Retreat Pattern and Dynamics of Glaciers and Ice Sheets: Reconstructions Based on Meltwater Features

Retreat pattern and dynamics of glaciers and ice sheets: reconstructions based on meltwater features

Martin Margold

Printed by Universitetsservice US-AB, Stockholm, Sweden Doctoral dissertation 2012 Department of Physical Geography and Quaternary Geology Stockholm University

ABSTRACT

Glaciers and ice sheets covered extensive areas in the Northern Hemisphere during the last glacial period. Subsequently to the Last Glacial Maximum (LGM), they retreated rapidly and, except for Greenland and some other ice caps and glaciers, they vanished after the last glacial termination. This thesis examines the dynamics of deglacial environments by analysing the glacial geomorphological record with focus on the landforms created by glacial meltwater. The aims are (i) to evaluate the data available for mapping glacial meltwater features at the regional scale, and (ii) to demonstrate the potential of such features for regional ice retreat reconstructions in high- relief landscapes. Meltwater landforms such as ice-marginal meltwater channels, eskers, deltas and fossil glacial lake shorelines are used to infer former ice surface slope directions and successive positions of retreating ice margins. Evaluated high-resolution satellite imagery and digital elevation models reveal their potential to replace aerial photographs as the primary data for regional mapping surveys including the glacial meltwater system. Following a methods study, reconstructions of the deglacial dynamics are carried out for the area of central Transbaikalia, Siberia, Russia, and for the Cordilleran Ice Sheet (CIS) in central British Columbia, Canada, using regional geomorphological mapping surveys. Mapped glacial landforms in central Transbaikalia show evidence of a significant glaciation that possibly extended beyond the high mountain areas. Large glacial lakes were formed as advancing glaciers blocked rivers, and of these, Glacial Lake Vitim was the most prominent. Traces of intensive fluvial erosion in the postulated area of glacial damming possibly indicate a high-magnitude outburst flood from this glacial lake. Deglacial dynamics of the CIS reconstructed from the meltwater landform record reveals that the configuration of its southern sector changed after the local LGM. The ice divide shifted to the Coast Mountains in north-central British Columbia and the eastern margin retreated from the Rocky Mountains. Similarly to the situation in central British Columbia, the Liard Lobe in the northeastern sector of the CIS also retreated in a western direction towards the ice divide. The role of eastern accumulation areas appears to have diminished after the LGM and little evidence is available for their survival during the later stages of deglaciation. The results presented in this thesis demonstrate the potential to reconstruct ice retreat patterns and deglacial dynamics at regional scales by interpretation of the meltwater landform record from shrinking glaciers and ice sheets. Retreat pattern and dynamics of glaciers and ice sheets: reconstructions based on meltwater features

Martin Margold

This thesis consists of a summary and six papers:

Paper I Margold, M., Jansson, K.N. (2012): Evaluation of data sources for mapping glacial meltwater features. International Journal of Remote Sensing 33, 2355–2377.

Paper II Margold, M., Jansson, K.N. (2011): Glacial geomorphology and glacial lakes of central Transbaikalia, Siberia, Russia. Journal of Maps 2011, 18–30. [Map in pdf format on enclosed CD]

Paper III Margold, M., Jansson, K.N., Kleman, J., Stroeven, A.P. (2011): Glacial meltwater features of central British Columbia, Canada. Journal of Maps 2011, 486–506. [Map in pdf format on enclosed CD]

Paper IV Margold, M., Jansson, K.N., Stroeven, A.P., Jansen, J.D. (2011): Glacial Lake Vitim, a 3000-km3 outburst flood from Siberia to the Arctic Ocean. Quaternary Research 76, 393–396.

Paper V Margold, M., Jansson, K.N., Kleman, J., Stroeven, A.P., Clague, J.J. (in review): Late-glacial retreat pattern of the Cordilleran Ice Sheet in central British Columbia reconstructed from glacial meltwater landforms. Quaternary Science Reviews. [Supplementary material on enclosed CD]

Paper VI Margold, M., Jansson, K.N., Kleman, J., Stroeven, A.P. (manuscript): Late-glacial ice dynamics of the Cordilleran Ice Sheet in northern British Columbia and southern Yukon Territory: retreat pattern of the Liard Lobe reconstructed from the glacial landform record.

Co-authorship

Paper I: I conducted the mapping, carried out the field-checking and wrote the manuscript. Krister Jansson supervised the mapping, contributed to the writing and participated in the field-checking.Arjen Stroeven helped with the final manuscript preparation.

Paper II: I conducted the mapping and wrote the manuscript; Krister Jansson supervised the mapping and contributed to the writing. Arjen Stroeven helped with the final manuscript preparation.

Paper III: Johan Kleman suggested the initial approach. I conducted the mapping, carried out the field-checking and wrote the manuscript. Krister Jansson and Arjen Stroeven contributed to the manuscript preparation; Johan Kleman reviewed the final draft of the manuscript.

Paper IV: I carried out the GIS analysis and the interpretations and wrote the manuscript. John Jansen, Krister Jansson and Arjen Stroeven contributed to the interpretations and writing.

Paper V: I did the data analysis and interpretation and wrote the manuscript. John Clague, Arjen Stroeven, Krister Jansson and Johan Kleman contributed to the writing.

Paper VI: I did the data analysis and interpretation and wrote the manuscript. Krister Jansson, Arjen Stroeven and Johan Kle- man contributed to the writing. Retreat pattern and dynamics of glaciers and ice sheets

1. Introduction North America from the north after their passage from Asia across the emerged Bering Strait land bridge (Elias et al., Ice sheets advanced and retreated over large parts of the 1996; Dixon, 2001). A long-lasting debate concerns possible Northern Hemisphere, and to a lesser extent in the high dispersal routes following their entry in North America, latitudes and altitudes of the Southern Hemisphere, during which might have lead them through an ice free corridor the Pleistocene (Mercer, 1976; Barendregt and Irving, 1998; between the retreating eastern Cordilleran and western Svendsen et al., 2004). The impact these ice sheets exerted Laurentide ice sheet margins or along the Canadian Pacific on the landscape varied in space and over time (Kleman et coast (Dixon, 2001; Mandryk et al., 2001; Waguespack, al., 2008; Lambeck et al., 2010), and in some regions ice 2007). A knowledge of ice flow history and ice sheet sheets were the primary geomorphological agents shaping dynamics has also a more utilitarian use as it allows for the modern relief (Sugden, 1974; Kleman et al., 2008). At the tracing of important minerals of economic value back to their same time, mountain glaciation has substantially modified source areas (Levson et al., 2001). Furthermore, understanding the appearance of most mountain ranges, and possibly also former ice sheets is important as a component of the climate played an active role in their rates of uplift (Molnar and system (Oerlemans, 1991) and results of paleoglaciological England, 1990; Champagnac et al., 2007; Shuster et al., reconstructions are used as constraints for numerical ice 2011). The presence and dynamics of glaciers and ice sheets sheet models and global climate models (Golledge et al., and the concurrent climate fluctuations of the Quaternary 2008; Stokes and Tarasov, 2010; Heyman et al., 2011). have directly influenced the evolution of modern humans In this thesis, I examine the merits of using glacial who settled the world during the middle and late Pleistocene meltwater landforms in paleoglaciological reconstruction (Dolukhanov, 1997; Hewitt, 2000; Gamble et al., 2004). The based on mapping from satellite imagery and digital elevation observed warming of recent decades (IPCC, 2007) directs an models (DEMs). Glacial geomorphology is mapped and late- attention to the behaviour of the Greenland and Antarctic ice glacial ice dynamics are reconstructed for two mountainous sheets (Oppenheimer, 1998; Overpeck et al., 2006) because regions of the Northern Hemisphere: the central parts of the the melting of these ice sheets would cause a widespread sea- Cordillera in western Canada and central Transbaikalia in level rise into densely populated coastal areas (Dowdeswell, Siberia, Russia. 2006; Bamber et al., 2009). This all motivates an interest in past glacial environments and efforts to reconstruct the 2. Motivation evolution and dynamics of the large ephemeral ice sheets (e.g., Svendsen et al., 2004; Kleman et al., 2010) and such Regions outside the core areas of the Fennoscandian, short-lived catastrophic events related to former glaciation Laurentide and British ice sheets (FIS, LIS and BIS that had the potential to change climate on regional or global respectively) frequently display a glacial landform record scales (e.g., Broecker, 2006; Murton et al., 2010). created under warm-based subglacial thermal conditions The most dramatic periods of the Quaternary were the (Kleman et al., 1997; Jansson and Glasser, 2005; Kleman terminations, times of rapid ice sheet retreat and meltwater and Glasser, 2007). Reconstructions of successive ice margin release to the oceans in a rapidly ameliorating climate (Petit positions, examining the ice sheet retreat pattern in these et al., 1999; Denton et al., 2010). These periods of climate areas, have most commonly been based on the spatial warming and ice sheets retreat were interrupted by shorter distribution of moraines, eskers and glacial lineations periods when climate deteriorated abruptly and possibly (Punkari, 1982; Kleman et al., 1997; Boulton et al., 2001). switched back to full glacial conditions (Broecker et al., The core areas of these ice sheets have, however, mostly 2010; Denton et al., 2010). The period that offers the best been covered by cold-based ice frozen to its substrate insight into the environmental response to this dramatic and (Hindmarsh and Boulton, 1989; Dyke, 1993; Heine and extensive change in climate, particularly in the Northern McTigue, 1996; Kleman and Hättestrand, 1999; Jansson and Hemisphere, is the last glacial termination (Rasmussen et al., Glasser, 2005; Hubbard et al., 2009), as witnessed by the 2006; Denton et al., 2010). During the deglaciation, a profuse widespread occurrence of relict surfaces (Sugden and Watts, amount of meltwater was produced by the decaying ice 1977; Kleman and Stroeven, 1997; Goodfellow et al., 2008). sheets. Part of the meltwater drained directly to the oceans Cold-based conditions prohibited the formation of subglacial causing sea levels to rise rapidly (Fairbanks, 1989) which, in landforms but stimulated the formation of ice-marginal turn, contributed to enhanced retreat of ocean-terminating meltwater features (Sugden and John, 1976; Dyke, 1993). ice margins (e.g., Booth et al., 2003). Meltwater was also Meltwater features were successfully incorporated in local- stored in glacial lakes wherever retreating ice margins and regional-scale detailed reconstructions of ice retreat blocked natural drainage routes (Leverington et al., 2000, (e.g., Borgström, 1989; Johansson, 1995; Jansson, 2003; 2002; Jakobsson et al., 2007). Rapid discharges from glacial Stokes and Clark, 2004). The potential for employing lakes are suggested to have caused major climate meltwater landforms in ice retreat reconstructions at ice deteriorations. This is because the thermohaline circulation, sheet scales, and thus including both formerly cold-based redistributing energy on earth, was disrupted by such influx and warm-based areas, has been described by Kleman et al. of cool freshwater into the North Atlantic and Arctic oceans (2006). However, only few examples exist where this has (Barber et al., 1999, Teller et al., 2002; Tarasov and Peltier, been fully achieved (e.g., Clark et al., in press). To allow for 2005). At the same time, humans were closely trailing the the successful use of meltwater features in ice retreat retreating ice margins and settled recently deglaciated areas reconstructions on ice sheet sector to ice sheet scales, (Mithen, 2003). Of particular interest is the peopling of mapping procedures and an evaluation of potential data 5 Martin Margold sources were yet to be explored. Mapping of glacial 2003; Enikeev, 2009; Paper II; Paper IV). Moreover, the geomorphology from remotely sensed and digital elevation region of Transbaikalia displays sharp contrasts between data has previously been addressed in methodological studies non-glacial landscapes and glacially modified terrains of by for example Clark (1997) and Smith et al. (2006), but different character. The mapping survey of central meltwater features were not considered in these studies. Transbaikalia (Paper II) comprises an inventory of the glacial Therefore, a methodological study focusing on the mapping geomorphology and a reconstruction of former glacial lakes. of meltwater features from remotely sensed data represents This survey has also served as a basis for a GIS analysis of the necessary foundation of this PhD project (Paper I). Glacial Lake Vitim and its drainage (Paper IV). The aim of the methods study was to evaluate the results The retreat patterns of the FIS, LIS and BIS are relatively of a mapping of all meltwater landforms that are of well known (Dyke and Prest, 1987; Kleman et al., 1997; importance for ice retreat reconstructions from remotely Boulton et al., 2001; Dyke et al., 2003; Clark et al., in press). sensed data and DEMs against field control. However, fossil In contrast, the demise of the Cordilleran Ice Sheet (CIS), the glacial lake shorelines were not identified in the remote westerly neighbour of the LIS, is still poorly understood. sensing imagery of the three study areas (Paper I), even Reconstructions of ice marginal retreat patterns of the CIS in though, for example, the study area in northern Finland is the Canadian Cordillera are complicated by the complex known to host glacial lake shorelines (Johansson, 1995; topography and hindered by a sparseness of recessional Helmens et al., 2009). Furthermore, no delta morphology moraines. The abundant occurrence of meltwater features in was distinguished in the data although one was identified in central British Columbia (e.g., Tipper, 1971a), on the other the Scotland field site (Paper I). Glacial lakes constitute an hand, would form the prerequisite for conducting a successful important part of the meltwater system and glacial lake ice sheet retreat reconstruction on a regional scale. Hence, landforms are important features in ice marginal retreat regional CIS retreat reconstructions based on meltwater reconstructions as these features form both in the cold- and landforms were accomplished in central and northern British warm-based subglacial environment (Borgström, 1989; Columbia and in southern Yukon Territory (Papers III, V and Jansson, 2003). Therefore, a mapping survey was required to VI). test the potential of remotely sensed data and DEMs to map these features. The region of central Transbaikalia in central 3. Objectives Siberia, Russia, was selected for this mapping survey. This area has thus far received scanty interest in international The objectives of this PhD project are to (i) evaluate data literature. Fossil shorelines and deltas identified in this area sources for mapping of glacial meltwater landforms, (ii) document the former existence of a large ice-dammed lake in explore the possibilities to include glacial meltwater features the catchment of the River Vitim (Krivonogov and Takahara, in regional-scale geomorphological mapping and, (iii) utilize

Papers III,V

Paper VI

Papers II,IV

70°N

50°N Paper I "

Figure 1. Location of the study areas. 6 Retreat pattern and dynamics of glaciers and ice sheets

STAGE 1 Paper I Problem assesment and data Evaluation of data sources is es for mapping glacial meltwater evaluation th features Fieldwork summer 2008 hD P

STAGE 2 Application of Paper III Paper II evaluated methods Glacial meltwater landforms in Glacial geomorphology and central British Columbia, glacial lakes of central Trans- in different formerly Canada baikalia, Siberia, Russia glaciated geographical regions Fieldwork summer 2009

STAGE 3 Paper V Paper VI Paper IV Late glacial retreat pattern Late-glacial ice dynamics Glacial Lake Vitim, Interpretation 3 of the Cordilleran Ice Sheet of the Cordilleran Ice a 3000-km outburst flood and analysis in central British Columbia Sheet in northern British from Siberia to the Arctic of conducted mapping reconstructed from glacial Columbia and southern Ocean meltwater landforms Yukon Territory: retreat pattern of the Liard Lobe Character and spatial reconstructed from the extents of Pleistocene glacial landform record glaciations in central Transbaikalia, Siberia

STAGE 4 Timing and dynamics of Ongoing Pleistocene outburst flood Absolute dating the ice retreat in British work from Glacial Lake Vitim, Columbia, Canada Transbaikalia, Siberia Fieldwork summer 2010 Fieldwork summer 2011

Glacial history of central Transbaikalia, Siberia Fieldwork summer 2012

Figure 2. Graphical illustration of the structure and timeline of the PhD project and its ofshoots.

landforms created by glacial meltwater in regional-scale reconstructions of ice sheet retreat and dynamics. Study Subsequently, the mapping study covering the area of central areas (Fig. 1) were selected based on the motivation given Transbaikalia (Paper II) developed into an independent above. To achieve the objectives, the following targets (see project concerning the drainage of Glacial Lake Vitim (Paper also Fig. 2) were developed: IV) and the glacial history of the area (in progress; outside the scope of the thesis). Stage 1 - Evaluate available digital data for regional-scale 4. Methods mapping of meltwater features. - Test the procedure of direct digitising from satellite 4.1. Landforms of the meltwater system imagery in a GIS environment against the traditional interpretation derived from stereoscopically viewed Glacial meltwater is produced by the melting of glacial ice. aerial photographs. Even though melting occurs in the ablation areas of glaciers Stage 2 and ice sheets during the advance stage, the majority of - Create a glacial geological map for the region of meltwater landforms in the landscape originate from the central Transbaikalia. retreat stage (Dyke, 1993; Kleman and Borgström, 1996) - Map meltwater landforms in British Columbia and because meltwater features, once formed, are not southern Yukon Territory. subsequently altered by glacial processes. Stage 3 Glacial meltwater landforms, whether erosional, such as - Reconstruct the ice retreat pattern of the CIS in meltwater channels or fossil shorelines of glacial lakes, or central British Columbia and southern Yukon depositional, such as eskers, perched deltas, outwash fans or Territory. plains, or glaciolacustrine sediment fills, constitute Stage 4 a deglacial envelope (e.g., Kleman et al., 2006), thus defining - Support the ice retreat reconstruction in central the style and direction of ice retreat at local and regional British Columbia with absolute dating of selected scales (Sugden and John, 1976, Kleman and Borgström, meltwater features (in progress; outside the scope of 1996). Meltwater landforms complement other indicators of the thesis). deglacial ice dynamics such as moraines or glacial lineations,

7 Martin Margold and they represent the main record of deglaciation, especially including the meltwater system, were collected for and tested where ice remained cold-based and where other traces are at three different study sites in Scotland, Finland and Sweden. absent (Kleman and Borgström 1996; Kleman et al., 2006). The data set also included aerial photographs (for two areas) An inversion model is applied to reconstruct the and one high-resolution DEM. The objectives were to configuration of successive glacier- or ice sheet margins evaluate the potential of these different data sets for the (Kleman and Borgström, 1996; Kleman et al., 2006; mapping glacial meltwater landforms and to offer Greenwood et al., 2007). In this process, the landform record a recommendation for their use in large scale mapping is classified into groups that form “fans” or “swarms” with efforts. glaciologically plausible patterns (Kleman and Borgström Most available scales of aerial photographs allow for 1996, Kleman et al., 2006). The principle of superposition detailed mapping. However, the transformation of analogue (e.g., Clark, 1997), where landforms of one swarm overprint mapping in aerial photographs to the digital format is landforms of another swarm, defines relative age relationships a relatively time-consuming process that introduces (Kleman and Borgström 1996, Kleman et al., 2006) and inaccuracies in the final results. The introduced inaccuracies allows for a relative age-stacking of individual swarms (e.g., could be minimized by using digital aerial photographs. The Kleman et al., 1997). Hence, landforms represented in the use of digital aerial photographs will, however, still be mapped geomorphological record do not necessarily define relatively more time-consuming than the use of satellite a single continuous evolution of the examined glacier or ice imagery in regional mapping efforts. High-resolution DEMs sheet. For example, cold-based subglacial thermal regimes alone or in combination with medium-resolution (15 m) facilitate the preservation of previously-formed glacial satellite imagery are suitable data sources for the mapping of landforms before a subsequent overprinting of deglaciation meltwater landforms. The potential for the mapping of landforms (Kleman, 1994). meltwater features was identified in the SPOT and ASTER imageries. When mapping meltwater landforms from digital 4.2. Data and software data, spatial resolution of the data is the most important attribute influencing the quality of the results while Satellite imagery and digital elevation models (Table 1, radiometric resolution is of additional significance in satellite Paper I) were acquired for the study areas of Paper I. Two of imagery. Our results show that mapping from digital data of the three test areas were also mapped in aerial photographs. medium resolution is likely to show a loss of detail when The mapping surveys presented in papers II and III were compared to mapping from aerial photographs but that based solely on freely available data. The glacial map of overall patterns might be captured. central Transbaikalia (Paper II) was mapped with the use of the Shuttle Radar Topographic Mission (SRTM, Jarvis et al., 5.2. Paper II 2008) DEM with 90 m spatial resolution and Landsat 7 ETM+ satellite imagery (USGS, 2010). The Transbaikalia Margold, M., Jansson, K.N. (2011): Glacial geomorphology study area was also mapped from Google Maps that display and glacial lakes of central Transbaikalia, Siberia, Russia. slope images from SRTM data combined with medium- and Journal of Maps 2011, 18–30. high-resolution satellite imagery. Data of higher spatial resolution were available for the This study presents the first glacial geomorphological map Canadian study area. This included the Canadian Digital covering the region of central Transbaikalia, a mountainous Elevation Data (2009) with a spatial resolution of c. 20 m area east of Lake Baikal in Siberia, Russia, and adds (0.75 arcseconds) and SPOT 4 and SPOT 5 satellite images. knowledge about the glacial geomorphology of this remote High resolution satellite imagery was available for most area. The extent of glacially modified terrain, glacial lake parts of the Canadian study area through Google Maps/ landforms, moraines, glacial lineations and meltwater Google Earth. channels were mapped in SRTM data, Landsat 7 ETM+ Mapping was performed at multiple scales in satellite imagery and Google Maps. The distribution of ESRI®AcrMap 9.2. Where applicable, digitizing was glacial lake landforms allows for the reconstruction of performed directly in Google Maps. Such mapping results several glacial lakes of which the one formed in the catchment were subsequently imported into Google Earth, saved as of the River Vitim was the most prominent. We suggest that kml-files, and converted to the shp-files for use in ArcGIS the mapped glacial record most probably represents the using the DNR Garmin (2009) application. product of several glacial stages. These glacial stages are represented by multiple moraines preserved in some valleys 5. Presentation of papers and by the existence of glacially-modified terrain in places extending beyond the outermost moraines. 5.1. Paper I 5.3. Paper III Margold, M., Jansson, K.N. (2012): Evaluation of data sources for mapping glacial meltwater features. International Margold, M., Jansson, K.N., Kleman, J., Stroeven, A.P. Journal of Remote Sensing, 33, 2355–2377. (2011): Glacial meltwater features of central British Columbia, Canada. Journal of Maps 2011, 486–506. Satellite imagery and digital elevation data suitable for mapping the glacial geomorphology at a regional scale, 8 Retreat pattern and dynamics of glaciers and ice sheets

This mapping survey focuses on glacial meltwater landforms is found for the existence of large accumulation areas in the in the area of central British Columbia. Ice-marginal east at the time of deglaciation. At the time when ice-marginal meltwater channels, eskers and deltas were mapped from meltwater channels were formed close to the Coast Mountains satellite imagery and digital elevation data. The results show accumulation areas, the eastern margin of the CIS retreated a consistent spatial pattern of high-elevated ice-marginal to the west. During the early phase of this retreat, glacial channels in the Skeena and Omineca mountains, in higher lakes were dammed by the ice margin in valleys of the Rocky areas of the Interior Plateau and in the marginal ranges west Mountains draining west. Subsequently, a major glacial lake of the plateau, and to a lesser extent also in the Rocky formed along the Fraser River, and drained once the ice Mountains. Eskers mapped in the study area can be classified margin retreated further to the west and southwest towards into three main groups: (i) small eskers with random the Coast Mountains beyond the Fraser River valley. An directions, (ii) mainly single-ridged, medium-sized eskers active frontal retreat is inferred to have occurred in the trending in directions consistent with the direction of regional valleys of the Omineca and Skeena mountains during the ice flow indicators (e.g., drumlins), and (iii) large multiple- final stages of deglaciation. At the same time, large eskers ridged esker accumulations, confined to depressions and formed in the main valleys of the Interior Plateau at oblique valleys on the Interior Plateau, that differ in direction from angles to the direction of last active ice flow in the area. This regional ice flow indicators. Spatial analysis of the glacial is interpreted to indicate the presence of inactive and meltwater landforms allows for the interpretation of the late stagnating ice remnants over the Interior Plateau during final glacial history of, and reconstruction of CIS retreat in, central deglaciation. British Columbia. 5.6. Paper VI 5.4. Paper IV Margold, M., Jansson, K.N., Kleman, J., Stroeven, A.P. Margold, M., Jansson, K.N., Stroeven, A.P., Jansen, J.D. (manuscript): Late-glacial ice dynamics of the Cordilleran (2011): Glacial Lake Vitim, a 3000-km3 outburst flood from Ice Sheet in northern British Columbia and southern Yukon Siberia to the Arctic Ocean. Quaternary Research 76, 393– Territory: retreat pattern of the Liard Lobe reconstructed 396. from the glacial landform record.

This paper builds on Paper II and includes geomorphological This paper contains a first reconstruction of the ice retreat evidence for the existence of a large glacial lake dammed on pattern of the Liard Lobe in the northeastern sector of the the River Vitim in central Transbaikalia, Siberia, and for its CIS across the boundaries between British Columbia, the catastrophic drainage. A prominent canyon perched on the Yukon Territory and the Northwest Territories. At the local slope of the River Vitim valley in the area of the postulated LGM, the Liard Lobe extended from ice divide areas in the ice-dam is interpreted as being formed by fluvial erosion at Skeena, Cassiar, Pelly and Selwyn Mountains across the the time of the breaching of the ice dam. Possible Liard Lowland into the Hyland Highland (Fig. 3) with environmental impacts of the postulated giant flood into the a consistent northeast oriented ice slope that stretched over Lena River catchment are discussed and the occurrence of 350 km. The retreat of the Liard Lobe is indicated by large a freshwater spike recorded in a marine sediment core drawn easterly-oriented meltwater channels in the Hyland Highland near the Lena River mouth in the Arctic Ocean is noted and formed by the drainage of glacial lakes dammed by the could potentially pinpoint the timing of this event to ~13 cal retreating ice margin. A southwestern direction of the ice ka BP. retreat is also indicated by sets of ice-marginal meltwater channels in higher areas of the Hyland Highland and at the 5.5. Paper V southeastern foot of the Selwyn Mountains. Two large dendritic esker systems running across the Liard Lowland Margold, M., Jansson, K.N., Kleman, J., Stroeven, A.P., indicate a consistent ice slope during the deglaciation. Esker Clague, J.J. (in review): Late-glacial retreat pattern of the deltas, outwash fans, ice-contact sediments and ice-marginal Cordilleran Ice Sheet in central British Columbia meltwater channels are found locally at the foot of the Cassiar reconstructed from glacial meltwater landforms. Quaternary Mountains and further up-valley in the Cassiar Mountains Science Reviews. indicating two positions of the retreating ice front late during deglaciation. In this paper, the late glacial history of the CIS in central British Columbia is reconstructed on the basis of a regional- 6. Discussion and summary scale mapping survey of glacial meltwater landforms (Paper III). A significant reconfiguration of the ice divide must have 6.1. Late glacial history of the Cordilleran Ice Sheet occurred in the period between the local LGM and the time when the highest ice-marginal meltwater channels were 6.1.1. LGM configuration formed. This is inferred from a consistent spatial pattern of high-elevated ice-marginal meltwater channels that indicate During the local LGM, the CIS covered all of the western, the ice divide to have been located above the Coast Mountains mountainous part of Canada except for areas in the western during the late glacial. This evidence locally conflicts with and northern Yukon Territory and ice-free areas isolated suggested LGM ice divide positions further east. No evidence between the CIS and the LIS in the Northwest Territories 9 Martin Margold

U.S.A 140°W 130°W Elevation (a) (b) (c) 6000 Yukon M m a.s.l. ac k St. Elias e Territory n Glaciated z 0 Mts. i e Pelly M

Mts. u 65°N configuration n Northwest Selwyn t a

C i ? 55°N Cassiar Mts. n Liard Lobe s

o Mts.

a LL HH Territories unknown British Columbia s C

t Skeena I L

Mts. R ?

S I

ND Omineca 60°N

Mts. k

Skeena R. y

M M

50°N o Interior

M n FR o t Plateau u a n 55°N

i t n a s Columbia i Columbia n Mountains s ? Ice divide 45°N U.S.A Ice flow 120°W Schematic 200 km 50°N ice margin

Figure 3. Cordilleran Ice Sheet. (a) Physiography of the Canadian Cordillera. LGM extent of the CIS is indicated in dark blue after Kleman et al. (2010), contemporary glaciers are indicated by green-blue. FR - Fraser River, ND - Nass Depression, LL - Liard Lowland, HH - Hyland Highland. (b) Schematic CIS configuration about 18,000 ka redrawn from Clague and Ward (2011). (c) Schematic depiction of the CIS in deglaciation. The ice divide in central British Columbia shifted to the Coast Mountains and the accumulation areas in the Columbia Mountains disappeared. A glacial lake formed along the upper Fraser River dammed by the retreating ice margin. In the north, the Liard Lobe retreated from the east towards the LGM position of the ice divide in the Cassiar Mountains. The post LGM development in place of the Skeena ice dome is not known as well as the ice configuration in the northern Coast Mountains.

(Prest, 1984; Dyke et al., 2003; Clague and Ward, 2011). The Even though the main LGM outlines of the CIS have CIS differed from other large Northern Hemisphere been established, our knowledge about the ice sheet at the Pleistocene ice sheets in that it developed over an area of peak of the last glacial period must be regarded as low. The high-mountain relief alternating with intermontane upland maximum extent was reached in different sectors of the ice plateaus (Fulton, 1991). A widely used conceptual model of sheet at different times; earlier in the north and later in the the CIS build-up (Davis and Mathews, 1944; Fulton 1991) south (Clague et al., 1980; Porter and Swanson, 1998; indicates four phases of ice sheet growth: (i) individual Stroeven et al., 2010). Regardless of the accepted existence alpine glaciers, (ii) mountain ice caps, (iii) coalescent of the Skeena ice dome, the style of glaciation during the piedmont lobes, and (iv) a fully developed CIS. Ice flow local LGM still remains an open question and questions during the fourth phase was ultimately independent of the regarding the ice thicknesses, main ice discharge routes and underlying topography (Fulton, 1991) and it only occurred the degree of dependence on the underlying topography still during relatively brief periods. In some areas, this final phase need to be answered (Bednarski and Smith, 2007; Kleman et may have never been attained (Tipper, 1971b; Clague, 1989; al., 2010; Stroeven et al., 2010). Fulton, 1991). It is suggested that an ice dome formed above the Skeena Mountains in northern British Columbia during 6.1.2. Ice retreat pattern the last glacial period (Fraser/McConnell glaciation, OIS 2; Ryder and Maynard, 1991; Stumpf et al., 2000). In the north, Late glacial ice dynamics have been examined for two the Skeena ice dome was connected by a major ice divide regions of the CIS using the meltwater landform record. Ice with an east-west oriented ice divide that stretched from the retreat patterns at a regional scale were interpreted using Mackenzie Mountains to the northern Coast Mountains and macro-scale ice-flow indicators such as glacial lineations and the Saint Elias Mountains (Fig. 3; Jackson et al., 1991; the “deglacial envelope” of meltwater landforms (Kleman Clague and Ward, 2011). To the south of the Skeena ice and Borgström, 1996; Kleman et al., 2006). Locally, ice dome, the main ice divide ran above the Omineca Mountains retreat patterns were reconstructed in greater detail, and across the Nechako Plateau towards the Coast Mountains, particularly where the record of meltwater landforms was which it then followed farther to the southeast (Stumpf et al., extensive (Paper V, Figs. 4, 5 and 7, Paper VI, Fig. 5). 2000; Clague and Ward, 2011). An ice saddle at approximately In north-central British Columbia an ice divide shift 51 °N connected the main ice divide above the Coast towards the Coast Mountains, postdating the local LGM, is Mountains with another ice dispersal centre located over the reconstructed from a consistent pattern of northeast trending Columbia Mountains (Fig. 3; Ryder et al., 1991; Clague and ice-marginal meltwater channels that occur in high elevations Ward, 2011). in the western parts of the Interior Plateau and in the eastern marginal ranges of the Coast Mountains. These northeast 10 Retreat pattern and dynamics of glaciers and ice sheets

Barents-Kara Ice Sheet 70°N 20 ka (LGM)

60 ka

90 ka V e

r k h o Lena y ans U r a l k n Glacial lakes i o r a t 60°N e d e a n F R u s s i

>140 ka

Bodaybo

Kodar

Yenisei Vitim

50°N l Ice cap a ik a Margold and Jansson (2011) B e k La Kazakhstan Altai China 500 km Mongolia 80°E 100°E 120°E 140°E

Figure 4. Palaeoglaciology of north-central Eurasia. Schematic outlines of the successivelly less extensive Barents-Kara Ice Sheet in the Middle and Late Pleistocene are indicated in dark blue after Svendsen et al. (2004) with glacial lakes dammed by the ice sheet indicated for 90 ka extent of the ice sheet (after Mangerud et al., 2004). The extents and chronology of glaciations in the mountains of north-central Eurasia have not yet been properly reconstructed. Glacially modified terrain mapped in Margold and Jansson (2011, black rectangle) for the area of central Transbaikalia is indicated in pink, Glacial Lake Vitim in bright blue. Ice cap identified by Grosswald in the headwaters of the Yenisei River (1965, in Komatsu et al., 2007) is indicated schematically by a dashed elipse. Extensive ice cover developed at some point also in the Altai Mountains (Lehmkuhl et al., 2004) and the Verkhoyansk Mountains (Stauch and Gualtieri, 2008; Stauch and Lehmkuhl, 2010).

trending channels conflict with the suggested LGM position Similarly to the ice retreat pattern in central British of the ice divide in north-central British Columbia established Columbia, also the region of northern British Columbia, the from the pattern of ice-flow indicators (Stumpf et al., 2000; southern Yukon Territory and the southwestern extremity of McCuaig and Roberts, 2002). The mapped pattern of ice- the Northwest Territories exhibits a dominance of a westerly- marginal meltwater channels implies the ice divide to have sourced ice after the local LGM with an ice marginal retreat been located above or close to the Coast Mountains when the towards the west during late glacial time. Active ice retreat channels were formed. Therefore, the ice divide must have towards a minor accumulation area in the Selwyn Mountains changed position before the summit areas of the eastern has been reconstructed by Dyke (1990). At the regional scale, marginal ranges of the Coast Mountains protruded through it appears that the role of accumulation areas in the eastern the ice surface. mountain ranges such as the Mackenzie Mountains and the A detachment of the eastern CIS margin from the western Rocky Mountains diminished strongly after the LGM. This slopes of the Rocky Mountains is documented by an was possibly a consequence of a strong west-east precipitation abundance of meltwater landforms in the north-central part gradient, which caused the eastern portions of the CIS to be of the Interior Plateau. The situation is more difficult to starved of precipitation. Together with the warming climate, establish farther south for this period, because the record of it then caused the eastern CIS margin to retreat towards the glacial meltwater landforms is sparse in the Columbia west. The mountain ranges that were vacated by the CIS Mountains and on their western slopes. However, high- might still have supported mountain glaciers because of elevation ice-marginal channels in the south-central part of a sufficiently low equilibrium line altitude (Smith, 2003, the Interior Plateau indicate an easterly sloping ice surface of 2004; Lakeman et al., 2008). Coast Mountains-sourced ice. No clear evidence is available The study areas of papers V (central British Columbia) for substantial ice dispersal centres remaining in the and VI (areas covered by the Liard Lobe) are separated by Columbia Mountains at this time. a large region where the interior area between the Coast

11 Martin Margold

Mountains and the Rocky Mountains (sensu Fulton, 1991) is occupied by mountain ranges (Fig. 3). As stated above, a prominent ice dome existed over the Skeena Mountains during the LGM time in this area (Fig. 3; Ryder and Maynard, 1991; Stumpf et al., 2000; McCuaig and Roberts, 2002). The highest ice-marginal meltwater channels in the Skeena and Omineca Mountains provide evidence for the existence of a uniform ice surface east of the LGM ice divide. Ice- marginal meltwater channels at gradually decreasing elevations on the mountain slopes then record a lowering of this uniform ice slope and a retreat of glacier lobes through the valleys towards the areas of the final ice divide. However, the scarcity of meltwater features in the areas to the west of the LGM ice divide precludes reconstructing the ice retreat pattern in this part of the CIS. The reconstruction of ice-flow directions (Stumpf et al., 2000) in the mountainous area to the northwest of the Interior Plateau suggests that once the Figure 5. Jakob Heyman sampling a granite erratic on the crest of Skeena ice dome vanished, ice dispersal centres from the CIS the Marble Range, British Columbia (see Fig. 1 in Paper V for loca- build-up stage were re-established in both the Coast tion). Local lithology are limestones. Mountains and in the Skeena Mountains. Retreat of ice lobes from the coast to the northeast has been described by Clague (1985) for the Skeena River area. Similarly, the pronounced glacial streamlining of the terrain in the Nass Depression valley emanating from the Kodar Mountains (Fig. 2a in further to the north from the Skeena River area and the lack Paper IV) could have been formed by fluvial erosion of ice stagnation landforms here has been interpreted as following repeated breaching of an ice dam in the form of an a possible indication of an active ice retreat towards the ice lobe descending from the Kodar Mountains and blocking accumulation area (Ryder and Maynard, 1991). The exact the Vitim valley. In contrast, the position and the orientation configuration of the retreating ice sheet in this wider region of the canyon, perched on the slope of the River Vitim valley still remains unclear. Either local ice dispersal centres were ca 15 km downstream from the escarpments (Fig. 2 in Paper re-established in the highest mountains such as described by IV), imply a more extensive ice cover during the time of the Stumpf et al. (2000) or the Skeena ice dome maintained its canyon formation, and the canyon is inferred to have been dominance throughout the deglaciation with the last remnants formed by a single high-magnitude fluvial erosion event. The of the diminishing ice sheet melting in the position of the configuration of the damming glaciers can be reconstructed LGM ice dome. in more detail once the regional glacial history is better understood. Reconstructing the chronology of the lake 6.2. Glacial lake dynamics in central Transbaikalia requires further stratigraphic investigations of the sedimentary record in the lake basin together with Glacial geomorphology has been mapped and glacial lakes a reconstruction of regional glacial chronologies and extents. have been reconstructed for the area of central Transbaikalia in Siberia, Russia. The most prominent of these glacial lakes 7. Future perspectives formed in the upper catchment of the River Vitim when the valley was blocked by glaciers descending from the Kodar 7.1. Late glacial history of the Cordilleran Ice Sheet Mountains (Fig. 4). The landform record, including fossil shorelines and perched deltas, allowed for reconstructing the Connecting the deglaciation histories of the areas of papers V maximum area and volume of Glacial Lake Vitim (23,500 and VI and reconstructing the fate of the Skeena ice dome km2, ~3000 km3). Its maximum stage was controlled by an after the LGM and thus establishing a CIS ice retreat pattern overflow to the Amur catchment in the south. Traces of at the full ice sheet scale remains a task for future research localized, high-magnitude fluvial erosion in the area of the efforts. The reconstruction of ice sheet retreat patterns and postulated ice dam imply that this lake drained the thus derived relative deglaciation history need to be catastrophically. However, because Quaternary climate is supported by an absolute chronology of deglaciation. To characterized by successive cold and warm stages, the history contribute to this, samples for terrestrial cosmogenic nuclide of Glacial Lake Vitim has to be regarded to have consisted of (TCN) dating were collected at two sites with high-elevated a complex succession of lake stages of different extents ice-marginal meltwater channels in central British Columbia interspersed with periods when the lake was absent. These (Fig. 5). These samples will help to establish when these inferences of multiple lake stages controlled by ice dams are summit areas bordering the Interior Plateau were deglaciated. to some extent supported by the record of glaciolacustrine Future, more extensive dating efforts should provide more sedimentation in the lake basin (Krivonogov and Takahara, information for the time correlation of ice retreat in different 2003; Enikeev, 2009) and by geological evidence of a rapid sectors of the CIS. Together with the framework provided by release of water from the lake. For example, steep escarpments ice sheet-scale reconstructions of CIS retreat and forthcoming in the River Vitim valley at the junction with the largest TCN dating, local ice retreat histories will have the potential 12 Retreat pattern and dynamics of glaciers and ice sheets

geomorphological mapping of the mountainous region to the (a) east of Lake Baikal revealed U-shape valleys and glacially- streamlined terrain away from the core areas with well developed alpine relief (Margold and Jansson, 2011). Northwest of the Kodar Mountains (the highest mountain range of the region reaching almost 3000 m above sea level), the valley of the River Vitim has been interpreted as glacially modified along a distance of more than 200 km from the water divide (Margold and Jansson, 2011). The observation of glacial polish and associated striae at outcrops in the town of Bodaybo (Figs. 4 and 6) and the indisputably glacial shape of the Vitim River valley (Fig. 6) support the notion of an extensive glaciation of the region. Such traces of extensive glaciers motivate attempts to establish the spatial pattern and chronology of former glaciation. A first step towards this objective is the glacial (b) geomorphology map of Margold and Jansson (2011) that displays multiple generations of moraines in most of the mountain ranges. Future studied, however, would need to confirm the furthermost glacial limits by detailed remote sensing studies and field surveying, and establish relative and absolute chronologies of the moraines using TCN dating of of boulders on moraine crests and of exposed glacially eroded surfaces. Information about the glacial history of the mountains of Transbaikalia would allow for a comparison with established glacial chronologies of other mountain regions of central and northeastern Eurasia (e.g., Stauch and Gualtieri, 2008; Stauch and Lehmkuhl, 2010). A Pleistocene ice cap has previously been identified in the headwaters of the Yenisei River (Fig. 4; Grosswald, 1965 in Komatsu et al., 2007) and (c) extensive glaciations have been described from the Altai Mountains (Lehmkuhl et al., 2004) and the Verkhoyansk Mountains (Stauch and Gualtieri, 2008; Stauch and Lehmkuhl, 2010), even though spatial extents for these glacial events remain to be fully established. Better knowledge of glacial extents and chronology in central Transbaikalia will also have the potential to help to understand how glacial histories of the mountains of central Siberia and the history of the Barents-Kara Ice Sheet relate to each other. The southeastern margin of the Barents-Kara Ice Sheet was during its maximum Pleistocene extent situated some 600 km to the northwest of the mountains of Transbaikalia (Fig. 4). Both the Barents-Kara Ice Sheet and the mountains of Transbaikalia received precipitation from the westerlies. The question, therefore, arises whether Figure 6. (a) Glacially modified valley of the River Vitim upstream maximum glacial extents occurred simultaneously in both of Bodaybo (see Fig. 4 for location). (b) Glacially striated bedrock regions or whether the Barents-Kara Ice Sheet blocked in Bodaybo. (c) Detail of the striated surface. moisture from reaching farther east and caused cold and arid conditions in the mountains of central Siberia, conditions unfavorable to the development of glaciers. If the former was true, did the extents of glaciation in the mountains of to add necessary detail to the development of late glacial and Transbaikalia follow the same trend as the Barents-Kara Ice deglacial environments in the Canadian Cordillera. Sheet, which occupied successively smaller extents during the last glacial period and which did not even reach onto the 7.2. Glacial history of central Transbaikalia, Siberia Eurasian continent east of the Ural Mountains during the LGM (Fig. 4)? The Pleistocene glacial history of the mountains of central Siberia has not received much attention and remains largely unknown for the international scientific community. Glacial 13 Martin Margold

8. Conclusions keep good spirits when needed. Johan has helped to define the research goals and has provided the funding for my PhD - Available digital data for mapping glacial meltwater position through his grant from the Swedish Space Agency. landforms were evaluated with the conclusion that aerial Arjen has always offered inspiring comments and managed photographs remain an ultimate source of detailed to improve my texts by his in-depth reading and valuable information. However, satellite imagery with medium to suggestions. Karin offered me to join her on fieldwork in high spatial resolution and especially detailed DEMs have winter Finnish Lapland that I really enjoyed. She also invited the potential to replace aerial photographs as a data source in me to teach on an excursion to northern Fennoscandia regional mapping surveys of the meltwater system. enabling me to spend a substantial part of my teaching hours - The landform record in central Transbaikalia shows the in wonderful Nordic nature. former existence of large glacial lakes in the area. Localized, I would like to thank Stefan Engels who joined me on high-magnitude fluvial erosion in the postulated ice-dam fieldwork in Finland, John Jansen and Artem Gurinov who area of Glacial Lake Vitim, the largest of the reconstructed joined me on fieldwork in Transbaikalia and fellow PhD glacial lakes in the area, indicates a possible outburst flood students and other colleagues at INK for creating a nice from this lake to the Arctic Ocean. working atmosphere. Jakob Heyman joined me on fieldwork - Central British Columbia reveals a consistent spatial in Canada and shared with me his thoughts about our research pattern of ice-marginal meltwater channels at high elevations. field that were valuable for my decisions. Julien Seguinot Medium-sized eskers consistent with the regional ice flow also joined me on fieldwork in Canada, and moreover, we direction occur on higher ground whereas large esker have shared the same study area and the study subject, which accumulations often at oblique angles to regional ice flow led to many fruitful discussions and hopefully will lead to indicators occur in the main topographic lows. a fruitful collaboration in the future. I would like to thank - CIS ice divide migrated towards the Coast Mountains Václav Treml, the supervisor of my Master’s project and his after the local LGM in central British Columbia. The eastern colleagues Marek Křížek and Zbyněk Engel, who offered me margin of the CIS was retreating towards the ice divide to join them on fieldwork in the Czech mountains. This across the Interior Plateau, damming a glacial lake along the together with Václav’s inspiring supervision of my Master‘s Fraser River. Ice retreat was possibly accompanied by project encouraged me to further engage in geomorphology a stagnation of ice lobes on the Interior Plateau. and the research of palaeo-environments. - The Liard Lobe of the CIS drained ice towards the Last but not least, I would like to thank my parents for northeast from ice-divide areas in northern British Columbia their support during my studies and especially my wife and southern Yukon Territory. Active retreat of its ice margin Barbora. She has joined me for fieldworks, helped to keep towards the west is reconstructed from the pattern of large good spirits when the work seemed to make no sense, and meltwater channels in the Hyland Highland and from esker managed to make the time we have spent together in Sweden complexes cross-cutting the Liard Lowland. Ice-marginal being wonderful years. positions from a late stage of the deglaciation were locally reconstructed at the foot of the Cassiar Mountains and in its 11. References easterly trending valleys. Bamber, J.L., Riva, R.E.M., Vermeersen, B.L.A., LeBrocq, A.M. 9. Financial support (2009): Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet. Science 324, 901–903. The studies contained in this thesis were made possible by Barber, D.C., Dyke, A., Hillaire-Marcel, C., Jennings, A.E., Andrews, J.T., Kerwin, M.W., Bilodeau, G., McNeely, R., a research grant from the Swedish Space Agency to Johan Southon, Morehead, M.D., Gagnonk, J.-M. (1999): Forcing of Kleman. I would like to thank Carl Mannerfelts Fond, Gerard the cold event of 8,200 years ago by catastrophic drainage of De Geers Fond, Albert och Maria Bergströms Stiftelse, Laurentide lakes. Nature 400, 344–348. Liljevalchs resestipendier, Augustinssons resestipendier, L. Barendregt, R.W., Irving, E. (1998): Changes in the extent of North and E. Kinanders Stiftelse, Rhodins Minne Stiftelse, the American ice sheets during the late Cenozoic. Canadian Swedish Society for Anthropology and Geography, and the Journal of Earth Sciences 35, 504–509. Bert Bolin Centre Climate Research School for providing me Bednarski, J.M., Smith, I.R. 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