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Northeast Mournes Complex - Northeast Mournes MorainesDown
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Summary Full report
Site Type: Inland exposure
Site Status:
Grid Reference: J345170, J370305, J330215
Rock Age: Quaternary (Late Midlandian)
Other interest: No data, No Data, recessional moraine

Summary of site:

In the north east Mournes region the impressive moraines divide naturally into two regions. The most southerly extends from Ballymartin Hill on the coast to the southern slopes of Slieve Binnian in the Crockanroe area and the north east including the entire Mourne Plain area from this line to Dunmore where the plain is completely pinched out as Chimney Rock Mountain flanks the coast. The northern region extends along the indented northern flank of the Mournes from Newcastle in the east to Kinnahalla and its adjacent valleys in the west and north of this wavering line in a belt up to 3 km deep.

Two large ice tongues dominated the southern Mourne Plain. In the west a major glacier flowed through the Newry gap into the Carlingford Lough area where it spread into the lowlands including what is now part of the Irish Sea. Its huge convex front swept in an arc whose eastern segment can be seen on the plain from Ballymartin Hill north to Crockanroe where it turned west along the lower flanks of Moolieve, Slievenagore, Slievemageogh, Slievebug and Rocky Mountain. The second ice tongue flowed down the North Channel of the Irish Sea and spread in a wide arc with its western, convex front almost meeting the western tongue along the same line from Ballymartin Hill to Crockanroe, then recurving to the east along the southern fringes of Slieve Binnian, Long Seefin, Spences Mountain and Chimney Rock Mountain. As these two ice fronts melted back, the gap between them filled with solid debris released from the ice to create the Ballymartin ridge 550 m wide at the coast expanding to about a kilometre against the mountain flank. This account deals only with the moraines from the eastern sheet flowing south through the North Channel. This sheet melted back rapidly from the Ballymartin ridge and the next stable front (with ice melting at the speed of flow) built the Longstone ridge to the east. The space between the two ridges is hummocky with many closed depressions where large ice masses were buried in glacial debris and melted to form kettle holes, one 500 m long by 200m wide. As the ice tongue retreated further north, its front was smaller and more tightly curved and the ridges reflect this geometry. Where the ridges meet the high ground of the Mourne front they turn tightly east and the further east they progress, the more bench-like they become, lateral moraines becoming kame terraces. Between Annalong and Glasdrumman where the plain first narrows and then pinches out completely, the ridges are dissected and separated by channels. To the north east only small segments of the convex faces persist and even then only as far north along the coast as Dunmore Hill. The lateral deposits become more crowded from here and by Glasdrumman they are so tightly spaced that they appear more like corrugations. All signs of the moraines are lost about a kilometre north of the Bloody Bridge car park where erosion has stripped them completely. In a small sand pit west of the road at Dunmore deposits varying from gravels to cobbles interbedded with lenses of silt and sand can be seen with cobble-lined channels cutting through them. These are typical ice front sediments reflecting strongly variable meltwater flow conditions and sediment supply. At the eastern end of the northern section of moraines the first evidence appears immediately west of Newcastle where massive, round crested ridges form a gently arc along the course of the Shimna river between the town and the eastern fringe of Tollymore Forest Park. The largest, up to 300 m wide and 10 m high, extends from just north of Manor House into Bryansford. Ridges ascend the lower slopes of Slievenabrock, Luke’s Mountain, Spellack (the north east ridge of Slieve Meelmore) and Slieve Meelbeg and their upslope extensions transform progressive into benches or terraces. They also cross the mouths of the intervening valleys. North west of Bryansford a regularly repeating pattern of ridges and benches can be seen in the valleys between McLean’s Hill and Moneyscalp Hill, Moneyscalp Hill and Tullyree Hill, Tullyree Hill and the north eastern skirts of Slievenaman and the northern slopes of Butter Mountain. They have a consistent pattern, concave to the north and occur in closely nested sets, up to 12 recognisable benches or ridges over a distance or 2.3 km in the valley between McLean’s Hill and Moneyscalp Hill. 7 arcuate moraines can be seen in the Shimna valley, retreat features from ice entering the upper valley between Slievenaman and Butter Mountain and a further 6 in the Slievenaman-Butter Mountain gap. Towards the north end of the gap ridges become straighter and much bigger as the valley opens onto the lower ground to the north. In general the ridges trend upslope onto the valley sides where they appear more bench-like. Similar bench-like forms cross the north west slopes of Kinnahalla, Craigdoo and Spelga Mountain. At the close of the last phase of Ireland’s final glaciation, ice sheets occupied the low ground to the north and extensions of the ice mass pressed into the northern flanks of the eastern Mournes entering the valleys in tongue-like forms, while abutting the northern faces of the intervening hills. As melting commenced, the tongues withdrew with many periods of adverse climatic conditions causing the ice snouts to stabilise sufficiently for ridges to form. This stuttering retreat northwards left behind the trains of nested moraines in the major valleys and even between the minor hills across the northern Mourne front. In the higher valleys there are complications where moraines are cross-cutting but the earlier moraines are survivals from a previous retreat across the col between Slievenamuck and Ott Mountain.

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