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Earth Science Conservation Review
| Magilligan Coastal Complex | Londonderry |
| Site number: | 10 | File Number: | C63 |
| ESCC: | IA | ||
| Locality Type: | Coastal section | Status: | ASSI |
| Grid Reference: | C665387 Centroid | ||
| Google maps: | 55.19137,-6.95585 | ||
| County: | Londonderry | Council area: | Causeway Coast & Glens Borough Council |
| Period: | Quaternary | ||
| Stages: | Holocene | ||
| Site Description | |
|---|---|
| Highlights: | |
Magilligan is the largest coastal accumulation form in Ireland forming a triangular cuspate foreland at the mouth of Lough Foyle. It is a Holocene beach-ridge plain with subsidiary aeolian deposits and inter-ridge peats and marls. The site in general is an important element in the sea-level history of Ireland, while its distal extremity, Magilligan Point, is an especially important geomorphological site as it demonstrates the relatively unusual phenomenon of prograding dunes. This contrasts with the pervasive retreat found generally in British and Irish dune systems. | |
| Introduction: | |
The Magilligan Foreland beach-ridge plain lies at the northeast corner of Lough Foyle covering an area of 32km2, and is Ireland's largest coastal accumulation form. Between the local maximum of the early Holocene eustatic transgression c. 7000-6500 years B.P. and the return to near present sea level around 2000-1500 years B.P. a raised beach plain prograded to the northeast from a gravel ridge nucleus just north of the River Roe. This raised beach plain has since been covered by a complex sequence of various thicknesses of lagoonal peats, freshwater marls, allogenic shell deposits and aeolian dunes. Since the early 1970s over 50 scientific papers have been published on the area covering geomorphological, pedological, archaeological and ecological aspects. This concentration of research activity in the last 25 years has made Magilligan the most intensively studied Holocene coastal site in Ireland. In a series of papers geomorphologists have elucidated the Holocene development of the Foreland (Carter 1975, 1982, 1986; Carter, Lowry and Stone 1982; Wilson and Carter 1984). Parallel work has been done on pedogenesis (Wilson and Bateman 1986; Wilson 1987; Wilson and Farrington 1989) while recently the tendency has been towards a more integrated approach (Carter and Wilson 1990). | |
| Description: | |
The beach-ridge plain comprises at least 150 (and perhaps as many as 300) northeast facing beach ridges which pass northward from a gravel ridge nucleus just north of the River Roe. Crestal elevation of the beach ridges declines from c. 7m O.D. in the south to the present high water mark of c. 2m O.D. at Magilligan Point. Carter (1986) identified three principal beach-ridge sets of which two compose the body of the Foreland and are related to its mid-Holocene progradation. These two older sets are Atlantic swash-aligned and are the product of onshore sediment transport. Internally the ridges are composed of mixed quartz and carbonate sands and occasional large lamellibranch valves. Structurally the ridges are characterized by seaward dipping low-angle (1° to 2°) parallel laminae. These wave-lain stratified units have a constant width of 100m to 300m. The third beach-ridge set consisting of tapering ridges is found at Magilligan Point and represents recent deposition at the distal margin. The raised beach plain is covered in places by younger deposits. Peat and freshwater marls are found in the inter-ridge depressions, while aeolian sands from two major depositional phases mantle the edges of the beach-ridge plain and form a relatively shallow (<1m) cover inland. The older more extensive deposit forms an almost horizontal planar cover for the beach ridges of the central and distal parts of the Foreland. The more recent aeolian deposits form dune ridges and mounds and are best developed on the seaward margins of the site. On the Lough Foyle shore sand depths do not exceed 5m, but on the Atlantic coast the dunes form a shore-parallel belt over 1km wide rising to a maximum elevation of c. 17m O.D. Shell accumulations both natural and anthropogenic occur within and under the dunes. Severe erosion is now affecting much of the Lough Foyle shore of the Foreland and even more intense erosion is taking place on the Atlantic shore west of Benone. In contrast the distal extremity, Magilligan Point, is prograding with new foredune ridges reaching crestal elevations of up to 5m O.D. However map and photographic evidence indicates that progradation is not progressive as there is a cycle of growth and decay. | |
| Importance: | |
The Magilligan Foreland is an internationally recognised classic landform. It is the best example of a beach-ridge foreland in Northern Ireland and is comparable to any in Britain or Europe. It forms an essential element of the network of representative geomorphological features of this region. The site has been the subject of many research projects covering geomorphological, palaeoecological and pedological aspects. One result of this is that the Lough Foyle shore of the Foreland is probably the most intensively dated area of land in Ireland, with a total of 28 14C dates. Magilligan has the well-documented baseline status required for investigation of the future response of low-lying soft coasts to the conjectured sea-level rise consequent on global warming. It represents the only site in Ireland, and one of only a handful in Europe, sufficiently well researched for elucidation of a reliable sea level and sand dune chronology. The site is already a fine educational facility at all levels for understanding the concepts of "soft" coastal geomorphology and has some capacity for further development in that direction (although its potential value is limited by the land/access restrictions of defence and prison installations). | |
| Interpretation: | |
Evidence for the evolution of the Magilligan Foreland is visible in cliff sections along the Lough Foyle shoreline where fen peats and freshwater marls occupy inter-ridge depressions and podzolic soils occur on the ridge crests and slopes. During the post-glacial transgression sometime around 8000 to 9000 years B.P. the sea flooded into the lower Foyle Valley, rising to a peak of about 2-4m above present water level c. 7000- 6500 B.P. The degraded mid-Holocene cliff marking the maximum stand of this transgression can still be traced around Lough Foyle. On the eastern side this cliff was cut into boulder clay and eroded products were transported south prior to deposition in a gravel ridge complex (known locally as the Giant's Walk) just north of the estuary of the present River Roe. As the sea fell from the peak level (either due to isostatic rise or eustatic fall) it triggered a major phase of coastal sediment deposition. Falling wave base resulted in the onshore transfer of shelf sand and this, together with a gradual reduction in the tidal prism of the Lough, caused the formation of a series of Atlantic shore-parallel beach-ridges extending to the northeast from the gravel ridge nucleus formed by the Giant's Walk. As the Foreland grew by northwards addition of beach ridges, the inter-ridge depressions remained subject at first to either permanent or tidal marine influences. As the ridges stabilised peat formation was initiated in these depressions at various times between c. 2500 and c. 1000 years B.P. Contemporaneously podzolic soils formed on the freely-drained beach-ridge crests and slopes. As accretion of the beach-ridge plain neared completion soils also developed on prominent aeolian dunes which had formed on the seaward side of the beach ridges near the present-day Magilligan Point. Along the Lough Foyle shore, cliff sections show that these beach and dune podzolic soils pass laterally into fen peats and freshwater marls in the waterlogged inter-ridge depressions. Together the ridge and dune podzols and the peats in the inter-ridge depressions represent a buried palaeocatena i.e. a former land surface indicating a long period of stability. Ridge development continued from the onset of sea level fall to the return to near present sea level around 2000-1500 years B.P. when sediment supply ceased. As ridge building slowed with stabilising sea level, the Foreland was eroded on its Lough Foyle shore, which then extended further west. The area of eroded beach ridges is now occupied by the inter-tidal sands of Lough Foyle. This erosion of the beach-ridge sands released sediment for redistribution by aeolian processes. As a result, about 1100-600 years B.P. the Lough Foyle margin and much of the inner surface of the Foreland was buried by northward migrating aeolian dunes. These deposits consist of cross-bedded, aeolian sand that is texturally and mineralogically similar to the sand comprising the beach-ridge plain. The cross-bedded dune system was eroded to a machair-like planar surface which increases in height from north to south by only 1.1m over a distance of 2.6km. In time the onset of pedogenesis resulted in the formation of a thin pararendzina soil which serves to mark the former land surface. The sands of this planar surface were in turn overlain by modern discontinuous dune sands. These dunes are lithologically similar to the older sand deposits and therefore are locally derived but were not reworked from the earlier underlying buried sand onshore. These dunes also aggraded northwards and probably derive from erosion and aeolian redistribution of the seaward beach ridges. On the Lough Foyle shore the modern dunes may have originated during the 17th and 18th centuries when Magilligan contained Ireland's largest rabbit warren. Along the northeast (Atlantic) coast the belt of modern dunes rises to a maximum elevation of 17m O.D. The height and morphology (multiple shore-parallel ridges) of these substantial dunes suggest that they developed as sand released by slow erosion of the beach ridge/dune system was transported landward by onshore winds. Radiocarbon dating indicates that they have developed since c. 700 years B.P. These more recent dune sands have also developed sand pararendzinas. In several places shell mounds crop out under and within the dune sands at c. 2.5-3.5m O.D. Some of these are shell middens dating from Early Christian times and contain anthropogenic artefacts, but many are natural storm-generated shell accumulations. Variations in erosion of the Magilligan shore over short time periods are due to a complex interplay of climatic factors, particularly storm frequency and wind direction, tidal levels and wave refraction characteristics. The Atlantic coast is stable from Benone through the Umbra eastwards to Downhill, and wave erosion of the dune toe is a rare occurrence. Indeed there may be a tendency towards slow accretion although only in the order of 8m to 15m per century. However recreation activity adjacent to the access road at Benone is causing die-back of sand-fixing vegetation leading to extensive blowouts and loss of sediment inland. At the eastern extremity of the site, at Downhill, the beach and dunes abut against the Tertiary basalts. Here very large ramp dunes are banked against the cliffs. Occasional rockfalls and landslips have modified the dunes creating complex intercalations of the two deposits. West of Benone the stable sector passes laterally into a section of severe shoreline erosion encompassing virtually all of the remaining Atlantic shoreline of the Foreland. Here the frontal sand dunes are eroding rapidly. Between 1949 and 1980 the duneline has retreated by between 80m and 150m at average rates of 2.7m to 5m per year, the fastest coastal erosion anywhere in Northern Ireland. A proportion of the sediment is lost offshore, some is incorporated in the beach or blown into the dunes while the remainder is transported to the west towards the distal extremity of the Foreland, Magilligan Point. The highest dunes in this coastal section lie just west of Benone at Ballymaclary where massive inland blowouts are conspicuous features. While a few of these do breach the dune line they are essentially "natural" features (although over-grazing may have played some part in their early development). On the southwest flank of Magilligan Point, i.e. the Lough Foyle shore, erosion is equally persistent and spatially more consistent since 1949, but the rate of erosion has been markedly less at c. 1.2m per year. Here erosion products are either moved into deeper water, into the Lough estuary-mouth bedforms or northwards towards the distal end of the spit. Between these two zones of erosion lies the complex geomorphological unit of Magilligan Point. The point itself is maintained by the existence of two independent but counteractive wave regimes, viz. wind waves generated within Lough Foyle and refracted swell waves from the Atlantic. The wave transport gradient declines very sharply towards the Point making it a zone of net accumulation. Rapid erosion along both the Lough Foyle and Atlantic shores since the early 1950s and the transport of the products alongshore has provided the sediment for a 250m progradation at the Point. Reduction in the tidal prism of the Lough due to land reclamation in the mid-nineteenth century may well be a contributory factor in this process. However progradation is not progressive. Documentary evidence shows that between 1830-1970 the total area varied by only c. 40ha owing to alternating phases of erosion and accretion. It is believed that the size and shape of the Lough Foyle ebb shoal, the Tunns Bank, is crucial in determining the erosion/progradation status of the adjacent Magilligan shore. The sub-aerial and sub-tidal accumulations are linked together in a counterbalanced feedback system with a periodicity of c. 40 years. As the shoal expands so the shore erodes. As the shoal contracts the shoreline progrades. The link between the shore and offshore elements is provided by the degree to which the Tunns Bank controls wave refraction. The shoal will increase in size and the adjacent shore will erode until a threshold is passed after which the increased size of the shoal alters incident wave conditions to such an extent that sand begins to feed back towards the shore thus building up the Point. Progradation of the shore and diminution of the shoal will proceed until once again alterations in the wave refraction pattern allows renewed erosion of the shore. Accretion at the Point takes the form of beach-ridge welding. This is a process whereby sediment eroded from the flanks of the foreland is transported alongshore towards the Point where it moves onshore as a discrete mound or ridge. Deflation of this beach ridge then results in the formation of a new foredune. The dune ridge will grow until the stranding of another beach ridge provides sediment for a new dune to seaward thus cutting off sand supply to the earlier ridge. | |
| Conclusions: | |
The Magilligan Foreland is a Holocene beach-ridge plain with subsidiary deposits of inter-ridge peats and aeolian sand. It formed at the northeast corner of Lough Foyle as sea level fell from a Holocene peak 2m to 4m above present level about 6500 to 7000 years B.P. The site is important in that it is the largest and by far the best documented coastal accumulation form in Ireland; indeed only a few in Europe have been the subject of such thorough study. | |
| Keywords | |
|---|---|
| Rocks: | Sand |
| Relations: | Beach deposit |
| Geomorph: | beach ridge, sand dune |
| Access | |
|---|---|
| Restrictions: | Access is restricted due to presence of defence and prison installations. |
| Threats: | Extreme coastal erosion. |
| Uses | |
| Uses: | Location of defence and prison installations. |
| Educ. Level: | Adult education / GCSE / Secondary / Advanced level / Undergraduate / Postgraduate |
| References (9) | |||
|---|---|---|---|
| Carter, R.W.G., 1975. Recent changes in the coastal geomorphology of the Magilligan Foreland, Co. Londonderry. Proceedings of the Royal Irish Academy, vol. 75B, pp.469-497. | |||
| Carter, R.W.G., 1982. Sea-level changes in Northern Ireland. Proceedings of the Geologists Association of London, vol. 93, pp.7-23. | |||
| Carter, R.W.G., 1986. The morphodynamics of beach-ridge formation at Magilligan, Northern Ireland. Marine Geology, vol. 73, pp.191-214. | |||
| Carter, R.W.G. & Wilson, P., 1990. The geomorphological, ecological and pedological development of coastal foredunes at Magilligan Point, Northern Ireland. In Coastal Dunes: Form and Process John Wiley & Sons Ltd. | |||
| Carter, R.W.G., Lowry, P. & Stone, G.W., 1982. Sub-tidal ebb-shoal control of shoreline erosion via wave refraction, Magilligan Foreland, Northern Ireland. Marine Geology, vol. 48, pp.17-25. | |||
| Wilson, P., 1987. Soil formation on coastal beach and dune sands at Magilligan Point Nature Reserve, Co Londonderry. Irish Geography, vol. 20, pp.43-49. | |||
| Wilson, P. & Bateman, R.M., 1986. Nature and palaeoenvironmental significance of a buried soil sequence from Magilligan Foreland, Northern Ireland. Boreas, vol. 15, pp.137-153. | |||
| Wilson, P. & Carter, R.W.G., 1984. Field Guide No. 7: North East Co. Donegal and North West Co. Londonderry. Irish Association for Quaternary Studies. | |||
| Wilson, P. & Farrington, O., 1989. Radiocarbon dating of Holocene evolution of Magilligan Foreland, Co. Londonderry. Proceedings of the Royal Irish Academy, vol. 89B, pp.1-23. | |||
| Map(s): | See the 1:50,000 O.S. Sheet 4 (Coleraine). | ||
| Record type: | Environment Serv. GIS, ESCR report | ||
| Entered by: | Crowther, P.R. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Magilligan Coastal Complex, County Londonderry, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=10. Accessed on 2026-11-06. |
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