ISSN 1476-1580

North West Geography

Volume 11, Number 1, 2011

North West Geography, Volume 11, 2011 14 The last glacier in Dovedale,

Peter Wilson

Environmental Sciences Research Institute, School of Environmental Sciences, University of Ulster, Coleraine, Northern Ireland

Email: [email protected]

Abstract Field mapping of moraine ridges and mounds in Dovedale, Lake District, has enabled the reconstruction of a small valley glacier. At its maximum extent the glacier covered an area of 3.39 km2 and had an equilibrium line altitude of ~522 m. The presence of moraines in both the lower and upper parts of the valley suggests that the glacier underwent active retreat. Some of the ‘moraine ridges’ may have resulted from or been enhanced by fluvial erosion of thick drift sheets. Although the age of the moraines has not been determined it is inferred that the glacier developed during the Loch Lomond Stadial (12.9-11.7 ka BP). If this inference is correct the Dovedale glacier was the largest glacier to have developed in the eastern Lake District during this interval, and it probably connected across parts of the drainage divide with glaciers in neighbouring valleys.

Key words Moraines, Glacier reconstruction, Loch Lomond Stadial, Lake District.

Introduction 2002; Wilson 2002, 2004a), thus extending the total area of Moraine ridges and mounds associated with the last glaciers glacier ice in the LLS. that occupied the cirques and upper reaches of valleys in In some Lake District valleys there are moraines the Lake District of northwest have been mapped that Sissons (1980) thought were related to stillstands or and their significance discussed on many occasions since readvances of an ice cover that pre-dated the LLS. These Ward (1873, 1875) drew attention to them. It has been argued moraines were said to be ‘… larger and more rounded on the basis of biostratigraphical data from sites inside than the sharp forms typically associated with the local and outside of the moraine limits in some valleys that the glaciers …’. Several of these moraines were reinterpreted by glaciers developed during the Loch Lomond Stadial (LLS) McDougall (2001) and placed within the context of a more of 12.9-11.7 ka BP (Pennington 1964, 1978; Walker 1965). extensive LLS glaciation. Moraines in other valleys have been correlated with those At Dovedale a number of moraine ridges were at the biostratigraphically constrained sites because of their identified by Hay (1934) and their presence is also depicted locational and morphological similarities. on small-scale diagrams by Manley (1959) and Pennington Detailed mapping by Sissons (1980) revealed that 64 (1978). However, these moraines were not recognised by glaciers existed during the LLS. Although a few of these Sissons (1980), consequently in his scheme the cirques at the glaciers were linked across cols and ridges, and others had valley head were thought not to have nourished LLS glacier multiple source areas, no former summit or plateau icefields ice. Because the Dovedale moraines have not previously were recognised. In contrast, McDougall (2001) presented been described in detail it is the purpose of this paper to geomorphological evidence for plateau icefields in the report the results of a recent field mapping exercise aimed central Lake District and contended that outlet glaciers from at delimiting the moraines and to discuss the implications the icefields extended farther down valley than had the arising from the findings. cirque and valley glaciers proposed by Sissons (1980). At a number of other cirque and valley sites moraine ridges and Dovedale mounds have been mapped and ascribed to LLS glaciation Dovedale (NY 38/39 10/11, Fig. 1) is a southwest-to- (Clark 1992; Evans 1994, 1997; Oxford 1994; Evans and Cox northeast trending glaciated valley in the upper reaches of 1995; Wilson and Clark 1998, 1999; Clark and Wilson 2001, the Ullswater catchment in the eastern sector of the Lake

North West Geography, Volume 11, 2011 7 Figure 1: Moraine ridges and mounds in Dovedale. Scale is given by 1 km grid. Contours are in metres. © Crown copyright Ordnance Survey; all rights reserved.

District. The lower part of the valley between the Dovedale noted that moraine ridges were better developed on the Beck and Hogget Gill confluence and Hall is flat- north side of the valley than on the south side. The highest floored and flanked by the steep slopes of Hartsop above moraines recognised were at the foot of the steep slope How to the north and High to the south, below Black Crag. In a later paper Clark (2006) discussed the on each of which are a number of low cliffs. Above the morphology of a hillside drift bench that extends north for confluence the valley rises steeply to the cirques of Black 300 m from Hartsop Hall and queried its relationship and Brow, Little Hogget, Hogget Gill Head and Hunsett Cove significance with respect to the moraines. (Evans and Cox 1995), and the basin of Houndshope Cove. Prominent crags separate the cirques and cove from each Methods other, as at Stangs and . Rocks of the Borrowdale Moraine margins and crest lines, and gullied drift sheets Volcanic Group, principally lavas and tuffs, underlie the were mapped in the field onto 1:10,000 scale base maps with entire valley (British Geological Survey 1999). a contour interval of 10 m, using a hand-held GPS unit with The most comprehensive mapping of moraines in a resolution of <10 m. From these and geomorphological Dovedale (and the whole Ullswater catchment) is that of intuition the former glacier was reconstructed with surface Hay (1934). He depicted a number of discrete moraine contours at 50 m intervals following procedures used by ridges and an area of thick drift deposits in the lower part Sissons (1974) and adopted in other studies of Lake District of the valley, rather fewer moraines were recorded at higher LLS glaciers (Wilson and Clark 1998, 1999; Wilson 2002). The levels, but there was little description or discussion of their planimetric area between adjacent contours was determined morphology. Clark (1992) regarded the moraines at Hartsop and used to calculate the equilibrium line altitude (ELA) Hall as the outermost limit of the Dovedale LLS glacier. He using the area-weighted mean altitude (AWMA) method of

North West Geography, Volume 11, 2011 8 Sissons (1974) and the balance ratio (BR) method of Furbish and Andrews (1984). For the latter calculation BR values of 1.67, 1.8 and 2.0 were used as these most likely encompass the actual BR for mid-latitude glaciers (Furbish and Andrews 1984; Benn and Gemmell 1997; Ballantyne 2007). ELA was also estimated from accumulation area ratios (AAR) of 0.6 and 0.5 derived from a glacier area-altitude curve constructed for the former glacier.

Moraine Description Figure 2A: Moraine ridges on the north side of Dovedale The outermost moraines of the Dovedale glacier are Beck as seen from part way up the rock step. taken to be several low mounds with scattered boulders in the vicinity of Hartsop Hall (Fig. 1). Moraines are more extensive and evident with increasing distance up-valley where they occupy the break of slope zone between steep hillside and flat valley floor to the north of Dovedale Beck for distances of 200-550 m (Figs 1 and 2A). The downslope margins of the moraines (180-190 m OD) are everywhere sharply defined, but the upslope margins (210-240 m OD) are more difficult to delimit as the moraines grade into the steepening hillslope. Moraine crestlines trend oblique to or parallel with the valley axis and, again, scattered surface Figure 2B: Boulder-strewn moraine mound on the flood- boulders are present. An isolated and boulder-strewn plain of Dovedale Beck. Another mound in Thin Side Park, moraine mound on the floodplain (Fig. 2B) is likely to be on the south side of the beck, can be seen towards the top left. a remnant of more extensive valley floor moraines. On the south side of Dovedale Beck moraine ridges are considerably less prominent than on the north side, as noted by Clark (1992). Several low subdued ridges are present in Thin Side Park within a height range similar to those to the north and most have a trend that is perpendicular or slightly oblique to the valley axis (Fig. 1). The outermost limit of the glacier may have been in the vicinity of the cluster of large erratic boulders about 300 m south of Hartsop Hall and incorporated into prehistoric earthworks. Figure 3: The moraine ridges in Houndshope Cove. Between about 200 m and 300 m OD Dovedale is steepened considerably by a prominent rock step below the crest of Stangs. Immediately above the step in a slight bedrock outcrops. Wet ground in the depressions between widening of the valley there is a small area of moraine with the ridges suggests that these act as routes of sub-surface both parallel and obliquely aligned crests. A short distance flow. Boulder tongues from the backslope extend a short beyond this moraine the valley steepens again and the distance along some depressions and on some of the ridges beck divides. One branch falls from Hunsett Cove, which there are scattered boulder clusters and individual ice- is devoid of moraine ridges and mounds, the other branch transported boulders. falls from Houndshope Cove in which there is an extensive In the Hogget Gill branch of Dovedale thick drift and area of moraine ridges and mounds (Figs 1 and 3). The ridges moraine ridges are only present in the Black Brow cirque. descend from the base of a boulder-covered slope rising In the centre and below the backwall of the cirque an area to . In long profile the ridges are stepped with of drift is characterised by downslope-aligned ridges with each riser forming a lobe-like front to that section of ridge an amplitude of 1-4 m (Fig. 4A). On the eastern flank of the which it terminates. At the downslope limit of the ridges, cirque, at lower elevation (440-350 m OD) there are several just above the lip of the cove, there are several upstanding downslope-aligned ridges with maximum amplitude in

North West Geography, Volume 11, 2011 9 Figure 4A: Downslope-aligned, low-amplitude ridges in the centre of the Black Brow cirque. Figure 5: Short moraine ridges at the slope foot (left) and moraine mounds (centre right), highlighted by paler vegetation, at Bakestones Moss. The mounds are partly buried by Holocene peat.

indicate that the glacier underwent active retreat from its maximal position, therefore the reconstructed ice margins have been placed above all the moraines and gullied drift sheets. The moraine ridges and mounds are taken to be marginal features of the downwasting ice mass rather than Figure 4B: Downslope-aligned ridges on the eastern flank having formed subglacially at maximal extent. of Black Brow cirque. The upper margin of the glacier above Little Hogget and Black Brow is shown as coincident with part of the drainage divide between and Dove Crag the range 10-20 m (Fig. 4B). Depressions between some (Fig. 6). This is because there is clear evidence for the former ridges have open fluvial channels, others have wet ground existence of glacier ice at Bakestones Moss and around suggestive of sub-surface flow. Scandale Tarn (Figs 1 and 5). Therefore it seems reasonable Further areas of moraine ridges and mounds that may to infer that the Dovedale and Scandale glaciers straddled be significant with respect to the Dovedale glacier occur the ridge between their respective valleys. Similarly the immediately south of the Dovedale–Scandale drainage margin of the northwest sector of the Dovedale glacier is divide at Bakestones Moss and around Scandale Tarn to the inferred to have followed part of the broad ridge between south of Little Hart Crag (Fig. 1). At Bakestones Moss short Hart Crag and , and the glacier may and low ridges trend downslope at the foot of the slope have connected with the southern headward limit of the rising to Dove Crag and on the flatter ground ridges and glacier mapped by Sissons (1980) in Link Cove at about mounds are partly buried by the Holocene peat cover (Fig. 600-750 m OD. However, unlike at Bakestones Moss, there 5). The moraines at Scandale Tarn and downslope thereof are no moraine ridges or mounds along the ridge to support have not been mapped in detail. such a connection. At both Houndshope Cove and Black Brow it is not Discussion clear whether the mapped ridges are constructional or The low moraine mounds with scattered surface boulders erosional features. If they are the former then they can be in the vicinity of Hartsop Hall are regarded as representing used to delimit glacier margins during the final stages of the downvalley limit of the former Dovedale glacier, as ice wastage; if they are the latter then they are yet another previously proposed by Clark (1992). These have been used example of thick drift having undergone severe fluvial to delimit the position of the glacier snout at 160-170 m OD dissection (Ward 1873; Hay 1934; Wilson and Clark 1999; (Fig. 6). Lateral and upper limits of the glacier are not clearly Wilson 2004b). Drift dissection depths of up to 10-15 m have defined on the ground and have been inferred. The extensive previously been reported; the ridges at Houndshope Cove moraine ridges and mounds upvalley from Hartsop Hall and Black Brow are commensurate with these figures.

North West Geography, Volume 11, 2011 10 Figure 6: Proposed reconstruction of the Dovedale glacier at its maximum extent. Scale is given by 1 km grid. Contours are in metres. © Crown copyright Ordnance Survey; all rights reserved.

The reconstructed glacier (Fig. 6) had maximum is only slightly greater (by 3 m) than the mean of the BR- length of 3 km, maximum width of 2 km and a short and ELAs, a finding that is inconsistent with data from the Isle narrow snout. Glacier surface area was 3.39 km2; only three of Arran where AWMA-ELA values are generally 25-30 m of the 64 LLS glaciers mapped by Sissons (1980) had greater higher. However, taken together the AWMA and mean BR individual areas and these were in the central Lake District ELAs indicate the ELA of the Dovedale glacier was ~522 m, (McDougall (2001) has since proposed that these glaciers and this is supported by the AAR-ELA of 523 m. were considerably more extensive than indicated by Sissons As with most of the other sites that nourished LLS (1980)). The Dovedale glacier was the largest ice mass and glaciers in the Lake District, the Dovedale glacier faced north it extended to a lower elevation than any of the other LLS and northeast and was therefore orientated unfavourably for glaciers in the eastern Lake District. receipt of direct solar radiation during the ablation season. Application of the AWMA method of ELA calculation Sissons (1980) argued that wind-drifted snow made a major yields a value of 524 m. Estimates of ELA using BR values contribution to many LLS glaciers in the Lake District, as of 1.67, 1.8 and 2.0 are 524 m, 522 m and 518 m respectively did Mitchell (1996) for LLS glaciers in the western Pennines. (mean = 521 m). The ELAs determined using AAR of 0.6 Winds from southerly (Sissons, 1980) and westerly (Mitchell, and 0.5 are 523 m and 555 m respectively. The maximum 1996) directions are believed to have been responsible for difference of 6 m in the range of BR-ELA estimates indicates transferring snow to glaciers that faced between north and that choice of BR has little effect on calculated ELA, a finding east. In the case of Dovedale, there is a sizable area of high that is consistent with results derived for LLS glaciers in the ground around the summit of Dove Crag from which snow Isle of Arran (Ballantyne 2007). However, the AWMA-ELA might have been blown to nourish the glacier (Fig. 6). This

North West Geography, Volume 11, 2011 11 area includes slopes of low gradient facing between south Conclusions and west (i.e. away from the glacier). It has generally been Although moraine ridges and mounds are abundant in most assumed that only areas with continuous downhill slope valleys of the Lake District and in spite of numerous reports towards the glaciers would contribute to nourishment by describing their location and morphology, and assessing snowblow, but Shakesby and Matthews (1993) and Wilson their significance, it is clear, in the light of other recent work, and Clark (1995) contend that snow blown uphill and that much remains to be discovered about the extent, activity over escarpments and snow blown across slopes is also and timing of the last glaciers. The Dovedale glacier is a case likely to have made a significant contribution to glacier in point; its moraines have been included and excluded in accumulation. Therefore conventional snowblow factors different schemes portraying the extent of LLS glaciation. should be regarded as minimum indications of additional There is evidence to indicate that following the LGM Lake accumulation because they do not take into account upslope District glaciers did not simply decay in situ and fail to leave and across-slope snow transfers. behind ice-marginal moraines. However, in the absence of For some of the large LLS glaciers in the eastern biostratigaphic data and/or absolute age determinations Lake District (e.g. Grisedale, Deepdale and Blea Water) for many of the moraines, determining which relate to the with small snowblow factors, Sissons (1980) invoked high LLS glaciation and which are associated with a pre-LLS – precipitation in order to explain their existence. While this post-LGM stillstand/readvance of decaying valley glaciers may have been the case, snowblow factors would invariable remains a major challenge. be higher if windward facing slopes were to be included in the calculations. Although seemingly easy to rectify, the issue is intractable because of the difficulty in deciding on Acknowledgements a downslope altitudinal limit on the windward slopes for Kilian McDaid at the University of Ulster prepared the use in deriving snowblow factors. diagrams for publication, and Alastair Gemmell at the No direct age has been determined for the Dovedale University of Aberdeen kindly provided a copy of the ELA moraines. With the exception of the moraines at Rosthwaite calculation spreadsheet. in Borrowdale, Pennington (1978) thought that Lake District valley moraines could be assigned to the LLS. She claimed that the general absence of pre-LLS valley moraines indicated rapid decay of Lake District glaciers following the Last Glacial Maximum (LGM). In contrast, Sissons (1980) believed that moraines in several valleys pre-dated the LLS and therefore he did not include them in his scheme of LLS glaciation, whereas McDougall (2001) argued in favour of a LLS age for those in the central Lake District. Recent work by McCarroll et al. (2010) has indicated that following the LGM the Wasdale valley glacier may have persisted longer than previously envisaged, thus reopening the debate on valley moraine ages. At present it is inferred that the Dovedale moraines are of LLS age rather than associated with a late stillstand or readvance of a valley glacier pre-dating the LLS, but this inference may ultimately prove to be unfounded. Assuming that the Dovedale moraines were created in the LLS, a similar age probably applies to the moraines at Bakestones Moss and the head of Scandale. Likewise, moraine ridges and mounds at Caiston Glen, and Caudale Bridge are probably contemporary with those in Dovedale and indicate a more extensive LLS ice cover in this part of the Lake District than previously envisaged.

North West Geography, Volume 11, 2011 12 References Ballantyne C K 2007 The Loch Lomond Readvance on north Arran, Scotland: glacier reconstruction and palaeoclimatic implications Journal of Quaternary Science 22 343-359 Benn D I and Gemmell A M D 1997 Calculating equilibrium-line altitudes of former glaciers by the balance ratio method: a new computer spreadsheet Glacial Geology and Geomorphology http://ggg.qub.ac.uk/ggg/paper/full1997/tno11997/tn0.1.htm British Geological Survey 1999 Keswick England and Wales Sheet 29. Solid and Drift Geology. 1:50,000. Keyworth, Nottingham Clark R 1992 Quaternary features north of the Kirkstone Pass. In Dodd M ed Lakeland rocks and landscape. Ellenbank Press, Maryport. 88-94 Clark R 2006 On identifying frontal positions of Lake District valley glaciers Proceedings, Cumberland Geological Society 7 162-176 Clark R and Wilson P 2001 Origin of some slope-foot debris accumulations in the upland, northern Lake District Proceedings of the Yorkshire Geological Society 53 303-310 Clark R and Wilson P 2002 Landform studies in Mosedale, northeastern Lake District: opportunities for field investigations Field Studies 10 177-206 Evans I S 1994 Cirques and moraines of the northern , : Bowscale and Bannerdale In Boardman J and Walden J eds The Quaternary of Cumbria: field guide. Quaternary Research Association, Oxford 129-142 Evans I S 1997 Cirques and moraines of the range, Cumbria: Grisedale and Ullswater In Boardman J ed Geomorphology of the Lake District: a field guide. British Geomorphological Research Group, Oxford 63-87 Evans I S and Cox N J 1995 The form of glacial cirques in the English Lake District, Cumbria Zeitschrift für Geomorphologie 39 175-202 Furbish D J and Andrews J T 1984 The use of hypsometry to indicate long-term stability and response of valley glaciers to changes in mass transfer Journal of Glaciology 30 199-211 Hay T 1934 The glaciology of the Ullswater area Geographical Journal 84 136-148 Manley G 1959 The Late-glacial climate of north-west England Liverpool and Manchester Geological Journal 2 188-215 McCarroll D Stone J O Ballantyne C K Scourse J D Fifield L K Evans D J A and Hiemstra J F 2010 Exposure-age constraints on the extent, timing and rate of retreat of the last Irish Sea ice stream Quaternary Science Reviews 29 1844-1852 McDougall D 2001 The geomorphological impact of Loch Lomond (Younger Dryas) Stadial plateau icefields in the central Lake District, northwest England Journal of Quaternary Science 16 531-543 Mitchell W A 1996 Significance of snowblow in the generation of Loch Lomond Stadial (Younger Dryas) glaciers in the western Pennines, northern England Journal of Quaternary Science 11 233-248 Oxford S P 1994 Periglacial snowbed landforms at Dead Crags, Cumbria. 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