tactics during the battle that
worked great and were continued to be used during the war. The wreckage was
cleaned up on the island but still remains in the lagoon. Kwajalein and Roi-Namur
islands are great to visit to learn about the battles. In 1942 Japan was
defeated in Midway Atoll.
Mururoa and Fangataufa Atolls:
Mururoa and Fangtataufa Atolls have also been used for nuclear testing. These two atolls are in French Indonesia, which is located between Australia and South America. The French started doing testing on the two atolls in 1966. They used the atolls to test nuclear weapons and safety tests on nuclear weapons. There was little fallout from the bombs but later, they did the testing in the shafts that were under the islands and ocean. After almost 200 nuclear tests, the atolls were tested for nuclear waste. Plutonium and cesium 137 had leaked into the water and soil because the shafts were not completely sealed off due to the carelessness of the scientists. Instead of removing the waste, the buried and covered it, leaving it in the atolls. The marine life is counted very low due to the high levels of waste in the water. Also people living in French Indonesia are becoming sick.
Coral reefs are a fragile but elegant ecosystem. We need to learn to care for them or we will ruin species of plants and animals we can find no place else.