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Earth Science Conservation Review
| Glarryford | Antrim |
| Site number: | 466 | ||
| ESCC: | IS | ||
| Locality Type: | Inland exposure, Quarry (disused), Quarry (working | Status: | ASSI |
| Grid Reference: | D047094,D030197 End(s) of linear site, Not Entered | ||
| Google maps: | 54.92169,-6.36705 | ||
| County: | Antrim | Council area: | Causeway Coast & Glens Borough Council |
| Period: | Quaternary | ||
| Site Description | |
|---|---|
| Highlights: | |
The glaciofluvial topography along the axis of the upper Main depression represents part of a subglacial palaeohydraulic system, which conducted meltwater generally northwards during the last deglacial event. The palaeoflow is associated with a high piezometric surface which forced meltwater flow uphill against the local topographic gradient within a Nye-type depression. Erosion and sedimentation events record initial erosion of the scooped, elongated depression into bedrock, tunnel sedimentation within the depression, followed by streamlining, subglacial esker sedimentation, and finally local deposition and channelling around stagnant ice masses. The scientific importance of the complex lies in the sequential history of sedimentation and erosive events which have not been described before in Ireland. Aesthetically, the network of gravelly mounds and ridges along the axis of the valley provide the physical framework upon which the post-glacial raised bogs (e.g. Big Frosses) and alluvial flats have developed. As the glacigenic landscape is still largely intact it provides a distinctive complex flanked by streamlined bedforms which is unique to eastern Ulster. | |
| Description: | |
This glaciofluvial system occurs as a narrow (<1km) belt running in a south to north arc about 12km in length. It is sited along the axis of the present upper River Main, which seems to occupy a broad, scooped shaped linear depression eroded into basaltic bedrock with rising ground to the east (Clough) and west (Long Mountain). The depression is generally below 100m O.D. and is flanked by streamlined drumlins and rock ridges associated with fast ice flow to the northwest. The depression closes northward towards Ballymoney where thick glacigenic diamicts and drumlins fill the low ground. Upstanding glaciofluvial deposits are at least 12m in thickness but probably infill the base of the depression below the postglacial drapes. There are three main topographic elements within the glaciofluvial complex: 1. The entire system is bordered on both flanks by streamlined drumlin forms. 2. At the western margin of the feature, especially along the Dunloy/Glarryford road, hummocky and streamlined topography seems to be largely composed of stratified drift but good exposures are not common. 3. The most distinctive element of the complex is a sharp-crested, discrete esker ridge which can be traced for about 11km. It starts abruptly at Dunnstown (304700 409400) immediately north of rock ridges. In the south it hugs the western margin of the depression, is up to 10m in height with a low meander amplitude. At Killycreen North (304400 415600) it swings north eastwards into the axis of the depression and seems to rise over and partially erode into broad glaciofluvial spreads. Northwards it is more discontinuous, forming a series of isolated to weakly-joined mounds of gravel which rise above the thick postglacial infills. It peters out as a series of gravelly mounds at The Isles and Illanneyoon (300400 421900). Exposures at Bells pit (304500 416500) comprise up to 12m of stratified sediments which are mostly derived from basaltic bedrock (95%) with occasional chalk and flint erratics (approx. 3%) (see Fieldsheet GLE0101A). The basal 3m consist of coarse sands, granules and pebbly gravels. This is abruptly truncated by 8m of amalgamated beds of chaotic boulder gravels. The latter are mainly massively bedded cobble gravels with discontinuous boulder lags. Weakly defined involutions occur in the top metre of sediments. Other exposures at Killycreen North (304900 415600) and Boyd's Bridge (304100 418400) contain similar sedimentary sequences but are partially grassed and now degraded with pit abandonment. 4. Isolated mounds of stratified sediment at a variety of scales occur at intervals east of the main Glarryford esker ridge. They generally consist of cross-bedded sand and pebbly gravel though exposure is poor. They lie 5-7m above the post-glacial valley fill and are probably more extensive with depth. Some of their margins show evidence of meltwater erosion and channelling. Several of these provide sites for recorded archaeological sites such as Dundermot Motte (306100 413300). | |
| Importance: | |
The Glarryford esker is classed as highly scientific important. Although esker systems occur at other locations in Ulster, the Glarryford system demonstrates the dynamic links between sedimentation, erosion and ice-sheet activity. The model presented above is the first attempt in Ireland to identify these links within a major tunnel valley/basal ice setting. It is of national importance in this respect. Further sedimentological work on this complex should result in important advances in geological knowledge from this unique geological setting. | |
| Interpretation: | |
Field relationships between the landscape elements, their relative positions within the Glarryford depression, formative meltwater conditions and sedimentary expression can be explained by the following sequence of events. 1. The scale and general form of the main depression suggests it is part of the subglacial tunnel valley system that operated during the deglaciation phase, though it was probably initiated much earlier. It is likely that at least part of the initial topography is a legacy from block faulting within the basalts. However the absence of streamlined subglacial bedforms along the main channel axis suggests that meltwater erosion continued during and after the later streamlining phases. 2. Some of the marginal glaciofluvial mounds show evidence of streamlining (e.g. Cabragh/Dernaveagh 308600 407900) and indicate tunnel sedimentation. Their location especially on the western margin of the depression and absence from axial locations suggest they are remnants of a sedimentary fill which was later modified by the event producing the surrounding the drumlin forms. 3. The crestlines of the streamlined forms show a strong orientation associated with ice flow to the northwest, slightly skewed (20-40ยง) to the tunnel axis. Drumlinoid and fluted forms may be a direct result of glacial erosion, though the streamlining of some stratified drift may be a reflection of catastrophic meltwater flow which focused along the axis of the tunnel valley (cf. Brennand and Sharpe, 1993). 4. Discontinuous and isolated gravelly mounds within the tunnel valley are difficult to evaluate genetically given the poor exposure. Some may relate to ice sheet hydraulic lifting, where pressure increases along major bends caused ice sheet erosion/lifting and lateral accretion away from the main conduit. However the available sedimentary evidence of multi-channelled infills suggests that these mounds are eroded remnants of gravelly spreads formed during final ice wastage, with sediment displacement over ice or ice-rich sediment towards the centre-line of the depression. The absence of clay drapes or a resedimented diamict indicates that no deep lakes existed after ice melting and the end of deglaciation. 5. The intact nature, continuity, and well preserved ice contact slopes of the discrete esker ridges together with lack of glaciotectonic disturbance indicate that they post date the streamlining event. In glaciofluvial terms they are likely to be a direct result of this event, which downdrew the main ice-sheet and decreased active forward motion. The major Glarryford esker and smaller discontinuous esker segments within the tunnel channel comprise coarse-grained gravels typical of high density flows in a subglacial tunnel (R-channel). The relative continuity of the eskers argues for synchronous sedimentation rather than time-transgressive sedimentation. Furthermore, the lack of ice-marginal features (delta splays, subglacial fans, cross-valley moraines) along the system also point to subglacial deposition and not to phased ice-marginal retreat. Wholesale ice stagnation at this time is also ruled out by the absence of extensive kettle holes and thermokarstic erosion. In a wider context the abrupt start and finish of the esker together with its high energy load suggest it represents deposition within a narrow R-channel driven by a south to north local piezometric surface and ice gradient (cf. Shreve, 1985). If this is the case then both ends of the palaeochannel where englacial. The absence of diamict overlying the esker sediments and absence of glaciotectonic deformation indicate two important conditions. First, the previous streamlining episode largely depleted the basal ice debris and detritus was transported from further south. Second, the ice sheet was almost glaciologically dead with very little forward motion or at least not sufficient motion to result in subglacial tunnel closure. The main sequence of events during the evolution of this glaciofluvial complex is as follows: 1) Tunnel valley erosion 2) Subglacial glaciofluvial deposition in the tunnel valley 3) Streamlining event and erosion of the infill 4) Subglacial esker resedimentation 5) Minor sediment shift to valley axis and channelling of all infills. | |
| Notes: | |
For general information and references on the sand and gravel landscapes of N. Ireland, and for directions to other regional sand and gravel sites, see the following site: Key Site 439 - Introduction to the Sand and Gravel Landscapes of N. Ireland | |
| Keywords | |
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| Rocks: | Gravel |
| Relations: | Deglacial sediments, Glacial streamlining |
| Geomorph: | esker, gravel ridge |
| Measurements | |||||
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| Length: | 12km | Width: | Height: | ||
| Depth: | Area: | 12km2 | |||
| Access | |
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| Management: | |
The Glarryford esker is classed as having a high aesthetic value. The general setting of the glaciofluvial subglacial complex along the axis of a tunnel valley provides a visually attractive landscape in a variety of ways, namely: 1. Most important is the visual mix of local topographic contrasts provided by the post glacial alluvial infill and raised bogs which drape the gravel topography. Seasonal changes in colour hues generated from this biological backcloth and the green fields of the raised gravelly hummocks and ridges provide a distinct pattern to this rural landscape. 2. The southern portion of the Glarryford esker ridge is in pristine condition and forms an exciting picture of a winding subglacial palaeoglacial channel fill paralleling the Main River. This aesthetic aspect of the esker is greatly enhanced by the mature stands of semi-hardwoods on the ridge sides and along the crest of the feature. 3. There is a minimum of new building development within the complex though in future construction on the drier ridge sites could create unwanted skyline disruption. 4. The raised bog around Ballyhutherland and Big Frosses has been recently drained and partially planted with conifers. Clearly such developments will not preserve the current biological mix in the area and will only increase the effectiveness of water supply to the River Main. 5. There are only four small gravel quarries within the complex with one operating using modern plant. The latter is gradually working northward along the main esker ridge (304600 416700). The other quarries have been recently (1-2yrs) abandoned but little landscaping has occurred. The Boyd's Bridge (304400 417900) quarry contains a large spoil heap directly along the roadside. It is generally recommended for this complex, that no further wildcat quarry operators should be permitted unless sites are chosen which can be finally landscaped to emulate the local topography. For example, if part of the main ridge is removed, unwanted quarry detritus should be fashioned into either a small winding ridge, discontinuous hummocks or rolling topography. Occasionally, steep quarry faces could be fashioned into arcs resembling meltwater scars in appropriate situations. With revegetation, biological diversity could be developed. Finally, the pristine esker ridge south of Glarryford has a uniqueness value and landscape position unrivalled in the eastern part of the province. | |
| Uses | |
| Uses: | There is one small gravel quarry currently operating within the complext. It is gradually being worked northward along the main esker ridge (304600 416700). |
| References (2) | |||
|---|---|---|---|
| Brennard, T.A. & Sharpe, D.R., 1993. Ice-sheet dynamics and subglacial meltwater regime inferred from form and sedimentology of glaciofluvial systems: Victoria Island, District of Franklin, Northwest Territories Canadian Journal of Earth Science, vol. 30, pp.928-944. | |||
| Shreve, R.L., 1985. Esker characteristics in terms of glacier physics, Katahdin esker system, Maine Bulletin of the Geological Society of America, vol. 96, pp.639-646. | |||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 6 Jun 2005 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Glarryford, County Antrim, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=466. Accessed on 2026-11-06. |
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