A high‐resolution, three‐dimensional, thermomechanical ice‐flow model is used to investigate the glaciodynamics of the Last Glacial Maximum Welsh Ice Cap – a large, independent ice centre of the ...British–Irish Ice Sheet. The model uses higher‐order physics to solve longitudinal stresses, and is coupled to climate via a distributed, positive degree‐day mass‐balance scheme. A suite of model experiments driven by the GISP2 δ18O curve was initiated from a climatic optimum at 38.3 ka BP through to the Devensian/Holocene boundary to identify an icecap configuration compatible with available empirical evidence. An enhanced cooling from present of 11.85°C and strong precipitation suppression are required between 27.4 and 23.5 ka BP for the modelled icecap to attain well‐established empirical limits, a scenario probably associated with Heinrich Event‐2 and the potential collapse of thermohaline circulation in the North Atlantic. The experiments indicate ice‐dispersal centres located in North and Mid Wales, the latter being essential for forcing ice southwards of the Brecon Beacons during the Last Glacial Maximum. Deglaciation of the Welsh Ice Cap was relatively rapid, occurring within one millennium. Dynamic stability is governed largely by the dominance and vigour with which fast‐flowing outlet glaciers drain the icecap interior, which in turn are linked to variations in the climatic forcing. The distribution of permanently cold‐based ice across the uplands and summits indicates the probable preservation of relict landscapes in these areas throughout the full glacial cycle.
During the Last Glacial Maximum, the British–Irish Ice Sheet was dominated by a number of accumulation centres, including a terrestrially based, semi‐independent icecap centred on Wales. The dynamics ...of this Welsh Ice Cap (WIC) over the last glacial period are still relatively poorly understood, with few studies taking into consideration the dynamic evolution of the icecap as a whole. Here we contrast results from two modelled reconstructions of the WIC in conjunction with the wider glacial geomorphological record to elucidate understanding of its form, extent and dynamics. Model output was analysed to yield zones of high basal motion and the spatial distribution of potential glacial erosion. We conclude that coherent flowsets of streamlined bedforms are linked to fast‐flowing outlets dominated by basal sliding. Large‐scale changes in dynamics are discussed, with a number of possible major advances proposed over the glacial cycle. Maximum ice thicknesses of ∼1200 m in Mid Wales indicate that all mountain summits were probably ice‐covered during the Last Glacial Maximum, even if it was with a thin protective mantle of cold‐based ice, leading to landscape preservation of these upland zones. The distribution, dynamism and landscape modification related to the WIC are further discussed at the regional scale. Model predictions of glacier distribution through the Younger Dryas stadial accord well with geologically reconstructed limits at this time.
Surge-type glaciers switch between phases of rapid and slow flow on timescales of a few years to decades. During the active surge phase, large volumes of ice are transported downglacier, creating ...distinct geomorphological signatures that reflect these dynamic events but ice and sediment transport remain poorly quantified. The impact of surge events, in comparison to non-surge activity, is also unclear. Here, we describe glacier-surface debris and elevation changes through surges on ten different Karakoram glaciers (Khurdopin, Drenmang, Kunyang, Braldu, Chong Kumdan II, Qiaogeli, Saxinitulu, Shakesiga, Skamri and North Crown). We use these data to characterise the surface geomorphological changes during the surges. We also calculate the mass redistribution during each of the surges and compare this to an estimate of overall glacier mass. Repeat geomorphological mapping shows that surface debris transport through the surges leads to widespread rearrangement of surface features, folding and the concentration of debris near glacier termini, confluences and margins. Ice and debris mass redistribution varies between 0.11 and 0.94 Gt per event and shows moderate correlation with total glacier volume (r2 = 0.57) and glacier length (r2 = 0.40). Mass change as a proportion of total glacier volume ranges from about 0.5 to 5% and is moderately correlated with total glacier volume (r2 = 0.43) but not glacier length (r2 = 0.10). The overall conclusion is that surge events in this region account for only a small proportion of overall mass transport, but have an important role in surface debris transport and redistribution, as well as glacier mass balance.
•We describe glacier-surface debris and surface elevation changes through surges on ten different Karakoram glaciers.•Surface debris transport through the glacier surges leads to folding and concentration of debris near glacier termini, confluences and margins•Ice and debris mass redistribution for the ten glaciers varies between 0.11 and 0.94 Gt per event
Glacial Lake Outburst Floods (GLOFs) have become increasingly common over the past century in response to climate change, posing risks for human activities in many mountain regions. In this paper we ...document and reconstruct the sequence of events and impact of a large GLOF that took place in December 2015 in the Chileno Valley, Patagonia. Hydrograph data suggests that the flood continued for around eight days with an estimated total discharge of 105.6 × 106 m3 of water. The sequence of events was as follows: (1) A large debris flow entered the lake from two steep and largely non-vegetated mountain gullies located northeast of the Chileno Glacier terminus. (2) Water displaced in the lake by the debris flow increased the discharge through the Chileno Lake outflow. (3) Lake and moraine sediments were eroded by the flood. (4) Eroded sediments were redistributed downstream by the GLOF. The post-GLOF channel at the lake outlet widened in some places by >130 m and the surface elevation of the terrain lowered by a maximum of 38.8 ± 1.5 m. Farther downstream, large amounts of entrained sediment were deposited at the head of an alluvial plain and these sediments produced an ~340 m wide fan with an average increase in surface elevation over the pre-GLOF surface of 4.6 ± 1.5 m. We estimate that around 3.5 million m3 of material was eroded from the flood-affected area whilst over 0.5 million m3 of material was deposited in the downstream GLOF fan. The large debris flow that triggered the GLOF was probably a paraglacial response to glacier recession from its Little Ice Age limits. We suggest that GLOFs will continue to occur in these settings in the future as glaciers further recede in response to global warming and produce potentially unstable lakes. Detailed studies of GLOF events are currently limited in Patagonia and the information presented here will therefore help to inform future glacial hazard assessments in this region.
Twelve 10Be and five 26Al samples from the mountains of Yr Wyddfa (Snowdon) (1085 m) (n = 7 10Be) and Y Glyderau (the Glyders) (1001 m) (n = 5 paired 10Be/26Al) in Wales provide new insights into ...landscape evolution in the highest mountains in the British Isles outside of Scotland. The summits of Y Glyderau are characterised by intensely modified frost-shattered surfaces and have long been recognised as exemplars of mountain summit periglacial activity in the British Isles. However, glacially transported boulders on the highest ground indicate that ice overran the summits. Bedrock and boulder surfaces at altitudes >900 m yield 10Be and 26Al exposure ages of 61–78 ka, indicating that the last Welsh Ice Cap did not override and erode Y Glyderau summits at the global Last Glacial Maximum (LGM) and the summits stood as nunataks. Both the geomorphological and the exposure dating evidence indicate ice overran the summits earlier in the last glacial cycle during MIS 4, although erosion was only partial. Thick ice over Wales at this time is consistent with evidence of an extensive British-Irish Ice Sheet that reached the continental shelf to the west in MIS 4. The ice-scoured lower slopes of Y Glyderau and the arêtes of Yr Wyddfa were exposed as the ice cap rapidly thinned between 20-16 ka marking a transition from ice cap to alpine-style glaciation. On Yr Wyddfa, the highest mountain in southern Britain, local ice breached and abraded the central parts of the Crib Goch-Crib y Ddysgl arête as high as 874 m until c. 16 ka. However, some arête crests yielded Holocene ages (4.4–9.3 ka), which reflect continual post-glacial stripping.
•10Be/26Al dating provides new insights into the history of glaciation over Wales.•The Welsh Ice Cap was last thickest in MIS 4 when ice submerged the highest peaks.•Ice was thinner at the global LGM when the highest summits existed as nunataks.•By 17-15 ka the ice cap had thinned forming localised alpine-style valley glaciers.•Arête rock surfaces have continued to erode by 1–2 m since deglaciation.
In this paper, we consider the application of Landsat 7 ETM+ imagery and Digital Terrain Models (DTM) for mapping glacial lineaments in a formerly glaciated area of Wales. A series of landform ...interpretation experiments were conducted using different false colour composites (FCC) and a DTM, both individually and in combination. The experiments indicate that the optimal FCC for detection of glacial lineaments at this scale includes the thermal-infrared (TIR) band. However, by performing the interpretation both in the TIR composite and in a visible and near-infrared (VNIR, bands 4, 3, and 2) draped over the DTM, we were able to substantially increase the number of lineaments identified. The glacial lineaments consist of fractured bedrock and are defined as rock drumlins. The landform system formed by these rock drumlins is characterized by convergent flow patterns at its head, attenuated lineaments, and abrupt lateral margins, which may indicate formation by fast-flowing ice.
Reliable dating of Southern Hemisphere glacier fluctuations since the Last Glacial Maximum (LGM) is crucial to resolving debates about millennial-scale climate change. Here we present 10Be dates for ...lateral, valley-mouth and cross-valley moraines formed between the contemporary South American North Patagonian Icefield (NPI) and its LGM position in four separate valleys around 47°S. This is an area near the core of the precipitation-bearing southern westerly winds, where it is known that rapid shifts in climate occurred during Lateglacial times. The dates indicate that outlet glaciers advanced, or at least stabilised, to form large moraines east of an expanded NPI at 11.0 ± 0.5/11.2 ± 0.6, 11.5 ± 0.6, 11.7 ± 0.6 and 12.8 ± 0.7 ka (Putnam southern-hemisphere production rates and Dunai scaling scheme, assumed boulder erosion rate of 2 mm/ka). Four of these ages are statistically indistinguishable and probably represent a single, regional ice advance. The dates indicate that glaciers in Patagonia were larger during these times than at any point since the LGM and provide evidence in Patagonia for glacier advances around the time of the European Younger Dryas (12.9–11.7 ka) and into the very early Holocene. Although palaeoclimatic records from this area are often contradictory, these glacier advances were probably associated with a period of cooling or regionally increased precipitation related to the changes in the position of the southern westerly winds.
► NPI advanced at 11.0 ± 0.5/11.2 ± 0.6, 11.5 ± 0.6, 11.7 ± 0.6 and 12.8 ± 0.7 ka. ► Evidence for a regional glacier advance at this time. ► Formation of terminal and lateral moraines synchronous with the European Younger Dryas (12.9–11.7 ka).
Glacier beds provide crucial information concerning past and present ice dynamics and thermal regime. In this paper we present structural and sedimentological data from four valley glaciers (Austre ...Lovenbreen, Midtre Lovenbreen, Vestre Lovenbreen and Austre Broggerbreen) on Broggerhalvoya, NW Spitsbergen. The main focus of this paper is Midtre and Austre Lovenbreen, two typical High-Arctic land-based polythermal valley glaciers; the former has a long record of documentation regarding its response to twentieth century climatic warming. Structural mapping on the glacier surface and analysis of sediments in the proglacial area of Midtre Lovenbreen indicate that the dynamic regime and thermal structure of the glacier have changed through time. Dynamically, Midtre Lovenbreen was once heavily crevassed and relatively fast moving, but now is virtually crevasse-free and slow moving. The sedimentary record indicates that extensive areas of this glacier were wet-based when it was in a more advanced state, probably at its Neoglacial maximum (late nineteenth/early twentieth centuries). During this advance, a thin deforming layer of diamicton, commonly fluted, was draped over the existing morphology in the presently exposed proglacial area. This morphology consisted of large streamlined ridges aligned parallel to ice flow. Erosion of the underlying bedrock appears to have been limited. Radio-echo soundings of the glacier show that, at present, it is characterized by a polythermal basal thermal regime, with wet-based subglacial conditions only beneath its thicker parts. Modification of the bed is limited under this thermal regime and, as a result, the supraglacial environment dominates modern sedimentation. Comparative studies on Austre Lovenbreen, which also is probably polythermal, indicate similar sedimentary characteristics and facies associations, although here there are much more extensive areas of striated bedrock indicative of former basal sliding. In contrast both Austre Broggerbreen and, by analogy, Vestre Lovenbreen are known to be predominantly cold-based. Collectively, these four glaciers suggest a trend of glacier recession and thinning accompanied by a change in thermal regime from predominantly wet-based, through partly frozen, to completely frozen. This study suggests that Svalbard valley glaciers have several dynamic modes and that glaciers switch between these modes largely as a reaction to changes in mass balance.
Structural glaciological maps can be used to study the structural evolution and past dynamics of glaciers. The map described here documents the glacier-wide structural characteristics of Austre ...Brøggerbreen, a c. 12 km
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predominantly cold-based valley glacier in northwest Svalbard. The structural map reveals that the glacier is dominated by deep-penetrating fractures that are now relict (crevasse traces). These structures indicate that, despite being relatively inactive at present, the glacier was once much more dynamic, presumably during its last advance in the Neoglacial (c. 1900 AD). Contemporary glacier structures (i.e. those that are actively forming) include primary stratification, longitudinal foliation and rare surface fracturing (crevasses and water-healed crevasses). Relict fracture sets become increasingly re-orientated and folded down-glacier as a result of ductile flow. Individual flow units show large differences in the evolution of structures, indicating that the flow units have been subject to different flow histories and dynamics. The map will also be useful for future change-detection studies on this rapidly receding glacier.
We present a 3D reconstruction of ice thickness distribution across the New Zealand Southern Alps at the Last Glacial Maximum (LGM, c. 30–18 ka). To achieve this, we used a perfect plasticity model ...which could easily be applied to other regions, hereafter termed REVOLTA (Reconstruction of Volume and Topography Automation). REVOLTA is driven by a Digital Elevation Model (DEM), which was modified to best represent LGM bed topography. Specifically, we removed contemporary ice, integrated offshore bathymetry and removed contemporary lakes. A review of valley in-fill sediments, uplift and denudation was also undertaken. Down-valley ice extents were constrained to an updated geo-database of LGM ice limits, whilst the model was tuned to best-fit known vertical limits from geomorphological and geochronological dating studies. We estimate a total LGM ice volume of 6,800 km3, characterised predominantly by valley style glaciation but with an ice cap across Fiordland. With a contemporary ice volume of approximately 50 km3, this represents a loss of 99.25% since the LGM. Using the newly created ice surface, equilibrium line altitudes (ELAs) for each glacier were reconstructed, revealing an average ELA depression of approximately 950 m from present. Analysis of the spatial variation of glacier-specific ELAs and their depression relative to today shows that whilst an east-west ELA gradient existed during the LGM it was less pronounced than at present. The reduced ELA gradient is attributed to an overall weakening of westerlies, a conclusion consistent with those derived from the latest independent climate models.
•LGM ice thickness reconstructed on a glacier-by-glacier basis, driven by geomorphological evidence.•During the LGM the Southern Alps contained approximately 6,800 km3 ice, of which 99.25% has subsequently been lost.•Predominant valley style of glaciation across Southern Alps but ice cap across Fiordland.•The spatial patterns of precipitation and temperature were markedly different at the LGM compared to present.•Westerly circulation was apparently reduced during the LGM when compared to present.
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