A pseudo-atoll, like an
atoll
An atoll () is a ring-shaped island, including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical oceans and seas where corals can gro ...
, is an
island
An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An isla ...
that encircles a
lagoon
A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into '' coastal lagoons'' (or ''barrier lagoons ...
, either partially or completely. A pseudo-atoll differs from an atoll as established by several authorities, such as how it is formed (not by
subsidence
Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...
, nor by
coral
Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and se ...
). It is considered a preferable term to "near-atoll". There is a need for rigorous definition of "pseudo-atoll" before it can be accepted as a general term.
Definitions
Alexander Agassiz gave the term pseudo-atoll to "any ring-shaped
reef
A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes—deposition of sand, wave erosion planing down rock ...
s not formed as a result of
subsidence
Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...
".
while
Norman D. Newell and J. Keith Rigby called such reefs non-coral. and "We conclude that almost-atoll should be retained as a descriptive term as defined by Davis and Tayama, and that the use of "near-atoll" as a synonym be abandoned. The value of terms such as "semi-atoll" and "pseudo-atoll" needs close examination and more rigorous definition before being generally accepted." H. Mergner yet states that micro-atolls classify as pseudo-atolls. Professor David R. Stoddart of
Berkeley states an "almost-atoll" is an atoll with a central island of left over residue.
Usage
Dr. Edward J. Petuch, author of ''Cenozoic seas: the view from eastern North America'', refers to pseudo-atolls as pseudoatolls with the
Everglades Pseudoatoll as an example.
[Petuch, Edward J., Cenozoic Seas: The View From Eastern North America, CRC Press; 1 edition (December 29, 2003), .]
See also
*
Coral reef
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of Colony (biology), colonies of coral polyp (zoology), polyps held together by calcium carbonate. Most coral reefs are built from stony corals, wh ...
*
Depression (geology)
In geology, a depression is a landform sunken or depressed below the surrounding area. Depressions form by various mechanisms.
Types
Erosion-related:
* Blowout: a depression created by wind erosion typically in either a partially vegetated sa ...
References
Further reading
David R. Stottart, Department of Geography, University of California-Berkeley
*B. V. Preobrazhenskiĭ, B. V., Contemporary reefs; CRC Press; 1 edition, 1993, .
Pseudo-atoll
Coastal and oceanic landforms
Islands
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