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Attical Complex - Attical Valley MorainesDown
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Summary Full report
Site Type: Inland exposure
Site Status:
District:
Grid Reference: J293258, J265270, J276197, J260175
Rocks
Rock Age: Quaternary (Late Midlandian)
Interest
Other interest: No data, No Data, moraine ridge, readvance moraine

Summary of site:

The eastern and western Mournes divide along the junction of the third and fourth of the five granite pulses that laid the foundations of the Mourne massif around 56 million years ago. Two rivers mark this division; the Bann flowing north west from its source in Deers Meadow into Spelga Dam and beyond, and the White Water flowing almost due south to enter Carlingford Lough just north of Greencastle. Attical is a small village about 1km to the east of the confluence of the Yellow Water and Windy Gap rivers with the White Water. It is the glacial deposits in the valleys and on the flanks of these three rivers (including also a short stretch of the Minerís Hole River south of Lough Shannagh) and the upper reaches of the Bann around the Spelga Dam that are the subject of this account.

Reading the evidence of the ice flow and retreat in this area is difficult because of the profusion and confusion of criss-crossing low mounds and ridges of glacial debris that abound in the area. The picture is further complicated by the interaction between the vast regional ice sheets in the last stages of melting and the mountain glaciers which appear to have been the final stages of the glaciation in the Mournes. The deposits reach as far south as the valley between Rocky Mountain and Knockchree, where a long ridge spans the valley. North of here, around Brown Hill, a whole series of ridges across the White Water are cross-cut by a second series that appear to originate in the Windy Gap valley. Attical appears to have been the confluence of ice flow from the north and west along the valleys which are, west to east, the Windy Gap, White Water and Yellow Water. On the White Water at least 21 ridges have been recognised from Crocknafeola into the upper reaches at Deers Meadow, a distance of about 4km, each representing a brief period of stability of the glacial front in its general retreat. A ridge of glacial deposits extends south from Slieve Muck and separates the Yellow Water valley from the White Water to the west. Ridges and benches are features of the western slopes of the valley on the eastern flank of Slieve Muck. In the upper valley under Carn Mountain, south of Lough Shannagh, there are more ridges on the valley floor and a boulder field. The Windy Gap valley runs north west from its confluence with the White Water, the cliffs and corrie (glacial basin) of Shanlieve and Eagle Mountain defining its western wall and the slopes of Pigeon Rock its eastern. Features in the valley include a series of broad hummocks and a rather odd ringed flat. Throughout the area, small excavations provide glimpses into the glacial debris. In almost all cases, sands and gravels with mixed glacial pastes predominate and almost all seem to be unstable torrent-swept mounds. Only one or two suggest deposition in standing water. The story that emerges from all these deposits is of a time when the area was submerged beneath two massive, co-existing ice sheets. One pushed north from Carlingford, its snout reaching into the White Water valley at least as far as Rocky Mountain about 2km north of Glenloughan. The other, originating in the Lough Neagh basin, pressed over the northern summits of the central Mournes and may have met the southern ice somewhere in the valley between Knockchree and Rocky Mountain. The southerly mass appears to have receded first, melting from the lowlands on to higher ground, and there is evidence that the moraines formed at the snout of the northerly ice cut across those defining the final limits of the southern ice. As the iron grip of the ice gradually relaxed in the final stages of the Midlandian (the last Irish glaciation), rock began to emerge through the deflating ice surface and the glaciers became confined to the valleys. For a time the White Water and the Yellow Water glaciers merged low in their valleys, creating the median moraine that is now the ridge between the two. Further climatic improvement saw the glacier in the White Water valley retreat northwards in a series of pulses until finally it departed through the Slievenamisken/Spelga gap along the line of Spelga Pass. The same retreat is reflected in the Yellow Water valley in the main moraine across the entrance. As the ice flow feeding into the northern end of the valley between Slieve Meelbeg and Slieve Meelmore ceased, the ice in the upper valley (in the present Lough Shannagh area) became stagnant and dropped its load of boulders to create the present boulder field. Similarly the ice in the Windy Gap valley also became static and melted in the warming climate. In the very final stages of the Midlandian there was a brief period of intense cold which allowed snow and ice to thicken in the high corries on Slieve Muck and Shanlieve; local valley glaciers, with pulsing snouts, again became active for a time but they never achieved the size and length to merge before temperate conditions obliterated them completely, sometime around 13,000 years ago.


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