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| Titel |
A coral-rubble ridge as evidence for hurricane overwash, Anegada (British Virgin Islands) |
| VerfasserIn |
M. Spiske, R. B. Halley |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7340
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| Digitales Dokument |
URL |
| Erschienen |
In: Caribbean Waves 2 Conference ; Nr. 38 (2014-01-28), S.9-20 |
| Datensatznummer |
250121293
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| Publikation (Nr.) |
 copernicus.org/adgeo-38-9-2014.pdf |
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| Zusammenfassung |
A coral-rubble ridge fringes part of the north shore of Anegada, a low-lying
island in the northern Caribbean. Both historical reports and the geological
record underline its vulnerability to tsunami and hurricanes. In this study
we document the sedimentary characteristics of a coral-rubble ridge, which
extends discontinuously along 1.5–1.8 km of chiefly north-facing
shores at Soldier Wash. The ridge is less distinctive and appears only in
patches along the west-facing shoreline at Windless Bight, where the wave
regime is calmer. It is located ca. 8 m from the fair-weather shore,
has a maximum width of 15 m and a maximum thickness of 0.8 m.
The lower seaward-facing slope of the ridge is relatively flat, probably due
to successive reworking, whereas the upper seaward slope is steep and partly
displays avalanching faces. The landward flank is gently sloping and
terminates abruptly. The ridge is mainly composed of well-rounded, encrusted
and bored coral rubble (average diameter of 16 cm) that has been
reworked in the shallow marine environment prior to transport. Only a few
pieces of angular beach rock and karstified Pleistocene limestone are
incorporated. The components build a clast-supported framework. No sand is
present in the interstices. Imbrication of flat clasts indicates a deposition
during landward bed load transport. The ridge morphology, composition and
related hydrodynamic conditions during its emplacement are typical for
coral-rubble ridges deposited by hurricane-induced storm surges. In
comparison, nearby evidence for tsunami inundation is very different because
the tsunami-transported coral boulders on Anegada are much bigger
(2 m) than the biggest components in the ridge, they are deposited
much farther inland (up to 1.5 km), and the corals seem to have been
freshly broken out of the reef by the tsunami.
The age of the ridge is difficult to estimate. The dark grey surface of the
ridge is caused by bioweathering by endolithic organisms that takes tens of
years and may give a very rough estimate of the minimum age of the ridge.
Storms and related surges that built the ridge were likely stronger than 2010
hurricane Earl, which attained category 4 north of the island. Earl was able
to slightly rework the lower seaward part of the ridge, but transported only
few and smaller pieces of coral rubble and sand onshore. Therefore, the
coral-rubble ridge found at the north shore of Anegada may imply that the
island is vulnerable to hurricane-induced surges of greater impact (in
relation to storm path and intensity) compared with the any of the recently
documented storms which were only able to rework the ridge. |
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