a r t i c l e i n f o
1. Introduction
The Younger Dryas (Greenland Stadial 1; 12.9e11.7 cal. ka BP;
Lowe et al., 2008), the last major cold period before the onset of the
present interglacial, is one of the most intensively studied events in
the palaeoclimate record (Broecker et al., 2010). It occurred during a
time of high summer insolation at the end of the Last Glacial, and its
impact appears to have been most pronounced in the northern
hemisphere, especially the North Atlantic region where a return to
a full glacial climate is indicated by a range of proxy data (e.g. Lowe
et al., 2008; Palmer et al., 2012). The Younger Dryas in Britain
(where it is also known as the Loch Lomond Stadial) witnessed
renewed glaciation, with the readvance of ice masses that had
survived the preceding Lateglacial Interstadial (Greenland Interstadial
1; 14.7e12.9 cal. ka BP; Lowe et al., 2008) (e.g. Finlayson
et al., 2011) as well as the formation of new glaciers. Studies have
shown that the main area of glacierisation was in the western
highlands of Scotland, where an ice cap developed, with smaller ice
masses forming in other parts of upland Britain (e.g. Gray and
Coxon, 1991; Golledge, 2010) (Fig. 1).
The extents of these former glaciers have been mapped by many
workers over the past ﬁfty years, usually as a basis for palaeoclimatic
reconstructions, and the result is a large and growing
volume of published work. To some extent this level of interest
stems from the striking clarity of many Younger Dryas moraines in
upland Britain, which is considered to contrast markedly with the
more subdued appearance of depositional landforms associated
with the last (Late Devensian) ice sheet (e.g. Manley, 1959). Indeed,
it was frequently asserted in studies published during the 1970s
and early 1980s that the well-deﬁned nature of the geomorphological
evidence allowed the accurate reconstruction of Younger
Dryas glaciers at or near maximum extents (e.g. Lowe and Walker,
1984, p. 27; Ballantyne and Harris, 1994, p. 18). More recent
studies, however, have shown that this conﬁdence is not always
warranted, and there is a growing body of evidence to suggest that
previous investigators underestimated the extent and importance
of summit glaciation in Britain during the Younger Dryas (e.g.
McDougall, 2001; Finlayson, 2006). This is not altogether surprising;
investigations in contemporary glacial environments demonstrate
that the geomorphological impact of summit iceﬁelds tends
to be limited due to low basal shear stresses and locally cold-based
ice, which in turn makes them difﬁcult to recognise in the landform
record (e.g. Gellatly et al., 1988; Rea et al., 1998). The failure to account
for such iceﬁelds may result in outlet glaciers being incorrectly
reconstructed as valley glaciers, which in turn will produce
an over-estimation of equilibrium line altitude (ELA) lowering (Rea
et al., 1998).
Although much work remains to be done, there is now a better
understanding of the glaciological signiﬁcance and geomorphological
impact of the summit iceﬁelds that developed in Britain
during the Younger Dryas. Unfortunately, less attention has been
devoted to investigating the inﬂuence this style of glaciation had on
valley-ﬂoor landform development at this time. Evans (1990),
working in NW Ellesmere Island, demonstrated that glacier
morphology is one of a number of factors inﬂuencing moraine
development on valley ﬂoors, in part because it determines the
extent and location of extraglacial debris source areas. Nevertheless,
the extent to which such observations have informed the
interpretation of the geomorphological record in Britain is not
entirely clear, although some examples exist in which marked
variations in valley-ﬂoor glacial landform development have been
attributed, at least in part, to glacier morphology (e.g. McDougall,
1998).
Fig. 1. Glacier development in northern Britain during the Younger Dryas (after Price, 1983; Golledge, 2010; Brown et al., 2011; Finlayson et al., 2011). Glaciers also developed in
other parts of Britain, most notably in the Welsh uplands (e.g. Hughes, 2009; Bendle and Glasser, 2012).
49
The inﬂuence of glaciation style on the geomorphological record
is important and worth studying, not least because contrasts in
moraine morphology have been employed in the literature to
distinguish between Younger Dryas and older glacial landforms.
This paper explores the inﬂuence of glacier morphology on valleyﬂoor
landform development in the eastern Lake District, northwest
England, where detailed geomorphological mapping by the author
has revealed evidence for a more extensive and complex pattern of
mountain glaciation than was previously thought to be the case (c.f.
Sissons, 1980).
2. Study area
The study area is located in the eastern Lake District, a lowrelief
mountain environment in northwest England (Fig. 2), and
covers approximately 200 km2
. It is underlain by basaltic,
andesitic, dacitic, and rhyolitic lavas, sills and tuffs with interstratiﬁed
volcaniclastic sedimentary rocks; these are thought to
record subaerial arc volcanism and subsequent caldera collapse
(Branney and Kokelaar, 1994). Extensive faulting, most of which is
volcano-tectonic in origin, has inﬂuenced landscape development;
many valleys have been excavated along fault lines, creating
a complex topography. In the west and south of the study area, for
example, valley axes tend to have a NeS orientation, whereas this
becomes WeE in the central area and SWeNE in the northeast
section.
Evidence for glacial modiﬁcation of the landscape within the
study area is widespread, and includes classic examples of troughs
(e.g. the Haweswater valley) and cirques (e.g. Mardale Head).
Nevertheless, there are some valleys that bear little evidence for
glaciation, particularly in the northeast and southeast of the study
area. The intervening high ground mostly lies between 700 m and
800 m, with the highest summit being Racecourse Hill at 828 m.
3. Previous work
Although visually impressive moraines in the cirques and valley
heads of the Lake District have long attracted attention (e.g. Ward,
1873; Marr, 1895), Manley (1959) was the ﬁrst to use them in a
regional assessment of Lateglacial climate. The former existence of
glaciers in the Lake District at this time had already been demonstrated
by Pennington (1947) and Walker (1955) on the basis of
varved lake sediments. Manley was of the opinion that the cirque
and valley-head moraines could be distinguished from others in the
area on account of their ‘freshness’, a quality he attributed to their
relatively steep gradients (20e25) and sharp breaks of slope with
the valley-ﬂoor. Older moraines, he reasoned, would be more
subdued following intense periglacial weathering during the colder
part of the Lateglacial. Manley used the distribution of these
younger-looking moraines to produce a map of Younger Dryas
glacier extents, but unfortunately the scale prevents any detailed
consideration of their margins here. Careful inspection of his map,
however, reveals the existence of glaciers in most of the central
valleys within the study area, and an attempt has been made in
Fig. 2 (see inset map) to show their approximate extents. He estimated
ELAs of 500e550 m for all glaciers in the study area,
assuming in most cases that the ELA was located halfway between
the terminus and the base of the upper crags. For the Lake District
as a whole, he estimated that the July mean temperature during
this period was 7.5 C, with annual precipitation totals similar to
today [for full details, see Manley (1959)].
A reassessment of Younger Dryas glaciation in the Lake District
was undertaken by Sissons (1980), who employed what was by
then a well-established approach to glacier reconstruction [see
Sutherland (1984)]. Like Manley before him, Sissons considered
moraine morphology (or ‘freshness’) when determining the
downvalley extents of these former glaciers, but he also took into
account Pennington’s (1947, 1978) analyses of lake sediment cores
in the region, in particular evidence for sites that remained ice-free
throughout the Lateglacial. His results for the study area are presented
in Fig. 2; glacier outlines are shown, along with the
geomorphological evidence on which these are based.
Sissons was conﬁdent that the clarity of the geomorphological
evidence enabled him to accurately reconstruct these glaciers, but
it is worth noting that the positions of the ice margins are mostly
inferred, reﬂecting his professional judgement rather than deﬁnitive
ice-marginal evidence. Extrapolated ice margins in the upper
reaches assume an alpine style of glaciation, with glaciers
emanating from cirques and valley heads but with summits
remaining ice-free.
ELAs for the reconstructed glaciers were calculated using the
area weighted mean altitude (AWMA) approach (see Sissons and
Sutherland, 1976) which, within the study area, resulted in values
ranging from 476 m to 625 m. For the Lake District as a whole,
Sissons estimated that the July mean temperature during this time
was 8 C and, in the central area, precipitation was in the range of
2700e4000 mm aÀ1
.
Sissons (1980) did not provide a detailed comparison of his and
Manley’s (1959) reconstructions, but he did challenge the evidence
for some of the larger glaciers identiﬁed by Manley. Within
the study area, this includes the Kent Valley glacier which, according
to Sissons, is based on subdued (rather than ‘fresh’) moraines,
with no evidence suggesting a former ice margin. The only
substantive issue that Sissons identiﬁed in relation to his own
reconstruction (within the present study area) is the adverselysituated
glacier at the head of Longsleddale (Glacier 59 in
Fig. 2). Its location in a shallow, SE-facing valley implied more
favourable conditions for glacierisation than was suggested by his
work in the northern and southern parts of the Lake District,
where glaciers tended to be much smaller and dependent on
optimal topographic settings. In fact, Sissons noted the presence
of a number of other seemingly unfavourably-situated glaciers, all
of which were located within a broad east-west belt across the
central Lake District. From this, he concluded that this zone e
which incorporates the present study area e experienced heavier
snowfall during the Younger Dryas than the northern and
southern parts of the Lake District.
More recent investigations within the study area by Wilson and
Clark (1998) provide evidence for three additional Younger Dryas
glaciers, the largest of which was located in Fordingdale and had an
ELA (calculated using the accumulation area ratio method) of
600 m. Evidence was also presented for smaller glaciers in Swindale
and Wet Sleddale, with ELAs of 390 m and 400 m respectively
(Fig. 2). It should be noted that Manley (1959) had previously
proposed glaciers in Swindale and Fordingdale, although he provided
no evidence for them.
With the exception of the additional glaciers proposed by
Wilson and Clark (1998), Sissons’ (1980) reconstruction of
Younger Dryas glaciers within the study area remains unchallenged.
However, this is not the case for his work in the adjacent
central and south-western Lake District, where reconstructed icemargins
produced during deglaciation and other geomorphological
evidence have been used to demonstrate that some of his
valley glaciers were actually outlet glaciers draining plateau iceﬁelds
(McDougall, 2001; Pearce, 2010; Brown et al., 2011). This
reassessment of glaciation style has not only resulted in a revised
palaeoclimatic assessment for the area, but also removed the need
to invoke locally heavier snowfall to explain the adversely-located
glaciers and unusual ELAs present in Sissons’ (1980)
reconstruction.
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4. Methods
Glacial landforms were initially mapped using a geographical
information system (GIS), with the results being subsequently
ﬁeld-checked and modiﬁed as appropriate. The GIS included
elevation data, geological data, and three sets of digital
orthophotos. In addition, a number of older aerial photographs
were scanned, imported and georeferenced for some sites. The use
of more than one set of imagery is important because it enables
landscapes to be viewed under different lighting conditions, which
in turn assists in the conﬁdent interpretation of subtle landforms
(see McDougall, 1998).
Fig. 2. The Eastern Lake District, including Younger Dryas glacier extents according to Sissons (1980) and Wilson and Clark (1998). The smaller inset map shows the approximate
extents of Manley’s (1959) glaciers. See text for details. Ó
Crown Copyright/database right 2013. An Ordnance Survey/EDINA supplied service.
51
Geomorphological mapping focused on identifying ice-marginal
evidence (e.g. moraines, meltwater channels). The ability to
reconstruct ice-margins during deglaciation is important because:
(i) they provide information on changing glacier conﬁgurations
through time; and (ii) they assist in the recognition and interpretation
of subtle yet important ice-marginal evidence. Some moraines
have undergone signiﬁcant slumping on steep valley sides,
leaving little more than fragments on valley sides, but these are
nevertheless useful in delineating former ice margins (see Chinn,
1979). All recognisable moraines were mapped, irrespective of
prominence (freshness).
5. Geomorphological evidence
5.1. Introduction
Moraines occur throughout the study area, as can be seen in
Fig. 3, but they are most common and best-developed in central
and south-western parts. In general, the extents of Sissons’ (1980)
glaciers correspond to the areas in which the most prominent
glacial depositional landforms occur, with particularly impressive
examples in Hayeswater (‘A’ in Fig. 3; Fig. 4a), Pasture Bottom (‘B’;
Fig. 4b) and the northern slopes of Mardale Head (‘C’). Nevertheless,
Fig. 3. Geomorphological map of the study area. Ó
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52
well-developed moraines also occur beyond the limits of Sissons’
glaciers, such as at Kirkstone Pass (‘D’) and the vicinity of Caudale
Bridge (‘E’; Fig. 4c). Elsewhere, many of the moraines are less
obvious. Those in Woundale (‘F’; Fig. 4d), Troutbeck Valley (‘G’) and
Kent Valley (‘H’), for example, are mostly low-relief landforms.
Their relatively subdued nature e sometimes no more than one
metre or so in height e is in marked contrast to the well-developed
features in the valleys immediately to the north.
Although varying in clarity, most of the moraines in the study
area appear to be ice-marginal, an interpretation based on their
characteristic lobate planform with bifurcating ridges (see Benn,
1992; Bennett and Boulton, 1993). In addition to showing that
active deglaciation occurred more or less throughout the study
area, the reconstructed ice-marginal positions shown in Fig. 5
demonstrate that the most recent glaciation to affect the area was
characterised by widespread summit iceﬁelds, with outlet glaciers
descending into the surrounding valleys. Although space precludes
a detailed review of all the geomorphological evidence, it is
worthwhile considering some sites in a little more detail in order to
illustrate the nature of the landform record and its interpretation.
5.2. Evidence for summit iceﬁelds
The ice-marginal moraines produced during deglaciation provide
both direct and indirect evidence for summit iceﬁelds within
the study area. Direct evidence occurs where former ice margins on
the valley-sides can be mapped onto the high ground above,
thereby demonstrating the presence of contemporaneous glacierized
summits. At the southern edge of the Caudale Moor plateau,
for example, lateral moraine fragments document the descent of
outlet glaciers onto the steep slopes below (‘A’ in Fig. 5). Similarly,
very faint lateral moraines at the northern margin of the same
plateau (‘B’ in Fig. 5) show that ice in the Caudale cirque originated
on the high ground above. Direct evidence for iceﬁelds can also be
found on the Racecourse Hill e Thornthwaite Crag summit area.
The clearest evidence occurs just above the head of the Kent Valley
(‘C’), where lateral moraines and drift limits record the drainage of
ice from the high ground into the valley below. Additional evidence
can be found at the head of Hayeswater valley, where several faint
lateral moraines extend onto high ground in the vicinity of
Thornthwaite Crag (‘D’).
Direct evidence for summit iceﬁelds, similar to the examples
outlined above, occurs at numerous other sites within the study
area. In all cases, however, it is worth noting that ice margin interpretations
are mostly based on subtle and fragmentary lateral
moraines and drift limits. These are challenging to map, whether in
the ﬁeld or using aerial photographs.
Former iceﬁelds can also be inferred from the planform and
development of ice-marginal moraines in valleys. In Hayeswater
valley, for example, reconstructed ice-marginal positions on the
eastern slopes (‘E’) are much steeper than those on the western
slopes, a situation that reﬂects the supply of ice into the valley
from the iceﬁeld on Racecourse Hill to the east. The latter
supplemented ice originating on the high ground above the
valley head to the south (the evidence for which has already
been outlined). As deglaciation progressed, however, the
geomorphological evidence reveals a declining contribution of
ice from Racecourse Hill, with deglaciation focussed on the high
Fig. 4. a) Hayeswater Valley moraines; b) Pature Bottom moraines; c) Caudale Bridge moraines; d) Woundale moraines.
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ground above the valley head. This situation led to the development
of pronounced moraine asymmetry, which is most
obvious in the upper part of the valley. Here, ice-margin stability
on the western slopes resulted in the development of a very
large lateral moraine, whereas greater movement on the eastern
slopes produced multiple, smaller and steeper lateral moraines
(Fig. 6).
In many cases, the former existence of summit iceﬁelds can be
inferred by studying the distribution of ice masses in the surrounding
valleys. For example, the presence of ice-marginal moraines
in all of the valleys adjacent to Loadpot Hill (‘F’ in Fig. 5) is
tentatively interpreted as evidence for outlet glaciers draining a
glacierized summit. Whilst the distribution of moraines is certainly
consistent with an outlet glacier interpretation, it is not in itself
diagnostic. The alternative interpretation is to assume an alpine
style of glaciation, with summits remaining ice-free. However, such
an approach would result in unusual, adversely-situated glaciers at
a number of sites within the study area (for example, at ‘G’ and ‘H’
in the southeast) and, for this reason, the iceﬁeld interpretation is
preferred. A more rigorous assessment, based on glaciological
modelling and palaeoclimatic assessment, is beyond the scope of
the present study.
Fig. 5. Reconstructed ice-marginal positions. Ó
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54
5.3. Downvalley glacier extents
Valley-ﬂoor moraine development is highly variable in the
study area, with marked differences between valleys, and sometimes
also within individual valleys. These variations, which relate
to both size and spacing of moraines, create difﬁculties when
attempting to assess the downvalley extents of these former glaciers.
For example, glacial depositional landforms in Caudale Head
(‘I’ in Fig. 5), Pasture Bottom (‘J’) and Hayeswater Valley are
generally well-developed, with the latter two valleys in particular
displaying impressive assemblages of closely-spaced, hummocky
recessional moraines, typically 5 m high. In contrast, the valleys
immediately to the south e Woundale (‘K’), Troutbeck (‘L’) and Kent
(‘M’) e appear, at ﬁrst glance, to lack moraines of any sort. A closer
examination, however, reveals the presence of numerous icemarginal
moraines in Woundale. These are mostly low-relief,
hummocky features, typically 0.5e2 m high, documenting the
active retreat of an outlet glacier towards Caudale Moor. Unfortunately,
it is not obvious from the geomorphological evidence how
far downvalley this ice mass extended; recessional moraines of
varying clarity can be identiﬁed only as far as the point at which the
ground steepens markedly on the descent to the Troutbeck valley, a
distance of over 2 km from the valley head.
The landform records in the Troutbeck and Kent valleys are even
more difﬁcult to interpret. Whereas Woundale appears to have
been supplied with ice primarily via the valley head, ice-marginal
moraines demonstrate that both the Troutbeck and Kent valleys
received ice from multiple high-level sources above the valley
sides. This would have been in addition to ice originating from the
high ground above the valley heads. The geomorphological record
shows that deglaciation in these two valleys was probably dominated
by actively-retreating outlet glaciers on the valley-sides. In
neither valley is there clear evidence for maximum downvalley ice
extents. The subdued and complex nature of the geomorphological
record in these valleys is not particularly unusual for the study area;
plenty of other examples exist, particularly in the north and east, a
situation that most likely reﬂects the impact of glaciation style on
debris supply to the ice margins (see Section 6).
Determining the downvalley extents of former glaciers can be
difﬁcult even in those valleys characterised by well-developed,
prominent ice-marginal moraines. For example, the impressive
moraines in Hayeswater appear to fade out at the northern end of
the valley, where it becomes steeper and narrower as it curves and
descends to the west. Whilst not obvious in the ﬁeld, careful
interpretation of the GIS imagery reveals the presence of very faint
lateral moraine fragments on the northern slopes beyond this
point. The southern slopes are debris-mantled and gullied, possibly
reﬂecting the operation of paraglacial processes. Unfortunately,
there is no clear geomorphological evidence for a glacier terminus
in the lower reaches.
6. Glaciation style and the geomorphological record
The geomorphological mapping presented above demonstrates
that summit iceﬁelds occurred extensively throughout the eastern
Lake District during the most recent glaciation to affect the area.
These former iceﬁelds are mainly evidenced by ice-marginal moraines
produced during the late stages of deglaciation. In some
cases these moraines can be traced from the valleys onto the high
ground, thus providing direct evidence for summit glacierisation
(such as occur at the heads of the Hayeswater and the Kent valleys,
for example). In other instances, notably in relation to Racecourse
Hill, the presence of ice on the summits is clearly implied by the
planimetric arrangement of ice-marginal moraines in the surrounding
valleys. Other types of geomorphological evidence
commonly associated with summit glaciation, such as meltwater
channels and ice-moulded bedrock (e.g. McDougall, 2001), are not
well-developed in the study area.
It is worth emphasising that conﬁdence in these iceﬁeld interpretations
varies spatially. Whereas there is unequivocal
geomorphological evidence for summit glacierisation in the central
zone, the situation is less clear to the northeast and southeast due
to the subtle and fragmentary nature of the landform record.
The interpretation of the geomorphological record is further
complicated by the impact of glacieretopographic interactions,
which appear to have exerted a strong inﬂuence on valley-ﬂoor
landform development. These interactions may be responsible for
signiﬁcant variations in glacial landform development between
valleys. For example, the impressive suites of recessional moraines
in Pasture Bottom are in marked contrast to the subdued, fragmentary
moraines in the Troutbeck valley to the south. It is suggested
here that the development of clear recessional moraines in
the Troutbeck valley was inhibited because ice descended into the
valley from multiple directions, which would have: (i) limited the
availability of extraglacial slopes for supraglacial debris input; and
(ii) prevented the development of a ‘classic’ pattern of ice-marginal
moraines documenting retreat towards the valley-head. This association
between subdued, fragmentary geomorphological evidence
and the supply of ice into valleys from multiple high-level
sources can be observed elsewhere within the study area, most
notably in the Kent Valley.
Changing glacieretopographic interactions over time may also
explain spatial differences in landform development within
Fig. 6. a) Large lateral moraine on the western slopes of Hayeswater valley; b) Smaller,
steeper lateral moraines on the eastern slopes of Hayeswater valley.
55
individual valleys, although at this scale the presence or absence
of moraines at any given location also reﬂects ice-margin
behaviour during deglaciation. For example, the only reasonably
clear moraines within Riggindale (northeast of Racecourse
Hill) document the presence of a small outlet glacier in the
southwest corner of the valley (‘N’ in Fig. 5). However, this does
not represent the maximum extent of ice; evidence from the
surrounding valleys and nearby high ground demonstrates that
the volume of ice in Riggindale was formerly much greater, with
ice descending down the valley sides from the north as well as
being supplied from the high ground to the west and southwest.
Thus there would be limited opportunities for the development
of ice-marginal moraines under these conditions. Of course, it is
possible that the distribution of moraines in Riggindale merely
reﬂects ice-margin behaviour, with those in the southwest corner
forming during a pause in what was otherwise a period of uninterrupted
retreat. Such a pattern of retreat is not, however,
evident in Mardale Head immediately to the south, where there
is an extensive tract of recessional moraines on the northern
slopes.
Fig. 7. Speculative reconstruction of ice masses in the eastern Lake District. Ó
Crown Copyright/database right 2013. An Ordnance Survey/EDINA supplied service.
56
Interpreting the landform record of mountain glaciation in the
eastern Lake District is, therefore, far from straightforward. This
complexity largely results from the impact that glaciation style
has had on the geomorphological record, particularly (i) the
challenge of identifying former summit iceﬁelds; and (ii) the inﬂuence
that local glacieretopographic interactions had on valleyﬂoor
landform development. Glaciation style, along with paraglacial
reworking, has resulted in a landform record that varies
spatially, from being impressively clear through to being
demonstrably incomplete.
The limitations of the geomorphological record, combined with
the absence of dating control, mean that the empirically-based ice
mass reconstruction in Fig. 7 should be regarded as highly speculative.
Its purpose here is solely to illustrate the potential extent of
glacierisation in the study area, which in turn can be compared
with previous interpretations of glacier extents (see Fig. 2).
7. Discussion
It is argued in this paper that the geomorphological evidence for
mountain glaciation in the eastern Lake District is considerably
more complex than previously thought. Despite the challenges
presented locally by the subtle and incomplete nature of the
landform record, as well as the problems resulting from poor
chronological control, it can nevertheless be shown that the last
glaciation to affect the area (presumably during the Younger Dryas)
was characterised by extensive summit iceﬁelds and outlet glaciers.
In terms of both glaciation style and ice coverage, therefore, this
paper differs signiﬁcantly from previous interpretations.
The presence of iceﬁelds in the study area during the Younger
Dryas is not in itself surprising; after all, it has already been shown
that this style of glaciation affected the central and southwest parts
of the Lake District (McDougall, 1998, 2001; Pearce, 2010; Brown
et al., 2011). The failure of Sissons (1980) to identify these former
iceﬁelds reﬂects the poor understanding at that time of (i) their
glaciological signiﬁcance in supplying ice to the surrounding valleys;
and (ii) their subtle and sometimes non-existent geomorphological
signature, resulting from low basal shear stresses and/or
cold-based ice (see Gellatly et al., 1988, 1989). It should also be
noted that the subsequent recognition of summit iceﬁelds is in
many cases a result of careful study of reconstructed ice-margins in
the late stages of deglaciation, which in turn builds on the work of
Benn (1992) and Bennett and Boulton (1993). Prior to this, it was
generally assumed that Younger Dryas glaciers in Britain stagnated
in situ, at or near maximum extents.
The inﬂuence of spatial and temporal variations in glaciation
style on the development of valley-ﬂoor glacial depositional landforms
is arguably the most interesting aspect of this research. For
the study area at least, it can be shown that variations in moraine
development in part reﬂect changing glacieretopographic interactions
over both space and time, primarily through controls on
debris supply. This observation, which is consistent with the work
of Evans (1990) in NW Ellesmere Island, means that the absence of
well-developed landforms does not necessarily indicate ice-free
conditions at this time.
It is clear, then, that a robust reconstruction of Younger Dryas
glaciers in the eastern Lake District is not possible based on the
geomorphological evidence alone. This assessment differs from
that of Sissons (1980), who was conﬁdent that in most cases the
geomorphological record enabled Younger Dryas glaciers to be
accurately reconstructed at or near maximum extents. This view,
which was widespread in glacier reconstructions for upland
Britain published during the 1970s and 1980s, may have stemmed
in part from an over-reliance on moraine morphology (‘freshness’)
as a relative dating technique. This resulted in only sharplydeﬁned,
prominent glacial depositional landform assemblages
being attributed to the Younger Dryas; more subdued features
were thought to be older, their appearance resulting from the
effects of intense periglacial weathering and erosion, and as such
they were not considered in these reconstructions. The current
research demonstrates that the use of moraine morphology as a
relative dating technique is inherently unreliable within the study
area.
The relevance of this research extends beyond the eastern Lake
District, and to this end there are two key points to be made. Firstly,
approaches to mapping glaciers that assume a distinctive
geomorphological signature may underestimate the extents of
these former ice masses in areas where glacieretopographic interactions
were complex. In the context of upland Britain, this may
mean that Younger Dryas glaciation was more extensive than previously
thought. Secondly, there will be situations where glacier
reconstructions are not possible based on the geomorphological
evidence alone. Although gaps in the landform record can be circumvented
to an extent by numerical modelling techniques (e.g.
Benn and Hulton, 2010), perhaps the main challenge is to recognise
where these gaps occur in the ﬁrst place. This may not always be
straightforward.
8. Conclusion
1. Detailed geomorphological mapping in the eastern Lake District
has revealed that the last glaciation to affect the area was
more extensive and complex than previously thought. Summit
iceﬁelds were widespread, with outlet glaciers descending into
the surrounding valleys.
2. Active deglaciation occurred more or less throughout, with
reconstructed ice-margins in the ﬁnal stages of local deglaciation
demonstrating that summits were amongst the last areas
to become ice-free.
3. Marked variations in glacial landform development between
and within valleys appear to reﬂect glacieretopographic interactions,
speciﬁcally the ways in which these affect (i) sediment
supply to ice margins; and (ii) the complexity of local ice
ﬂow and patterns of deglaciation. The impact of paraglacial
reworking on both valley-sides and ﬂoors further complicates
matters.
4. Although moraine morphology is widely employed in the
literature as a relative dating technique, this approach is unreliable
within the study area because it fails to account for
glacieretopographic interactions and, as such, signiﬁcantly
underestimates glacier extents.
5. The fragmentary and incomplete nature of the geomorphological
evidence, together with dating uncertainties, means
that the conﬁdent reconstruction of these former ice masses
will depend in part on glaciological modelling.
6. It seems most unlikely that this geomorphological complexity
is limited to the eastern Lake District. The former presence of
summit iceﬁelds and outlet glaciers in other upland areas in
Britain and beyond is likely to present similar challenges in the
interpretation of the landform record, particularly where valleys
were supplied with ice from multiple high-level sources.
Acknowledgements
57
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