Late Holocene dune formation on the Sefton coast, northwest England

Abstract

Abstract Coastal dunes fringe the coast between Southport and Liverpool in northwest England, forming a natural barrier which prevents marine flooding of low-lying agricultural land in West Lancashire and north Merseyside. The dunes are best developed at Formby Point, where they reach 25 m above sea-level and blown sand extends some 4 km inland. This paper presents the results of an initial programme of field drilling, sediment analysis and radiocarbon dating which suggest that the dune complex developed from a large offshore sandbank, which was in existence by 6800 years ago. Behind the bank lay a large area of intertidal mudflats and sandflats with fringing saltmarsh. Dunes may have first become established on the emergent sand bank around 6000 years ago, but the oldest dunes for which there is direct dating evidence formed between 5700 and 5800 years ago. A period of dune stability, possibly associated with seaward progradation of beach and foredune ridges, appears to have occurred between 2500 years ago and the early Middle Ages. During the earlier part of this period oak and alder woodland covered the dunes and the sands were deeply podsolized. Historical and documentary evidence indicates that extensive sandblowing occurred all along the coast during the early Middle Ages, which was a period of exceptional storminess and rapid coastal erosion. Several settlements and farms were lost to the sea or were overwhelmed by blown sand as the coast eroded. Active sand tongues extended across the full width of the barrier and buried the backbarrier peats and silts along the western margin of Downholland Moss. Dune instability has continued intermittently until the present, although on a smaller scale, and consequently most of the present dune forms are relatively recent. Sand stabilization and foreshore reclamation measures undertaken in the second half of the nineteenth century were highly effective and contributed to a net seaward progradation of the entire Formby coastline between 1850 and 1900. Abandonment of these measures around the time of the First World War contributed to, but did not ultimately cause, a return to shoreline erosion and a new phase of frontal dune instability which is still in progress.