East Lough Neagh Points 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 East Lough Neagh Points is a rolling agricultural landscape with relatively small fields and overgrown hedgerows on an area underlain by Lough Neagh Clays on the eastern fringes of Lough Neagh. There is a strong contrast in the scale and pattern of the farmland between the rolling margins of the basalt plateau and the flat clay landscape on the fringes of Lough Neagh. In the latter, there are long views across a completely flat landscape. The restoration of abandoned sand and gravel extraction sites as farmland or as nature reserves may provide opportunities for future public access to the Lough shore. Within the original Landscape Character Assessment much of the LCA 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

Comprises two ages of rock strata. 60% of the LCA comprises the Tertiary Antrim Lava Group (Upper and Lower Basalt Formations) the remainder being an outcrop in the centre of the LCA of Tertiary Lough Neagh Group mudstones and lignites (extracted for brick-clay and lignite). These formations are disposed in a series of NE-SW trending, fault-bounded tracts of a few kilometres width.

The southern outcrops of Lough Neagh Group sediments underlie the ovate Lough Beg and also form Rams Island in Lough Neagh.

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 of the area shows that it is dominated by Late Midlandian till associated with the ice mass that was centred on the Lough Neagh Basin. Within this till, McCabe and Hirons (1986) describe a series of N-S oriented sand-cored drumlins in the south of the LCA. Manning et al (1970) also indicate a number of NW-SE trending drumlins and drumlin=like features in the east of the LCA and north of Portmore Lough. The orientation of these features can be used to confirm the southeastwards flow of this ice. Within Northern Ireland drumlins take a variety of forms; some are rounded in plan, although the majority are elongated in the direction of ice flow. Although most drumlins are composed of glacial till or tills, a small number are 'drumlinoid features' are rock-cored and some are composed of sand and gravel. It is generally accepted that the drumlins of Northern Ireland were formed by deposition beneath fast flowing ice. In the majority of cases this has resulted in a thick layer of Upper (younger) Till overlying a core of Lower (older) Till. This pattern has been observed across Northern Ireland, apart from a limited area in the north of County Down. The precise temporal relationship between the two tills has not been definitively resolved, but Davies and Stephens (1978) refer to an organic layer between the tills in County Fermanagh that has been dated at 30 500 ± 1170/1030 years B.P. and shelly material between the tills on the Ards Peninsula dated at 24 050 ± 650 years B.P.. However, these deposits only indicate that the Lower Till is older than the dates obtained.

Around the Lough shore there is a narrow band of lacustrine alluvium that has most probably been exposed by the lowering of Lough Neagh in historical times to improve drainage conditions within the Basin. There are also small areas of river alluvium associated with streams draining into Lough Neagh - most notably at Lennymore Bay, where there is also a small area of blown sand. Of more significance regionally are limited areas (0.5km2) of glaciofluvial sand and gravel that form part of the the Lagan Valley Deglacial Complex. This is a discontinuous belt of glaciofluvial and glaciolacustrine deposits occurs for 40km along the axis of the Lagan valley from Belfast WSW to Aghalee, Co. Antrim. In this LCA, the Complex consists of deltaic and esker deposits. These reflect drainage to the west during the final deglaciation, indicating a reversal in the drainage gradient probably due to isostatic depression of the Lough Neagh Lowlands during the last glacial cycle. Most of the Complex can be found in LCAs 97, 106 and 107, with minor areas in LCAs, 108 and 109. 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.

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.

Deglacial Complexes

LAGAN VALLEY DEGLACIAL COMPLEX,

The Lagan Valley Deglacial Complex is highly important in understanding the complexity of deglacial processes. A lobe of Irish ice located in the valley, related to ice pressure from the Lough Neagh Lowlands contained subglacial conduits now recorded by eskers. The phased retreat of the ice lobe further westward is recorded by cross-valley ice-contact ridges.

Other sites/units identified in the Earth Science Conservation Review

8 Aghnadarragh

Pleistocene.