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GlarryfordAntrim
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Summary Full report
Site Type: Inland exposure, Quarry (disused), Quarry (working)
Site Status:
District:
Grid Reference: X30474094, X30304197
Rocks
Rock Age: Quaternary
Rock Type: Gravel
Interest
Other interest: No data, Deglacial sediments, Glacial streamlining, esker, gravel ridge

Summary of site:

In this intimate and beautiful landscape, along the line of the Main River, there is a series of glacial retreat features that have revealed a detailed story of a sequence of events, never previously described in Northern Ireland, during the final stages of Irelandís last glaciation. This combination of aesthetics and science bestows national importance on this site.

Within a narrow belt of land around 12km long, extending along the Main Valley from Craigs in the south to The Isles east of Dunloy in the north, a retreating ice sheet and its meltwaters carved features and shed and shaped its load of solid debris. These landforms lie in a depression that closes towards Ballymoney. It lies largely below the 100m contour and is flanked by streamlined bedrock and drumlins, indicating ice flow to the north west. About 12m of deposits can be seen but they are probably only part of a much larger mass now buried beneath more recent valley fill. There are four obvious components to the system:

  1. on both flanks there are glacially streamlined forms, mostly drumlins;
  2. on the western margin, more streamlined landforms can be seen to consist of layered glacial drift;
  3. an esker 11km long extends from Dunnstown in the south to the The Isles in the north where it takes the form of discontinuous ridges in the valley bottom. The few exposures in the ridge reveal boulder gravels, mostly of local basalt, with some sand and fine gravels. It appears to erode into glacial spreads in places; and
  4. east of the esker there are many isolated mounds of cross-bedded sands and gravels standing up to 7m above the recent valley fill deposits and probably more extensive below them.
These deposits have been subjected to detailed analysis and the following sequence of events emerges:
  1. The hollow was occupied by glacial ice flowing south to north, with a head of water within the ice forcing a northern flow of meltwater. The water flow was concentrated through a main meltwater tunnel, under the ice, incised into the valley floor.
  2. Streamlined marginal mounds were possibly subsidiary deposits formed in a network of side tunnels that linked with the main flow.
  3. The long axes of the streamlined landforms show that ice flowed over them towards the north west but was influenced by the valley axis. Some of the streamlining could be the result of massive floods of meltwater.
  4. The isolated mounds could be formed either by water lifting ice from its bed and filling the space between with washed deposits or (and more likely) they are isolated remnants of the formerly more extensive gravely spreads laid down as the ice flow ceased and progressively melted southwards. They do not appear to be glacial lake sediments.
  5. The sharpness of the esker and the absence of structures caused by the pressure of ice flow indicate that it formed after the general streamlining event by the filling of a late ice tunnel, just before the wholesale melting of the stranded and static ice.
Activity since has reversed the drainage from north to south as the valley became ice-free, allowing direct access to the lowlands towards Ballymena. There has also been later erosion and resedimentation of the valley. The Glarryford esker and its associated deposits as explained here relate the dynamic links of a complex series of events to a major tunnel cutting through basal ice to bedrock. This is the first model to be advanced for such a sequence in Northern Ireland and is of considerable scientific interest. The glacial deposits and landforms are the foundations of this exceptional landscape, with its wooded mounds, winding ridges, sparse modern development and a generally unspoiled nature. Although there is relatively little sand and gravel working, one well capitalised quarry is exploiting the main esker ridge and has the potential to do great scientific and aesthetic damage. Planning permissions in this area should receive careful scrutiny and major scars should be healed with sympathetic remedial works.


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