1. Examining dynamics, extent and timings of the British Ice SheetExamining dynamics, extent and timings of the British Ice Sheet
during the Last Glacial Maximumduring the Last Glacial Maximumduring the Last Glacial Maximum
Emma Reynolds, Department of Earth Sciences, Durham UniversityEmma Reynolds, Department of Earth Sciences, Durham University
1. INTRODUCTION 5. LIMITATIONS4. RESULTS & DISCUSSIONS I; dynamics
To examine nature of the BIS, the Alston Block area in northern England was zoomed in upon, showing ice
3°0'0"E2°5'0"W7°10'0"W
60°0'0"N 60°0'0"N
35,000 years ago, Britain was ice-free, when growth of
plateau ice fields started until the height of the last ice age.
Field observations indicate that the ice cap slowly advanced
•DEMs: Resolution was maximum 30m and so landforms are hazy. But,
with funding, 5m resolution is available. The inconsistencies between
DEM tiles are rectified by mosaicking, but cannot be projected into
To examine nature of the BIS, the Alston Block area in northern England was zoomed in upon, showing ice
dynamics on a macroscopic scale. Analysis revealed complex flow patterns, individual glacier dynamics, and a
late readvance.
Figure 3; Map showing
line of maximum extent
of the BIS, dependent
60°0'0"N
Field observations indicate that the ice cap slowly advanced
and then retreated due to climate change.
This project involved creating and analysing datasets, using
DEM tiles are rectified by mosaicking, but cannot be projected into
ArcScene. On ASTER DEMs, some clouded areas appear bright and
water bodies can have several elevation values2. Therefore, these
Glacier nature
Fluvial erosional and depositional features such as drumlins, eskers and subglacial channels over the UK
late readvance.of the BIS, dependent
upon locations of glacial
landforms over the UK1.
This project involved creating and analysing datasets, using
techniques of GIS cartography and spatial analysis. This was
to a) examine the dynamics of the ice sheet, using an area of
Northern England, and b) determine maximum ice extent of
water bodies can have several elevation values2. Therefore, these
could be manually edited, similar to other DEM sources.
•BRITICE: Incomplete, patchy coverage, variable approaches, and
spans centuries of field research; a solution is to map all landforms
Fluvial erosional and depositional features such as drumlins, eskers and subglacial channels over the UK
(Figure 3) indicate water presence, proving subsurface reached sufficient temperatures and pressures for a
warm base. Anastomosing inset valleys sub-parallel to contours (Figure 5) indicate supraglacial lateral57°55'0"N 57°55'0"N
Northern England, and b) determine maximum ice extent of
the British Ice Sheet (BIS) during the Last Glacial Maximum
(LGM), and the dates associated with it.
spans centuries of field research; a solution is to map all landforms
from satellite images5. These uncertainties apply to isochron dataset
(basis from BRITICE).
warm base. Anastomosing inset valleys sub-parallel to contours (Figure 5) indicate supraglacial lateral
channels, thus erosion from surface meltwater instead of ice – a cold-based glacial system, especially
during retreat. Figure 5 shows lateral channels to be
(LGM), and the dates associated with it. (basis from BRITICE).
•My interpretations: Creating ischron dataset was subjective;
systematic quantitative moraine dating could minimise limitations. My
2. METHODS
during retreat. Figure 5 shows lateral channels to be
only in upland areas.
Interpretation: BIS was warm-
based except in few upland areas
Lateral channels running
parallel to contours
Figure 5; Lateral
channels sub-parallel to
65
55°50'0"N 55°50'0"N
systematic quantitative moraine dating could minimise limitations. My
line of extent is subjective; averaging several glaciologists’
interpretations would be more accurate.
•Timing for LGM: Time-transgressive nature of the BIS advance and
2. METHODS
Data sources
based except in few upland areas
where ice sheet was much thinner.
channels sub-parallel to
contours.
65 •Timing for LGM: Time-transgressive nature of the BIS advance and
dynamic nature of different ice centers causes different margins to
reach maximum extent at different times8. Complete ice coverage is
Data sources
Three datasets were needed:
1.The BRITICE project1; thematic layers of different UK glacial
landforms.
53°45'0"N 53°45'0"N
reach maximum extent at different times8. Complete ice coverage is
assumed behind each isochron (Figure 3), particularly during early
growth and late retreat where ice only existed in upland areas. To
reduce uncertainty, a more detailed analysis from greater number of
landforms.
2.DEMs; sourced from ASTER2 (30m resolution), CGIAR3 (90m
resolution) and NERC Bluesky4 (5m resolution).
Complex flow patterns
Cross-cutting drumlins indicate changing flow
Eden Valley
Solway
Stainmore Gap
reduce uncertainty, a more detailed analysis from greater number of
sites is needed.
resolution) and NERC Bluesky4 (5m resolution).
3.Dated glacial sites; a new dataset of chronological lines was
created, based upon site locations5,6 using average ages for
Cross-cutting drumlins indicate changing flow
directions. Lower drumlins show earlier south
flow up Eden Valley and over Stainmore Gap,
51°40'0"N 51°40'0"N
Data preparation
created, based upon site locations using average ages for
advance and terminus sites.
6. CONCLUSIONS
Line of
maximum
extent
flow up Eden Valley and over Stainmore Gap,
overprinted by later west flow towards Solway.
Figure 4; Carboniferous Alston Block area. Arrows showing Interpretation: During retreat of the BIS, main
65
Data preparation
All datasets were combined together into a readable format.
After unzipping, DEMs were mosaicked using Data
Management Tools in ArcCatalog. Coordinate systems were
6. CONCLUSIONS
The dynamics of the British Ice Sheet at the Last Glacial Maximum
were very variable. The BIS was heterogenous in extent and nature,
extent
(thick blue)
Late readvance
Figure 4; Carboniferous Alston Block area. Arrows showing
zoomed-in locations discussed.
Interpretation: During retreat of the BIS, main
Scottish ice flow was overrun by regional radial
ice dispersal centers; Pennines
65Management Tools in ArcCatalog. Coordinate systems were
aligned; DEMs were WGS_1984, BRITICE data was BNG OS_36.
Using ArcToolbox, new projections were defined for each layer
were very variable. The BIS was heterogenous in extent and nature,
reaching maximum at different times. Dynamics are summarised
below in different evolutionary stages, using the Pennines and Lake
Late readvance
Elongated drumlins in the Solway dated at 17 Ka
show south flow drawn west towards water bodies. A
ice dispersal centers; Pennines
and Lake District. Can assume
opposite occurred during
growth.
0 50 100 150 20025
Kilometers
3°0'0"E2°5'0"W7°10'0"W
Using ArcToolbox, new projections were defined for each layer
in the BRITICE dataset, to configure the entire dataframe to
WGS_1984. Isochron dataset was georeferenced to relate to
below in different evolutionary stages, using the Pennines and Lake
District to represent the UK (Figure 9):
GROWTH
show south flow drawn west towards water bodies. A
push moraine south supports Scottish flow direction.
i)Interpretation: Flow was
growth.
i)
Data analysis
WGS_1984. Isochron dataset was georeferenced to relate to
the others.
GROWTH
Upland areas such as the Lake District and Pennines
initiated growth of plateau ice fields. These terrain
surfaces were glaciated thinly very fast, then spilled
i)Interpretation: Flow was
south but drawn towards
Irish Sea, at a time ScottishData analysis
Analysis was split up into elements for each part of the
question.
surfaces were glaciated thinly very fast, then spilled
over into surrounding valleys by radial regional flow
(Figure 9 i)) to become thick, warm-based glaciers.
Scottish
readvance
south
Flow drawn
westwards
Irish Sea, at a time
when local flow
should be dominant.
Thus, a late re-
Scottish
flow south Regional flow
west
question.
a) To investigate ice sheet dynamics: i) Individual glacier
nature; different erosional features were looked at in 3D. ii)
Complex flow patterns; aerial imagery and DEM data was
LGM
During full glaciation at 27 Ka, southerly Scottish
south
westwards
Thus, a late re-
advance of Scottish
ice, unconstrained
ii)
Complex flow patterns; aerial imagery and DEM data was
combined with drumlin data and projected in ArcScene (Figure
1) to determine flow sequences. iii) Late readvance; drumlins
During full glaciation at 27 Ka, southerly Scottish
ice flow was dominant, overprinting local patterns
(Figure 9 ii)). The BIS extended south as far as
southern Wales and the Wash, although mid-
Push
moraine
ii)
ice, unconstrained
by topographic influence. Figure 6; Two different main flow directions
inferred from drumlin orientations. Inset:
NEXTMap image showing cross-cuttingFigure 7; i) Drumlin flow1) to determine flow sequences. iii) Late readvance; drumlins
and moraines were draped over DEMs in ArcScene to examine
ice dominance.
southern Wales and the Wash, although mid-
landmass it v’d, only reaching the Peak District.
NEXTMap4 image showing cross-cutting
drumlins (red: Scottish overprinting, green:
early local flow).
Figure 7; i) Drumlin flow
mainly south but drawn towards sea. ii) Push moraine (south orient-
ation) supports southerly flow. Inset: NEXTMap4 image showing detail.
iii)
ice dominance.
RETREAT
Figure 2; Editing vertices
on extent shapefile.
3. RESULTS & DISCUSSIONS II; extent & timing
Figure 9; i) ii)
and iii)
Summary
iii)
65
RETREAT
After 27 Ka, the ice sheet started to retreat, reaching a minimum at 14 Ka.
Conversely to growth, regional dispersal centres became more influential, and
upland areas were last to be ice-free, (curve on Figure 9 iii)) leaving some
on extent shapefile.
3. RESULTS & DISCUSSIONS II; extent & timing
To answer the question of extent, the isochron map shown in Figure 8 was
produced from analysis of glacial site dates. Analysis of the oldest isochron in
Summary
maps with
major flow
(blue arrows)65 upland areas were last to be ice-free, (curve on Figure 9 iii)) leaving some
zones in the south isolated. At 17 Ka, there was a late readvance of Scottish ice.
Location
produced from analysis of glacial site dates. Analysis of the oldest isochron in
showed a correlation with the line of maximum extent from Figure 3.
(blue arrows)
and ice cover.
Figure 1;
65
Location
Line of maximum extent was drawn primarily around ice terminus features;
moraines, lateral meltwater channels, eskers, and ice-dammed lakes. These
7. REFERENCES
Figure 1;
Projection in ArcScene.
65
moraines, lateral meltwater channels, eskers, and ice-dammed lakes. These
marginal features imply extension backwards of the ice sheet, if complete
coverage is assumed.
Line of
maximum
extent
(thick blue)
[1] Clark, C.D., Evans, D.J.A., Khatwa, A., Bradwell, T., Jordan, C.J., Marsh, S.H., Mitchell, W.A., and Bateman., M.D. (2004) Map and GIS
database of landforms and features related to the last British Ice Sheet. Boreas, 33(4), 359-375.
[2] ASTER GDEM data product is courtesy of an online data pool from METI and NASA.
b) To investigate maximum glacial extent and timing: i) Timing;
isochrons were defined based upon groups of similar dates,
converted from point to line data in ArcMap. ii) Location;
65
Timing
Figure 8 shows maximum ice extent to have occurred at approximately 27 Ka.
(thick blue)
[2] ASTER GDEM data product is courtesy of an online data pool from METI and NASA.
[3] Jarvis, A., Reuter, H.I., Nelson, A. And Guevara, E. (2008) Hole-filled SRTM for the glove Version 4, available from CGIAR-CSI SRTM
90m Database (http://srtm.csi.cgiar.org).
[4] NEXTMap Britain data from Intermap Technologies Inc., provided courtesy of NERC via the NERC Earth Observation Data Centre
(NEODC).converted from point to line data in ArcMap. ii) Location;
landforms focused upon as diagnostic of the BIS margin were
terminal and marginal – moraines, meltwater channels, eskers,
Figure 8 shows maximum ice extent to have occurred at approximately 27 Ka.
After reaching a maximum, the BIS is shown to retreat in Figure 8 until 15 Ka,
implying that the LGM was very short, due to the sensitivity of the UK as a0 50 100 150 20025
Kilometers
(NEODC).
[5] Clark, C.D., Hughes, A.L., Greenwood, S.L., Jordan, C. And Sejrup, H.P. (2012) Pattern and timing of the retreat of the last British-
Irish ice sheet. Quaternary Science Reviews, 44, 112-146.
[6] Hughes, A.L.C., Greenwood, S.L. And Clark, C.D. (2011) Dating constraints on the last British-Irish Ice Sheet: a map and a database.terminal and marginal – moraines, meltwater channels, eskers,
tunnel valleys and ice-dammed lakes. In ArcMap, a shapefile
was drawn along moraine boundaries (Figure 2) and adjusted
implying that the LGM was very short, due to the sensitivity of the UK as a
climate receptor7. Retreat was at a steady rate, although margin variation was
due to water presence. Outlying upland areas are left whilst ice retreats rapidly
across water.
Figure 8; Map showing retreat isochrons, ice distribution centers (white
lines) and flow directions (blue arrows) overlaid onto CGIAR DEMs .
Kilometers
[6] Hughes, A.L.C., Greenwood, S.L. And Clark, C.D. (2011) Dating constraints on the last British-Irish Ice Sheet: a map and a database.
Journal of Maps, v2011, 156-183.
[7] Evans, D.J.A., Livingstone, S.J., Veili, A. And O Cofaigh, C. (2009) The paleoglaciology of the central sector of the British and Irish Ice
Sheet: reconciling glacial geomorphology and preliminary ice sheet modelling. Quaternary Science Reviews, 28, 740-758.was drawn along moraine boundaries (Figure 2) and adjusted
using other features for best fit.
across water.lines) and flow directions (blue arrows) overlaid onto CGIAR DEMs3. Sheet: reconciling glacial geomorphology and preliminary ice sheet modelling. Quaternary Science Reviews, 28, 740-758.
[8] Evans, D.J.A. And Stokes, C. (2015) Personal communication on field trip 7th Feb 2015.