Magilligan Lowlands Geodiversity Profile

Outline Geomorphology and Landscape Setting

The use of a cultural overlay in defining Landscape Character Areas (LCAs) means that they frequently subdivide natural physiographic units. It is common therefore for significant geomorphological features to run across more than one LCA. It is also possible in turn, to group physiographic units into a smaller number of natural regions. These regions invariably reflect underlying geological, topographic and, often, visual continuities between their component physiographic units, and have generally formed the basis for defining landscape areas such as AONBs. It is essential therefore, that in considering the 'Geodiversity' of an individual LCA, regard should be given to adjacent LCAs and to the larger regions within which they sit. In the original Land Utilisation Survey of Northern Ireland, Symons (1962) identified twelve such natural regions.

This LCA lies within the region described as the Lough Foyle Lowland. The chief morphological features of this lowland region are a series of postglacial raised beaches, the nineteenth century enclosure of large areas of saltmarsh and slobland beside the Foyle estuary and the sand and shingle ridges and blown sand of the Magilligan foreland. Inland from the coastal zone, the lowland continues along the floodplains of the Roe and Faughan rivers into areas that are underlain by till and glaciofluvial deposits, especially an important moraine complex between Limavady and Ballykelly. The Levees along these rivers testify to their previous tendency to flood.

The Magilligan Lowlands are found on the eastern shores of Lough Foyle, at the foot of the basalt escarpment of Binevenagh. The beach ridge plain of Magilligan Foreland is the largest coastal accumulation feature in Ireland, it covers an area of 32km2 and consists of up to 300 swash-aligned beach ridges. In the depressions between these ridges are later peats that began to accumulate as long ago as ca 2 500 B.P.. Much of the foreland has in turn been overlain by sand dunes. The dramatic cliffs of Binevenagh form a striking backdrop to this flat coastal plain and the mountains of Donegal are visible as a distant horizon to the west of Lough Foyle. The rugged outline of the sand dunes along the edge of Magilligan Strand stand out clearly as a contrast to the flat, expansive lowland to the south. The lowlands are artificially drained, by a combination of mechanical pumping and drainage ditches and the resultant sandy soils are some of the most productive farmland in the Province. The rugged, natural forms of the sand dunes, which shelter Magilligan Strand, are in strong contrast to the flat, smooth arable fields to the south. The dunes are exposed, with only a few stunted mounds of hawthorn and gorse. The landscape can therefore be summarised as one of a flat alluvial plain, dominated by the Binevenagh cliffs and rugged sand dune ridges shelter Magilligan Strand. For further information see section by P. Wilson in Knight, J. (2002).

Pre-Quaternary (Solid) Geology

The stratigraphy of this area is made up of the mapped formations in the table, the youngest of which usually overlie the oldest.

Stratigraphic Table (youngest rocks at the top of the table)

This LCA extends inland from Magilligan Point and contains igneous and sedimentary rocks of Triassic, Jurassic and Tertiary age. The Jurassic Waterloo Mudstone Formation is intruded by a large, east-west striking dolerite sill.

Quaternary (Drift) Geology

Northern Ireland has experienced repeated glaciations during the Pleistocene period that produced vast amounts of debris to form the glacigenic deposits that cover more than 90% of the landscape. Their present morphology was shaped principally during the last glacial cycle (the Midlandian), with subsequent modification throughout the post-glacial Holocene period. The Late Midlandian, the last main phases of ice sheet flow, occurred between 23 and 13ka B.P. from dispersion centres in the Lough Neagh Basin, the Omagh Basin and Lower Lough Erne/Donegal. The clearest imprint of these ice flows are flow transverse rogen moraines and flow parallel drumlin swarms which developed across thick covers of till, mostly below 150m O.D. during a period that referred to as the Drumlin Readvance. At the very end of the Midlandian, Scottish ice moved southwards and overrode parts of the north coast. Evidence for deglaciation of the landscape is found in features formed between the glacial maximum to the onset of the present warm stage from 17 and 13ka B.P. - a period of gradual climatic improvement. Most commonly these are of glaciofluvial and glaciolacustrine origin and include: eskers, outwash mounds and spreads, proglacial lacustrine deposits, kame terraces, kettle holes and meltwater channels (McCarron et al. 2002). During the Holocene, marine, fluvial, aeolian and mass movement processes, combined with human activities and climate and sea-level fluctuations, have modified the appearance of the landscape. The landforms and associated deposits derived from all of these processes are essentially fossil. Once damaged or destroyed they cannot be replaced since the processes or process combinations that created them no longer exist. They therefore represent a finite scientific and economic resource and are a notable determinant of landscape character.

The drift geology map for this LCA emphasises the arcuate structure of interdigitated raised beach deposits and peats that comprise most of the foreland. It also illustrates the extensive accumulation of wind blown sand behind the seaward margin.

Key Elements

ASSIs

068 MAGILLIGAN

Internationally recognised classical beach-ridge cuspate foreland, with active prograding dunes which contain a wide range of plant communites and a number of rare vascular and bryophyte species. The beach ridge complex evolved in response to sea level change and is thought to relate to a fall in relative sea level some time before 5 000 yr B.P. This facilitated the onshore movement of shelf sediment. Growth eventually came to an end, possibly in response to a combination of either a decline or reversal in the sea level fall and the disruption of the inshore wave field by the growth of an ebb shoal at the mouth of Lough Foyle. The foreland, and the beach ridges in particular, therefore present a detailed record of Holocene sea-level changes.

051 Lough foyle

Contemporary coastal processes especially chenier ridge development. Exposure through the southern (earliest) portion of the Magilligan foreland complex.

AONB

The LCA lies within the North Derry AONB (1966). This designation is indicative of the scenic quality of the landscape.