Geomorphological mapping is a well-established method for examining earth surface processes and landscape evolution in a range of environmental contexts. In glacial research, it provides crucial data for a wide range of process-oriented studies and palaeoglaciological reconstructions; in the latter case providing an essential geomorphological framework for establishing glacial chronologies. In recent decades, there have been significant developments in remote sensing and Geographical Information Systems (GIS), with a plethora of high quality remotely-sensed datasets now (often freely) available. Most recently, the emergence of unmanned aerial vehicle (UAV) technology has allowed sub-decimetre scale aerial images and Digital Elevation Models (DEMs) to be obtained. Traditional field mapping methods still have an important role in glacial geomorphology, particularly in cirque glacier, valley glacier and icefield/ice-cap outlet settings. Field mapping is also used in ice sheet settings, but often takes the form of necessarily highly-selective ground-truthing of remote mapping. Given the increasing abundance of datasets and methods available for mapping, effective approaches are necessary to enable assimilation of data and ensure robustness. This paper provides a review and assessment of the various glacial geomorphological methods and datasets currently available, with a focus on their applicability in particular glacial settings. We distinguish two overarching 'work streams' that recognise the different approaches typically used in mapping landforms produced by ice masses of different sizes: (i) mapping of ice sheet geomorphological imprints using a combined remote sensing approach, with some field checking (where feasible); and (ii) mapping of alpine and plateau-style ice mass (cirque glacier, valley glacier, icefield and ice-cap) geomorphological imprints using remote sensing and considerable field mapping. Key challenges to accurate and robust geomorphological mapping are highlighted, often necessitating compromises and pragmatic solutions. The importance of combining multiple datasets and/or mapping approaches is emphasised, akin to multi-proxy approaches used in many Earth Science disciplines. Based on our review, we provide idealised frameworks and general recommendations to ensure best practice in future studies and aid in accuracy assessment, comparison, and integration of geomorphological data. These will be of particular value where geomorphological data are incorporated in large compilations and subsequently used for palaeoglaciological reconstructions. Finally, we stress that robust interpretations of glacial landforms and landscapes invariably requires additional chronological and/or sedimentological evidence, and that such data should ideally be collected as part of a holistic assessment of the overall glacier system.

During the Last Interglacial, global mean sea level reached approximately 6 to 9 m above the present level. This period of high sea level may have been punctuated by a fall of more than 4 m, but a cause for such a widespread sea-level fall has been elusive. Reconstructions of global mean sea level account for solid Earth processes and so the rapid growth and decay of ice sheets is the most obvious explanation for the sea-level fluctuation. Here, we synthesize published geomorphological and stratigraphic indicators from the Last Interglacial, and find no evidence for ice-sheet regrowth within the warm interglacial climate. We also identify uncertainties in the interpretation of local relative sea-level data that underpin the reconstructions of global mean sea level. Given this uncertainty, and taking into account our inability to identify any plausible processes that would cause global sea level to fall by 4 m during warm climate conditions, we question the occurrence of a rapid sea-level fluctuation within the Last Interglacial. We therefore recommend caution in interpreting the high rates of global mean sea-level rise in excess of 3 to 7 m per 1,000 years that have been proposed for the period following the Last Interglacial sea-level lowstand.

This paper reconstructs the deglaciation of the Laurentide Ice Sheet (LIS; including the Innuitian Ice Sheet) from the Last Glacial Maximum (LGM), with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides. We build on a recent inventory of Laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the LIS, which we depict in a series of palaeogeographic maps. Results show that the drainage network at the LGM was similar to modern-day Antarctica. The majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation, until the ice sheet lost its marine margin. Ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build-up, peak-phase and collapse of the Cordilleran-Laurentide ice saddle. The south-eastern marine margin in Atlantic Canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the LGM. In contrast, the ice streams draining towards the north-western and north-eastern marine margins in the Beaufort Sea and in Baffin Bay appear to have remained stable throughout most of the Late Glacial, and some of them continued to function until after the Younger Dryas (YD). The YD influenced the dynamics of the deglaciation, but there remains uncertainty about the response of the ice sheet in several sectors. We tentatively ascribe the switching-on of some major ice streams during this period (e.g. M'Clintock Channel Ice Stream at the north-west margin), but for other large ice streams whose timing partially overlaps with the YD, the drivers are less clear and ice-dynamical processes, rather than effects of climate and surface mass balance are viewed as more likely drivers. Retreat rates markedly increased after the YD and the ice sheet became limited to the Canadian Shield. This hard-bed substrate brought a change in the character of ice streaming, which became less frequent but generated much broader terrestrial ice streams. The final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around Hudson Bay. Our reconstruction indicates that the LIS underwent a transition from a topographically-controlled ice drainage network at the LGM to an ice drainage network characterised by less frequent, broad ice streams during the later stages of deglaciation. These deglacial ice streams are mostly interpreted as a reaction to localised ice-dynamical forcing (flotation and calving of the ice front in glacial lakes and transgressing sea; basal de-coupling due to large amount of meltwater reaching the bed, debuttressing due to rapid changes in ice sheet geometry) rather than as conveyors of excess mass from the accumulation area of the ice sheet. At an ice sheet scale, the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet, the final elimination of which was mostly driven by surface melt.

Cataclysmic outburst floods transformed landscapes and caused abrupt climate change during the last deglaciation. Whether such events have also characterized previous deglaciations is not known. Arctic marine cores hint at megafloods prior to Oxygen Isotope Stage (OIS) 2, but the overprint of successive glaciations means that geomorphological traces of ancient floods remain scarce in Eurasia and North America. Here we present the first well-constrained terrestrial megaflood record to be linked with Arctic archives. Based on cosmogenic-nuclide exposure dating and optically stimulated luminescence dating applied to glacial-lake sediments, a 300-m deep bedrock spillway, and giant eddy-bars > 200-m high, we reconstruct a history of cataclysmic outburst floods from glacial Lake Vitim, Siberia, to the Arctic Ocean over the past 60,000-years. Three megafloods have reflected the rhythm of Eurasian glaciations, leaving traces that stretch more than 3500 km to the Lena Delta. The first flood was coincident with deglaciation from OIS-4 and the largest meltwater spike in Arctic marine-cores within the past 100,000 years (isotope-event 3.31 at 55.5 ka). The second flood marked the lead up to the local Last Glacial Maximum, and the third flood occurred during the last deglaciation. This final 3000 km(3) megaflood stands as one of the largest freshwater floods ever documented, with peak discharge of 4.0-6.5 million m(3)s(-1), mean flow depths of 120-150 m, and average flow velocities up to 21 ms(-1)

The Cordilleran Ice Sheet (CIS) once covered an area comparable to that of Greenland. Previous geologic evidence and numerical models indicate that the ice sheet covered much of westernmost Canada as late as 12.5 thousand years ago (ka). New data indicate that substantial areas throughout westernmost Canada were ice free prior to 12.5 ka and some as early as 14.0 ka, with implications for climate dynamics and the timing of meltwater discharge to the Pacific and Arctic oceans. Early Bolling-Allerod warmth halved the mass of the CIS in as little as 500 years, causing 2.5 to 3.0 meters of sea-level rise. Dozens of cirque and valley glaciers, along with the southern margin of the CIS, advanced into recently deglaciated regions during the Bolling-Allerod and Younger Dryas.

A comprehensive map of glacial landforms is presented for the area of northwest Saskatchewan, Canada. Remote sensing of 1-arc (similar to 30 m resolution) Shuttle Radar Topography Mission digital elevation models over an area of approximately 15,000 km(2) were used as the primary data source for landform identification. A total of 16,856 landforms were identified pertaining to Quaternary glacial and postglacial activity. Ten landform types were mapped: ice flow parallel lineations (flutings, drumlins, mega-scale glacial lineations, and crag-and-tail ridges), moraines (major and minor), ice-thrust ridges, crevasse-fill ridges, meltwater landforms (major and minor meltwater channels and eskers), palaeo-shorelines and dunes. Collectively, these landforms constitute a glacial and postglacial landform record, which exhibits a more complex pattern than previously recognised, with evidence of multiple cross cutting ice flow directions. This geomorphological mapping of the regional landform record provides the prerequisite for future reconstructions of the glacial dynamics and chronology of northwest Saskatchewan.

Successively smaller glacial extents have been proposed for continental Eurasia during the stadials of the last glacial period leading up to the Last Glacial Maximum (LGM). At the same time the large mountainous region east of Lake Baikal, Transbaikalia, has remained unexplored in terms of glacial chronology despite clear geomorphological evidence of substantial past glaciations. We have applied cosmogenic Be-10 exposure dating and optically stimulated luminescence to establish the first quantitative glacial chronology for this region. Based on eighteen exposure ages from five moraine complexes, we propose that large mountain ice fields existed in the Kodar and Udokan mountains during Oxygen Isotope Stage 2, commensurate with the global LGM. These ice fields fed valley glaciers (>100 km in length) reaching down to the Chara Depression between the Kodar and Udokan mountains and to the valley of the Vitim River northwest of the Kodar Mountains. Two of the investigated moraines date to the Late Glacial, but indications of incomplete exposure among some of the sampled boulders obscure the specific details of the post-LGM glacial history. In addition to the LGM ice fields in the highest mountains of Transbaikalia, we report geomorphological evidence of a much more extensive, ice-cap type glaciation at a time that is yet to be firmly resolved.

After more than a century of geological research, the Cordilleran ice sheet of North America remains among the least understood in terms of its former extent, volume, and dynamics. Because of the mountainous topography on which the ice sheet formed, geological studies have often had only local or regional relevance and shown such a complexity that ice-sheet-wide spatial reconstructions of advance and retreat patterns are lacking. Here we use a numerical ice sheet model calibrated against field-based evidence to attempt a quantitative reconstruction of the Cordilleran ice sheet history through the last glacial cycle. A series of simulations is driven by time-dependent temperature offsets from six proxy records located around the globe. Although this approach reveals large variations in model response to evolving climate forcing, all simulations produce two major glaciations during marine oxygen isotope stages 4 (62.2-56.9 ka) and 2 (23.2-16.9 ka). The timing of glaciation is better reproduced using temperature reconstructions from Greenland and Antarctic ice cores than from regional oceanic sediment cores. During most of the last glacial cycle, the modelled ice cover is discontinuous and restricted to high mountain areas. However, widespread precipitation over the Skeena Mountains favours the persistence of a central ice dome throughout the glacial cycle. It acts as a nucleation centre before the Last Glacial Maximum and hosts the last remains of Cordilleran ice until the middle Holocene (6.7 ka).

Meltwater drainage through ice sheets has recently been a key focus of glaciological research due to its influence on the dynamics of ice sheets in a warming climate. However, the processes, topologies and products of ice sheet hydrology are some of the least understood components of both past and modem ice sheets. This is to some extent a result of a disconnect between the fields of theoretical, contemporary observational and palaeo-glaciology that each approach ice sheet hydrology from a different perspective and with different research objectives. With an increasing realisation of the potential of using the past to inform on the future of contemporary ice sheets, bridging the gaps in the understanding of ice sheet hydrology has become paramount. Here, we review the current state of knowledge about ice sheet hydrology from the perspectives of theoretical, observational and palaeo-glaciology. We then explore and discuss some of the key questions in understanding and interpretation between these research fields, including: 1) disagreement between the palaeo-record, glaciological theory and contemporary observations in the operational extent of channelised subglacial drainage and the topology of drainage systems; 2) uncertainty over the magnitude and frequency of drainage events associated with geomorphic activity; and 3) contrasts in scale between the three fields of research, both in a spatial and temporal context The main concluding points are that modem observations, modelling experiments and inferences from the palaeo-record indicate that drainage topologies may comprise a multiplicity of forms in an amalgam of drainage modes occurring in different contexts and at different scales. Drainage under high pressure appears to dominate at ice sheet scale and might in some cases be considered efficient; the sustainability of a particular drainage mode is governed primarily by the stability of discharge. To gain better understanding of meltwater drainage under thick ice, determining what drainage topologies are reached under high pressure conditions is of primary importance. Our review attests that the interconnectivity between research sub-disciplines in progressing the field is essential, both in interpreting the palaeo-record and in developing physical understanding of glacial hydrological processes and systems.

Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding mechanisms of global climate change and associated sea-level fluctuations in the past, present and future. The significance of palaeo-ice sheets is further underlined by the broad range of disciplines concerned with reconstructing their behaviour, many of which have undergone a rapid expansion since the 1980s. In particular, there has been a major increase in the size and qualitative diversity of empirical data used to reconstruct and date ice sheets, and major improvements in our ability to simulate their dynamics in numerical ice sheet models. These developments have made it increasingly necessary to forge interdisciplinary links between sub-disciplines and to link numerical modelling with observations and dating of proxy records. The aim of this paper is to evaluate recent developments in the methods used to reconstruct ice sheets and outline some key challenges that remain, with an emphasis on how future work might integrate terrestrial and marine evidence together with numerical modelling. Our focus is on pan-ice sheet reconstructions of the last deglaciation, but regional case studies are used to illustrate methodological achievements, challenges and opportunities. Whilst various disciplines have made important progress in our understanding of ice-sheet dynamics, it is clear that data-model integration remains under-used, and that uncertainties remain poorly quantified in both empirically-based and numerical ice-Sheet reconstructions. The representation of past climate will continue to be the largest source of uncertainty for numerical modelling. As such, palaeo-observations are critical to constrain and validate modelling. State-of-the-art numerical models will continue to improve both in model resolution and in the breadth of inclusion of relevant processes, thereby enabling more accurate and more direct comparison with the increasing range of palaeo-observations. Thus, the capability is developing to use all relevant palaeo-records to more strongly constrain deglacial (and to a lesser extent pre-LGM) ice sheet evolution. In working towards that goal, the accurate representation of uncertainties is required for both constraint data and model outputs. Close cooperation between modelling and data-gathering communities is essential to ensure this capability is realised and continues to progress.