North Lough Neagh Shores 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 Central Lowlands. This region owes its large-scale morphology to the early Tertiary subsidence of the Lough Neagh basin into the magma chamber from which the basalts that underlie much of the landscape originated. This has produced a largely centripetal drainage system from the rim of the basin into Lough Neagh that ultimately drains northwards via the Lower Bann. To the south of the Lough Neagh basin, the lowlands extend southwestwards along a Caledonian structural trend into the Monaghan-Clones depression. In the east of the region the lowlands extend northeastwards along the fault-guided Lagan Valley. There are no strong topographical barriers in the region and boundaries between LCAs tend to be subtle. The low gradients of the rivers, especially on the clay lowlands immediately around Lough Neagh, create inherent drainage problems and frequently it is only the slopes of the many drumlins that provide permanently dry sites. The Lough Neagh Basin was a major ice accumulation centre during the Late Midlandian and much of the lowland areas to the north and south of the Lough are dominated by extensive drumlin swarms.

The North Lough Neagh Shores have much in common with the East Lough Neagh Points. It comprises a 2km to 3km wide belt of flat land that fringes the northern shores of Lough Neagh between Toome and Antrim. The Lough banks are carved into localised troughs and hummocks with incised streams but remain predominantly flat. The shoreline itself follows a meandering line of bays, inlets and headlands and to its west in particular, countless tiny islands a few metres off shore. In the west, the area merges seamlessly with lower slopes of the Long Mountain Ridge. Long Mountain Ridge extends almost to the Lough but to the east, the land rises quite steeply from the Lough shore. Within the original Landscape Character Assessment much of the area is identified as part of the Lough shore Fringe area of scenic quality that is sensitive to any development.

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)

Tertiary stratigraphic succession

Tertiary-aged basalts comprise a crudely-bedded succession of lava flows, ashes and red-weathered horizons (or boles) of the Antrim Lava Group. The Lower Basalt Formation crops out in two areas of LCA 61: the western area just south of the town of Toome and the eastern area north of Aldergrove Airport. The eastern exposure contains a bed of andesite: this is a fine-banded extrusive volcanic rock. The Upper Basalt Formation comprises over 60% of the LCA in a strip around the shore of Lough Neagh. An intra-Upper Basalt Formation andesite is also recorded in Randalstown Forest. This is unusual in that most andesites are found in the Lower Basalts: it is possible that the Randalstown exposure is a fault slice of the older formation.

The eastern area of LCA61 is underlain by clays and lignites of the Lough Neagh Group, north of Ardmore Point. These supra-basalt non-marine deposits have been extracted for brick clays and lignite, they are probably in faulted contact with the Lower Basalts in this area.

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 >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 shows it to be dominated by Late Midlandian till associated with the ice mass that was centred on the Lough Neagh Basin. An exception to this is the area of glacioflucial sand and gravel that occurs at the mouth of the Six Mile Water and underlies a large part of Antrim. This represents the western extremity of the Six Mile Water Glaciofluvial Complex (5.4km2) that occurs in a discontinuous, low-relief linear belt for approximately 18 km from Antrim to Ballyclare. It probably records both subglacial and subareal channelised glaciofluvial sedimentation during the deglacial period as an ice lobe retreated westwards along the depression towards the Lough Neagh lowlands. As such, they assist our understanding the complexity of deglacial processes during the recent glacial history of Northern Ireland. The narrow band of lacustrine alluvium around the Lough shore has most probably been exposed by arterial drainage works, such as those completed in 1942, designed to lower Lough Neagh and to improve drainage conditions within the surrounding Basin. There are also localised areas of river alluvium associated with the lower floodplain of the Main and the small streams that flow off the Long Mountain ridge.

Key Elements

ASSI

030 lough neagh

Largest lake in the British Isles, supporting beds of submerged aquatic vegetation with marginal swampy woodland and wet grassland.