Plateau Icefield Research Articles

Accelerating glacier volume loss on Juneau Icefield driven by hypsometry and melt-accelerating feedbacks

Globally, glaciers and icefields contribute significantly to sea level rise. Here we show that ice loss from Juneau Icefield, a plateau icefield in Alaska, accelerated after 2005 AD. Rates of area shrinkage were 5 times faster from 2015–2019 than from 1979–1990. Glacier volume loss remained fairly consistent (0.65–1.01 km3 a−1) from 1770–1979 AD, rising to 3.08–3.72 km3 a−1 from 1979–2010, and then doubling after 2010 AD, reaching 5.91 ± 0.80 km3 a−1 (2010–2020). Thinning has become pervasive across the icefield plateau since 2005, accompanied by glacier recession and fragmentation. Rising equilibrium line altitudes and increasing ablation across the plateau has driven a series of hypsometrically controlled melt-accelerating feedbacks and resulted in the observed acceleration in mass loss. As glacier thinning on the plateau continues, a mass balance-elevation feedback is likely to inhibit future glacier regrowth, potentially pushing glaciers beyond a dynamic tipping point.

Reconstructing the Holocene glacial history of northern Troms and western Finnmark, Arctic Norway

Here we present the first Lateglacial and Holocene glacial history from Rotsunddalen, northern Troms and western Finnmark county, northern Norway, based on both relative and numerical moraine dating using Schmidt hammer, soil chronosequencing and terrestrial cosmogenic nuclide dating. We combine these chronological data with a regional map of the glacial geomorphology to hypothesize key events in the glacial history from around 14 ka to present. Our reconstruction shows that, following deglaciation of the main ice sheet across central Troms and Finnmark, mountain glaciers were terminating on land, close to the coast, between around 12.1 and 10.6 ka. Continued recession of the main Fennoscandian Ice Sheet margin towards the SE led to the isolation of several large plateau icefields and outlet glaciers that generated moraines at around 10.2–9.2 ka, which we ascribe to the Erdalen Event, and 8.4–8.2 ka, which is broadly contemporaneous with the 8.2 ka cold event. Although the latter corresponds with the Scandinavian Finse Event, very few moraines have been dated to this time and we therefore view it as a tentative hypothesis for future work to test. During the Holocene Thermal Maximum (~6.6 to 6.3 ka) most (if not all) glaciers in the region disappeared, but then regrew during the Neoglaciation and produced large moraines dated to around 4.7 ka that lie a few hundred metres distal to the prominent Little Ice Age moraines (previously dated to AD 1810s–1870s). Given the limitations of our dating approach, the preservation of moraines dated to this period in northern Norway also warrants further investigation. We also highlight that terrestrial cosmogenic nuclide dating of the moraines is not consistent with other dating approaches and the widely established deglaciation history of the region, probably owing to cosmogenic inheritance and insufficient glacial erosion.

Past glaciation of temperate‐continental mountains: A model for a debris‐charged plateau icefield/cirque glacier landsystem in the Southern Carpathians, Romania

AbstractReconstructing the extent, style, timing and drivers of past mountain glaciation is crucial in both understanding past atmospheric circulation and predicting future climate change. Unlike in high‐elevation mountains situated in maritime and continental climates, less is known of past glaciation in mid‐altitude mountains, located in transitional climates, such as the Southern Carpathians of Romania. Despite these mountains harbouring a rich glacial geomorphology, this has never been systematically mapped according to well‐established morphological criteria, nor confidently related to former styles of glaciation. Therefore, filling this gap is important for not only accurately identifying glacial extents but also for establishing past glaciation styles and relating them to past ice dynamics and climate. Here, we devise the first glacial landsystem model for the Southern Carpathians, to enhance our understanding of the glaciation style and dynamics of past mountain glaciers in temperate‐continental climates. We present a geomorphological map, from which we infer the spatial and temporal evolution of glacial, periglacial and paraglacial landforms. We then assess the links between the mountain geomorphology and glaciation style and dynamics to construct a glacial landsystem model for debris‐charged plateau icefields and cirque glaciers in temperate‐continental mountain settings.

Long-term glacial and fluvial system coupling in southern Greece and evidence for glaciation during Marine Isotope Stage 16

Pleistocene glacial activity was a major influence on runoff and sediment supply in many river systems across the Mediterranean. The geomorphological impacts of changes in sediment supply between glaciated headwater terrains and downstream depocentres spanning several glacial cycles are, however, poorly understood. By applying uranium-series and optically stimulated luminescence dating to fluvial and glacial sediments preserved on Mount Chelmos (2355 m a.s.l.) in southern Greece, we show how changes in the long-term coupling between glacial and fluvial systems are preserved within a major glaciofluvial outwash fan system that functioned during multiple cold stages. We also present evidence in the form of a cemented till unit, stratigraphically below younger Middle Pleistocene glacial deposits, yielding a U-series age close to the limit of the technique, indicating glaciation during Marine Isotope Stage (MIS) 16 - one of the most severe cold stages recorded in the Mediterranean. This is the first time such early glaciation has been directly recorded in Greece and the wider Balkans and is defined here as the Valvousian Stage based on glacial deposits on Mount Chelmos. Geomorphological and geochronological data point to the formation of a more extensive plateau ice field over Chelmos during MIS 12, another severe glacial period in the Balkans that corresponds with the Skamnellian Stage glaciation of Northern Greece. During this phase, very strong coupling of glacial and fluvial systems led to meltwater flood events transferring large volumes of sediment to lower valley zones culminating in the formation of an extensive glaciofluvial outwash fan complex and glaciofluvial terraces. A smaller plateau ice field during MIS 6 and localised valley glaciers between MIS 5d to 5c correlate with the Vlasian and early Tymphian Stage glaciations in Greece, respectively. The delivery of much less meltwater and sediment through a single valley during MIS 6 and MIS 5b to MIS 4 signalled the transition to progressively weaker glacial and fluvial system coupling. After MIS 4 the uncoupling of depositional zones from sediment sources in glaciated catchments led to fluvial incision of glaciofluvial outwash deposits in several valleys. Despite this incision, the glaciofluvial outwash fans preserve a record of glacial and fluvial system interactions during the Middle Pleistocene and early stages of the Late Pleistocene.

The role of topography in landform development at an active temperate glacier in Arctic Norway

AbstractTopography exerts a strong control on how glaciers respond to changes in climate. Increased understanding of this role is important for both refining model predictions of future rates of glacier recession and for reconstructing climatic change from the glacial geological record. In this paper, we examine the geomorphological and sedimentological evidence in the foreland of Fingerbreen, a temperate outlet of the plateau icefield Østre Svartisen. The aim is to investigate the relationship between processes of landform generation and the changing influence of topography as recession progressed. The Fingerbreen foreland is dominated by bouldery Little Ice Age moraines and extensive areas of striated bedrock. A heavily fluted zone occurs in the central part of the foreland that is cross‐cut by annual transverse and sawtooth moraines. Systematic investigations of the structural architecture of moraines at various locations in the foreland provide evidence for a range of moraine‐forming processes, which can be linked to the topographic setting (e.g. deposition on a reverse bedrock slope) and drainage conditions. This includes push and bulldozing of proglacial sediments and squeezing of sub‐glacial sediments and submarginal freeze‐on of sediment slabs. We also identify variations in moraine spacing as a result of topography. This research demonstrates the importance of topography when interpreting moraine records in the context of climate and glacier dynamics.

Topographic controls on ice flow and recession for Juneau Icefield (Alaska/British Columbia)

AbstractGlobally, mountain glaciers and ice caps are losing dramatic volumes of ice. The resultant sea‐level rise is dominated by contributions from Alaska. Plateau icefields may be especially sensitive to climate change due to the non‐linear controls their topography imparts on their response to climate change. However, Alaskan plateau icefields have been subject to little structural glaciological or regional geomorphological assessment, which makes the controls on their present and former mass balance difficult to ascertain.We inventoried 1050 glaciers and 368 lakes in the Juneau Icefield region for the year 2019. We found that 63 glaciers had disappeared since the 2005 inventory, with a reduction in glacier area of 422 km2 (10.0%). We also present the first structural glaciological and geomorphological map for an entire icefield in Alaska. Glaciological mapping of >20 800 features included crevasses, debris cover, foliation, ogives, medial moraines and, importantly, areas of glacier fragmentation, where glaciers either separated from tributaries via lateral recession (n = 59), or disconnected within areas of former icefalls (n = 281). Geomorphological mapping of >10 200 landforms included glacial moraines, glacial lakes, trimlines, flutes and cirques. These landforms were generated by a temperate icefield during the Little Ice Age (LIA) neoglaciation. These data demonstrate that the present‐day outlet glaciers, which have a similar thermal and ice‐flow regime, have undergone largely continuous recession since the LIA. Importantly, disconnections occurring within glaciers can separate accumulation and ablation zones, increasing rates of glacier mass loss. We show that glacier disconnections are widespread across the icefield and should be critically taken into consideration when icefield vulnerability to climate change is considered.

Reconstructing the Little Ice Age extent of Langfjordjøkelen, Arctic mainland Norway, as a baseline for assessing centennial-scale icefield recession

Current warming in the Arctic is occurring at a rate two to three times higher than that of the rest of the world, leading to rapid glacier wastage. In Arctic mainland Norway, the plateau icefield Langfjordjøkelen has experienced the greatest mass loss of all Norwegian glaciers (excluding Svalbard) in recent decades. In this article, we examine this decline in a centennial-scale context through geomorphological mapping and the analysis of historical aerial photographs and maps. This allows Langfjordjøkelen’s maximum Little Ice Age extent (ca. 1925) to be reconstructed, providing an important baseline for a long-term assessment of icefield change. At the LIA maximum, Langfjordjøkelen covered an area of 14.9 km2. A comparison of the LIA dimensions with the icefield extent in 1891/1902, as displayed on a historical map, reveals a substantial overestimation of the map-based glacier outline. The post-LIA evolution of Langfjordjøkelen has been characterized by sustained high rates of glacier recession. By 2018, the icefield had lost 57% (8.5 km2) of its original LIA area, at a decadal rate of 9%, and its outlet glaciers had reduced in average length by 42% (1 km), at an annual rate of 11 m. Langfjordjøkelen’s percentage area decline has been greater than that of Norwegian ice masses at lower latitudes where comparable long-term glacier change data are available. This indicates that there is a significant latitudinal variation in Norwegian glacier response to 20th century warming, likely influenced by an enhanced warming signal in Arctic Norway compared to the rest of the Norwegian mainland.

The glacial history of Greece: a comprehensive review

This paper reviews the glacial history of the mountains of Greece at the southernmost tip of the Balkans, providing a new synthesis of our current understanding of glaciations. The ice cover during the largest Middle Pleistocene glaciations (MIS 12/MIS 6) was more extensive than previously thought. Latest evidence from Mt Chelmos suggests that valley glaciers radiated from a central plateau ice field, whereas the findings of other glacial studies in western Balkans further indicate that extensive ice field/ice caps formed on mountains throughout this region during the Middle Pleistocene glaciations. Ice extent was considerably smaller during the Tymphian Stage (MIS 5d–MIS 2) and this has been confirmed by cosmogenic exposure ages in recent studies on Mt Olympus and Mt Chelmos. During the Holocene, only very small glaciers formed in some deep cirques where they survived because of strong local topoclimatic controls. A comparative analysis with the findings of other glacial and palaeoclimatic studies in the Balkans is also presented to highlight correlations between them. Moisture supply seems to have been the most critical factor for the formation of glaciers in the mountains of Greece. The comparison of Late Pleistocene Equilibrium Line Altitudes (ELAs) across the Balkans indicates a wetter climate in southern Greece that can be attributed to different palaeoatmospheric circulation mechanisms and precipitation regime in central Mediterranean. Conclusively, whilst important information has been added in the last 2 decades, this paper highlights the need for further research in Greece and the wider Balkans to establish the timing and extent of glaciations.

Processes of ‘hummocky moraine’ formation in the Gaick, Scotland: insights into the ice‐marginal dynamics of a Younger Dryas plateau icefield

Younger Dryas ice‐marginal (‘hummocky’) moraines in Scotland represent valuable terrestrial archives that can be used to obtain important information on ice‐marginal dynamics and glacier thermal regimes during a period of rapid climatic change. In this paper, we present detailed sedimentological studies of Younger Dryas ice‐marginal moraines in the Gaick, central Scotland, the former site of a spatially restricted plateau icefield. Exposures demonstrate that moraines in the Gaick represent terrestrial ice‐contact fans, with evidence of proglacial and subglacial glaciotectonization, as reported elsewhere in Scotland. The exposures also reveal the influence of local hydrogeological conditions, with pressurization of the groundwater system leading to the formation of hydrofracture fills within some moraines. Clast shape analysis shows that all the moraines contain debris consistent with transport in the subglacial traction zone. The sedimentological data, and the planform arrangement of the moraines as nested arcs or chevrons, indicate that retreat of the Younger Dryas Gaick Icefield outlets was incremental and oscillatory. This evidence strongly suggests a mainly temperate thermal regime and short glacier response times, but with narrow cold‐ice zones near the margins facilitating the elevation of basal debris to the glacier surface. Analogous glaciodynamic regimes occur at modern ice‐cap and plateau icefield outlets in Iceland and Norway, although there are significant differences in the nature of ice‐marginal deposition. The glaciodynamic signature recorded by moraines in the Gaick has allowed us to shed new light on the ice‐marginal dynamics and thermal regime of one of the most easterly Younger Dryas icefields in Scotland.

Evolution of the Norwegian plateau icefield Hardangerjøkulen since the ‘Little Ice Age’

The maximum ‘Little Ice Age’ (LIA) glacier extent provides a significant baseline to assess long-term glacier change and to place currently observed rates of glacier recession in a broader temporal context. To that end, we examine the evolution of the plateau icefield Hardangerjøkulen since the LIA. First, we reconstruct Hardangerjøkulen’s maximum LIA extent (~AD 1750) and subsequent recession based on the glacial landform record and aided by historical map interpretation. Ice-marginal moraines, glacial drift limits, trimlines, and identifiable erosion and weathering boundaries provide evidence of a LIA icefield with an area of 110 km2. Existing LIA model simulations of Hardangerjøkulen are not yet fully able to reproduce our reconstructed extent. Second, we compile a set of remotely sensed icefield outlines from successive time points in the 20th and 21st century to calculate icefield area and length change since the LIA. This reveals a substantial reduction in icefield size, with a total area loss of 41 km2 (37%; 2% 10 a–1) by 2010 and a cumulative frontal retreat averaging 1.3 km (29%; 5 m a–1) by 2013. Icefield recession has been greatest since the end of the 20th century, when rates of areal shrinkage increased to 6.5–10% 10 a–1 in 1995–2010, and the rate of average terminus retreat accelerated to 17 m a–1 in 2003–2010. Third, we present a relative dating approach, based on the known age of the different icefield outlines, that allows bracketing ages to be assigned to all ice-marginal landforms between any two outlines. This approach shows that episodes of moraine formation vary temporally between individual outlet glaciers of Hardangerjøkulen, suggesting that the moraine record of a single outlet glacier alone may not be sufficient to derive an icefield-wide picture of past ice advances, and thereby climate fluctuations.

Topographic controls on plateau icefield recession: insights from the Younger Dryas Monadhliath Icefield, Scotland

ABSTRACTPlateau icefields are a common form of mountain ice mass, frequently found in mid‐latitude to high‐arctic regions and increasingly recognized in the Quaternary record. Their top‐heavy hypsometry makes them highly sensitive to changes in climate when the equilibriaum line altitude (ELA) lies above the plateau edge, allowing ice to expand significantly as regional ELAs decrease, and causing rapid recession as climate warms. With respect to future climate warming, it is important to understand the controls on plateau icefield response to climate change in order to better predict recession rates, with implications for water resources and sea‐level rise. Improving knowledge of the controls on glacier recession may also enable further palaeoclimatic information to be extracted from the Quaternary glacial record. We use the distribution of moraines to examine topographic controls on Younger Dryas icefield recession in Scotland. We find that overall valley morphology influences the style of recession, through microclimatic and geometric controls, with bed gradient affecting moraine spacing. Ice mass reconfiguration may occur as recession progresses because ice divide migration could alter the expected response based on hypsometric distribution. These results add to a growing body of research examining controls on glacier recession and offer a step towards unravelling non‐linear ice mass behaviour. Copyright © 2019 John Wiley & Sons, Ltd.

A spatially-restricted Younger Dryas plateau icefield in the Gaick, Scotland: Reconstruction and palaeoclimatic implications

Considerable research has been conducted in Scotland to reconstruct Younger Dryas glaciers and palaeoclimatic conditions, but our understanding remains incomplete. In this contribution, we examine the Gaick, a dissected plateau that extends over ∼520 km2 in the Central Grampians, Scotland. The extent and style of Younger Dryas glaciation in the Gaick has been repeatedly contested, although a model of extensive plateau icefield glaciation has become generally accepted. This is despite well-documented issues with key elements of the plateau icefield reconstruction. We synthesise the results of recent geomorphological mapping in the Gaick and recognise a distinct morphostratigraphic signature in the upper parts of the western catchments. This differs markedly from sediment-landform associations in other parts of the area, and we argue this provides a strong indication of spatially-restricted Younger Dryas (∼12.9–11.7 ka) glaciation in the Gaick. Our interpretation is independently supported by glacierisation threshold analysis, which implies that the eastern Gaick was unable to nourish Younger Dryas ice. We therefore contest the accepted paradigm of extensive Younger Dryas glaciation in this area. Based on the geomorphological evidence and glacier surface profile modelling, we reconstruct a ∼42 km2 plateau icefield that yields an equilibrium line altitude of 751 ± 46 m. Using this value, a sea-level precipitation value of 826 ± 331 mm a−1 is inferred for the Younger Dryas, which suggests considerably drier conditions than at present. Using recalculated glacier-derived precipitation estimates from Scotland, we present regional climate analysis that corroborates arguments for a strong west-east precipitation gradient across Scotland.

Glacial landsystems, retreat dynamics and controls on Loch Lomond Stadial (Younger Dryas) glaciation in Britain

Glacial geomorphology relating to the Loch Lomond Stadial (Younger Dryas) in Britain is used to construct five glacial landsystem models. These landsystems lie on a continuum of increasing ice thickness and decreasing topographic control and typify the principal styles of glaciation during the stadial. The landsystems comprise: the cirque/niche glacier landsystem, the alpine icefield landsystem, the lowland piedmont lobe landsystem, the plateau icefield landsystem and the icecap landsystem. Geomorphological features representing the icecap landsystem are present only at the centre of the West Highland Glacier Complex, which was flanked primarily by satellite alpine and plateau icefields. The cirque/niche glacier landsystem was present predominantly in areas that experienced conditions only marginally favourable for glacier development at peripheral sites. Three styles of glacier retreat are recorded by the geomorphology: active, two‐phase and uninterrupted retreat. Of these, active retreat appears to be most widespread within the Loch Lomond Stadial limits. These retreat styles reflect a combination of climatic and topographic conditions, coupled with local factors influencing the preservation of landforms from which retreat dynamics can be inferred. Likewise, the distribution of landsystems was influenced by an interplay between topography and climate, with glacier formation being facilitated in locations where topographical conditions aided in the accumulation of snow. The pattern also supports the existence of previously recognized northward and eastward precipitation gradients across Britain during the stadial.

Multiple subglacial till deposition: A modern exemplar for Quaternary palaeoglaciology

The sedimentology of a vertical succession of alternating beds of massive and fissile diamictons on a þorisjökull plateau icefield outlet foreland is employed to assess the evolution of subglacial traction tills at the margins of active temperate glaciers with deformable substrates, where tills appear to form sub-marginal incrementally thickened wedges that display multiple till emplacement events, potentially of annual scale. Lodged boulders display strong A-axes and surface striae alignments which parallel surface flutings, indicating that fluting construction and till emplacement were related to moulding by consistent glacier flow from the SSW during the Little Ice Age. In contrast, clast macrofabrics at the sub-boulder size, not unlike those reported from other Icelandic tills, are not as strong as would be expected in a subglacially sheared medium, indicating shear strains too low for a steady state strain signature. This separation of fabric data has isolated the strain signatures of the lodgement and deformation components of subglacial traction till, whereby the orientations of the largest, lodged clasts record high cumulative shear strains and those of the sub-boulder sized clasts record greater susceptibility to deformation of their enclosing matrix. This is likely due to the effect of clast collisions in clast rich till and the perturbations set up by the numerous large boulders, consistent with observations on till fabrics in flutings and around lodged clasts. A/B plane macrofabric data display unusually high degrees of isotropy, reflective of the more variable orientations of A/B planes, which are thought to reflect A/B plane susceptibility to dip parallel or anastomosing shear planes. A wide range of clast angularity values reflects the localized input of freshly plucked and hence relatively highly angular blocks to the deforming layer, a characteristic of stepped bedrock profiles beneath the snouts of mountain glaciers. Finally, we hypothesize that the massive and fissile units may represent A and B horizons of subglacial deforming layer couplets, and that each couplet could record seasonal emplacement and partial inter-couplet modification near the ice margin. If the latter is the case, then less than 1 m of subglacial till is advected to the glacier margin per (annual?) deformation event.

Evidence for restricted Loch Lomond Stadial plateau ice in Glen Turret and implications for the age of the Turret Fan

Despite a wealth of research on the patterns and timing of glaciation in Glen Roy over the last 150 years, glacial events within Glen Turret remain heavily debated. These debates centre on the extent and source of Loch Lomond Stadial (Younger Dryas) ice in Glen Turret, and the implications for the age and genesis of the Turret Fan. Here we present details of recent systematic geomorphological mapping of Glen Turret and the neighbouring valleys to the north and east. The geomorphological evidence recorded indicates a plateau icefield style of glaciation centred on the Carn Dearg plateau, of which the Turret Glacier was an outlet. A morphostratigraphical approach is used to identify a relative chronology of glacial events, and suggests that the Turret Fan may have formed prior to the Loch Lomond Stadial. A reconstruction of the Carn Dearg plateau icefield is presented, which was connected to the larger Monadhliath Icefield to the east. Equilibrium line altitudes for the outlet glaciers range from 560±20m to 646±20m and are comparable with those calculated for surrounding regions. This research suggests that the Turret Fan is predominantly an older feature that was deposited by a more extensive plateau ice-sourced Turret Glacier prior to the Loch Lomond Stadial, most likely during or immediately after deglaciation of the last ice sheet.

Pleistocene plateau ice fields in the High Atlas, Morocco

Abstract Large ice fields (>25 km 2 ) formed over the Tazaghart and Iouzagner plateaus of the High Atlas, Morocco during the Late Pleistocene. The plateau ice fields were drained by large valley glaciers forming a series of moraine assemblages. Four moraine units have been mapped and subdivided on the basis of their morphostratigraphy and the degree of soil weathering. Soil profile development index values indicate that the moraine units are widely separated in time; the oldest moraines are deeply weathered and degraded, whereas soils are absent on the youngest moraines. The highest moraine unit was formed by a small niche glacier that was present as recently as the mid-twentieth century. The Pleistocene glaciers are likely to have been associated with wetter conditions than today and colder air temperatures. Combined with ice in neighbouring areas, such as the Toubkal massif, the SW High Atlas supported some of the largest glaciers in Africa during the Pleistocene. The extent of glaciation, with ice exploiting and breaching drainage divides, has major implications for landscape development. The evolution of the High Atlas has been strongly shaped by glaciation that was closely intertwined with tectonic, fluvial and slope processes.

Glacial history of Mt Chelmos, Peloponnesus, Greece

Abstract Mt Chelmos in the Peloponnesus was glaciated by a plateau ice field during the most extensive Pleistocene glaciation. Valley glaciers radiated out from an ice field over the central plateau of the massif. The largest glaciations are likely to be Middle Pleistocene in age. Smaller valley and cirque glaciers formed later and boulders on the moraines of these glacial phases have been dated using 36 Cl terrestrial cosmogenic nuclide exposure dating. These ages indicate a Late Pleistocene age with glacier advance/stabilization at 40–30 ka, glacier retreat at 23–21 ka and advance/stabilization at 13–10 ka. This indicates that the glacial maximum of the last cold stage occurred during Marine Isotope Stage 3, several thousand years before the global Last Glacial Maximum (Marine Isotope Stage 2). The last phase of moraine-building occurred at the end of the Pleistocene, possibly during the Younger Dryas.

Former plateau ice fields in the Godeanu Mountains, Southern Carpathians: First evidence of glaciated peneplains in the Carpathians

The existence of plateau ice fields in the Southern Carpathians has long been suggested due to the widespread presence of the Borăscu surface in the region. The Borăscu surface is a peneplain consisting of flat plateaus in the elevation range of 1800–2200 m a.s.l. It is present throughout the Southern Carpathians with the most typical appearance in the Godeanu Mountains. These plateaus could have served as ice accumulation sites during the Pleistocene glaciations as they were well above the steady-state equilibrium-line altitude (ELA0). Direct geomorphological evidence on the existence of plateau ice fields, and thus well founded reconstructions, are absent due to the lack of glacial landforms on the plateaus. In order to test the existence of plateau ice fields a previous geomorphological survey and theoretical ice surface profiles, based on a steady-state perfectly plastic ice flow model, were used. Based on these methods maps and three-dimensional surface models of the former glaciers were created. The ELA0s of the paleoglaciers were estimated by the accumulation-area ratio (AAR) method. According to our results, three major ice fields on the central plateaus and several smaller ice fields on wide saddles were present in the Godeanu Mountains during the maximal glaciation. The ice fields fed numerous surrounding valley glaciers. Several independent valley and cirque glaciers, completely separated from the ice fields, were also present further from the central mass of the mountain range. The average ELA0 of the northern, 1855 ± 2 m a.s.l., and the southern, 1700 ± 2 m a.s.l., glaciers differed greatly. We suggest that the surprisingly high average ELA0 of the northern glaciers was mostly caused by the missing lower sections of these paleoglaciers from our reconstructions, due to the destroyed terminal glacial landforms. However, the terminal glacial landforms are quite well preserved in the southern valleys. Thus, the average ELA0 of the southern paleoglaciers was suitable to correlate the maximal glaciation of the Godeanu Mountains with the maximal glaciation of the neighbouring Retezat Mountains.

Eiríksjökull plateau icefield landsystem, Iceland

ABSTRACTA 1:9500 scale map of the Eiríksjökull plateau icefield and its post-Little Ice Age (LIA) foreland geomorphology and surficial geology is presented as a modern exemplar of an asymmetrically developed mountain glacier typical of the style of glacierization that dominated during mid-latitude Quaternary cold stages. Features regarded as diagnostic for this setting include (a) ice-cored hummocky terrain, indicative of controlled moraine construction in polythermal snouts, and localized breach lobe development, incremental stagnation and rock glacierization, all indicative of a debris-charged glacier snout; (b) fluted till and moraines, indicative of temperate basal ice conditions up-ice from polythermal glacier margins and (c) glacifluvial and debris flow deposits, occurring as steep fans emanating from glacier snouts at the plateau edge and in ice-contact fans or ramps fed directly by debris-covered glacier margins at the LIA. Although this plateau icefield landsystem is similar to those previously reported from Iceland, a remarkable debris-covered snout/ice-cored moraine complex on the foreland of Klofajökull is a more extreme example of the depositional zone that characterizes the valleys surrounding the more sediment-starved plateau ice dispersal centres.

A Younger Dryas plateau icefield in the Monadhliath, Scotland, and implications for regional palaeoclimate

A record of Younger Dryas glaciation in Scotland is well established. However, the role of the Monadhliath, a significant plateau area extending over 840 km2 in central Scotland, has never been investigated systematically. We present the first systematic glacial geomorphological mapping across the whole region, which has led to the identification of hitherto-unrecorded glacial and associated landforms. The spatial distribution of these landforms indicates that the last phase of glaciation in the area was that of a local plateau icefield. In addition, a clear morphostratigraphical signature provides a strong indication that the icefield dates to the Younger Dryas (12.9–11.7 ka), which is supported by numerical ages in the southeast of the study area. Based on the geomorphological evidence and 2D glacier surface profile modelling, a 280 km2 icefield is reconstructed. A novel approach is introduced to quantify plateau icefield thickness for equilibrium line altitude (ELA) and palaeoprecipitation calculations, resulting in greater overall data confidence compared to traditional reconstruction methods. The ELA for the whole icefield is calculated to be 714 ± 25 m, whilst the ELAs of individual outlet glaciers range from 560 m in the west to 816 m in the east, demonstrating a significant W–E precipitation gradient across the region during the Younger Dryas. These ELAs compare well with those calculated for Younger Dryas ice masses reconstructed in neighbouring regions and are in good agreement with overall precipitation patterns suggested for Scotland during this time. Whilst the total amount of precipitation calculated from these ELAs is highly dependent on the method used, irrespective of this, the study suggests a more arid Younger Dryas climate in the region compared to the present day.