Glover's Atoll Earthcache EarthCache

What is an Atoll?

Atolls are islands of coral reef that encircle a lagoon partially or completely. They are circular, oval or horseshoe in shape, and the central lagoon is shallow. The small islands of coral reef are broken by channels that lead from the sea into the central lagoon. Viewed from above, it looks like a flat ring of sandy land with a shallow pool (you can see the color of the water change) in the center.

Atoll Formation

Charles Darwin was one of the first people to think about how coral atolls were formed and his “subsidence theory of coral reef formation” has received empirical support. In 1842, based on his observations of atolls in the South Pacific, Darwin concluded that these unique land creations were a result of two factors that occurred simultaneously – coral reef growth and the gradual sinking of an oceanic island.

The process of atoll formation takes as long as 30 million years. An atoll is thought to begin as living corals colonize and build a fringing reef around the flanks of a seamount or volcano. Over hundreds of thousands of years, as the volcano cools and becomes denser, it gradually sinks below the sea surface. The corals, whose symbiotic algae require light to grow, continue to build the reef upward towards the sea surface, maintaining the top of the reef in the photic zone. New corals grow on top of older or dead ones, and the process continues as the volcanic island begins to sink. Over time, the reef gradually becomes separated from the subsiding island by a lagoon, thus forming a barrier reef. Eventually the cold volcano sinks so far that it disappears beneath the surface, leaving behind the characteristic ring-shaped reef surrounding a central shallow lagoon. Eventually, due to wind and wave erosion, corals break into pieces and become sandy, creating a land surface called a caye (pronounced “key”).

Thus, atolls are built on thick layers of dead coral reefs. Scientists have drilled over 1400 m through coral limestone before striking volcanic rock on Pacific atolls, supporting Darwin's hypothesis that atolls develop as fringing reefs subside.

Location Background

Located off the coast of Belize, the Mesoamerican Barrier Reef is the largest coral reef system in the Western Hemisphere. Situated at the southern most end of the Belize Barrier reef approximately 28 miles offshore is Glover’s Reef Atoll, named after pirate brothers, John and Rodger Glover, in the1750's. It is an oval-shaped atoll measuring approximately 20 miles long and 7 miles wide.

At a glance, Glovers Reef is composed of a deep lagoon studded with about 850 patch reefs and pinnacles rising to the surface, six sand cays located on the reef crest along the southern edge, and a peripheral reef broken in three places by deep channels. Glovers Reef has three main habitats; the lagoon floor, the peripheral reefs and the patch reefs, and is recognized as the most biologically developed atoll within the Belize Barrier Reef.

The posted coordinates take you to the Glover’s Reef Marine Reserve. There is a dock at the coordinates, and visitors are welcome during daylight hours.

To Log this Earthcache you need to complete the following tasks:

• Take a photo of yourself holding your GPS at the coordinates with the sign in the background. Post your photo with your log.
• Send me an e-mail with the answers to the following questions:
  (1). On your way to the coordinates, observe the conditions as you come through the coral wall into the lagoon. Estimate the width of the coral wall above sea level, and the depth of the lagoon as you cross over from the open sea.
  (2). At the coordinates, observe the ground below you. Describe the materials you find in the sand here (color, consistency, identifiable items within it).