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Earth Science Conservation Review
| Lagan Valley | Antrim |
| Site number: | 489 | ||
| ESCC: | IS | ||
| Locality Type: | Inland exposure, Pit | Status: | TBC |
| Grid Reference: | J335731,J122649 End(s) of linear site, Not Entered | ||
| Google maps: | 54.58896,-5.93483 | ||
| County: | Antrim | Council area: | Belfast City Council |
| Period: | Quaternary | ||
| Site Description | |
|---|---|
| Highlights: | |
The Lagan valley complex, located along a densely populated and intensively farmed lowland valley, records important regional scale events during deglaciation. Streamlined landforms along the margins of the valley axis and glacially moulded bedforms indicate ice advance and episodes of fast ice flow through the area from the west. The occurrence of glaciolacustrine deposits indicates that during the initial stages of the Lagan valley's deglaciation, the lower valley which is now the location of Greater Belfast contained an ice-dammed lake probably impounded by an ice mass of Scottish origin located in outer Belfast Lough. The area of the valley formed a separation zone between Scottish and Irish ice after the main phases of drumlinisation and deglaciation of the Irish Sea basin area to the southeast. A lobe of Irish ice located in the valley, related to ice pressure from the Lough Neagh Lowlands to the west, contained subglacial conduits now recorded by eskers along the valley which probably supplied sediment during the formation of the Malone deltaic sands which now underlie most of south Belfast. The phased retreat of the ice lobe further westward is recorded by a sequence of cross-valley ice-contact cross-valley ridges at located at Drumbeg, Sandymount and Hillhall. During the final stages of deglaciation, drainage of the valley was to the west, indicating a reversal in the drainage gradient probably due to isostatic depression of the Lough Neagh Lowlands during the last glacial cycle possibly coupled with the presence of Scottish ice at the mouth of Belfast Lough. | |
| Description: | |
The deposits of the Lagan valley which occur predominately in the northeastern part of the valley are described from east to west, from Belfast Lough to the shores of Lough Neagh. The description of the glaciofluvial and glaciolacustrine deposits contains many references to the borehole logs and detailed surveying documented by the members of the Geological Survey of Northern Ireland [G.S.N.I.] (1904, 1970). Many of the exposures upon which they based their interpretations of the deglacial events in the Lagan valley are no longer available for evaluation. Interpretations are based therefore on the limited sedimentology documented by the Geological Survey, the observed morphology of the landforms, field relationships between the morphological elements, and the regional deglacial chronology inferred from other areas and literature sources (e.g. Charlesworth, 1939; Synge and Stephens,1966; Stephens, 1963). 1. Malone delta A 3km wide, northeast sloping spread occurs from between the Ballydrain (330400 368000) to Purdysburn (333700 367500) area (at 40m O.D.) to the southern margins of Belfast city centre (at approximately Bradbury Place (333500 373100)) (at 20m O.D.). The southern part of the deposit around Ballydrain and Upper Malone to 2-3km northeastwards is undulating, but generally occurs at a similar height (40m O.D.). To the northeast of this area, the spread slopes gently towards Belfast Lough and the flood plains of the Lagan and Blackstaff rivers to the east and west respectively. The steep-sided southern margin of the ridge at Ballydrain (331100 367600) forms the bank of the Lagan river. Three exposures on the crest of the ridge showed 19.4m of sand containing clay streaks overlain by 4.3m of 'boulder clay' at Queens University (333700 372600), 11m of sand containing mud 'streaks' overlain by 'boulder clay' 0.25km south at Stranmillis Road (333400 372300), and 7m of sand at Lennoxvale (333400 372200) (G.S.N.I., 1970). In three exposures near its southern margins at Shaws Bridge (332500 369100) 1.2m of gravel overlay 0.9m of sand, 1.2m of sandy gravel overlay 1.8m of sand and 2.4m of sandy gravel overlay 4.6m of boulder clay (G.S.N.I., 1970). Near these locations the Ballydrain lake (331100 367600) occupies an enclosed depression in the spread. The sediment sequence on northeastern margins of the spread, along the depression of the Lagan valley generally consisted of laminated muds underlain and overlain by 'boulder clay' facies (G.S.N.I., 1904, 1970). To the northwest of the spread and the Blackstaff channel, on the elevated ground forming the footslopes of the Cave Hill massif, two sections showed boulder clay overlying up to 5.5m of laminated clay and sand (G.S.N.I., 1970). It is not clear if all the facies described as boulder clay (G.S.N.I., 1904, 1970) are subglacial in origin, and may be of different provenance and/or diverse origins. The diamict facies consistently overlie fine-grained sandy and laminated sequences in the northern, western and northeastern parts of the area. 2. Drumbeg ridge At Drumbeg, 0.5km to the southwest of Ballydrain, a 1.2km long smooth-crested, asymmetric cross-valley ridge with oversteepened southern slopes occurs to 30m O.D. at Drumbeg (330000 367100). A borehole on the ridge crest showed a 7.5m of fining upward sandy clay overlain by 1.5m of laminated clay (G.S.N.I., 1970). The topography is smoothly undulating to the south of the ridge for 200m, with a local relief of <2m. The ground then rises southwards to the northern edge of the Sandymount ridge. 3. Sandymount ridge A 2km long (0.5km2) curvilinear, asymmetric cross-valley ridge with an undulating top occurs as a generally northwest/southeast oriented ridge up to 35m O.D. immediately north of Sandymount (328400 365900). The ridge has steeper southern slopes adjoining which are two <0.25km long southwest/northeast oriented linear ridges and a detached mound. The gross morphology of the ridge is concave to the north, curving towards the southern margins of the Drumbeg ridge at the northeastern end and forming the bank of the River Lagan at the northwest end. Two water-filled enclosed depressions occur immediately next to its northern margin. 4. Hillhall ridge A 0.7km long, up to 0.2km wide belt of generally west/east oriented linear ridge segments and dissected mounds occurs at 40m O.D. from Hillhall (329400 364400) to the northeast part of Lisburn. A water-filled kettle-hole depression occurs at (329100 364600) immediately north of the belt. 5. Lisburn esker Remnants of a linear ridge, which is now largely removed or built over, occurred along the northwest margin of the Lagan Valley axis from the southwest of Dunmurry (329500 368500) to the northeast margins of Lisburn (326500 364300). 6. Causeway End esker Remnants of a steep-sided linear ridge oriented west/east occur between Brookmount (321900 365100) and the western margins of Lisburn at up to 60m O.D. The ridge has been the site of extensive commercial sand and gravel extraction. Pebbles from a disused pit at (323600 364600) consist of Triassic sandstone (70%), Cretaceous chalk (3-5%), Tertiary dolerite(<1%) and basalt (5%). In addition, Dwerryhouse (1923) documented erratics of red granite (Tyrone), Tardree rhyolite and fossil wood derived from the Lough Neagh Clays to the west. 7. Maze Plain A 12km2 continuous area of flat and gently undulating topography occurs along the central axis of the Lagan Valley from Blaris (324700 362800) 1km southwest of Lisburn, to Soldierstown (315300 362800). The belt is bordered to the north and south by generally west/east oriented subglacial landforms including drumlins and streamlined ridges. Exposures within the belt showed up to 14m of sand at Blaris, 4.5m of laminated mud overlain by 1.8m of (yellow) sand at Halftown (323400 362600), and 11m of sand containing lenses of pebble gravel at Mazetown (322200 362600) (G.S.N.I., 1970). 8. Aghalee delta A 0.15km2 flat-topped spread of sand and gravel located at 30m O.D. occurs at Aghalee (312400 364900). The deposit occurs at the western exit of the steep-sided, flat-bottomed 3.5km long channel at Soldierstown (315300 362800). The channel drains northwestwards from an intake at 39m O.D. at Soldierstown on the western edge of the Maze plain to 20m O.D. at the southeast corner of the Lough Neagh lowlands. 9. Glacial striae Glacial striae and roches moutonn‚es have been documented at Carryduff (336900 365400) oriented north-northwest to south-southeast, and at Upper Ballinderry (316300 367100) possibly oriented east to west (G.S.N.I., 1970). 10. Raised Beach A generally 2-3km wide bank consisting mainly of diamict (G.S.N.I., 1970), which levels off to a plateau top at 50m O.D., occurs along the western edge of the Lagan valley against the rising bedrock slopes of the Antrim Plateau scarp. The belt occurs along the western margins of the city from Newtownabbey (334500 382500) in the north to White Mountain (324000 367700) in the west over a distance of 10km. Contained in the belt at Fortwilliam (333700 377600) is a notch located at 6m O.D., which possibly records a post-glacial high relative sea level in Belfast Lough (cf. Stephens, 1963). | |
| Importance: | |
Model Summary The model presented here agrees with evidence from other areas of the province on the regional deglaciation pattern and generally with the models of other authors. Dwerryhouse (1923) postulated that north east Ireland was inundated twice by Scottish ice during the last glacial period. An early glaciation resulted in the widespread distribution of Ailsa Craig microgranite, whereas during the last glacial cycle, an Irish ice mass centred to the west of the Lagan valley prevented the intrusion of Scottish ice deep into the Lough Neagh lowlands. The presence of southward advancing Scottish ice inland from the east coast of Ireland has been shown by several documented occurrences of Ailsa Craig (G.S.N.I., 1904, 1970; Hartley, 1937) and Cushendun microgranite erratics (Dwerryhouse, 1923; Hill and Prior, 1968) at Red Hill near Lisburn. It is postulated here that the deglacial pattern in the Lagan valley shows: 1) Drumlin and striae orientations indicate a north/south advance of Scottish ice and west to east advance of Irish ice across the valley. The deflection of the Scottish ice southwards in Belfast Lough (Dwerryhouse, 1923) and the pressure of Irish ice shown by the later formation of the glaciolacustrine deposits in the valley confirms that the deflection was probably caused by the presence of Irish ice. The deglacial model fits the postulated models of ice advance and drumlinisation events within the region. 2) The formation of a temporary, Glacial Lake Lagan indicates that the eastern end of the Lagan valley was probably impounded by an ice mass of Scottish provenance during the last deglacial period. The pattern of deglaciation in the Lagan valley indicates a separation of Irish and Scottish ice masses at this location after collapse of the Irish Sea Glacier (Eyles and Mc Cabe, 1989). The timing of lake impoundment and the presence of the Irish ice margin indicates a difference in the retreat rates of the two ice lobes, possibly due to the larger extent of the Scottish ice mass. The postulated model for the deglacial sequence in the Lagan valley requires an extension of concepts into hypotheses on the deglaciation of the Irish Sea basin. More specifically these concepts concern the relative timing and importance of the two great ice sheets which amalgamated to form the Irish Sea Glacier (Eyles, and Mc Cabe, 1989) 3) The Lagan valley eskers probably represent conduits within the Irish ice mass, the sediments within which contained clasts of predominately local, indigenous origin (Cretaceous chalk, Triassic sandstone, Tyrone igneous, Tardree rhyolite) and occasional, reworked erratics (e.g. Ailsa Craig microgranite) from a previous inundation of Scottish ice. 4) The Soldierstown channel post-dated the formation of the Malone delta and the cross-valley ridges along the valley with isostatic depression of the Lough Neagh basin causing east to west drainage of Glacial Lake Lagan. A similar reversal of regional drainage gradients due to the isostatic depression of the Lough Neagh basin has also been postulated in the model of the Pomeroy area (see Key Site 482 - Pomeroy). 5) The field association of deposits and meltwater channels indicates that the Lough Neagh basin to the west was probably isostatically depressed during the deglacial period. Evidence for the Lough Neagh basin forming one of the principal dispersion and lowland decay centres of Irish based ice during the last glacial period has been documented in other reports and extensively in the literature on Northern Ireland's glacial geology (e.g. Dardis, 1985; Eyles and Mc Cabe, 1987). 6) The deposits at Aghalee support the presence of a Glacial Lake Neagh at 30m O.D. (Charlesworth, 1939). 7) The morphology and internal geometry of the deposits in the Lagan valley complex have been obscured by the construction of urban areas. Sediment exposures have however been documented by the workers of the Geological Survey (e.g. Manning et al., 1970). | |
| Interpretation: | |
The pattern and chronology of deglacial events in the Lagan valley is inferred largely from sedimentological evidence documented by workers of the Geological Survey (1904, 1970), the morphology and field relationships between landforms. The area lacks the sedimentological exposures necessary for detailed palaeoenvironmental reconstructions. The pattern of gross ice movement and chronology is schematically illustrated and for the purposes of explanation divided into four principal stages: 1) Ice advance Scottish ice advanced into the area of Belfast lough, coincident with the advance of Irish ice from a distribution centre to the west recorded by the roche mountonn‚e at Upper Ballinderry and streamlined landforms along the margins of the Lagan valley. The confluence of the two ice masses resulted in the deflection of flow southwards, recorded by the striae observed at Carryduff (G.S.N.I., 1970). Other ice-flow indicators in southeast Antrim suggest ice flows were complex in this area and are not fully understood. For example directional indicators around Glengormley suggest that ice may have moved northwards through the area. This may indicate that ice sheet divides and domes shifted, and thus ice flow patterns changed, during the course of the last glacial cycle. 2) Deglaciation and formation of glacial Lake Lagan The collapse of the Irish Sea Glacier (Eyles and Mc Cabe, 1989) resulted in the withdrawal of ice northwards along the Irish Sea basin area and retreat of Irish ice towards the decay centre of Lough Neagh. The morphological form of the Malone delta, which decreases in elevation northwards and consists of generally northward fining sediment sequence, indicates that it was sediment from an Irish land based ice mass which the delta is composed of. The red staining of the sand indicates a local origin in the (highly erodable) red Triassic sandstones. The subaqueous deposition of the sand and laminated muds documents the position of Glacial Lake Lagan between an Irish ice margin located across the Lagan valley between Dunmurry, Ballydrain and Purdysburn and Scottish ice, probably occupying the topographic low of Belfast Lough (cf. Dwerryhouse, 1923). Sediment supplied by the meltwaters issuing from the Irish ice which was possibly conducted along the conduit paths marked by the Causeway end and Lisburn eskers, prograded into the lake and formed the Malone delta as a subaqueous spread. Sedimentological evidence shows that the sediments generally fine northeastwards from Shaw's Bridge/Ballydrain along the length of the delta body (G.S.N.I., 1970). Laminated clays exposed at the northeast and northwest margins of the spread possibly resulted from suspension fallout and underflow. The burial of ice blocks at the ice margin resulted in the formation of a kettle hole at Ballydrain. The maximum elevation (40m O.D.) of the spread at this location indicates a lake depth in the valley to at least 40m O.D. A variable retreat rate of the Irish ice margin westwards along the Lagan valley resulted in the accumulation of cross-valley ridges at Drumbeg, Sandymount (with eskers at its western margin possibly indicating continued sediment supply along the Causeway End/Lisburn conduit) and Hillhall. The elevation of the ridges (30m O.D.) possibly indicates a lowering of the waterbody surface with the expansion of the lake area. The burial of ice blocks at the ridges and oversteepened, western slopes indicates an ice-contact origin for the ridges. 3) Glacial Lake Lagan drainage Initially Glacial Lake Lagan probably drained to the west associated with either the opening of a route to the Poyntzpass channel as the ice-margins contracted towards the Lough Neagh lowlands or subglacial drainage into the decaying ice mass. Later, the Soldierstown channel, which intakes at 39m O.D., formed a westward draining outlet of meltwater in the Lagan Valley and formed the Aghalee delta in a waterbody ponded at 30m O.D. at the eastern margin of the Lough Neagh lowlands. Deposition of the delta probably occurred into the 30m O.D. Glacial Lake Neagh (Charlesworth, 1939) which occupied the Lough Neagh basin during the late-glacial period. Dardis (1986) documents a prominent notch in south central Ulster at this elevation probably related to shoreline erosion. It is inferred that the flat sandy outwash deposits occurring from the Maze up to the intake of the Soldierstown channel were formed by the westward flowing water and the dissection of cross-valley ridges at Drumbeg, Sandymount and Hillhall. Much of the original morphology of the cross valley moraines may have been completely removed. The present topography therefore represents remnant ice-contact morphology. 4) Isostatic recovery The regional drainage gradient, based on the association of the Soldierstown channel and formation of the delta at Aghalee was therefore westwards, contrasting with the present drainage of the Lagan valley towards the east. This reversal is probably associated with deep relative isostatic depression of the Lough Neagh basin during the final stages of deglaciation. The late-glacial isostatic depression of the landmass is shown by the raised beach notch occurring at 6m O.D. along the northwest margins of the estuary. Final melting of the Irish ice mass ice and isostatic recovery sometime during the Late or Early Post-glacial returned the Lagan river drainage to its present eastward course. | |
| 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 | |
|---|---|
| Rocks: | Gravel, Sand |
| Relations: | Glacio-fluvial sediment, Glaciolacustrine deposit, Isostatic depression |
| Geomorph: | deltas, esker, meltwater channel |
| Access | |
|---|---|
| Management: | |
The area is predominately urban and improved farmland. The has been extensive removal of deposits in selected locations, principally the Lisburn esker. The majority of sand in the valley is contained within the Malone delta, which is now covered by the Greater Belfast urban area. Topographic diversity and scenic enhancement are added along the valley axis, especially when travelling along the M1 motorway, by the arcuate cross-valley ridges at Drumbeg and Sandymount and the flat outwash plain at the Maze. | |
| Uses | |
| Uses: | Predominately urban and improved farmland. |
| References (7) | |||
|---|---|---|---|
| Dardis, G.F., 1986. Late Pleistocene lakes in south-central Ulster, Northern Ireland Irish Journal of Earth Sciences, vol. 7, pp.133-144. | |||
| Dwerryhouse, A.R., 1923. The glaciation of north-eastern Ireland Journal of the Geological Society of London, vol. 79, pp.352-422. | |||
| Eyles, N. & McCabe, A.M., 1989. The late Devensian (< 22,000 B.P.>) Irish Sea Basin: The Sedimentary record of a collapsed ice sheet margin. Quaternary Science Reviews, vol. 8, pp.307-351. | |||
| Hartley, J.J., 1937. Lisburn Esker Irish Naturalists Journal, vol. 6, pp.208-. | |||
| Kilroe, J.R.et al., 1904. Geology of Belfast and the Lagan Valley Memoirs of the Geological Society of London, numb. 36 HMSO. | |||
| Manning, P.I., Robbie, J.A. & Wilson, H.E., 1970. Geology of Belfast and the Lagan Valley. Memoirs of the Geological Survey Northern Ireland. | |||
| Wilson, H.E., 1972. Regional Geology of Northern Ireland. HMSO, Belfast. | |||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 6 Jun 2005 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Lagan Valley, County Antrim, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=489. Accessed on 2026-11-06. |
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