ESCR - Portstewart Strand Sand Dunes

Earth Science Conservation Review

Summary Full report
Portstewart Strand Sand Dunes	Londonderry

Site number:	1139
ESCC:	IS
Locality Type:	Coastal section	Status:	ASSI
Grid Reference:	C805365 Centroid
Google maps:	55.16954,-6.73672
County:	Londonderry	Council area:	Causeway Coast & Glens Borough Council
Period:	Quaternary
Stages:	Holocene

Site Description
Highlights:
The sand dunes at Portstewart border the northern side of the River Bann estuary and are part of the same, single physiographic unit (i.e beach, dunes and river mouth), as the dunes at Castlerock and Grangemore, and have evolved within the last 6,000 years. The dunes are based on a ridge of raised beach gravels that developed at the river mouth as relative sea level began to fall away from its Holocene maximum. Within the beach gravels are shells of locally extinct marine mollusca and ventifacts (stones abraded by wind-blown sand). The dunes contain occupation surfaces/buried soils and artifacts of earlier cultural phases; together these indicate periods of landsurface stability and human activity during the course of dune development. Evidence for barrier overwash, in the form of fine gravel and fragmented marine shell, occurs between some of the dunes. On the higher ground east of Portstewart Strand, low-relief aeolian sands extend beneath the golf course and neighbouring residential area. These sands overlie glacial drift containing a buried soil. The sands were deposited in two phases between which a podzol developed in the lower sand unit. Thus, the Portstewart dunes contain a valuable and varied record of coastal changes since the mid-Holocene.
Introduction:
The Portstewart dunes are located on the north coast of Co. Londonderry and form the northern boundary of the estuary of the River Bann. They cover an area of c. 1.5km2 and extend for almost 3km from Strandhead in the east to Ballyaghran Point in the west. In the east the dune belt is c. 1km in width but tapers to less than 0.5km in width in the west. The highest dunes are found in the eastern half of the system where they rise to c. 30m O.D. Management of the dunes is undertaken currently by the National Trust and Portstewart Golf Club. As with the dunes at Castlerock and Grangemore, the Portstewart dunes attracted considerable attention during the late nineteenth century when antiquarian collectors reported numerous finds of worked flints, hearth stones, bones, shells and pottery (Gray, 1879; Knowles, 1887, 1891; Hass‚, 1890). Finds have continued to be reported during the present century (Coffey & Praeger, 1904; Hewson, 1934; May & Batty, 1948) and embrace cultures spanning the Neolithic to Medieval periods. The existence of a ridge of raised beach gravels beneath the dunes was noted by Symes et al. (1888) and Coffey & Praeger (1904). The discovery of shells of locally extinct species of marine mollusca associated with the gravels was reported by Fisher (1935). More recently, Carter & Wilson (1990) and Wilson & McKenna (1996) outlined a sequence of stages in the evolution of the Bann estuary and associated the beach gravels with the maximum relative height of the Holocene transgression. Wilson (1991a) described basalt ventifacts from the beach gravels and Wilson & McKenna (1996) provided radiocarbon dated evidence for barrier overwash within the last millennium. From the higher ground to the east of Portstewart Strand, Wilson (1991b) identified buried soils beneath and within low-relief aeolian sands and reported radiocarbon dates on the soil organic matter.
Description:
Many of the exposures from which the evolution of the Portstewart dune system has been inferred no longer exist because of dune landscaping and/or redevelopment of the adjacent residential area. These activities have obscured the sites from which archaeological materials were recovered and the section described by Wilson (1991b) at the site of the former Strand Hotel. The raised beach gravels that underlie the dune system (Symes et al., 1888; Coffey & Praeger, 1904) may still be seen at several places between the dunes. They consist of well-rounded basalt and flint clasts, with the former lithology predominant. The elevation of these gravels ranges from +4.4m O.D. in the east to +1.4m O.D. in the west (Wilcock, 1976). One hundred and thirteen species of marine mollusca were recorded in association with the gravels (Fisher, 1935) including Scrobicularia plana, a species now extinct in north-eastern Ireland, and Paphia decussata, which is extremely rare. Also present within the gravels are basalt ventifacts (stones abraded by wind blown sand). Wilson (1991a) described eight ventifacts from two sites between the dunes; all had one or two well developed facets separated by a sharp and prominent ridge. Sites of archaeological interest, although no longer exposed, have provided some stratigraphical information pertinent to dune evolution and chronology. Many of the reports that document archaeological materials failed to present details of site stratigraphy (e.g. Gray, 1879; Knowles, 1887, 1889; Hass‚, 1890; Hewson, 1934) but Coffey & Praeger (1904) and May & Batty (1948) recorded the existence of two distinctive 'black bands' (occupation surfaces/buried soils) containing Neolithic/Bronze Age and Iron Age artifacts respectively. In at least one inter-dune depression at Portstewart a surface scatter of fragmented marine shell and small pebbles occurs. A radiocarbon date of 1,050+/-80 years BP (Beta-36942) from fragments of Arctica islandica picked from these materials is reported by Wilson & McKenna (1996). Present dune morphology is that of a narrow, shore parallel foredune ridge that gives way to large established transverse ridges (at right angles to the shore). These latter dunes comprise loose, granular, windward faces, with well-vegetated lee slopes. Sections in the dunes reveal a preponderance of low-angle concave bedding, interrupted in places by steeper avalanche structures. The dunes have been dissected by wind erosion (exacerbated by human damage), creating a range of blowout forms including 'saucers' (low relief hollows), 'basins' (deep, enclosed hollows), and 'corridors' (longitudinal, canyon-like features). In one or two places blowouts are 'stacked' on top of each other. Except in the active blowouts the dunes are well- vegetated, notably with Elymus farctus, Ammophilia arenaria, Festuca rubra and F. ovina. The invasive shrub Hippophae rhamnoides was introduced in the 1930s for erosion control and to reduce access and has spread extensively throughout the dunes. In 1989-90 structural alterations at the Strand Hotel created a 2m thick exposure in the sands that cover the higher ground to the east of Portstewart Strand. The most striking feature of this exposure was a buried podzolised sand unit 1.4m thick. This was underlain by a basalt-rich sandy loam (glacial drift), which also contained a buried soil, and was overlain by sand and made ground. Two radiocarbon dates were obtained from these buried soils by Wilson (1991b). The organic-rich horizon of the buried soil in the basalt-rich sandy loam produced an age estimate of 4,780+/-45 years BP (SRR-3766) while the organic-rich horizon of the buried podzol gave an age estimate of 525+/-45 years BP (SRR-3765).
Importance:
The Portstewart dune system is of international (European) importance as it contains a variety of evidence for coastal changes over the period since the mid-Holocene transgression and is one of the few dune systems from which such varied evidence has been collected. The ventifacts are the first to be recorded from coastal dunes in Ireland and are thus of international (Irish) importance. International (European) significance can also be accorded to the buried podzolic soil at the Strand Hotel site, as this offers the opportunity for detailed assessment of soil development processes in temperate aeolian sand deposits. As part of the single physiographic unit (beach, dunes and river mouth) at the estuary of the longest river in Northern Ireland, the dune system is of national importance to an understanding of land-ocean interactions during the Holocene.
Interpretation:
The raised beach gravels that underlie the Portstewart sand dunes are considered to represent a gravel beach that formed in association with the maximum relative height of the Holocene marine transgression c. 6,000-5,500 years BP. The gravels most probably derive from glacial debris deposited on the continental shelf that was reworked by the rising sea, causing the coarser components to be moved onshore. Species of marine mollusca recorded in the gravels by Fisher (1935) comprise both littoral species and those found living in deeper water. Their intimate association is suggestive of the reworking of certain species from the mid-Holocene estuarine clays (e.g Scorbicularia and Paphia) that probably underlie the gravels but are nowhere exposed. Wilson (1991a) argued that the basalt ventifacts were probably fashioned as aeolian sand began to accumulate on the beach gravels. An earlier (Pleistocene) age for the ventifacts was thought unlikely as marine transport would have dulled the sharp ridges between the facets. Ventifact formation requires sufficient wind-blown sand to abrade facets but not enough for the clasts to be buried by accumulating sand. The ventifacts were found in large inter-dune depressions that may have functioned as sand transport corridors throughout much of the late Holocene. Distinct 'black bands' or occupation surfaces within the dunes, as recorded by Coffey & Praeger (1904) and May & Batty (1948) indicate stability phases during dune construction. These phases, dated by the artifacts recovered from the surfaces, occurred apparently in the late Neolithic/Bronze Age and again in the Iron Age and demonstrate that the dunes are composite landforms constructed to their present form over several millennia. Fragments of Arctica islandica dated to 1,050+/-80 years BP (Beta-36942) (Wilson & McKenna, 1996) were probably deposited by barrier overwash during periods of temporary supra-elevated water levels associated with storm conditions. The depression, in which these materials are found, has since been closed at its seaward end by development of shore-parallel dunes. Radiocarbon dates from the aeolian sands at the Strand Hotel site do not support the views expressed by Wilcock (1976) and Wilson & Manning (1978) that these sands are of mid-Holocene age and related to a higher stand of sea level. The maximum relative height of the Holocene transgression is now believed to have occurred c. 6,000-5,500 years BP, some 700-1,200 years before sand was first deposited at the Strand Hotel. The later phase of sand deposition is constrained by radiocarbon dating to the Middle Ages - a period of well-documented climatic deterioration and increased storminess, and it is tempting to suggest this as the cause of sand accumulation. The radiocarbon dates also indicate that a long period of landsurface stability prevailed at the site (c. 4,300 years) during which the podzol developed, while elsewhere along the coast of Northern Ireland sand accumulated on several occasions during this period (Wilson, 1990).
Conclusions:
The Portstewart sand dunes contain evidence relating to a variety of coastal changes at the estuary of the River Bann over the last 6,000 years. The raised beach gravels with their extinct marine mollusca record a sea level higher than at present and the ventifacts are testimony to strong winds and a sufficiency of fine, abrasive sediment moving across the gravels. The dunes possess a record of human activities extending back to the Neolithic period and in some inter-dune depressions shell and gravel debris represents barrier overwash prior to development of the foredune ridges. Aeolian sands that cover the higher ground east of the strand, buried a pre-existing soil developed in glacial drift and accumulated in at least two phases, between which a thick podzolic soil formed.
Notes:
A significant proportion of the scientific interest and value claimed for the Portstewart dunes is based on work undertaken and observations made between 1880 and 1950 and many of the sites, sections and materials described have not been available for re-inspection and/or re-interpretation in the light of more recent scientific knowledge. To remedy this a series of cores and/or excavations are required in selected areas of the dunes in order to facilitate detailed assessment of stratigraphy and materials by a multi-disciplinary team comprising sedimentologists, pedologists and archaeologists. Note: all age estimates used in this report are in uncalibrated radiocarbon years Before Present (BP).

Keywords
Fossil List:	Arctica islandica , Scrobicularia plana
Relations:	Beach deposit, Coastal processes
Geomorph:	buried podzol, buried topography, radiocarbon dating, raised beach gravel, sand dune, ventifact, washover barrier

Measurements
Length:	3,000 m	Width:	1,000-500 m	Height:
Depth:		Area:

Access
Approach:	Portstewart Strand lies to the SW of Portstewart.
Management:
Current management by Portstewart Golf Club and the National Trust appears adequate to maintain the scientific interest of the dune system.
Uses
Uses:	Recreational activities.

References (16)
Carter, R.W.G. & Wilson, P., 1990. Portstewart Strand and the Bann Estuary. In Field Guide No. 13. North Antrim and Londonderry., pp.18-23 Irish Association for Quaternary Studies, Dublin.
Coffey, G. & Praeger, R.L., 1904. The Antrim raised beach: a contribution to the Neolithic history of the north of Ireland. Proceedings of the Royal Irish Academy, vol. 25C, pp.143-200.
Fisher, N., 1935. Locally extinct marine mollusca at Portstewart. Journal of Conchology, vol. 20, pp.117-126.
Gray, W., 1879. The character and distribution of the rudely-worked flints of the north of Ireland, chiefly in Antrim and Down. Journal of the Royal Historical and Archaeological Association of Ireland, vol. 5 (ser.4), pp.109-143.
Hasse, L., 1890. Objects from the sandhills at Portstewart and Grangemore, and their antiquity. Proceedings and Papers of the Royal Society of Antiquaries of Ireland, vol. 1 (ser.5), pp.130-138.
Hewson, L.M., 1934. Notes on Irish sandhills. Journal of the Royal Society of Antiquaries of Ireland, vol. 4 (ser.7), pp.231-244.
Knowles, W.J., 1887. The prehistoric sites of Portstewart, County Londonderry. Journal of the Royal Historical and Archaeological Association of Ireland, vol. 8 (ser.4), pp.221-237.
Knowles, W.J., 1891. Report on the prehistoric remains from the sandhills of the coast of Ireland . Proceedings of the Royal Irish Academy, vol. 17, pp.173-187.
May, A.McL. & Batty, J., 1948. The sandhill cultures of the River Bann estuary, Co. Londonderry. Journal of the Royal Society of Antiquaries of Ireland, vol. 78, pp.130-156.
Symes, R.G., Egan, F.W. & McHenry, A., 1888. Explanatory Memoir to accompany Sheets 7 and 8. Memoirs of the Geological Survey of Ireland.
Wilcock, F.A., 1976. Dune physiography and the impact of recreation on the north coast of Ireland (D. Phil. thesis). (Thesis) University of Ulster.
Wilson, H.E. & Manning, P.I., 1978. Geology of the Causeway coast. Memoir for one-inch geological sheet 7. Memoirs of the Geological Survey Northern Ireland, HMSO, Belfast.
Wilson, P., 1990. Coastal dune chronology in the North of Ireland. Catena, suppl. 18 In Dunes of the European Coasts.
Wilson, P., 1991a. Sediment clasts and ventifacts from the north coast of Northern Ireland. Irish Naturalists Journal, vol. 23, pp.446-450.
Wilson, P., 1991b. Buried soils and coastal aeolian sands at Portstewart, Co. Londonderry, Northern Ireland. Scottish Geographical Magazine, vol. 107, pp.198-202.
Wilson, P. & McKenna, J., 1996. Holocene evolution of the River Bann estuary and adjacent coast, Northern Ireland. Proceedings of the Geologists Association of London, vol. 107, pp.241-252.

Map(s):	See the 1:50,000 O.S. Sheet 4 (Coleraine).
Record type:	ESCR report
Entered by:	E M Porter

Enlander, I., Dempster, M. & Doughty, P., 2026. Portstewart Strand Sand Dunes, County Londonderry, site details. [In] Earth Science Conservation Review.
https://www.habitas.org.uk/escr/site.php?item=1139. Accessed on 2026-11-08.