The structure and development of foredunes on a locally prograding coast: insights from ground‐penetrating radar surveys, Norfolk, UK

Abstract

The internal structure of coastal foredunes from three sites along the north Norfolk coast has been investigated using ground‐penetrating radar (GPR), which provides a unique insight into the internal structure of these dunes that cannot be achieved by any other non‐destructive or geophysical technique. Combining geomorphological and geophysical investigations into the structure and morphology of these coastal foredunes has enabled a more accurate determination of their development and evolution. The radar profiles show the internal structures, which include foreslope accretion, trough cut and fill, roll‐over and beach deposits. Foredune ridges contain large sets of low‐angle cross‐stratification from dune foreslope accretion with trough‐shaped structures from cut and fill on the crest and rearslope. Foreslope accretion indicates sand supply from the beach to the foreslope, while troughs on the dune crest and rearslope are attributed to reworking by offshore winds. Bounding surfaces between dunes are clearly resolved and reveal the relative chronology of dune emplacement. Radar sequence boundaries within dunes have been traced below the water‐table passing into beach erosion surfaces. These are believed to result from storm activity, which erodes the upper beach and dunes. In one example, at Brancaster, a dune scarp and erosion surface may be correlated with erosion in the 1950s, possibly the 1953 storm. Results suggest that dune ridge development is intimately linked to changes in the shoreline, with dune development associated with coastal progradation while dunes are eroded during storms and, where beaches are eroding, a stable coast provides more time for dune development, resulting in higher foredune ridges. A model for coastal dune evolution is presented, which illustrates stages of dune development in response to beach evolution and sand supply. In contrast to many other coastal dune fields where the prevailing wind is onshore, on the north Norfolk coast, the prevailing wind is directed along the coast and offshore, which reduces the landward migration of sand dunes.

The origin of centennial- to millennial-scale chronological gaps in storm emplaced beach ridge plains

“…Similar curvilinear ridge morphologies elsewhere have been suggested to develop through swash processes (e.g. Bristow et al, 2000;Curray et al, 1969;Donoghue et al, 1998;Missimer, 1973;Stapor et al, 1991;Tanner and Stapor, 1971). Coastal plains with some recurved ridges have been ascribed an aeolian origin elsewhere (eg Thom and Hall, 1991) but these could have developed from an aeolian capping of a wave deposited recurved berm.…”

Geomorfologia e arquitetura deposicional de uma planície de cordões litorâneos na margem NE da Lagoa dos Quadros, RS, Brasil

“…Ainda na costa do Rio de Janeiro, radarfácies semelhantes foram descritas por Moulton et al (2013), num estudo sobre a gê-nese e morfologia de dunas frontais. Cabe ressaltar trabalhos precursores de GPR associados à fácies eólicas, como Bristow et al (2000aBristow et al ( , 2000b.…”

Faciologia E Evolução Dos Depósitos Eólicos Costeiros Do Oeste Do Ceará (Brasil) No Holoceno Tardio

“…No desenvolvimento das dunas frontais, a totalidade dos processos erosivos e deposicionais imprimem conjuntos distintivos de estratifi cações cruzadas de alto ângulo que podem ser acopladas ao estágio de evolução da duna frontal (BRISTOW et al, 2000).…”

“…Características como estratificações cruzadas de baixo ângulo (<15º), preservação de estratifi cações dorsais (backset), com mergulho para o mar e de topo de duna (topset), além da escassez de feições de avalanche são feições comumente encontradas em dunas desse tipo (HUNTER, 1977;HESP 1983HESP ,1988HESP , 2002BRISTOW, et al, 2000;GIANNINI, 2007). O conjunto dessas estruturas, associadas a rizólitos da fácies AMr, sugere um contexto semelhante ao de dunas frontais intensamente vegetadas como principal elemento morfológico associado à deposição das fácies AMb e AMr.…”