Origin of barrier islands on sandy coasts
- Florida State Univ., Tallahassee (USA)
Many barrier islands on the coasts of the Gulf of Mexico contain one or more nuclei; island growth has taken place more or less seaward from these nuclei, which are the oldest parts of the islands. The nuclei were, at one time, separate islands; the oldest beach ridges wrap around them on two or three sides, showing that they were not remnants of spits or earlier larger features. The nuclei grew larger with time because of a local equilibrium of abundance of sand, rather than a regime of erosion. The younger growth areas are commonly marked by sequences, or sets, of beach ridges; such features are not visible in the nuclei. The question of the origin of many barrier islands on sandy coasts must be closely related to the question of the origin of the nuclei. But the nuclei appear to have no distinguishing marks that in themselves might help explain their origin. Johnson Shoal (Lee County, on the lower west coast of the Florida peninsula) may provide some insight into the origin of nuclei. It appeared for the first time, more recently than 1853, in water 2-6 m deep, and has been migrating landward (eastward) ever since. Seven maps and charts from various dates and many sets of black-and-white aerial photographs have been used to produce a history of shoal migration. By December 1988, welding of the remnants of the shoal onto the shore of Cayo Costa island was already under way. The migrating shoal contained more than 10 million m{sup 3} of sand (13 million yd{sup 3}), with a mass of 10 trillion kg. Known nuclei on other islands are commonly about this size, or smaller. The moving shoal did not develop from dredge spoil (there has been no dredging of this magnitude in the area), a spit, a drowned dune, or a fault. It must have been a natural nontectonic event: emergence of a shoal since 1853 without notable changes in sea level or wave climate. Perhaps such events, common a few thousand years ago, account for barrier island nuclei.
- OSTI ID:
- 5920189
- Report Number(s):
- CONF-9010204-; CODEN: AABUD
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 74:9; Conference: Gulf Coast Association of Geological Societies and Gulf Coast Section of SEPM (Society of Economics, Paleontologists, and Mineralogist) meeting, Lafayette, LA (USA), 17-19 Oct 1990; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COASTAL REGIONS
GEOMORPHOLOGY
ISLANDS
ORIGIN
DREDGING
EROSION
FLORIDA
GEOLOGIC FAULTS
GULF OF MEXICO
MAPS
MIGRATION
SAND
SEA LEVEL
TECTONICS
ATLANTIC OCEAN
CARIBBEAN SEA
FEDERAL REGION IV
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOLOGY
LEVELS
NORTH AMERICA
SEAS
SURFACE WATERS
USA
580000* - Geosciences