First cosmogenic 10Be age constraint on the timing of Younger Dryas glaciation and ice cap thickness,western Scottish Highlands

We use cosmogenic ¹⁰Be surface exposure age techniques at a locality close to Rannoch Moor, western Scottish Highlands, in order to establish the age and chronology of its most recent glaciation. Glacial erratics and an in situ bedrock quartz vein sampled from this site—the summit of Beinn Inverveigh—have yielded zero‐erosion exposure ages of 12.9 ± 1.5 ka to 11.6 ± 1.0 ka, implying complete ice cover of the mountain during the Younger Dryas, or Loch Lomond Stadial. These results fit closely with published ¹⁴C dates that bracket the maximum (lateral) extent of ice cap outlet glaciers, and are the first internally consistent ages to specifically address this period of glaciation in Scotland. Furthermore, the dates imply that previous palaeoglaciological reconstructions for this area may have underestimated both the thickness of the former ice cap and, by implication, its volume. © British Geological Survey/Natural Environment Research Council copyright 2007. Reproduced with the permission of BGS/NERC. Published by John Wiley & Sons, Ltd.     

A study of fluted moraines in the Torridon area,NW Scotland

A study of certain small-scale fluted moraines, all less than 4m high but up to 400m long, in the Torridon area has shown that they are subglacial features composed of a clast-rich till, and formed in the Loch Lomond Stadial beneath ice with a maximum depth of 100-200m. The evidence from lithological analysis of till samples from the fluted moraines suggests that they were formed by subglacial deformation of a pre-existing till with little in the way of net down-glacier movement of the material.     

Late Devensian and Flandrian palaeoenvironmental changes on the Scottish continental shelf west of the Outer Hebrides

Examination of two radiocarbon-dated vibrocores taken from south of St Kilda at a water depth of about 155 m, a short distance within the maximum position of the Late Devensian (Dimlington Stadial) ice sheet, suggests that the St Kilda Basin became free of glacier ice after 15250 yr BP. Sedimentation in a shallow, low energy, high arctic, muddy environment continued until after 13500 yr BP. There followed a higher energy temperate episode during which water depths were roughly about 40 m: this is correlated with the latter part of the Windermere Interstadial and with the warmer interval known in shallow Scottish seas about or a little before 11 000 yr BP. The Loch Lomond (Younger Dryas) Stadial is marked in the vibrocores by the return of muddy sediments and a cold-water fauna. Relatively shallow water conditions seem to have persisted into the earliest Flandrian, when the water depth was still roughly 60 m, corresponding to a sea-level in the area 90–100 m below present. It is suggested that pack ice was widespread in the northeast Atlantic before the Windermere Interstadial and also during the Loch Lomond Stadial, when it transported shards of Icelandic volcanic ash into the St Kilda basin. Estimates of sea-surface temperature for the last part of the Windermere Interstadial are close to those derived from the deep-sea record for the same period.     

The lateglacial lakes of Glens Roy,Spean and vicinity (Lochaber district,Scottish Highlands)

This paper summarises the evidence for glacial ice advance into lower Glen Spean during the Loch Lomond Stadial which involved the blockage of westward-flowing drainage to form a series of ice-dammed lakes, the former surfaces of which are marked by prominent shorelines. Detailed mapping of glacigenic landforms and instrumental levelling of the shorelines reveals a dynamic interplay between the glacier margins and lake formation. Subsequent deglaciation led to lowering of the lake levels, at times by catastrophic drainage beneath the ice (jökulhlaup). The abandoned shorelines have been warped and dislocated in numerous places as a result of glacio-isostatic deformation, faulting and landslip activity. The pattern of retreat of the ice can be deduced from the mapped distributions of retreat moraines and the levelled altitudes of numerous kame and fluvial terrace fragments. The sequence of events outlined in this paper provides important context for understanding the evolution of the landscape of the Glen Roy area during the Loch Lomond Stadial, and a prelude to more recent studies reported in other contributions to this thematic issue.     

Windpolished boulders and bedrock in the Scottish Highlands: evidence and implications of Late Devensian wind activity

The present day maritime climate of Scotland is primarily characterized by strong winds which, in very exposed sites, lead to modern windpolish of rock surfaces. The widespread existence of in situ relict windpolished boulders and bedrock surfaces in Scotland has enabled a reconstruction of prevalent Late Devensian (Late Weichselian) including Loch Lomond Stadial (Younger Dryas) palaeo-wind directions. Previous reconstructions of palaeo-wind directions have been indirect and based mainly on the distribution of aeolian sediments and former glaciers. Observations of relict windpolished microforms and their distribution on boulders and bedrock outcrops on various rock types at 55 sites in different parts of the Scottish Highlands have been used to establish a palaeo-wind map for the area. The reconstruction indicates two sets of dominating wind directions, one between SE and SW and one between NW and N. The maximum age of the windpolish is 16-10 cal. ka BP, but most of it presumably developed during the Loch Lomond Stadial 13-12 cal. ka BP, inferred from the distribution of windpolish sites in relation to the deglaciation chronology and establishment of vegetation.     

The gravel fans of upper Glen Roy,Lochaber, Scotland: their importance for understanding glacial,proglacial and glaciolacustrine dynamics during the Younger Dryas cold period in an Atlantic margin setting

Over the past 200 years significant research effort has gone into explaining the origin of the obvious former shorelines in Glen Roy (the so-called “Parallel Roads”). The large gravel deposit at the mouth of Glen Turret has attracted similar interest, but a solution to its origin and age remains contested: the same applies to the associated gravel fans in upper Glen Roy. This paper presents the results of systematic mapping and instrumental levelling of these features and new evidence from two previously unrecorded gravel fans in the nearby Allt Chonnal valley. Interpretation of altitudinal and lithofacies data indicates that all the fans (including the one at the mouth of Glen Turret) were deposited in a series of ice-dammed lakes during the Loch Lomond Stadial (Younger Dryas). The largest gravel fans were deposited in the shallow lake heads of the 260 m, 325 m and 350 m lakes in upper Glen Roy, infilling these areas to the extent that deposition was in part subaerial. The absence of foreset bedding from the deposits is explained by the relatively shallow depth of lake waters, which inhibited development of classic Gilbert-type deltas and encouraged Hjulström-type fans. The previous assumption that gravel deposition into the 325 m and 350 m lakes was relatively limited is shown to be erroneous. The Allt Chonnal gravel fans, deposited into these lakes, have an estimated combined volume of 6,000,000 m³ deposited in about 200 years. Significant gravel deposition into these former lakes continued at least until glaciers started to retreat in Glen Roy. When glacier retreat began, gravel deposition was reduced by over 85%. This research also concludes that the glacier which deposited the Turret fan emanated from Glen Gloy, supplied not only by ice from the south but also from ice that spilled into Glen Gloy from the adjacent Great Glen. The Loch Lomond Stadial (LLS) ice cap mapped in the Monadhliath Mountains was connected to the west Highland ice cap, which at the time filled the Great Glen. Regional equilibrium line altitude (ELA) estimates, based solely on the Monadhliath LLS ice cap evidence, may therefore be altitudinally too high.     

The Dimlington Stadial/Dimlington Chronozone: a proposal for naming the main glacial episode of the Late Devensian in Britain

The term Dimlington Stadial is proposed as a climatostratigraphic name fer the main glacial episode of the Late Devensian in Britain, in preference to stratigraphically unsatisfactory terms, such as Late Devensian Glaciation (which includes the Windermere Interstadial and the Loch Lomond Stadial), icesheet glaciation or maximum of ice expansion, that are currently in use. The name is selected from a site on the East Yorkshire coast and refers to the interval between 26,000 and 13,000 radiocarbon years B.P. Dimlington Chronozone is the formal chronostratigraphic term for the equivalent period of time, and comprises the main part of the Late Devensian Sub-stage.     

A high‐resolution seismic stratigraphy from a Scottish sea loch and its implications for Loch Lomond Stadial deglaciation

A detailed high‐resolution seismic stratigraphy, calibrated by core data and terrestrial geomorphological mapping, has been constructed for Loch Ainort, Isle of Skye. This study has provided a palaeoenvironmental history of the area as well as important corroborative evidence for the stepped deglaciation of the Loch Lomond Stadial ice‐field on Skye. The Ainort Glacier reworked pre‐Loch Lomond glacial deposits terminating in a grounded tidewater ice‐front potentially 800 m beyond the previously extrapolated limit. The first stage of deglaciation was characterised by the formation of De Geer moraines indicative of a period of interrupted retreat. The second phase, by contrast, produced hummocky relief with sporadic linear moraines suggesting periods of uninterrupted retreat with occasional stillstands/readvances. Paraglacial reworking of terrestrial slopes resulted in the deposition of thick, subaqueous, debris flows which graded into fluvioglacial dominated sediments and ultimately modern fjordic deposits. The identification of an initial period of active retreat punctuated by numerous readvances correlates directly with the terrestrial record. However, the offshore stratigraphy suggests that although the second phase was dominated by uninterrupted retreat, occasional stillstands/ readvances did occur. Copyright © 2000 John Wiley & Sons, Ltd.     

Glacial activity and paraglacial landsliding in the Devensian Lateglacial: evidence from Craig Cerrig-gleisiad and Fan Dringarth,Fforest Fawr (Brecon Beacons), South Wales

The tongue-shaped mass of debris and associated ridges on the cirque floor below Craig Cerrig-gleisiad, Brecon Beacons National Park is important and controversial because it has been attributed to more than one glacier advance during the Late Devensian. A new origin is proposed involving landslide development from the collapse of part of the western headwall followed by a single phase of glacier development in the Loch Lomond Stadial (Younger Dryas), which reworked the landslide sediments. Evidence for this landslide, which provides useful criteria for differentiating moraines formed by small glaciers from landslides, lies in tension cracks, backward-tilted blocks and bedrock joints dipping out of the western headwall, together with lateral levées, upstanding termini and angular clasts with only occasional, indistinct striae on the tongue-shaped mass, which is interpreted as a flowslide. Glacier reworking of debris in the upper part of the Cwm Cerrig-gleisiad landslide is indicated by subparallel ridges rising to 20 m above the cirque floor containing abraded clasts (16-32% striated). This interpretation is supported by a comparison with the morphological and sedimentary characteristics of a neighbouring landslide at Fan Dringarth, where no glacier developed in the Loch Lomond Stadial. The existence of paraglacial landsliding has significant palaeoenvironmental implications leading to: (1) erroneously large estimates of equilibrium line depression ($Δ$ELA) in the Loch Lomond Stadial; (2) consequent underestimates of summer palaeotemperatures and/or overestimates of the contribution of wind-drifted snow to glacier accumulation; and (3) larger moraines than usual and overestimation of the efficacy of glacial erosion because of antecedent processes.     

Deglaciation of the younger dryas or Loch Lomond Stadial ice-field in the northern Highlands,Scotland

When viewed from the air, Scottish ‘hummocky moraine’ can be resolved into a series of linear ridges that resemble those found at the margins of actively retreating glaciers today. Recent work has supported the interpretation of these linear ridges as ice-marginal landforms and the authors believe that the majority of ‘hummocky moraine’ deposits can be interpreted in this way. Consequently the pattern of deglaciation can be established fairly precisely from the pattern of linear ridges. This approach is applied to the landforms of the northern part of the Loch Lomond Stadial ice-field in order to reconstruct the regional pattern of deglaciation. This leads to important inferences about the significance of topographic control during deglaciation and more importantly it provides fresh insight into the environment of the British Isles during the Loch Lomond Stadial.     

Evidence for restricted Loch Lomond Stadial plateau ice in Glen Turret and implications for the age of the Turret Fan

Despite a wealth of research on the patterns and timing of glaciation in Glen Roy over the last 150 years, glacial events within Glen Turret remain heavily debated. These debates centre on the extent and source of Loch Lomond Stadial (Younger Dryas) ice in Glen Turret, and the implications for the age and genesis of the Turret Fan. Here we present details of recent systematic geomorphological mapping of Glen Turret and the neighbouring valleys to the north and east. The geomorphological evidence recorded indicates a plateau icefield style of glaciation centred on the Carn Dearg plateau, of which the Turret Glacier was an outlet. A morphostratigraphical approach is used to identify a relative chronology of glacial events, and suggests that the Turret Fan may have formed prior to the Loch Lomond Stadial. A reconstruction of the Carn Dearg plateau icefield is presented, which was connected to the larger Monadhliath Icefield to the east. Equilibrium line altitudes for the outlet glaciers range from 560 ± 20 m to 646 ± 20 m and are comparable with those calculated for surrounding regions. This research suggests that the Turret Fan is predominantly an older feature that was deposited by a more extensive plateau ice-sourced Turret Glacier prior to the Loch Lomond Stadial, most likely during or immediately after deglaciation of the last ice sheet.     

A marine seismic study of late Quaternary sedimentaion and inferred glacier fluctuations along western Inverness-shire, Scotland

A sparker survey was undertaken of the sea area inshore of the peninsula of sleat and the islands of Eigg and Muck in Western Scotland. This revealed major submarine moraines across the mouths of Loch Nevis and Loch Ailort, which help define the margin of a major glacier readvance phase, presumed to be equivalent to the late-glacial Loch Lomond Readvance. Formation names are suggested for the seismic para-stratigraphy. West of the moraines, there is a till (Minch Para-formation) resting on bedrock, overlain by a stratum (Muck para-formation) with well-defined internal layering parallel to the substratum. The till is presumed to have been deposited by an ice cap which at its maximum reached the western edge of the continental shelf at some time after 27,000 B.P. The Muck para-formation probably represents a glaciomarine unit deposited during the retreat of this ice cap, and has been deeply eroded. Above this erosion surface occur a series of sediments which infill local basins, and which appear to be of Flandrian age (Arisaig para-formation). East of the moraines in Loch Nevis and Loch Ailort the draped sediments are missing and the till is overlain by apparent equivalents (Nevis para-formation) of the marine sediments of Flandrian age to the west     

The Loch Lomond Readvance on the Isle of Skye,Scotland: Glacier reconstruction and palaeoclimatic implications

Geomorphological mapping of southern Skye indicates evidence for a single readvance of locally-nourished glaciers. These comprised a major icefield that occupied c. 155 km² of the main mountain area, a small icefield c. 10 km² in extent in the Kyleakin hills and ten corrie glaciers with a total area of c. 16 km². The absence of Lateglacial pollen sites, shorelines and periglacial features within the limits of local glaciation implies a Loch Lomond Readvance age for this glacial event. The area-weighted mean equilibrium line altitude (ELA) of the reconstructed Loch Lomond Readvance glaciers (319 m) conforms with a regional eastwards rise in ELAs that indicates dominant westerly airstreams during the Loch Lomond Stadial. An easterly decline in ELAs across the former icefields is interpreted in terms of easterly transfer of snow across ice-sheds by westerly winds, though the altitudes of corrie glacier ELAs suggest that the dominant snow-bearing winds were southerlies. Calculations based on the area-weighted mean ELA for the major icefield (308 m) indicate a stadial mean July sea-level temperature of c. 6 °C. The anomalously low gradients of certain former icefield outlet glaciers are attributed to deformation of subglacial sediment, an effect that may vitiate the assumption of linear ablation/accumulation gradients in the calculation of former ELAs for reconstructed glaciers.     

Modern glacier characteristics as a basis for inferring former climates with particular reference to the Loch Lomond Stadial

Studies of the mass balance of modern glaciers have indicated that the equilibrium line altitude (ELA) is the most critical parameter in the link between glaciers and climate. Average accumulation on a glacier includes components derived from direct precipitation on the glacier surface as well as wind-drifting and avalanching of snow, and approximates closely to accumulation at the equilibrium line. Ablation is most usefully predicted by mean summer temperature and there is a close, non-linear relationship between accumulation and mean summer temperature at the equilibrium line. Following discussion of methods of reconstructing former glaciers and calculating their equilibrium line altitudes, the application of the above relationships to the Loch Lomond Readvance glaciers of Highland Britain is considered and an outline of the precipitation pattern and the mean summer temperature of the Loch Lomond Stadial is given.     

Quaternary sea-level changes in Western Scotland

In recent years, major advances have been made in our understanding of Late Quaternary sea-level changes in western Scotland. In particular, new hypotheses have been advanced to explain the ages and origins of high-level rock platform fragments and high-level marine shell beds. Certain raised shorelines in Islay and Jura, SW Argyll and Wester Ross have been related to former margins of the last ice sheet and are associated with drops in the Lateglacial marine limit. In some areas the decline in Lateglacial sea-level took place in association with a stationary ice margin while in others the fall in sea-level occurred in conjunction with considerable ice retreat.During the Lateglacial Interstadial, relative sea-level fell rapidly between ca. 13 and ca. 12 ka BP and thereafter more slowly until ca. 11 ka BP. Renewed marine erosion during the cold climate of the Loch Lomond (Younger Dryas) Stadial (ca. 11-10 ka BP) resulted in the production of the Main Lateglacial Shoreline, which declines in altitude to the W, SW and S away from the centre of glacio-isostatic uplift in the W Highlands. The shoreline has a maximum altitude of 10–11 m O.D. in the Oban area and passes below sea-level in NE Islay, Ardnamurchan, Colonsay, W Mull, Kintyre and Arran.During the early Holocene a pronounced marine transgression took place, probably culminating between 6.6 and 7.0 ka BP. The culmination of the transgression is represented by the Main Postglacial Shoreline that reaches a maximum altitude of ca. 14 m in the Oban area and declines gently in altitude away from the centre of glacio-isostatic uplift. Reconstruction of the uplift isobases for this shoreline appears to indicate a slight eastward migration of the uplift centre since the Younger Dryas. In peripheral areas of western Scotland the Main Postglacial Shoreline is not present owing to the effect of Holocene submergence.     

The Late Devensian periglaciation of upland Scotland

A wide variety of Late Devensian periglacial landforms developed on Scottish mountains both before ca. 13,000 BP and during the Loch Lomond Stadial of ca. 11,000-10,000 BP. Nearly all such features are now inactive. Late Devensian periglacial weathering produced three types of regolith mantle (openwork block deposits, sandy diamicts and silt-rich frost-susceptible diamicts), each of which supports a characteristic assemblage of relict landforms. On upper slopes these include large-scale sorted circles and stripes, earth hummocks and nonsorted relief stripes, sorted and nonsorted solifluction features, massive boulder sheets and lobes, and nivation benches. Talus, protalus ramparts, rock glaciers and alluvial fans also developed at the base of mountain slopes.The distribution of Late Devensian periglacial features on Scottish mountains is locally controlled by topography, the response of underlying rocks to periglacial weathering and the limits of former glaciers. Regional variations in the altitude of certain forms of Loch Lomond Stadial age (particularly protalus ramparts and rock glaciers) indicate a decrease in former snowfall eastwards across the Scottish Highlands and northwards from the Highland Boundary Fault. Several upland periglacial features are also diagnostic of former permafrost, and complement palaeotemperature reconstructions based on ice-wedge casts and the equilibrium firn line altitudes of stadial glaciers. These suggest that under stadial conditions mean January temperatures at 600 m and 1000 m on mountains in the Western Grampians must have been no higher than −20°C and −23°C respectively, and possibly several degrees lower.     

Local and regional constraints on relative sea-level changes in southern Isle of Skye,Scotland, since the Last Glacial Maximum

New relative sea-level (RSL) data constrain the timing and magnitude of RSL changes in the southern Isle of Skye following the Last Glacial Maximum (LGM). We identify a marine limit at ~23 m OD, indicating RSL ~20 m above present c. 15.1 ka. Isolation basin data, supported by terrestrial and marine limiting dates, record an RSL fall to 11.59 m above present by c. 14.2 ka. This RSL fall occurs across the time of global Meltwater Pulse 1A, supporting recent research on the sources of ice melting. Our new data also help to resolve some of the chronological issues within the existing Isle of Skye RSL record and provide details of the sub-Arctic marine environment associated with the transition into Devensian Lateglacial climate at c. 14.5 k cal a bp , and the timing of changes in response to the Loch Lomond Stadial climate. Glacio-isostatic adjustment (GIA) model predictions of RSL deviate from the RSL constraints and reflect uncertainties in local and global ice models used within the GIA models. An empirical RSL curve provides a target for future research.     

Devensian Late-glacial and early Flandrian environmental history of the Vale of Pickering,Yorkshire, England

Pollen, sedimentological and charcoal particle analyses are presented from Devensian Late-glacial and early- to mid-Flandrian deposits from a former lake in the Vale of Pickering, Yorkshire. The combined analytical methods provide evidence for a short-lived climatic deterioration towards the end of the Late-glacial Interstadial, followed by a brief recovery prior to the Loch Lomond Stadial. This deterioration may be correlated with one of the ‘pre-Younger Dryas’ cooling periods identified not only in other pollen sequences from Britain and Europe, but from such diverse sources as Foraminifera from the Norwegian Sea and electrical conductivity measurements from the Greenland ice sheet. Loss-on-ignition and magnetic susceptibility data suggest that the Loch Lomond Stadial was characterised by an initial prolonged temperature decline, followed by a sudden more severe downturn resulting in particularly intense solifluction. Radiocarbon accelerator dating of the early Flandrian marl deposits illustrates the problem of age determination in calcareous lakes, and an estimate of the magnitude of ‘hard water error’ is obtained. The local population expansion of Alnus glutinosa is dated to 7640 ± 85 yr BP, but there is possible evidence for a Late-glacial presence of the tree, the significance of which is discussed in relation to other sites in east Yorkshire. © 1996 John Wiley & Sons, Ltd.     

A reinterpretation of the Lateglacial environmental history of the Isle of Skye,Inner Hebrides,Scotland

This paper presents a major revision of the Late Devensian Lateglacial environmental history of the Isle of Skye, Scotland, based upon a combination of geomorphological, biostratigraphical and radiocarbon evidence. The distribution of glacial and periglacial landforms, and of raised shorelines, suggests that there was only one extensive readvance of local glaciers in southern Skye following the wastage of the Late Devensian ice sheet. Pollen-stratigraphic evidence from 10 sites inside and 4 sites outside the mapped ice limits indicates that this readvance occurred during the Loch Lomond Stadial. At that time over 180km² of the uplands of south-central Skye were covered by glacier ice, a much more extensive glaciation than previously envisaged. Palynological evidence from four Lateglacial profiles implies that degree of exposure to strong westerly winds was the principal factor determing vegetational contrasts on the island, and that regional differences in vegetational type were less pronounced than has hitherto been suggested. The glacial and palaeobotanical reconstructions reported here are more compatible with Lateglacial data from the Scottish mainland and Hebridean islands than were the previously-published accounts for the Isle of Skye.     

Late Quaternary glaciation and environmental change on St. Kilda, Scotland, and their palaeoclimatic significance

On Hirta, the largest island of the St. Kilda archipelago near the western edge of the Scottish continental shelf, evidence has been found for four cold periods and one intervening mild period. During the most recent cold period (the Loch Lomond Stadial), two protalus ramparts were formed. Prior to this there occurred two periods of valley glaciation separated by a mild interval during which the local vegetation was dominated by grasses and sedges. For the most recent valley glaciation (= Late Devensian glacial maximum) a mean July temperature of 4°C is inferred. At this time intensive periglacial processes were operative down to present sea level. At some earlier, pre-Dcvensian, time St. Kilda was invaded by the Scottish ice sheet.