Sandy Spits Research Articles

Late Holocene diatom biostratigraphy and sea-level changes in the southeastern Beaufort Sea

Late Holocene sediments from the Atkinson Point area were analysed to provide quantitative reconstructions of recent sea-level changes in the southeastern Beaufort Sea. The succession of diatom assemblages in five cores revealed paleoenvironmental changes induced by the transgression of the Beaufort Sea during successive periods of lacustrine conditions, breaching and flooding of thermokarst lakes by the sea, and the landward migration of sandy spits. Based on radiocarbon dates and quantitative paleodepth determinations, a relative sea-level curve for the late Holocene has been developed. Despite a loss of temporal precision due to old carbon contamination, an envelope of sea-level change has been defined for the last 2 ka BP, suggesting a sea-level rise in the order of 1.1 mm a-1 for the last millennium. This paper presents the first sea-level reconstruction inferred from a diatom-based transfer function. It represents an improvement over traditional methods which were limited to qualitative estimates of past sea levels.

Coastal evolution in Senegal and Mauritania at 103, 102 and 101-year scales: Natural and human records

Previous works have shown that the range of marine level eustatic changes on the coast of the Senegalo-Mauritanian basin after 5500 BP must have been relatively small. On the basis of regional geological mapping this position is confirmed in two littoral regions in Mauritania (Baie de Saint Jean, Cape Timiris) and in Senegal (Saloum Delta). The evolution of the shoreline is linked mainly to the balance between deposition and reworking by the sea. In Mauritania, the reworking capacity is high before 4000 BP, under a more humid climate than the present one. It becomes insufficient around 3000 BP, as areas of aeolo-marine progradation develop in the sebkhas at the inner part and the shorelines of the Baie de Saint Jean. The deposits are subjected to a constant sea level and are therefore formed by the rhythm of recurrent aridity crises on the millenary or the centenary scale. In the Saloum delta, the evolution of the shoreline results from several processes involving more varied timescales. An essential factor is the positioning of littoral sand barriers, shaped like long sandy spits which divert the flow of the river towards the South and are arranged according to a basal surface also adjusted to a constant sea level. The development of sand barriers, such as the present Sangomar spit and also the Langue de Barbarie, occurs at a centennial rhythm. Higher probability events (at the decade scale) are likely to perturb this development by inducing gaps in the sand barrier and, as the river goes beyond the sand barrier, the latter becomes incorporated in the deltaic plain, forcing the littoral drift to build a new sand barrier further forward. These events are linked to a conjunction of factors involving different timescales: aridity crises at the 10 3 or 10 2 -year scales, sedimentation waves at the 10-year scale, seasonal exceptional swells, river floods, variations of the tidal range determined by modifications in the estuarian morphology.

The geomorphological basis of beach resort sites— Some Malaysian examples

The erosion problem faced by many beach resorts can often be attributed to the omission or inadequate consideration of the coastal geomorphology of the resort sites. This paper evaluates, on a geomorphological basis, the existing and potential beach resort sites on the east coast of Peninsular Malaysia. The evaluation of the aspects of the coastal environment relevant to the resort sites include the beach, backshore, nearshore zone, hinterland, vegetation, rivers and monsoons. Several types of beach resort sites can be identified: zetaform bays with a protected upcoast curve in the lee of a headland; non-zetaform bays which are usually small; barrier beaches which are straight and exposed; low linear coasts; sandy spits; and estuaries. This typology can be used as a guide for future resort development.

GEOMORPHOLOGY OF THE SOUTHERN COAST OF ALASKA

The shoreline of southern Alaska is a narrow coastal plain dominated by large glaciers, periodic earthquake activity, and strong extratropical cyclones. Studies on the coastal geomorphology and sediments carried out in 1969-71 and in the summer of 1975 were directed at defining geological hazards with respect to developing shore facilities for OCS oil exploration activities. Most of the shoreline was found to undergo rapid changes and experience a variety of serious environmental hazards. The safest potential port areas are located inside Icy Bay and Yakutat Bay. The coastal areas in the vicinity of the Malaspina Glacier and the Copper River delta are examples of the two principal shoreline types (glacial outwash plain and deltaic). The coastal area surrounding the Malaspina Glacier, the largest piedmont glacier in the world, was classified into 5 categories on the basis of its geomorphology, sediments, and local glacial history: 1. Regional retreating coast: This area, which is located at the mouth of Icy Bay, is eroding rapidly (approximately 1.5 km since 1900) as a result of retreat of a glacier (up the bay) a distance of over 40 km since 1900. Consequently, it should not be developed. 2. Prograding spits: Sandy spits that have built into either side of Icy Bay since the retreat of the glacier are also unstable because of the general recession of the shoreline as a result of erosion at the mouth of the bay. 3. Abandoned glacial coasts: These areas, located on the inner eastern shores of Icy Bay and Yakutat Bay, are coastlines of relatively low wave energy composed of. abandoned glacial tills, kame terraces, and outwash sediments. These are the most stable and least hazardous areas on the southern Alaska coast. 4. Actively eroding glacial margins: This area, located at Sitkagi Bluffs on the southernmost terminus of the Malaspina Glacier, is an eroding scarp of glacial till jutting into the Gulf of Alaska. 5. Glacial outwash coasts: These shorelines are highly variable and are usually dominated by prograding spits composed of sand and gravel.