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Clast shape analysis and clast transport paths in glacial environments: A critical review of methods and the role of lithology

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... The measured parameters included clast shape (the relative dimensions of the long, intermediate, and short axes), Power's roundness (the overall smoothness of the clast outline), and texture (small-scale surface features) (cf. Evans and Benn 2004;Hubbard and Glasser 2005;Hambrey and Glasser 2012;Lukas et al. 2013). Roundness was assessed visually using histogram plots and statistically by calculating the percentage of clasts that are angular (A) and very angular (VA) providing a summary index for roundness (RA value), and the percentage of clasts in the rounded (R) and well-rounded (WR) categories (RWR value;Benn 2004;Lukas et al. 2013). ...
... Evans and Benn 2004;Hubbard and Glasser 2005;Hambrey and Glasser 2012;Lukas et al. 2013). Roundness was assessed visually using histogram plots and statistically by calculating the percentage of clasts that are angular (A) and very angular (VA) providing a summary index for roundness (RA value), and the percentage of clasts in the rounded (R) and well-rounded (WR) categories (RWR value;Benn 2004;Lukas et al. 2013). Clast shape was analysed statistically by using clast shape triangles (Benn 2004) from which the percentage of clasts with a c:a (short:long axis) ratio of ≤0.4 is calculated. ...
... C 40 indices were compared to RA values in co-variance plots following procedures outlined in Benn and Ballantyne (1994). Data derived from different depositional environments in New Zealand (Evans et al. 2010;Brook and Lukas 2012;Lukas et al. 2013) were also plotted to aid assessments of inter-sample variability. The control samples were taken from Greywacke, Argillite and Schist clasts in laterofrontal moraine loops of Fox Glacier in Westland. ...
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The extent of the Southern Alps icefield in New Zealand is well-constrained chronologically for the last glacial cycle. The sediment-landform imprint of this glacial system, however, offers insight into ice-marginal processes that chronological control cannot. We present the first detailed investigation of sediments along the southwestern shores of Lake Tekapo, South Island. We identify seven lithofacies, from which a five-stage palaeoglaciological reconstruction of depositional and glaciotectonic events is proposed: (i) ice-marginal advance and deposition of outwash gravels in lithofacies (LF) 1; (ii) ice-marginal recession and the development of an ice-contact lake, manifest in rhythmite deposition and iceberg rafting of dropstones (LF 2), followed by a depositional hiatus; (iii) ice-marginal recession recorded in ice-proximal aggradation of glaciofluvial hyperconcentrated flows (LFs 3, 4); (iv) ice-marginal advance documented by glaciotectonic disturbance and localized hydrofracturing, coeval with the deposition of delta foresets and a subglacial diamicton/till (LFs 5, 6); (v) final stages of ice-marginal recession and deposition of outwash gravels in LF 7. Two infrared stimulated luminescence ages were obtained from the glaciolacustrine sediments and, whilst the dating has some limitations, the sediments pre-date both the global and local Last Glacial Maximum. Overall, this sequence, consistent with sediment fills recorded elsewhere across South Island, suggests recurrence of processes from different glacial advances and the role of topographic constraints on maintaining lake positions.
... Many researchers (Sawicki, 1912;Pawłowski, 1936;Świderski, 1938) emphasize the difficulty of distinguishing moraines of small glaciers from landslides and other colluvial-type deposits in this area. This highlights the necessity for careful examination of the geomorphological and sedimentological context of glacial sediments in flysch lithology which should be supplemented with systematic analysis of clast shape (Lukas et al., 2013;Kłapyta, 2020) before ice-marginal moraines are used to reconstruct former glacier geometry and infer past climatic conditions (Carr et al., 2010;Kirkbride and Winkler, 2012). ...
... Subsequently, the C40 index (percentage of clasts with axial ratio c/a < 0.4) was calculated for each sample site. The RA ratio (the percentage of angular and very angular clasts in any sample) and the RWR ratio (the percentage of rounded to well-rounded clasts; Lukas et al., 2013) were determined for each site. To distinguish transportation and depositional clast histories, covariance plots using RA-C40 were presented (Benn and Ballantyne, 1994;Lukas et al., 2013). ...
... The RA ratio (the percentage of angular and very angular clasts in any sample) and the RWR ratio (the percentage of rounded to well-rounded clasts; Lukas et al., 2013) were determined for each site. To distinguish transportation and depositional clast histories, covariance plots using RA-C40 were presented (Benn and Ballantyne, 1994;Lukas et al., 2013). Additionally, the data from the study area were compared with published clast morphology data from the Svydovets massif (Kłapyta et al., 2021b, Supplementary Data 1) to assess the effects of flysch lithology on moraine clast shape. ...
... However, the localized subglacial incorporation of debris that occupied the foreland prior to glacier advance can significantly increase the percentage of rounded and blocky clasts in a sample collected from frontal moraines, thereby diluting the subglacial abrasion signature with an inheritance signal, especially in areas of widespread glacifluvial deposits (e.g. Evans, 2000;Evans and Twigg, 2002;Lukas et al., 2013). In contrast, the quarrying of fresh blocks from bedrock protuberances that bridge the subglacial deforming layer can introduce anomalously angular material to down-glacier till deposits . ...
... Debris transport pathways in glaciers have been evaluated widely by employing clast form analysis (see Benn, 2004a; 2007 for a review; Lukas et al., 2013), a technique that has proven to be very effective in identifying the spatial operation of glacial processes in debris modification (e.g. Matthews and Petch, 1982;Benn, 1989;Benn and Ballantyne, 1994;Evans, 1999Evans, , 2010. ...
... Sharp, 1982;Krüger, 1984;Benn, 2004a). Analysis of the data followed the procedures outlined in Benn (2004aBenn ( , 2007 and involved: a) calculation of the C 40 index (the percentage of clasts with a C:A axis ratio of <0.4; Benn and Ballantyne, 1993); b) clast roundness, classified according to Powers (1953) and then used to calculate the RA summary index (percentage of angular and very angular clasts within a sample; Benn and Ballantyne, 1993) and the RWR summary index (percentage of rounded and well-rounded clasts; Benn et al., 2004;Lukas et al., 2013); and c) mean roundness, based upon a numerical classification of Powers roundness as VA ¼ 0 to WR ¼ 5 (cf. Spedding and Evans, 2002;Evans, 2010). ...
... These data were then used to characterize lithofacies types and to allocate facies codes following the procedures of Evans and Benn (2004). Clast form analysis was undertaken on samples of 50 chalk clasts and involved assessments of Powers roundness and clast shape following procedures outlined by Benn (2004) and Lukas et al. (2013). ...
... Predominantly subangular and platy to elongate clasts indicate short fluvial transport distances and would not be unusual in permafrost or periglacial, nival-fed rivers (Tomlinson, 1940;Lewin, 1969;Williams, 1971;West and Williams, 2012;Newell et al., 2015;West, 2015), although the dominant chalk lithologies in the region tend to impart a strong control on the slabbiness of clasts in the study area and hence RA and average roundness rather than C40 values are the best discriminators for clast modification. Very little data are available on clast form in periglaciated and glaciated limestone and chalk catchments but the slabbiness and elevated C40 of argillaceous rocks identified by Lukas et al. (2013) makes them a suitable comparator for the analysis of the North Cave data. Hence, the Type II covariance plot of Lukas et al. (2013) indicates a fluvial signature for the clasts of LF1 (Fig. 8), even though the elevated C40 values indicate unusually high levels of slabs and elongates controlled by the local chalk macrostructure. ...
... Very little data are available on clast form in periglaciated and glaciated limestone and chalk catchments but the slabbiness and elevated C40 of argillaceous rocks identified by Lukas et al. (2013) makes them a suitable comparator for the analysis of the North Cave data. Hence, the Type II covariance plot of Lukas et al. (2013) indicates a fluvial signature for the clasts of LF1 (Fig. 8), even though the elevated C40 values indicate unusually high levels of slabs and elongates controlled by the local chalk macrostructure. Clast lithologies, being dominated by chalk but including also minor components of limestone, sandstone and flint, indicate entirely local derivation, specifically from the Wolds scarp valleys where all these bedrock types outcrop but with chalk being the most extensive surface material. ...
Article
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The stratigraphic sequence at North Cave, on the eastern margins of the Lake Humber basin, records the deposition of a fluvioperiglacial fan (LFs 1–4), with early sedimentation (LF1) dating to Marine Isotope Stage (MIS) 3 (optically stimulated luminescence date range 41.8–38.6 ka and ¹⁴C dates 41.6–49 ka BP). Three phases of permafrost and ice wedge development during MIS 3 are evident and indicate possible fan abandonment and hence periods of reduced nival runoff. Involution structures dated to 11.1 ka with large boulders and fine‐grained sorted circles in LF4b are interpreted as periglacially cryoturbated littoral deposits with boulders derived from anchor ice, initially deposited at the margins of Lake Humber up to an altitude of 8 m OD during MIS 2. The style and age of fluvioperiglacial fan deposition at North Cave is compatible with several mid‐Devensian sites around Britain characterized by significant nival melt and run‐off from steeply incised valleys in permafrozen cuesta landscapes. This phase of fluvioperiglacial fan aggradation to near or below 0 m OD is recorded around the glacial lakes Humber and Fenland basins and indicates that no glacial lakes existed at that time.
... Clast form was analysed from diamictons and matrix-supported gravels using 30 or 50 clasts depending on unit thickness. This involved assessments of Powers roundness and clast shape following procedures outlined by Evans and Benn (2004) and Lukas et al. (2013), whereby RA, average roundness and C40 values were derived and plotted on co-variance graphs to facilitate comparisons with deposits of known origin. ...
... Clast sizes then increase vertically (inverse grading) in the diamicton. Clast forms in the Gms (Fig. 4b) are sub-angular to sub-rounded (RA = 8%; RWR 6%; average roundness = 2.48) with a C40 value of 32%, typical of glacifluvial outwash (c.f., Lukas et al., 2013). In contrast, clast forms in the Dmm (Fig. 4b) are markedly more blocky (C40 = 9%) and more sub-angular (RA = 16%; RWR = 0%; average roundness 2.16) and no clasts display striae, suggesting subglacial reworking of glacifluvial materials. ...
... The covariance plot of all clast form samples from Hayberries (Fig. 4c) indicates a predominantly subglacial signature (cf. Benn and Ballantyne, 1994;Lukas et al., 2013). A clast macrofabric from the Dmm (Fig. 4b) is essentially isotropic (S1 = 0.41) but displays a very weak northerly girdle. ...
Article
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In glacial sedimentology there has been a recent improvement in the understanding of both progressive and polyphase deformation of glacigenic sequences, and the role played by water during these complex deformation histories. However, the processes occurring during the detachment and transport of sediment blocks during ice-marginal glaciotectonic thrusting remain poorly understood. This lack of understanding is addressed in detail through a macro- and microscale study of the deformation structures in the glacigenic sequence exposed at Hayberries, Teesdale, County Durham (UK), where esker sands and gravels and associated tills truncate and overlie a sequence of rhythmically bedded glacilacustrine sands, silts and clays. Thrusts within the glacilacustrine and glacifluvial sediments appear to be relatively sharp, planar structures. However, orientated thin sections reveal that these bedding-parallel detachments are marked by a thin layer of massive to foliated sand. The geometry of both meso and small-scale folds and sense of displacement on the thrusts is consistent with both brittle and ductile structures having formed in response to ice-push from the N/NW. Detailed analysis of the thin sections reveals that initial folding and thrusting was followed by the liquefaction and injection of a massive, matrix poor sand along the propagating thrust. Evidence for liquefaction and injection (sand-filled veins) increases towards the NW consistent with fluid flow and sediment injection accompanying SE-directed ice-push. These results suggest that the introduction of pressurised meltwater and sediment along the thrusts during deformation may facilitate decoupling and displacement along these detachments by thrust gliding.
... It allows to discriminate between the transported clasts, and this method is believed to be sometimes more efficient than the RA index (Lukas et al., 2013). The RWR index accounts for the population of rounded to well-rounded clast, which plotted against the C40 index allow us to tell the difference between clast transported by different processes in a given glacier foreland. ...
... 32 74 regarding their roundness even though the roundness varies more than their C40 index. The paper of Lukas et al. (2013) gives more information about clustering of results. These authors, in addition to assessing the role of the lithology when performing a clast shape co-variance analyze and the variability between different catchment were also interested in the variability of result which could be obtained within a catchment for one method. ...
... 32) cluster or not. In a paper byLukas et al. (2013) the limits and strength of the clast shape co-variance analyses were examined. These authors tell us that the analyses by the means of a co-variance in-between the RWR index versus the C40 index is in average more efficient than the analyses by the means of the use of .Figure 32displays the RWR versus the C40. ...
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A series of small mounds (< 3m) were sampled in the foreland of Midtdalsbreen outlet glacier, southern Norway. These landforms were interesting, especially at site number 1 because they were located very close to a higher Little Ice Age (LIA) moraine (> 5 m), thereby informing the dynamic of the glacier after the LIA at this location.
... The section logs presented in this paper all use a common style (Fig. 3). Clast shape and roundness were also analysed for each moraine following established methods, with C 40 , RA and RWR indices calculated for each sample using a modified version of TriPlot (Benn & Ballantyne 1993, 1994Graham & Midgley 2000;Lukas et al. 2013). ...
... Moreover, the clasts mainly have blocky forms (C 40 = 6-16%); oblate and prolate clasts are almost entirely absent. These characteristics are consistent with active transport in a subglacial environment (Benn & Ballantyne 1993, 1994Evans & Benn 2004;Lukas et al. 2013). Comparison of the moraine samples with 'control' samples (subglacial, fluvial and rockfall) on covariance plots of both RA-C 40 and RWR-C 40 (Fig. 9) also supports a subglacial transport pathway: all the moraine samples lie close to the subglacial control envelope on both plots. ...
... The occurrence of proglacial and subglacial glaciotectonic structures within moraine BCL-06 indicates dynamic ice-marginal responses in the Gaick and thus provides sedimentary evidence for incremental, oscillatory retreat of predominantly temperate Younger Dryas outlet glaciers. The characteristics of clast shape samples from the moraines (dominantly blocky, edge-rounded clasts; Figs 8, 9) are consistent with debris transport in the subglacial traction zone, which is also characteristic of temperate glacier systems (Benn & Ballantyne 1994;Lukas 2007;Lukas et al. 2013). However, the abundance of closely spaced moraines inside the Younger Dryas glacier limits in the Gaick requires a mechanism that is able to continuously elevate subglacially transported debris to the ice surface. ...
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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 glaciotectonisation, as reported elsewhere in Scotland. The exposures also reveal the influence of local hydrogeological conditions, with pressurisation 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.
... A lithofacies code, modified from Eyles et al. (1983) and Benn and Evans (2010), was employed for clear, effective and rapid description of the sedimentary logs ( Figure 4). Clast shape and roundness were also analysed for each moraine following established methods, with C 40 , RA, RWR and average roundness (AvR) indices calculated for each sample using a modified version of TriPlot (see Benn andBallantyne, 1993, 1994;Graham and Midgley, 2000;Spedding and Evans, 2002;Lukas et al., 2013). In this study, AvR was calculated using the scale VA = 0 to WR = 5, rather than the scale VA = 1 to WR = 6 employed by Spedding and Evans (2002), in Table I. ...
... Moreover, the low angularity and blocky nature of the clasts found within LF 1 (Figure 9a) are consistent with active transport at the ice-bed interface (cf. Boulton, 1978;Benn and Ballantyne, 1994;Lukas et al., 2013;Evans et al., 2018a). We therefore interpret LF 1 as a subglacial traction till, as in other ice-marginal/annual moraines elsewhere in Iceland (e.g. ...
... high levels of blockiness, low angularity) are also entirely consistent with transport in the subglacial traction zone (cf. Benn and Ballantyne, 1994;Lukas et al., 2013 ;Evans et al., 2018aEvans et al., , 2018bEvans et al., , 2018c. On this basis, we interpret the Dmm in moraine FJA-06 as a subglacial traction till. ...
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This paper presents detailed geomorphological and sedimentological investigations of small recessional moraines at Fjallsjökull, an active temperate outlet of Öræfajökull, southeast Iceland. The moraines are characterised by striking sawtooth or hairpin planforms, which are locally superimposed, giving rise to a complex spatial pattern. We recognise two distinct populations of moraines, namely a group of relatively prominent moraine ridges (mean height ~1.2 m) and a group of comparatively low-relief moraines (mean height ~0.4 m). These two groups often occur in sets/systems, comprising one pronounced outer ridge and several inset smaller moraines. Using a representative subsample of the moraines, we establish that they form by either (i) submarginal deformation and squeezing of subglacial till or (ii) pushing of extruded tills. Locally, proglacial (glaciofluvial) sediments are also incorporated within the moraines during pushing. For the first time, to our knowledge, we demonstrate categorically that these moraines formed sub-annually using repeat uncrewed aerial vehicle (UAV) imagery. We present a conceptual model for sub-annual moraine formation at Fjallsjökull that proposes the sawtooth moraine sequence comprises (i) sets of small squeeze moraines formed during melt-driven squeeze events and (ii) larger push moraines formed during winter re-advances. We suggest the development of this process-form regime is linked to a combination of elevated temperatures, high surface meltwater fluxes to the bed, and emerging basal topography (a depositional overdeepening). These factors result in highly saturated subglacial sediments and high porewater pressures, which induces submarginal deformation and ice-marginal squeezing during the melt season. Strong glacier recession during the summer, driven by elevated temperatures, allows several squeeze moraines to be emplaced. This process-form regime may be characteristic of active temperate glaciers receding into overdeepenings during phases of elevated temperatures, especially where their englacial drainage systems allow efficient transfer of surface meltwater to the glacier bed near the snout margin.
... Clast shape analysis was used to elucidate the transport pathways of clasts following the approach reviewed by Lukas et al. (2013). Fifty clasts of the local granite were randomly selected from each sampled unit. ...
... Clast shape data were displayed and interpreted following established approaches summarized by Lukas et al. (2013), using the percentage of angular and very angular clasts (RA index), percentage of rounded and well-rounded clasts (RWR index), and clasts with c:a axis ratios ≤0.4 (C 40 index). ...
... An alternative interpretation is that considerable fluvial reworking formed more rounded and well-rounded clasts and played a role in this environment of limited transport distance in an ice-proximal setting. Similarity between fluvial and subglacial samples in a high-mountain setting has been previously described specifically for Findelengletscher in the Swiss Alps (Lukas et al., 2013). In these settings, this has been interpreted as evidence of a strong coupling between the subglacial glaciofluvial and subglacial systems . ...
Chapter
Stephen C. Porter was an international leader in Quaternary science for several decades, having worked on most of the world’s continents and having led international organizations and a prominent interdisciplinary journal. His work influenced many individuals, and he played an essential role in linking Chinese Quaternary science with the broader international scientific community. This volume brings together nineteen papers of interdisciplinary Quaternary science honoring Porter. Special Paper 548 features papers from six continents, on wide-ranging topics including glaciation, paleoecology, landscape evolution, megafloods, and loess. The topical and geographical range of the papers, as well as their interdisciplinary nature, honor Porter’s distinct approach to Quaternary science and leadership that influences the field to this day.
... Wentworth, 1922;Allen, 1981), shape (e.g. Hambrey and Glasser, 2003;Hambrey et al., 2008;Lukas et al., 2013), roundness (e.g. Sneed and Folk, 1958;Ballantyne and Benn, 1994), surface weathering (e.g. ...
... Despite much of the volumetric erosion being achieved by these larger events, this bias within the sediment source in favor of small rockfall events means that the resultant erosion rates should be considered maximum estimates. Unique sediment exchange processes in the supraglacial environment (Ward and Anderson, 2011;Lukas et al., 2012Lukas et al., , 2013Lupker et al., 2012;Scherler et al., 2015), shifts in sediment source, sediment storage and remobilization, shifting geomorphic regimes and ice/snow shielding (Bierman and Steig, 1996;Scherler et al., 2014;Fame et al., 2018) are also likely to affect the 10 Be concentrations and sediment characteristics of each sample. Caution must therefore be exercised when analyzing these data. ...
... The covariance of clast shape and roundness indices are presented in RA-C 40 (angular, very angular) and RWR-C 40 (rounded, well rounded) plots for Gangotri glacier and previous studies in Figure 5. Distinguishing between transport pathways must be approached with care due to the pronounced overlap in facies indices, an important consideration when working in complex alpine settings (Lukas et al., 2013). The RA (85À94%) and C 40 (75À96%) indices and large proportion of bladed and extremely bladed grains suggest that the medial moraines of this study share a supraglacial transport history (Benn and Owen, 2002;Hubbard, 2004;Lukas et al., 2013). ...
Article
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Rockwall slope erosion is defined for the upper Bhagirathi catchment using cosmogenic 10Be concentrations in sediment from medial moraines on Gangotri glacier. Beryllium‐10 concentrations range from 1.1±0.2 to 2.7±0.3x104 at/g SiO2, yielding rockwall slope erosion rates from 2.4±0.4 to 6.9±1.9 mm/a. Slope erosion rates are likely to have varied over space and time and responded to shifts in climate, geomorphic and/or tectonic regime throughout the late Quaternary. Geomorphic and sedimentological analyses confirm that the moraines are predominately composed of rockfall and avalanche debris mobilized from steep relief rockwall slopes via periglacial weathering processes. Slope erosion affects sediment flux and storage of snow and ice at the catchment head on diurnal to millennial timescales, and more broadly influences catchment configuration and relief, glacier dynamics and microclimates. The slope erosion rates exceed the averaged catchment‐wide and exhumation rates of Bhagirathi and the Garhwal region on geomorphic timescales (103−105 years), supporting the view that erosion at the headwaters can outpace the wider catchment. The 10Be concentrations of medial moraine sediment for the upper Bhagirathi catchment and the catchments of Chhota Shigri in Lahul, northern India and Baltoro glacier in Central Karakoram, Pakistan show a tentative relationship between 10Be concentration and rainfall. As such there is more rapid slope erosion in the monsoon‐influenced Lesser and Greater Himalaya compared to the semi‐arid interior of the orogen. Rockwall slope erosion in the three study areas, and more broadly across the NW Himalaya is likely governed by individual catchment dynamics that vary across space and time.
... Many researchers (Sawicki, 1912;Pawłowski, 1936;Świderski, 1938) emphasize the difficulty of distinguishing moraines of small glaciers from landslides and other colluvial-type deposits in this area. This highlights the necessity for careful examination of the geomorphological and sedimentological context of glacial sediments in flysch lithology which should be supplemented with systematic analysis of clast shape (Lukas et al., 2013;Kłapyta, 2020) before ice-marginal moraines are used to reconstruct former glacier geometry and infer past climatic conditions (Carr et al., 2010;Kirkbride and Winkler, 2012). ...
... Subsequently, the C40 index (percentage of clasts with axial ratio c/a < 0.4) was calculated for each sample site. The RA ratio (the percentage of angular and very angular clasts in any sample) and the RWR ratio (the percentage of rounded to well-rounded clasts; Lukas et al., 2013) were determined for each site. To distinguish transportation and depositional clast histories, covariance plots using RA-C40 were presented (Benn and Ballantyne, 1994;Lukas et al., 2013). ...
... The RA ratio (the percentage of angular and very angular clasts in any sample) and the RWR ratio (the percentage of rounded to well-rounded clasts; Lukas et al., 2013) were determined for each site. To distinguish transportation and depositional clast histories, covariance plots using RA-C40 were presented (Benn and Ballantyne, 1994;Lukas et al., 2013). Additionally, the data from the study area were compared with published clast morphology data from the Svydovets massif (Kłapyta et al., 2021b, Supplementary Data 1) to assess the effects of flysch lithology on moraine clast shape. ...
Article
The Polonyna Rivna (1480 m asl) and Borzhava (1682 m asl) ranges represent medium-high mountain massifs located in the north-western part of the Ukrainian Carpathians, where the legacy of the Pleistocene glaciation has long been unexplored. Based on the first detailed mapping of glacial landforms and sedimentological analysis, we document the presence of freshly-shaped outer moraines and glacial cirques and reconstruct the extent and ice-surface geometry of the six very small (0.09–0.78 km² area) palaeoglaciers. The specific feature of the area is the presence of extensive mountain-top plateaus that play an important role as additional areas for snowblow accumulation. The equilibrium line altitudes (ELAs) calculated from hypsometry of reconstructed local Last Glacial Maximum (LLGM) using the area x altitude balance ratio (AABR) 1.6 method is exceptionally low at 1138 m asl in the Polonyna Rivna and 1230 m asl in the Borzhava range. Excluding the topographic effect produced by additional snow accumulation the ELA shift upwards between 120 and 180 m which corresponds to 25–53% of the glacier elevation range. The resulted climatic ELA (1282–1352 m asl) together with the mean cirque floor altitude (1194 m asl) and mean elevation of the glacier fronts (994 m asl) represent the lowest values in the entire Carpathian arc. Our data indicate glacier-friendly conditions in the mountain massifs exceeding 1400 m asl in the windward NW part of the Ukrainian Carpathians where due to relatively cold air temperatures and orographic induced precipitation local topolimatic factors dictated the development of marginal glaciation.
... The percentages of very angular (VA) and angular (A) were added to calculate the RA-index. RWRindex (% of rounded and well-rounded clasts) was also conducted according to the method proposed by Benn & Balllantyne (1994), and by Evans & Benn (2004), to distinguish between erosional, transportational, and depositional clast histories (Lukas et al. 2013). The graphs of granulometric and shape analysis were performed with GraphPad Prism software. ...
... Very angular and well-rounded materials are absent ( Figure 4, Table SI frost-weathered debris. Co-variance plots using both RA-C 40 and RWR-C 40 , which effectively differentiate passively-and actively-transported clasts (Benn & Ballantyne 1994), are shown in Figure 5 and display high C 40 , medium RA, and low RWR, which point to the processes of the entrance of clasts extraglacial/supraglacially, i.e., passively transported (Lukas et al. 2013). ...
... All areas show a high proportion of platy clasts (high C 40 - Fig. 4). As in the area of study, Lukas et al. (2013) observed in several glacial environments in north and south hemispheres that sandstone was related to the clasts with high C 40 , high RA, and low RWR. Although with the abundant presence of sandstone in Patriot Hills, Independence Hills, and in Elephant Head valley (Fig. 6), subangular clasts dominate in Independence and Patriot Hills, while in Elephant Head valley subrounded clasts prevail (Figure 4). ...
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Abstract This work aims to analyze and compare the sedimentological data of Ellsworth Mountains, West Antarctica: Patriot/Independence Hills and Union Glacier, and how sedimentological data can be used to infer sediment entrainment. Particular attention was concentrated on morainic deposits. Remote sensing data was used in the identification of deposits and the ice flow; granulometric, morphoscopic, and geochemical analyses were applied to investigate the sedimentary origin and transport history. Sediment rich in Si Al, Fe, and Ca predominate in Independence Hills and Rossman Cove but Ca prevails in Elephant Head. CIA indicated low values, which depict low chemical weathering processes. X-ray diffraction reveals the presence of minerals that constitute the local rocks in the Union Glacier area, and from the unexposed basement rocks in Independence Hills. Principal Component Analysis and Cluster Analysis results suggest the sediment is related to the local rocks in the Union Glacier and distinct exotic sources in Independence Hills, associated with far-traveled sediment. It is also observed the influence of distinct processes of entrainment sediment on its granulometric and morphoscopic characteristics.
... A second approach is based on characteristic boulder roundness that can yield information on transport position in the glacier and transport distance. High angularity is mostly related to passive supraglacial transport, while subangular to subrounded boulders were likely shaped during the transport in sub-or englacial position (Benn & Ballantyne 2005;Benn & Evans 2014) with significant differences due to clast lithology (Lukas et al. 2013). However, these works are mostly related to gravel-size clasts, while boulders can have been affected by different shaping and clustering processes (Boulton 1978). ...
... The provenance of 24 boulders (12 dated and 12 undated) has been assessed ( Table 2). Specific assignment is possible in part due to the particular geological setting of the Toce catchment, characterized by the juxtaposition of several tectonic slices of different metamorphic degree (Table 1, Fig. 2 The boulders are mostly characterized by hard and anisotropic lithologies, so lithological bias weakly affected their degree of roundness (Lukas et al. 2013). Most of the angular and subangular boulders belong to the outer moraines of the western sector of the amphitheatre (Figs 3A, 7). ...
Article
Knowledge of the glacial chronologies for the Last Glacial Maximum (LGM) helps in understanding the interactions between climate, topography and glacier development. In this sense, the investigation of the Lake Orta moraine amphitheatre (Alpine foreland, northern Italy) allowed spatial and temporal reconstruction of the Orta Glacier. The end‐moraine system was investigated by means of geomorphological field surveys, analysis of 13 rock samples for cosmogenic 10Be and 36Cl concentrations, and remote sensing analysis. The dating results indicate that the age of the outer moraine belt is concordant with the LGM culmination at 26.5–23 ka, as found in other amphitheatres in the Alps. This new age estimate of the outermost moraines shows that the maximum extent of the Orta Glacier during the LGM was significantly bigger than recently suggested. A younger stabilization phase of the glacier front at about 19 ka indicates that the onset of the withdrawal of glaciers from the lower Alpine valleys started later. Provenance analysis of the boulders shows that the greatest contribution of ice to the Orta Glacier came from the Anzasca Valley rather than the major Ossola Valley. This reflects the closeness (about 45 km) to the foreland of the high‐elevated accumulation area of the Monte Rosa massif (4634 m a.s.l.), whose eastern glacier seems to have reached the lower valley faster than the trunk Toce Glacier. This fact underlines the key role played by high‐elevation accumulation areas that are located close to the foreland in controlling the path and geometry of major glaciers in the Alps.
... Spedding and Evans, 2002;Evans, 2010). The Type I co-variance plot of Lukas et al. (2013) was then used to compare clast form results with glacial sediment types of known genesis and similar lithologies, because this plot ( Fig. 4) is representative of more massive (low anisotropy) lithologies like the local limestone. These analytical approaches facilitate an assessment of debris origin, transfer process and modification when considered in the context of parent debris band/ridge. ...
... The Type I co-variance plot ofLukas et al. (2013), used in this study to compare clast form results with glacial sediment types of known genesis and similar lithologies. ...
Article
The post Little Ice Age recession and downwasting of Hørbyebreen, a Svalbard polythermal glacier, has revealed a sub-polar glacial landsystem within which a geometric and sinuous ridge network (GSRN) has evolved by ice melt-out. Spatio-temporal evolution of these features is evaluated using time series of remote sensing data, aerial photography, DEMs and field observations. The GSRN is interpreted as an assemblage of crevasse and hydrofracture infills branching out from parent eskers, a signature of the rapid release of pressurised subglacial and englacial meltwater, likely related to surge-induced jökulhlaups. This gives rise to a range of component materials including till, gravel and interdigitated till and gravel. Ancient examples of such jökulhlaup-diagnostic GSRN in ice sheet settings are recognised as elongate zones of conjugate, reticulate and honeycomb patterned ridges in close association with eskers that often also displaying reticulate ridge patterns. We present a conceptual model of a process-form continuum for the production of different styles of GSRN that identifies: a) surge crevassing, indicated by glacier wide GRN and zig-zag eskers; b) ice stream surging plug flow, indicated by linear assemblages of GRN; c) sub-marginal till emplacement in radially crevassed active temperate snouts, indicated by narrow concentric arcs of GRN linked to push moraines; and d) jökulhlaup-induced hydrofracture, indicated by linear assemblages of GSRN.
... Our method results in an even distribution of points on the Sneed and Folk diagram, but clustering towards the top of the Zingg diagram ( Figure 2D). The shape continuum becomes increasingly distorted towards the bottom of the Zingg diagram, resulting in increased resolution within the part of the diagram representing elongated forms (rods and blades) (Benn and Ballantyne, 1993;Benn, 2004;Lukas et al., 2013). In the limiting case of an extreme rod (an infinitely long and thin particle), the particle does not plot uniquely. ...
... Similarly, other geometric representations of the shape continuum may be useful in particular circumstances (e.g. in archaeology, where orientation is important; Tarriño, 2015). However, from a sedimentological perspective it is most useful to present particle shape data in a form that most faithfully represents the shape continuum without distortion, and we contend that the ternary space of Sneed and Folk is therefore more appropriate (see also Benn and Ballantyne, 1993;Graham and Midgley, 2000;Benn, 2004;Lukas et al., 2013). This ternary space forms the basis of the definition of 'average' shape developed here for a sample of particles, and the definition of confidence regions for the population which is derived from it. ...
Article
This paper presents novel methods for robust statistical testing of particle shape data. Shape (the relative lengths of three orthogonal axes) is a key property of sedimentary particles, providing information on provenance, transport history and depositional environment. However, the usefulness of shape data, including the ability to make robust comparisons between samples, has been constrained by the absence of a satisfactory definition of the mean shape for a sample of particles. Such a definition is proposed and used to develop confidence regions for the population mean shape using both parametric (theoretical) and computational (bootstrap) methods. These techniques are based on a transform that permits multivariate statistical methods for the analysis of compositional data to be extended to shape. These techniques are validated with reference to a dataset of 169 clast samples and found to perform well. A statistical test on the mean – using the multivariate extension of Student's t‐test, Hotelling's T² – is presented. The benefits of the methods presented are demonstrated with reference to a case study.
... • (1) en sédimentologie, pour décrire du matériel sédimentaire (Wadell, 1932;Benn et Ballantyne, 1994;Lukas et al., 2013) ; • (2) pour comprendre des événements du passé et reconstituer l'histoire des matériaux (Wentworth, 1921;Wadell, 1932;Illenberger, 1991;Illenberger et Reddering, 1993;Graham et Midgley, 2000a;Szabó et al., 2015) ; • (3) pour identifier les sources des sédiments (Knighton, 1982;Lindsey et al., 2007;Roussillon et al., 2009;Bertoldi et al., 2012;Miller et al., 2014) ; • (4) pour analyser (Wentworth, 1919;Krumbein, 1941aKrumbein, , 1941bKuenen, 1956;Ashcroft, 1990;Wald, 1990;Yazawa, 1990) et modéliser les processus d'abrasion des particules (Durian et al., 2006;Le Bouteiller, 2011;Szabó, 2013;Domokos et Gibbons, 2013;Domokos et al., 2014) ; • (5) pour déterminer leur influence sur la mobilité des particules sédimentaires (Krumbein, 1942;Ashworth et Ferguson, 1989;Kirchner et al., 1990;Carling et al., 1992;Schmidt et Gintz, 1995;Sear et al., 2008;Stark et al., 2014), leur implication dans l'agencement des particules (Wittenberg, 2002;Stark et al., 2014) ou la développement de couches d'armurage (Gomez, 1994) et donc in fine sur le transport solide. ...
... The geometrical characteristics of pebbles have been subject to observation since Aristotle (Krynine, 1960). Such characteristics are an important physical property that enable the differentiation of transport pathways in glacial environments (Benn and Ballantyne, 1994;Lukas et al., 2013), provide indications about sedimentary history, help to characterize depositional environments (Graham and Midgley, 2000), target sediment sources at catchment scales (Knighton, 1982;Lindsey et al., 2007;Roussillon et al., 2009;Miller et al., 2014) and ...
Thesis
The influence of fluvial system dynamics on riverine landscape patterns is the consequence of complex ecosystem dynamics. These driving factors can be analysed at different spatiotemporal scales of the fluvial system (for example: river basin, functional units, alluvial megaforms or sediment particles). The dynamic of fluvial systems depends on the equilibrium between solid and liquid flows. For this reason, the geomorphological status of watercourses can be described from a sedimentary perspective taking into account general trends at large scale, local characteristics such as incision, aggradation, sedimentary migration or the alteration of particles’ geometrical properties that constitute bed load. Thus, a better understanding of the influence of past and present sedimentary flows on the geomorphological status of watercourses has at the same time an ecological impact (permeability of both the alluvial layer and the hyporheic zone and its self-filtration function (Datry et al., 2008)), a political impact (related to flood management, erosion risks and issues or hydraulic facilities) or even a philosophical issue (what is the appropriate reference for that fluvial system? What is the role of Humanity on these anthropized environments and to what extent?). Thus, the development of methodological tools to characterize sedimentary flows or the observed dynamics on rivers is considered a major and rising research issue. The research studies described in this thesis are structured in three distinct topics: (1) physical properties of sediment particles; (2) their mobility; (3) their transformation as a consequence of abrasion. In this context, we analysed the relationship between breakage and low recovery rates for natural tracers (limestone pebbles) equipped with low frequency passive transponders (PIT-tags). In addition, we tested the use of synthetic pebbles to create new tracers equipped with high frequency active transponders (a-UHF), more performant than PIT-tags. Secondly, we specifically developed a new search and location field methodology, adapted to these new transponders. Thirdly, we tested the sensibility of the toolbox developed by Roussillon et al. (2009), design to measure the roundness of coarse sedimentary particles, to different entry parameters. We confirmed its interest to (1) analyse the relationship between particles normalized abrasion and its roundness trends; (2) analyse the hydrosedimentary dynamics at a river basin scale. We included several recommendations to apply this toolbox in the appropriate conditions. Finally, we performed a comparative analysis between particles’density and shape and its influence on bedload transport. These results highlight the significant influence of shape on travelled distance in comparison with density.
... Clast shape and roundness were measured at 66 sites chosen as being representative of the range of different landforms and/or surface sediment types (Figure 1c). Except for the slate-dominated talus slopes, the sampled clasts (n = 50 per sample) were exclusively granitoids, which is the dominant lithology in the study area, and the sampling and statistical processing (RA and C 40 indices) followed standard procedures outlined in Lukas et al. (2013). Five samples were also collected for particle-size analyses from the surfaces of moraine ridges and an intermorainic zone. ...
... (b, c) RA/C 40 plots for moraine ridges, intermorainic plains and surface sediment types. SeeLukas et al. (2013) for comparison of these data with fluvial, talus and subglacial control envelopes collected from a range of glacial environments and different clast lithologies. ...
Article
The geomorphological signature of tropical glaciers has the potential to provide important information on the response of ice masses in high‐mountain environments to climate warming. This study investigates the glacial geomorphology of Charquini Sur, Bolivia. Detailed geomorphological mapping was conducted both in the field and from satellite imagery in order to produce a 1:4,000 scale geomorphological map of the glacier foreland. Sedimentological analyses (description of physical characteristics, clast shape and roundness, particle‐size distribution) provided additional insight into the landform‐sediment assemblage. Glacial landforms are well preserved and include up to 11 moraine ridge suites, seven of which are cross‐valley frontal moraine arcs. These can be linked to an existing lichenometric chronology from previous work and record glacier recession since the local Little Ice Age (LIA) maximum in the late‐1600s. Lateral moraine ridges also record continuous thinning of the glacier over this time period. Smaller groups of parallel ridges are interpreted as annual moraines formed during recession. Intermorainic areas consist of flutings and a typically thin sediment cover of subglacial, supraglacial and glaciofluvial origin, with prominent ice‐moulded bedrock protuberances in places. Analysis of the landform‐sediment assemblage provides an insight into the main controls on landform genesis in the basin and implies there have been temporal changes in ice‐marginal dynamics since the LIA. We present the first landsystem model for a tropical cirque glacier, documenting its behaviour since the LIA and providing an indication of glacier response in rapidly‐warming high‐mountain environments.
... To assess surface debris sizes, shapes and orientations, we measured the dimensions of clasts using a modified pebble count approach (after Ballantyne, 1982). The method has been developed to quantify debris size distributions in fluvial transport (Wolman, 1954), but has also been applied in glacier and rock glacier studies to track the debris origin and to evaluate erosional, transportational and depositional processes (Benn & Ballantyne, 1993, 1994Lukas et al., 2013;Sampson & Smith, 2006). Along two transects of about 150 m length covering furrows and ridges, perpendicular to the rock glacier ridges surface slope, we sampled size and shape of clasts at 16 samplings sites. ...
... These properties were preserved in the corresponding Section 2 and 3, while Section 1 indicates a stronger clast mixing due to former glacial and recent periglacial processes Clast size and shape analysis are commonly used to determine the source area, transport path or transport distances of supra-and subglacial debris (Benn & Ballantyne, 1994). Usually this methods is applied assuming a single lithological unit (Lukas et al., 2013). In our clast analysis we can clearly see the imprint of the two different lithological units, where the massive granodiorite produces blockier clasts while debris also sourced from the mylonite exhibits platy and elongated shapes as well. ...
Article
Full-text available
Rock glaciers are receiving increased attention as a potential source of water and indicator of climate change in periglacial landscapes. They consist of an ice‐debris mixture, which creeps downslope. Although rock glaciers are a wide‐spread feature on the Tibetan Plateau, characteristics such as its ice fraction are unknown as a superficial debris layer inhibits remote assessments. We investigate one rock glacier in the semiarid western Nyainqêntanglha range (WNR) with a multi‐method approach, which combines geophysical, geological and geomorphological field investigations with remote sensing techniques. Long‐term kinematics of the rock glacier are detected by 4‐year InSAR time series analysis. The ice content and the active layer are examined by electrical resistivity tomography, ground penetrating radar, and environmental seismology. Short‐term activity (11‐days) is captured by a seismic network. Clast analysis shows a sorting of the rock glacier's debris. The rock glacier has three zones, which are defined by the following characteristics: (a) Two predominant lithology types are preserved separately in the superficial debris patterns, (b) heterogeneous kinematics and seismic activity, and (c) distinct ice fractions. Conceptually, the studied rock glacier is discussed as an endmember of the glacier—debris‐covered glacier—rock glacier continuum. This, in turn, can be linked to its location on the semiarid lee‐side of the mountain range against the Indian summer monsoon. Geologically preconditioned and glacially overprinted, the studied rock glacier is suggested to be a recurring example for similar rock glaciers in the WNR. This study highlights how geology, topography and climate influence rock glacier characteristics and development.
... Roundness data were plotted as histograms and analysed statistically using RA and RWR indices (Evans and Benn, 2004). We use RWR indices alongside RA to mitigate for the influence of glaciofluvial reworking on the effectiveness of the RA index to distinguish transport pathways Lukas et al., 2013). Cosmogenic nuclide surface exposure ages were recalculated ( Fig. 1) using version 3 of the online exposure age calculator formerly known as the CRONUS-Earth online exposure age calculator (Balco et al., 2008) with a regional Patagonian production rate calculated from the Kaplan et al. (2011) calibration data set. ...
... Their association with kame terraces and stratified gravel and sand and diamictic composition (e.g., M8, Fig. 6) indicate significant sediment transport and deposition by meltwater at the glacier margins. RA-C 40 and RWR-C 40 covariance clast data at moraine sites throughout the Salto valley (Fig. 3) suggest glaciofluvial input and reworking within the subglacial transport system (Lukas et al., 2013). The shallow bed gradient of the Salto valley provides a setting in which an extensive, gently-sloping glacier would be sensitive to small changes in climate and ELA, leading to the formation of multiple cross valley moraine ridges due to numerous small ice margin fluctuations during overall recession. ...
Article
Full-text available
The geomorphological record in glaciated landscapes can provide important information for the study of the response of glaciers to rapid climate change. This study presents a new reconstruction of the glacial history of the northern Monte San Lorenzo ice cap, southern South America, during a period of accelerated warming and deglaciation following the Antarctic Cold Reversal (14.5–12.8 ka). We present a detailed geomorphological map of the valleys to the north of Monte San Lorenzo. Sediment-landform assemblages identified include lateral and terminal moraine ridges, flutes, deltas, ice-contact fans, palaeoshorelines, kame terraces and outwash plains. We map 14 primary ice-limits, 7 of which are newly identified, and 7 of which are from previous studies, mapped here in greater detail. We devise landsystem models to formalise and document spatial and temporal changes in glacial processes and environments. Our new geomorphological mapping and landsystem reconstructions provide an important insight into the response of temperate Patagonian glaciers to rapidly-warming climate.
... Spedding and Evans, 2002;Evans, 2010). These data are compared to available datasets on different glacigenic materials through the use of co-variance plots (Benn and Ballantyne, 1994;Evans, 2010;Lukas et al. 2013). Finally the morphological characteristics of clasts indicative of subglacial transport, including striae, facets and stoss/lee forms, were noted (cf. ...
Technical Report
This report provides a rationale and scientific basis for three multi-disciplinary research projects undertaken during the Smoking Hills fieldwork campaign of July, 2018 (Fig. 1.1). It summarizes their field sample collections and observations and discusses their future research plans. The first activity concerns the age and environment of deposition of Cretaceous strata (145-66 Ma) in the Canadian Arctic mainland. This study will provide new insights into the tectonostratigraphic evolution of the offshore Canada Basin and the regional Mackenzie-Beaufort and Sverdrup basins. This study is also expected to provide insight into Cretaceous climates of the Canadian Arctic. The second activity concerns the study of bocannes, areas of burning shale/mudrock for which the Smoking Hills is aptly named. It aims to collect samples of minerals from within the burning vents and also to study the chemistry of ponds and streams draining from these features and associated bedrock. The final activity is focused on kimberlite (diamond) indicator minerals and tries to draw comparisons between those found in deposits in the Smoking Hills with those previously recovered in related deposits on Banks Island. This activity will also examine sediments from mapped areas of Neogene fluvial Beaufort Formation (<23-2.58 Ma), and from Quaternary glacial deposits (<2.58 Ma).
... Detailed sedimentological investigations involved section logging, lithofacies analysis, as well as clast shape and structural geological analyses, following established procedures (e.g. Evans & Benn, 2004;Gribenski et al., 2016;Lukas, 2005;Lukas et al., 2013). Detailed discussions of sedimentary processes and their implications are beyond the scope of this paper; thus, section logs, descriptions and interpretations will be presented in future publications. ...
Article
Full-text available
The Gaick is an enigmatic glaciated landscape in the Central Grampians, Scotland, dominated by an expansive dissected plateau. Previous studies have postulated widely differing interpretations of the glacial landforms and current understanding of the glacial events in this area is partly restricted by the absence of detailed glacial geomorphological mapping. To address this issue, we present a comprehensive 1: 46,000-scale glacial geomorphological map, covering an area of ~520 km2. A combination of detailed field mapping and interpretation of aerial photographs and Digital Surface Models (DSMs) has revealed a variety of glacial, periglacial and fluvial landforms, including an abundance of moraines and meltwater channels within valleys. We also identify a glacial sediment-landform assemblage, dissected glaciogenic material, that has not previously been reported in the Scottish Highlands. The geomorphological map provides the necessary foundation for elucidating the extent, dynamics and timing of former glaciation in the area.
... Samples of 50 sandstone clasts were collected for clast shape and roundness analysis following Benn and Ballantyne (1994). Clast shape data were plotted as ternary diagrams using TriPlot (Graham and Midgley, 2000), clast roundness data were plotted as frequency distributions, and C 40 , RA and RWR indices were calculated (see Lukas et al., 2013). Bulk sediment samples were oven (diamict) or freeze (mud) dried and dry-sieved to separate the fraction finer than 2 f (250 mm). ...
Article
Most large tidewater glaciers in Svalbard are known to have surged at least once in the last few hundred years. However, very little information exists on the frequency, timing or magnitude of surges prior to the Little Ice Age (LIA) maximum in ∼1900. We investigate the sediment-landform assemblages produced by multiple advances of the Nathorstbreen glacier system (NGS) in order to reconstruct its Late Holocene surge history. The glacier has recently undergone one of the largest surges ever observed in Svalbard, advancing ∼16 km from 2008 to 2016. We present flow velocities and ice-marginal observations (terminus change, proglacial geomorphological processes) from the later stages of this surge. A first detailed assessment of the development of a glaciotectonic mud apron within the fjord during a surge is provided. Geomorphological and sedimentological examination of the terrestrial moraine areas formed prior to the most recent surge reveals that at least two advances were responsible for their formation, based on the identification of a previously unrecognised ice-contact zone recorded by the distribution of sediment facies in coastal exposures. We distinguish between an outer, older advance to the distal part of the moraine system and an inner, younger advance to a position ∼2 km upfjord. Radiocarbon dating of shells embedded in glaciotectonic composite ridges formed by the onshore bulldozing of marine mud during the outer (older) of the two advances shows that it occurred at some point during the interval 700–890 cal. yr BP (i.e. ∼1160 AD), and not during the LIA as previously assumed. We instead attribute the inner (younger) advance to the LIA at ∼1890. By combining these data with previous marine geological investigations in inner and outer Van Keulenfjorden, we demonstrate that NGS has advanced at least four times prior to the recent 2008–2016 surge: twice at ∼2.7 kyr BP, at ∼1160 AD, and in ∼1890. This represents a unique record of the timing and magnitude of Late Holocene tidewater glacier surges in Svalbard.
... Geomorphological mapping of rock glaciers in the Khumbu region can be supplemented by clast analysis of their constituent debris as a tool to discriminate between rock glacier types. This is a useful methodology because clast shape properties can identify their source areas in glaciated environments and specifically can distinguish between subglacial and supraglacial debris sources (Lukas et al., 2013). Measurements of individual clasts can be used to derive the RA ratio (the percentage of angular and very angular clasts in any sample) and the C 40 index (the ratio of c/a-axis lengths ≤0.4). ...
Article
Rock glaciers are an important geomorphic element of glaciated mountain landscapes, but our understanding of their distribution and ages, controls on their development, and their importance in regional mountain hydrology and mountain geomorphic evolution is incomplete. In part, this incomplete knowledge arises through problems associated with identifying rock glaciers on a morphological basis alone, amplified by the multiple ways in which rock glaciers can form in different glacial, periglacial, and paraglacial settings. This study focuses on rock glaciers as a paraglacial mountain landscape element and considers the relationships between rock glaciers and glacial, periglacial, and paraglacial processes. New geomorphic and sedimentary data on different rock glaciers from the Khumbu region of Nepal are presented. These data show that even within a single region, rock glaciers may have varied origins and thus likely ages and different climatic and environmental controls. We argue that rock glaciers in deglacierizing mountains may have a long residence time in the landscape, unlike many other glacially influenced mountain landforms, and can undergo significant morphodynamic changes as glaciated landscapes transition into paraglacial landscapes.
... In the larger cirques, the MIE was also marked by the prominent outer moraines which reach up to 10 m high and are easily distinguished in the field. Additionally, clast morphology analysis (Lukas et al., 2013; Supplementary Data 1) was used in single sites in the Cȃlimani Mountains to confirm the distribution of glacial sediments. Moraine clasts commonly display a high proportion of blade and elongate shapes and strong rounding in contrast to nonglacial sediments which indicate a large proportion of angular clasts (Supplementary Data 1). ...
Article
In the Northern Romanian Carpathians (NRC) small Pleistocene cirque glaciers have formed in several isolated mountain massifs exceeding 1800 m asl. This paper brings forward new geomorphological evidence of marginal glaciation in the Călimani, Suhard, and Gurghiu Mountains which are the southernmost glaciated areas of the NRC. We reconstructed the extent and ice-surface geometry for 12 palaeo-glaciers in the study area during the Maximal Ice Extent (MIE) which is attributed to LGM. The equilibrium line altitudes (ELAs) calculated using the area-altitude-balance-ratio (AABR) 1.6. were between 1740 m and 1870 m which is the highest value in the Eastern Carpathians and one of the highest in the entire Carpathians. The specific features of the Călimani and Gurghiu Mountains are the extensive, gentle outer slopes of volcanic calderas that play an important role as additional areas for snowblow accumulation. Inclusion of the potential snow contribution area (snowblow and avalanche accumulation) in the ELA calculation resulted in an additional upward ELA shift up to 66 m (up to 40% of the glacier elevation range). Our data indicate that small cirque glaciation in the NRC could develop when mountain ranges are at least 100 m above the extrapolated regional ELA. The general ELA pattern in the NRC shows a positive trend (∼3 m/km) which could reflect both the general rise in temperature and the starvation of precipitation toward the southeast. However, the observed eastward ELA rise on W-E transects in the Eastern Carpathians shows a pure precipitation effect and indicates the influence of zonal atmospheric circulation in the far interior of Europe during the LGM.
... The shape of pebbles provides information about the transport mechanisms (e.g., fluvial versus glacial), the depositional environment, and particularly about the origin of the clasts (e.g. Claude et al., 2017a;Lukas et al., 2013;Schlüchter, 1989). In the context of the material's provenance, it has been reported that rounded quartzite pebbles represent products of reworked fluvial sediments such as the Miocene Molasse conglomerates or older unconsolidated gravels, whereas sub-angular pebbles are interpreted to indicate rather fresh erosional products from the Alps (e.g. ...
Article
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In this paper, we document that glaciofluvial gravel sequences and glacial till deposits that are exposed in the Müntschemier and Finsterhennen gravel pits (Swiss Plateau west of Bern) record three glacial advances during the Birrfeld Glaciation, which corresponds to the last glacial cycle. Sedimentological logging shows that both gravel pits expose deposits of glaciofluvial braided river systems. These sediments are overlain by a till that was deposited during the Last Glacial Maximum (LGM). The results of the provenance analysis imply that the sediments were mainly supplied by the Valais Glacier, which originated in the Central Alps. A minor contribution of the material was supplied by the Saane Glacier with sources in the northern parts of the Alps. In addition, the morphometric analysis particularly of quartzite clasts in the till deposits indicate that while some clasts (the angular ones) were eroded and transported by the Valais Glacier from the Central Alps to the depositional site, the majority of the quartzite constituents (the rounded ones) were most likely reworked from the Molasse bedrock or older gravels. This implies that a large fraction of the sediments in the Müntschemier and Finsterhennen gravel pits could represent recycled material from older fluvial gravels and conglomerates that were then reworked by the glaciers as they advanced to the foreland. Based on the sedimentological data and considering published and new optically stimulated luminescence (OSL) chronological data, we propose a landscape evolution scenario where the first glacial advance occurred during Marine Isotope Stage (MIS) 5d. The second glacier advance followed during MIS 4, while the last one during the Last Glacial Maximum (LGM), which corresponds to the MIS 2. The MIS 5d advance is recorded by the lowest unit of the Müntschemier gravel pit and consists of a fining upward sequence made up of an alternation of gravel and sand beds. The MIS 4 advance is recorded by the unit beneath the LGM till at Müntschemier and by the lowermost layer in the Finsterhennen gravel pit. It comprises an alternation of gravel and sand beds, which coarsens and thickens upwards. The LGM advance, finally, resulted in the deposition of amalgamated gravel beds at Finsterhennen, which ended with the construction of a till that is encountered on the top of both gravel pits. Sediments related to the interstadial conditions between MIS 5a and MIS 5b and MIS 3 were not encountered, which suggests that the warmer periods were characterised by non-deposition and/or erosion, which possibly resulted in the observed sedimentary hiatus. Although the chronological results are still preliminary, the available information allows us to suggest that during the Birrfeld Glaciation, the Valais lobe advanced several times to the Swiss Plateau. In addition, the facies associations imply that the eastward expansion of the Valais lobe during the MIS 5d and MIS 4 were most likely shorter than during the LGM.
... MAL-02 is more complicated because one of the surfaces shows a very long exposure; it is the most angular of the samples and the long exposure is only recorded in one of the surfaces (Fig. 2b). The angularity may be an indicator of supraglacial transport (Benn and Ballantyne, 1994;Boulton, 1996Boulton, , 1978Lukas et al., 2013) because subglacial transport leads to more erosion and surface loss (Benn and Ballantyne, 1994;Boulton, 1978;MacGregor et al., 2009). We speculate that this boulder may have been exposed on the valley side for a considerable period, then transported supraglacially to the moraine deposit; it was probably exposed to light to some degree during transport, and one surface was presumably exposed immediately after deposition. ...
Article
In this study, we investigate the potential of rock surfaces to provide luminescence burial ages for boulders from moraine deposits. We sampled four boulders from a terminal moraine at the Malta Valley, Austria, all deposited ∼2 m below the present ground surface, and measured the IRSL signal as a function of depth into the boulder surfaces. It is clear from these profiles that all four boulders were exposed to at least some daylight prior to final deposition, and in one boulder, there is evidence for multiple exposure/burial events. The profiles show that the luminescence signal at the surface of two boulders must have been completely zeroed before burial. The burial doses derived from these two well-reset surfaces can thus be safely used to calculate burial ages, which may be the same as the depositional age of the terminal moraine. The IRSL signals from both boulders seem to suffer from anomalous fading with g-values of up to 15% decade⁻¹. The younger fading-corrected age of ∼14 ka is in agreement with the deposition of the terminal moraine and coincides with the assumed Gschnitz stadial, while the older age of ∼39 ka most likely represents an earlier event during which this boulder was exposed to light. Our results suggest that there is a high probability of sampling light-exposed and even well-bleached boulders from moraine deposits. We thus conclude that rock surface luminescence dating offers the possibility of obtaining reliable ages for moraine deposition. Even boulders which are partially bleached and thus not suitable for dating can provide insight into transportation pathways as well as depositional processes in glacial environments leading to a better understanding of the dynamics of glaciers.
... In our view, geomorphological mapping in cirque glacier, valley glacier, icefield and ice-cap settings should not be reliant solely on the morphological characteristics of features and should ideally be combined with detailed sedimentological investigations of available exposures as part of an inductivedeductive process, using standard procedures (cf. Evans and Benn, 2004;Lukas et al., 2013, and references therein). This reflects the fact that these glacier systems occupy more manageable study areas and, as such, sedimentological analyses can be more readily applied. ...
Article
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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.
... The geometrical characteristics of pebbles have been subject to observation since Aristotle (Krynine, 1960). Such characteristics are an important physical property that enable the differentiation of transport pathways in glacial environments (Benn and Ballantyne, 1994;Lukas et al., 2013), provide indications about sedimentary history, help to characterize depositional environments (Graham and Midgley, 2000), target sediment sources at catchment scales (Knighton, 1982;Lindsey et al., 2007;Roussillon et al., 2009;Miller et al., 2014) and allow for the investigation of particle transport history on Mars (Szabó et al., 2015). They also highlight hydraulic controls on downstream fining or abrasion processes (Wentworth, 1919;Kuenen, 1956;Durian et al., 2008;Manga et al., 2011;Domokos and Gibbons, 2013;Szabó et al., 2013;, and influence in-river particle mobilization and displacement (Komar and Li, 1986;Ashworth and Ferguson, 1989;Kirchner et al., 1990;Carling et al., 1992;Schmidt and Ergenzinger, 1992;Schmidt and Gintz, 1995;Sear et al., 2008;Stark et al., 2014). ...
... The degree of bedrock fracture can also be controlled by the compressive and tensile rock strength, which has been observed through field investigations of fracture spacing where the bedrock lithology varies on a large enough spatial scale (e.g., Sturzenegger et al., 2007). The term "lithology" is not commensurate with rock strength given the large variation in physical properties within a given mapped lithology, as noted in a study of clast shape versus lithology in glacier systems (Lukas et al., 2013). In our field area, we observe that the plutonic rocks are generally less fractured than the metasedimentary rocks, but the difference is not statistically significant. ...
... Glaciers transport debris at different levels: supraglacial (see chapter: Supraglacial Environments), englacial, basal ( Fig. 5.7A) and subglacial (Boulton, 1978;Alley et al., 1997). Although this is largely passive transport, these levels are not separated but interconnected (Schlüchter, 1979a,b;Lukas et al., 2013). Supraglacial debris can enter the glacier by falling into crevasses or by washing in by supraglacial meltwater; it will thus become englacial or even basal debris ( Fig. 5.7B). ...
Chapter
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Subglacial sediments are among the most prevalent sediments in glaciated terrains. The environments and processes that erode, transport and deposit/emplace subglacial sediments and landforms are described in the light of recent research developments. Tills and deforming beds and thermal/rheological conditions in subglacial environments are elucidated. The characteristics and origins of subglacial landforms such as drumlin, Rogen, fluted and hummocky moraine and eskers are discussed. Finally, future perspectives, challenges and possible new research opportunities in subglacial environments are considered.
... Lithology is particularly important to determining clast shape (Benn & Evans, 2004) (Lukas, et al., 2012), and the RWR-index co-variance plots are equally as useful as the RA-C40 co-variance plots, but when possible, both should be used together to decide which one is best for the given catchment (Lukas, et al., 2013). ...
Thesis
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This dissertation looks at sediments in regions of southwest Wales and southwest Cornwall. Similarities are held between sediments at Hunts Bay, Wales, and sediments found in situ at an exposed section of cliff face in Porth Nanven, Cornwall, which could be indicative of glacial process occurring in southwest Cornwall. Recent research suggested that glaciers may have extended much further south than previously thought in the Last Glacial Maximum, due to a niche-glacier system from the Last Glacial Maximum being identified at Rosemergy, Cornwall (Harrison, Knight & Rowan 2015). Clast fabric analysis and stereonet projections of Rotherslade, Hunts Bay and Porth Nanven were carried out and compared to identify whether the conclusion could be drawn that glacial processes occurred in Porth Nanven and Hunts Bay and that Rotherslade remained unglaciated in the Last Glacial Maximum, and the implications of this conclusion. Results suggest that Porth Nanven and Hunts Bay experienced glaciation and Rotherslade did not, which calls for a revision of British and Irish Ice Sheet limits.
... While it is generally recommended to describe clast shape and rounding on only similar lithologies (e.g. Lukas et al. 2013), we used all clasts, independent of lithology (except locally derived friable sandstones). This is because the total number of clasts in the drill core is limited and sampling for specific lithologies would significantly increase the sampling depth interval. ...
Article
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The cumulative effect of repeated extensive glaciations represents a poorly constrained component in the understanding of landscape evolution in mid-latitude mountain ranges such as the Alps. Timing, extent, and paleo-climatic conditions of these glaciations are generally poorly understood due to the often-fragmentary character of terrestrial Quaternary records. In this context, the sedimentary infills of subglacial basins may serve as important archives to complement the Quaternary stratigraphy over several glacial–interglacial cycles. In this study, sedimentary facies, valley-fill architecture, and luminescence dating are used to describe nine erosional and depositional cycles (Formations A–I) in the Lower Glatt valley, northern Switzerland. These cycles can be related to the ‘Birrfeld’ Glaciation (~ MIS2), the ‘Beringen’ Glaciation (~ MIS6), and up to three earlier Middle Pleistocene glaciations that can be tentatively correlated to the regional glaciation history. Evidence suggests that deep bedrock trough incision and/or partial re-excavation last occurred mainly during the ‘Beringen’ and ‘Habsburg’ Glaciations. Second-order, ‘inlaid’ glacial basins document separate glacier re-advances during the Beringen Glaciation. The arrangement of subglacial basins in the Glatt valley with different sub-parallel or bifurcating bedrock troughs, re-excavated segments, and inlaid basins document changes in the magnitude and the spatial focus of subglacial erosion over time. The Glatt valley may thus serve as a key example for the glacial landscape evolution in many other repeatedly glaciated forelands.
... Sedimentological analyses, following established procedures (e.g. Evans and Benn, 2004;Lukas et al., 2013), were conducted alongside field mapping to elucidate processes of landform formation. Morphostratigraphic procedures used to construct a relative glacial chronology (see Lukas, 2006), along with glacier and palaeoclimatic reconstruction methods, are outlined in later relevant sections. ...
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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.
... Based on the covariance of C 40 and RA indices and RA and RWS indices (cf. Benn and Ballantyne, 1994 for details), the gravels fall into the subglacial envelopes (Table 2; Lukas et al., 2013). In summary, it would appear that the majority of the clasts were only transported a relatively short distance by ice. ...
Article
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Previous investigation of isolated landforms, on the eastern margin of the East Anglian Fenland, England, has demonstrated that they represent an ice-marginal delta and alluvial fan complex deposited at the margin of an ice lobe that entered the Fenland during the ‘Tottenhill glaciation’ (termed the ‘Skertchly Line’). They have been attributed, based on regional correlations, to a glaciation during the Late Wolstonian (i.e. Late Saalian) Substage (Drenthe Stadial, early Marine Isotope Stage (MIS) 6). This paper aimed to test this correlation by directly optically luminescence dating, for the first time, sediments found within the Skertchly Line at Shouldham Thorpe, Norfolk, and Maidscross Hill, Suffolk, together with those in associated kame terrace deposits at Watlington, Norfolk. Ages ranged from 244 ± 10 ka to 12.8 ± 0.46 ka, all the results being younger than MIS 8 with some clearly showing the landforms have been subsequently subjected to periglacial processes, particularly during the Late Devensian Substage (∼MIS 2). Most of the remainder fall within the range 169–212 ka and could be assigned to MIS 6, thus confirming the previously proposed age of the glaciation. The local and regional implications of these conclusions are discussed, the maximum ice limit being linked to that of the Amersfoort–Nijmegen glaciotectonic ridge limit in the central Netherlands.
... In this approach, the a and b axes are always measured in the horizontal plane and a > b, while the c-axis is measured vertically and is not necessarily the smallest boulder dimension. This approach differs from classic particle fabric measurements (Benn and Evans, 2010;Lukas et al., 2013), where a > b > c. ...
Article
Pleistocene moraine complexes with glacial deposits well beyond the last glacial maximum (LGM) limit are rarely formed and preserved in the face of small valley glaciers due to topographic, tectonic, and glacier-size-specific factors. Here, we show the results of detailed mapping of the Pleistocene terminal moraines in the Białka Valley (High Tatra Mountains, Western Carpathians) formed by a 13 km long valley glacier. To portray post-depositional denudation process in the moraines, we mapped the size distribution of moraine boulders and measured their weathering index using the Schmidt Hammer test. In the moraine complex, three morphological units were distinguished from the younger (inner) to the oldest (outermost): Łysa Polana (ŁP), Rusinowa Polana (RP), and Hurkotne (H). The ŁP unit (LGM) features hummocky moraine relief which does not occur on the two older units. In contrast, surface boulders occur on the ŁP and RP units, but they have been cleared from the oldest H unit due to long-lasting erosion. Consequently, the most weathered boulders occurred in the intermediate age RP moraine (~MIS 6). Our results show that in Central Europe, the persistence of surface granite boulders in the landscape cannot be much longer than that of the penultimate glaciation, which highlights the problem of exposure age dating of old moraines in this area. Both pre-LGM glaciations extended ca. 1 km beyond the LGM moraines, but in the case of the H glaciation, this length reduction (7%) was accompanied by a 220 m valley incision at the glacier front. Therefore, the Białka valley glacier was able to achieve a self-limiting effect even in an area of considerable tectonic uplift. We suggest that vigorous, wet-based glacier erosion occurred in areas with high rates of ice accumulation and mass turnover in the windward NW part of the High Tatras exposed to orographic induced precipitation.
... A modified version of the lithofacies code from Eyles et al. (1983) was used to record lithofacies on the section logs (Fig. 3). Clast shape was analysed for selected lithofacies units, following established methods (see Lukas et al., 2013;Benn and Lukas, 2021). A modified version of TriPlot (Graham and Midgley, 2000) was used to calculate C 40 , RA, and RWR indices. ...
Article
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Many glaciated valleys in Scotland contain distinctive, closely spaced ridges and mounds, which have been termed ‘hummocky moraine’. The ridges and mounds are widely interpreted as ice-marginal moraines, constructed during active retreat of mainly temperate glaciers. However, hummocky terrain can form by various processes in glacial environments, and it may relate to a range of contrasting glaciodynamic regimes. Thus, detailed geomorphological and sedimentological studies of hummocky surfaces in Scottish glaciated valleys are important for robust interpretations of former depositional environments and glacier dynamics. In this contribution, we examine irregularly shaped ridges and mounds that occur outside the limits of former Loch Lomond Readvance (≈ Younger Dryas; ~ 12.9–11.7 ka) glaciers in the Gaick, Central Scotland. These ridges and mounds are intimately associated with series of sinuous channels, and their planform shape mimics the form of the adjacent channels. Available exposures through ridges in one valley reveal that those particular ridges contain lacustrine, subglacial, and glaciofluvial sediments. The internal sedimentary architecture is not related to the surface morphology; thus, we interpret the irregularly shaped ridges and mounds as erosional remnants (or interfluves). Based on the forms and spatial arrangement of the associated channels, we suggest that the ridges and mounds were generated by a combination of ice-marginal and proglacial glaciofluvial incision of glaciogenic sediments. The evidence for glaciofluvial incision, rather than ice-marginal moraine formation, at pre-Loch Lomond Readvance glacier margins in the Gaick may reflect differences in glaciodynamic regimes and/or efficient debris delivery from the glacier margins to the glaciofluvial systems.
... Particle morphology (PM) is of great interest in earth science and several other scientific fields and engineering disciplines. PM in sedimentology is a very useful shape parameter that contains information about the processes that the particle has undergone since its formation and during transport and deposition (Krumbein, 1941a;Lukas, 2013). This textural characteristic is the consequence of various processes involving a set of particles, such as collisions, abrasion, friction, comminution, exposure time, and pathway, among others (Krumbein, 1941b;Caballero et al., 2012;Caballero et al., 2014). ...
Article
Shape analysis is of paramount importance in sedimentology. Particle morphology is a very useful texture parameter that provides information about particle history and is used to characterize and classify sedimentary material. Particle shape description has been both an important and a controversial subject. The most convincing description of shape defines particle shape by three hierarchical parameters: form, roundness, and surface texture (Barrett, 1980). Many different methods have been proposed to measure these parameters. Among them, Fourier shape analysis is particularly notable. Fourier analysis separates the three parameters into frequency ranges. The low frequency range is related to form, the middle frequency range to roundness and the high frequency to surface texture. However, determining where the boundaries lie between the different morphological classes is not an easy task and has been an unsolvable problem since the FSA method was first proposed. The same is true for the signal-to-noise limit. To date, this information has been obtained empirically and with great uncertainty. One of the most important contributions of this work has been to quantitatively constrain the harmonic ranges corresponding to the morphological ranges proposed by Barrett, and to determine the best possible approximation for the upper limit of the signal and the onset of noise. To estimate these ranges, we propose here two original methodologies based on analysis of the cumulative amplitude spectrum (CAS), and on simulating the effect of artificial noise acting on a well-known geometric figure. The CAS of 3664 volcaniclastic particles and of 106 artificially silhouette charts have been quadrisected into form, roundness, roughness and noise using an optimization process. The analysis indicates overall that the limits are well constrained into a narrow range of harmonics with a small variance. The results obtained are reliable and allow the range of harmonics that contains a useful signal to be extended up to harmonic 256. The method has been successfully applied to the standard figures of Krumbein (1941a) and of Powers (1953), efficiently separating the different classes of roundness. As an example, the methodology has been applied to a real-life case where there was doubt about the pristine nature of the materials from some outcrops related to the block-and-ash flow deposit of the July 17, 1999 eruption of the Colima volcano. The results obtained applying the method show promising results, indicating the potential of FSA information to solve this ambiguity. The powerful, user-friendly FSA software that we distribute freely (open code) can be very useful for characterizing volcano-sedimentary and sedimentary deposits. To date, there is no other software for FSA studies. Moreover, FSA can be useful in other fields of science and engineering where quantitative particle shape analysis is needed.
... Differentiation of sediment cover proved to be challenging even in the field; experienced glacial sedimentologists found it difficult to ascertain whether a heterogenous sediment cover was a till stripped of fines or a talus deposit sourced from heterogenous bedrock lithologies. Clast angularity can be a key criterion in classifying sediments (Lukas et al., 2013), however, across both field campaigns, almost all the clasts we encountered were angular, characteristic of both tills and regoliths stripped of fines. Therefore, clast angularity was not a reliable deterministic characteristic as to whether or not mapped sediment cover is of glacial origin. ...
Article
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Reconstructing the response of present-day ice sheets to past global climate change is important for constraining and refining the numerical models which forecast future contributions of these ice sheets to sea-level change. Mapping landforms is an essential step in reconstructing glacial histories. Here we present a new map of glacial landforms and deposits on nunataks in western Dronning Maud Land, Antarctica. Nunataks are mountains or ridges that currently protrude through the ice sheet and may provide evidence that they have been wholly or partly covered by ice, thus indicating a formerly more extensive (thicker) ice sheet. The map was produced through a combination of mapping from Worldview satellite imagery and ground validation. The sub-metre spatial resolution of the satellite imagery enabled mapping with unprecedented detail. Ten landform categories have been mapped, and the landform distributions provide evidence constraining spatial patterns of a previously thicker ice sheet.
... The sedimentological investigations followed standard procedures and involved logging and lithofacies analysis, as well as clast fabric and clast shape analyses (e.g. Evans and Benn, 2004;Lukas et al., 2013). ...
Article
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This study assesses the spatial and temporal evolution of the glacial landsystem signature at Fjallsjökull, southeast Iceland, using (a) mapping of the glacial geomorphology and surficial geology and (b) repeat uncrewed aerial vehicle (UAV) surveys. A small-scale (1: 15,000 scale) landsystem map has been compiled using LiDAR data (2011−2012) and historical aerial photographs (1945–1998), along with a large-scale (1: 2000 scale) map based on UAV imagery from May 2019. From our mapping and UAV surveys, we identify sediment-landform assemblages that are typical of active temperate glacial landsystems, including recessional push/squeeze moraines and intervening flutings, overridden moraine arcs, proglacial outwash (sandur) fans and linear/ribbon sandar. We recognize three landform zones that are defined by changes in moraine morphology and the nature of proglacial outwash deposition: (1) the outer foreland is characterized by proglacial outwash fans, overridden moraine arcs and broadly linear recessional moraines; (2) the middle foreland contains sawtooth moraines and linear sandar; and (3) the innermost zone comprises extremely sawtooth and hairpin moraines as well as associated crevasse-squeeze ridge limbs. This landform zonation reflects spatio-temporal changes in moraine-forming processes and outwash deposition as determined by changes in snout morphology and proglacial drainage characteristics. Within this general tripartite zonation, we also identify localized (azonal/intrazonal) sediment-landform assemblages that are not typically found at active temperate glaciers, including ice-cored/hummocky terrain and localized kame and kettle topography. Repeat UAV surveying in 2016–2019 has allowed us to capture and quantify recent intrazonal landsystem change at the southern glacier margin. We identify a switch from moraine formation to the development of ice-cored terrain and an ice-cored esker complex in association with the uncovering of a depositional overdeepening. Our study demonstrates the important role that variations in local boundary conditions (e.g. topography) can play in the process-form response of individual active temperate outlet glaciers, contributing to the expanding database on modern glacial landsystems.
... A higher percentage of very angular and angular in situ-weathered clasts is the likely explanation for this difference in clast roundness because no general relationship between ir and altitude can be detected in the data for all sites (see below). The dominant subangular nature of surface material at the majority of sites is regarded as typical for tills in mountain environments (Evans and Benn, 2004;Lukas et al., 2013). Its limited variability seems not to have influenced the R Rock -data (Fig. 8). ...
Article
Measurements with an electronic Schmidt-hammer (RockSchmidt) were conducted on 23 sites of sorted stripes (periglacial patterned ground) on Juvflye, Jotunheimen (central South Norway). All were located above the current lower limit of alpine permafrost. Performing Schmidt-hammer exposure-age dating (SHD) based on application of a new local age-calibration equation for RRock-values yielded SHD-ages between 7975 ± 370 and 6660 ± 355 years ago, which are closely comparable to results obtained previously from sorted circles at the same location. The age estimates are interpreted as ‘composite’ ages indicative of upfreezing of boulders, lateral sorting, and subsequent stabilisation. Formation of patterned ground essentially ceased with the onset of the regional Holocene Thermal Maximum (HTM). Neither sorted stripe sites at higher altitude, continuously underlain by permafrost during the entire Holocene, nor those at lower altitudes affected by re-aggradation of permafrost in the late Holocene show signs of significant recent morphodynamic activity. Likely explanations for early- to mid-Holocene stabilisation include (1) substantial changes of soil moisture conditions and related thermodynamics within the active layer affecting frost action, (2) loss of fine-grained substrate matrix from the coarse stripes and hence reduced frost susceptibility, and (3) exhaustion of supply of boulders from the fines-dominated areas. Whereas the sorted stripe data set as a whole did not reproduce the altitudinal gradient characteristic of sorted circles on Juvflye, the strength of the relationship between sorted stripe mean RRock-values and altitude increased with declining slope gradient. Although interpretation of SHD-ages for patterned ground remains challenging, this successful application of the electronic Schmidt-hammer, with its increased efficiency and technical improvements over the mechanical Schmidt-hammer, offers considerable potential for future SHD-studies in both morphodynamic and palaeoclimatic contexts.
... The RA axis represents the percentage of clasts that are angular and very angular; the C 40 axis represents the proportion of clasts with a c:a axial ratio of ≤0.4 (i.e. more slabby and elongate shapes). The ellipses represent envelopes for characteristic sediment types; blue envelopes fromLukas et al. (2013) for high-mountain glaciers worldwide; red and black envelopes fromBrook and Lukas (2012) for Fox Glacier, New Zealand, for schist and greywacke, respectively; green envelope fromReznichenko et al. (2016) for a rock avalanche dominated moraine at Mueller Moraine, New Zealand. [Color figure can be viewed at wileyonlinelibrary.com] ...
Article
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Ambiguous landscape histories can arise from equivocal or incomplete geomorphological, sedimentological or geochronological evidence. In this study, we apply quantitative analyses to robustly assess the origin and age of a field of rounded mounds, known as ‘The Hillocks’. Using clast analysis, the sediment is shown to be consistent with a landslide origin but inconsistent with other glacial sediments in the region. Cosmogenic 10Be exposure age dating suggests The Hillocks formed ~8 ka. Ground‐penetrating radar reveals that the deposit rests upon deltaic foreset beds; combined with topographical data, we calculate a deposit volume of ~15–27 M m3, consistent with the estimated volume of the proposed source area. Overall, our data support a rock avalanche origin, indicating that by 8 ka the valley was ice‐free at The Hillocks’ location, and the level of Lake Wakatipu was lower than 340 m asl by this time. The Dart River delta shoreline was situated somewhere between The Hillocks and the present day shoreline at that time, and has prograded at a maximum average rate of 1 m a−1 since ~8 ka. These findings are significant given the lack of landforms by which to constrain glacial or post‐glacial landscape histories in this region of New Zealand.
... Both clean-ice glaciers and debris-covered glaciers transport sediments to downslope geomorphological units by sub-, endo-and supra-glacial processes (Boulton, 1978;Lukas et al., 2013). These transport routes are extremely complex, often mixed and highly variable in time (Fyffe et al., 2020), and thus very difficult to determine by means of the basin-scale remote sensing approach utilized here. ...
Article
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In the past decade, sediment connectivity has become a widely recognized characteristic of a geomorphic system. However, the quantification of functional connectivity (i.e. connectivity which arises due to the actual occurrence of sediment transport processes) and its variation over space and time is still a challenge. In this context, this study assesses the effects of expected future phenomena in the context of climate change (i.e. glacier retreat, permafrost degradation or meteorological extreme events) on sediment transport dynamics in a glacierised Alpine basin. The study area is the Sulden river basin (drainage area 130 km²) in the Italian Alps, which is composed of two geomorphologically diverse sub-basins. Based on graph theory, we evaluated the spatio-temporal variations in functional connectivity in these two sub-basins. The graph-object, obtained by manually mapping sediment transport processes between landforms, was adapted to 6 different hydro-meteorological scenarios, which derive from combining base, heatwave and rainstorm conditions with snowmelt and glacier-melt periods. For each scenario and each sub-basin, the sediment transport network and related catchment characteristics were analysed. To compare the effects of the scenarios on functional connectivity, we introduced a connectivity degree, calculated based on the area of the landforms involved in sediment cascades. Results indicate that the area of the basin connected to its outlet in terms of sediment transport might feature a six-fold increase in case of rainstorm conditions compared to “average” meteorological conditions assumed for the base scenario. Furthermore, markedly different effects of climate change on sediment connectivity are expected between the two sub-catchments due to their contrasting morphological and lithological characteristics, in terms of relative importance of rainfall-triggered colluvial processes vs temperature-driven proglacial fluvial dynamics.
... This ramp-like deposit is up to 50 m high and extends over 2 km across slope and 400 m downslope at its northern end, shown in Fig. 2a, where the feature lies at an altitude of 1900-1985 m a.s.l. Individual ridges, including those labelled M1-M6 in Fig. 2a, are composed of diamicton with a high (50-75%) concentration of angular to very angular boulders (Powers 1953;Matthews 1987;Lukas et al. 2013) and stand 1.0-5.0 m above the surrounding terrain. ...
Article
A Schmidt hammer was used in conjunction with lichenometry to examine the relative age of the outermost Neoglacial moraines in front of glaciers in the Jotunheimen mountains of southern Norway. Particular attention was directed at (1) the magnitude of the ‘Little Ice Age’ glacier expansion episode relative to any others of Neoglacial age, and (2) the potential and limitations of the Schmidt hammer in the context of Holocene glacial chronologies. Schmidt hammer R-values were measured at 34 glaciers and the sizes of the lichen Rhizocarpon geographicum agg. at 80 glaciers. Unusually low R-values and large lichens suggest the occurrence of pre- ‘Little lce Age’ Neoglacial moraines at only a small minority (< 10 %) of the sampled glaciers. The traditional model of relatively large southern Norwegian glaciers during the ‘Little Ice Age’ is substantiated and it is tentatively suggested that differences in climate or glacier type may account for a regional difference in the status of the ‘Little Ice Age’ between northern and southern Scandinavia. The incorporation of weathered boulders into ‘Little Ice Age’ moraines by glacier push mechanisms, and the altitudinally-related variation in boulder surface textures, are identified as major sources of potential error in the use of the Schmidt hammer R-values for relative-age determination of Neoglacial surfaces.
... The RA-C 40 index is applied mostly in glacial settings because it can differentiate between supraglaciallytransported angular clasts and subglacially-transported abraded clasts (Benn & Ballantyne, 1994;Benn, 2004;Brook & Lukas, 2012). The RWR-C 40 index, which targets the more rounded clasts, is more suitable in some settings for distinguishing between different transport mechanisms (Benn, 2004;Brook & Lukas, 2012;Evans et al., 2010;Lukas et al., 2013). To analyze the morphometry of the gravels at the study sites, we applied the technique proposed by Cailleux, (1947) because the reported shapes of the clasts in the Deckenschotter deposits at Irchel were sub-angular to sub-rounded (Graf, 1993). ...
Article
Cut-and-fill sequences are the result of climatically or tectonically induced alternating aggradation and incision phases of a fluvial system. A recently established cosmogenic nuclide chronology of the Cover Gravels ( Deckenschotter in German) in the northern Alpine Foreland, which are the oldest Quaternary glaciofluvial gravels and comprise evidence of early Pleistocene glaciations, suggests a cut-and-fill build-up. This suggested cut-and-fill architecture challenges the morphostratigraphy. The Deckenschotter deposits represent a suitable archive for reconstructing drainage patterns, base level changes, and the landscape evolution of the northern Alpine Foreland during the early Pleistocene. In this study, we focused on the highest morphostratigraphic Deckenschotter sites: three at Irchel and one in the area around Lake Constance. Sediment analyses were performed to determine their provenance and depositional environments. The geochronology was established using isochron-burial dating. The results indicate that the sediments were transported from the Central and eastern Central Alps, as well as from the Molasse, to the foreland and deposited in a proximal glaciofluvial environment. Based on these findings, we propose that the Deckenschotter are cut-and-fill sequences that accumulated in three stages during the early Pleistocene at ca. 2.5 Ma, ca. 1.5 Ma, and ca. 1 Ma. The presence of a cut-and-fill system implies that the regional base level was relatively constant during the early Pleistocene. In addition, the ca. 2.5 Ma glaciofluvial gravels document the first evidence of glaciers in the northern Alpine Foreland. This timing is synchronous with the onset of Quaternary glaciation in the northern hemisphere at ca. 2.7 Ma.
... Clast roundness was determined visually for each clast on a modified Powers (1953) scale. Given the potential influence of lithology in determining clast shape (see Lukas et al., 2013), we confined our sampling strategy to clasts of similar lithology (granitic gneiss). ...
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... In future studies, the morphology of Yuermeinak clasts (i.e. ratios of principal axes) might be used to test and refine this hypothesis of mountainous topography using the approach described by Lukas et al. (2013), although lithification may prove an obstacle. ...
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Ubiquitous glaciation was the hallmark of the Cryogenian Period (ca. 720 – 635 Ma), therefore understanding the character, behaviour, extent and configuration of Cryogenian ice bodies is a fundamental requirement in reconstructing climates and environments from the period. Unfortunately, despite abundant evidence for glaciation, there is a strong preservational bias towards basinal glaciogenic sedimentary strata and against subglacial strata. In particular subglacially striated surfaces, owing to their fragile millimetre-thickness, are very rare and represent only a tiny proportion of the global Cryogenian outcrop area. Thermal regime is one of the most important controls of glacial behaviour and subglacially striated surfaces are one of the very few means of determining an ancient temperate thermal regime. In this context we present sedimentological and detrital zircon detail of a fortuitously preserved Cryogenian (Marinoan) outcrop in the Aksu-Wushi area of the Tarim Craton, NW China. The Yuermeinak Formation preserves not only a subglacially striated surface and palaeotopography but also a thin, locally preserved, subglacial tillite. Together these indicate grounded ice. The remaining formation reveals glacial retreat and deposition of predominantly supraglacially-sourced debris within a dynamic, open-water, ice-proximal proglacial environment. A palaeogeographic reconstruction is proposed in which the Aksu-Wushi area developed from a deeper-water basinal environment, without clear evidence for glaciation, during the early Cryogenian, to an area of mountainous uplift with nearby grounded glacial ice, during the latter Cryogenian. Combining detrital zircon data of this study with published data it is further proposed that this development was linked to an active margin setting, either through expansion of an Andean-type mountain range to the north of the study area or flank-uplift of a back-arc basin.
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This paper provides a description and evaluation of the sedimentary facies and environments associated with a range of glacier thermal and dynamic regimes, with additional consideration given to the tectonic context. New and previously published data are evaluated together, and are presented from modern terrestrial and marine glacial sedimentary environments in order to identify a set of criteria that can be used to discriminate between different glacier thermal regimes and dynamic styles in the sedimentary record. Sedimentological data are presented from a total of 28 glaciers in 11 geographical areas that represent a wide range of contemporary thermal, dynamic and topographic regimes. In the context of “landsystems”, representatives from terrestrial environments include temperate glaciers in the European Alps, Patagonia, New Zealand, the Cordillera Blanca (Peru), cold glaciers in the Dry Valleys of Antarctica and the Antarctic Peninsula region, and polythermal valley glaciers in Svalbard, northern Sweden, the Yukon and the Khumbu Himal (Nepal). The glaciomarine environment is illustrated by data from cold and polythermal glacier margins on the East Antarctic continental shelf, and from a polythermal tidewater glacier in Svalbard, along with general observations from temperate glaciers in Alaska. These data show that temperate glacial systems, particularly in high-relief areas, are dominated by rockfall and avalanche processes, although sediments are largely reworked by glaciofluvial processes. Debris in polythermal glaciers is both thermally and topographically influenced. In areas of moderate relief, debris is mainly of basal glacial origin, and the resulting facies association is dominated by diamicton. In high-relief areas such as the Himalaya, the debris load in polythermal glaciers is dominated by rockfall and avalanche inputs, resulting in extensive accumulations of sandy boulder-gravel. Cold glaciers are dominated by basal debris-entrainment, but sediments are little modified from the source materials, which are typically sandy boulder-gravel from older till, and sand (from glaciofluvial, glaciolacustrine and aeolian sources). Similar facies associations, but with different facies geometry and thickness occur in equivalent glaciomarine settings. Application of these concepts can aid the interpretation of glacier thermal regime (and hence palaeoclimate) in Quaternary and ancient glacial systems.
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7.8% of 1105 clasts with a B-axis diameter of over 32 mm in lodgement tills from Skalafellsjokull, SE Iceland, had a stoss-and-lee form. Clasts deeply embedded in the tills were more likely to have such a form than those resting lightly on the surface. It is suggested that deeply embedded boulders acquire their rounded stoss-and-lee form by abrasion and fracture by over-riding debris-laden ice. This occurs after they have become firmly lodged by ploughing into the subglacial till bed and before they become buried by lodgement of debris around them. The long-axis orientation of deeply embedded boulders is a good indicator of former ice-flow directions. -from Author
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AzmraAci: The mathematical technique of R-mode factor analysis was applied to the long, intermediate and short axes of one synthetic random data set and three sets of natural pebbles to extract the three fundamental factors related to these parameters. One factor corresponds to size, which is best described by the mean of the axes. Two further factors correspond to shape: sphericity and disc-rodness. These factors are revealed whether synthetic data or natural pebble samples are analyzed. Extending the factor analysis to include shape indices revealed which indices are equivalent, which are most useful, and which should be discarded. Sphericity is best described with the Corey shape index, S/(IL) v', and disc-rodness is best described with the disc-rod index, (L -I)/(L -S). Accordingly, the most effective shape diagram is a triangular plot of these two shape indices; the three end-members of shape are spheres, discs and rods. Shape is best investigated using this shape diagram; a 2-D technique such as contouring point density on this diagram should be used to determine the mean and standard deviation of shape.
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The Younger Dryas (c.11-10 ka BP) moraine-mound complex ('hummocky moraine') in the historically important site of Cwm Idwal. North Wales, has previously been interpreted using periglacial, subglacial, ice-marginal and englacial models. In this paper the morphology and sedimentology of these landforms is described and the competing hypotheses tested against this evidence. It is demonstrated that an englacial thrusting model, developed for polythermal glaciers in Svalbard, best fits the available evidence. Thrusting probably resulted from longitudinal compression against a reverse bedrock slope, although a frozen snout, downglacier of sliding ice, may also have been a trigger. It is suggested that the role of ice-deformation, especially thrusting, in landform development has been underestimated, and that the englacial thrusting model may find application in the interpretation of other sites in the palaeo-landform record.
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Analysis of the shape of sedimentary particles can provide information about their transport history and aid facies differentiation and the characterization of depositional environments. Triangular (Sneed and Folk) diagrams, employing ratios of the three orthogonal particle axes, have been advocated as the most appropriate method for unbiased presentation of primary particle shape data. A spreadsheet method for the production of these diagrams is described. Clast data-sets from a range of environments are presented using this method. An alternative use of the spreadsheet for the presentation of sedimentary fabric shape is suggested. Copyright # 2000 John Wiley & Sons, Ltd.
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The changing geometry and thermal structure of Scott Turnerbreen, a 3.3 km2 glacier located at 78° N in the Svalbard archipelago, is documented. A net mass balance of −0.58 m a−1 w.e. is determined for the period 1936-93, by comparing a recent topographic survey with earlier maps. The thermal regime was investigated with multi-frequency radar and borehole thermistors. Basal temperatures of −4.1° and −3.3°C were measured, and observed temperature gradients indicate that the entire bed is frozen. This interpretation is confirmed by continuous radar profiling, which demonstrates the absence of high-frequency scattering from temperate ice. However, with the reconstructed 1936 ice-thickness distribution, at least 2 km of the length of the glacier bed would be at the pressure-melting temperature. The 20th century mass-balance history of Scott Turnerbreen is likely to have been influenced by a surge occurring around 1930, which meant that the glacier was already in a state of disequilibrium before the abrupt climate perturbation marking the termination of the Little Ice Age. A significant loss of mass has been accompanied by a transition from inferred polythermal to entirely non-temperate thermal conditions. Current driving stress and velocity are very low, and the glacier has almost certainly fallen out of the surge cycle. Within 60 years, there has therefore been a wholesale transformation in the geometry, thermal structure and dynamics of Scott Turnerbreen.
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The debris-covered ice-margins of three largely cold-based glaciers in central Spitsbergen were investigated to reconstruct their formation and degradation. Clast shapes indicate dominant englacial and supraglacial transport with a smaller subglacial component. Emplacement of material is inferred to have been through meltout along flowlines due to the relatively uniform and continuous debris cover along the glacier margins; no evidence of thrusting has been found. Degradation of all three belts is rapid and involves debris flows at unstable places—e.g., the margins of meltwater channels. Resultant exposure of underlying ice initiates or accelerates melting, thereby leading to further debris flows. Hence, once degradation starts, a self-reinforcing cycle that removes material from the glacier commences. Landform preservation potential on millennial time scales in a high-arctic, continuous permafrost environment is thus limited. This work has implications for the interpretation of Pleistocene landform associations that use modern analogues from Svalbard.
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Two small high-Arctic glaciers (Longyearbreen and Larsbreen) on Svalbard (78°N 15°E) were studied with respect to glaciological and hydrological characteristics. Fieldwork during the melting season of 1993 and 1994 was coupled with digital map analysis based on high-resolution digital elevation models (DEM) to reveal the dynamics and temperature regime of small glaciers in a high-Arctic environment, and its relationship to the material transport and sedimentation of these glaciers. The study showed Longyearbreen and Larsbreen to be low activity glaciers, cold-based with temperate patches, and thus having a low potential of basal erosion. The transport of ions and suspended solids in the glacial meltwater implies storage of material in and around the glacier which comes into contact with the meltwater. The study suggests that small Arctic glaciers couple the slope system with the fluvial system and therefore build a highly effective denudation system. Small polythermal glaciers are therefore important in understanding Pleistocene and Holocene landform development in cold regions.
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The relationship between supraglacial lateral moraines and lateral dump moraines at Arolla. Switzerland, is discussed. A detailed study of the lateral moraines of glacier de Tsidjiore Nouve reveals their complex form (as superimposed and nested ridges) and the current mode of development (possibly related to the passage of a kinematic wave). Sedimentological analysis indicates that much of the constituent debris is of supraglacial origin; it is transported either directly from the base of slopes flanking the Pigne d’Arolla ice-fall or via englacial septa comprising marginal sediment incorporated in the accumulation zone. A calculation of the volume of debris in the lateral moraines suggests that glacier de Tsidjiore Nouve has recently been more active in transporting and depositing supraglacial debris than in glacial erosion sensu stricto.
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7.8% of 1 105 clasts with a B-axis diameter of >32 mm in lodgement tills from Skálafellsjökull, south-east Iceland, had a stoss-and-lee form. Clasts deeply embedded in the tills were more likely to have such a form than those resting lightly on the surface. Deeply embedded basalt and andesite clasts were also more rounded than lightly embedded clasts of similar lithology, and more striated and more likely to have a stoss-and-lee form than deeply embedded gabbro and granophyre clasts. Lightly embedded basalt and andesite clasts were more striated than lightly embedded gabbro and granophyre clasts. Within each lithological class, larger clasts were more likely to have a stoss-and-lee form. It is suggested that deeply embedded boulders acquire their rounded stoss-and-lee form by abrasion and fracture by over-riding debris-laden ice. This occurs after they have become firmly lodged by ploughing into the subglacial till bed, and before they become buried by lodgement of debris around them. The degree of modification depends in part upon clast size and lithology. The long-axis orientation of deeply embedded boulders is a good indicator of former ice-flow directions.
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The Aoraki 1:250 000 geological map covers 24 000 km²of South Westland and central parts of the Canterbury region in the South Island of New Zealand. It encompasses the highest part of the Southern Alps, including 3754 m-high Aoraki/Mt Cook. The map area is crossed by the Alpine Fault - a major strike-slip fault that marks the boundary between the Australian and Pacific tectonic plates. Neogene movement along the plate boundary has brought together two different pre-Cretaceous geological provinces. Northwest of the Alpine Fault, Paleozoic metasedimentary and plutonic basement rocks are fragments of the Gondwanaland supercontinent. Southeast of the Alpine Fault, the Torlesse composite terrane is a thick, deformed package of Carboniferous-Jurassic sedimentary and metasedimentary basement rocks that were accreted to the Gondwanaland margin. The break-up of Gondwanaland began in the Early Cretaceous with associated igneous activity, extension and subsidence. Progressive regional submergence in the eastern part of the map area through the Late Cretaceous and Paleogene was accompanied by deposition of a terrestrial to marine transgressive sequence of conglomerates, sandstones and mudstones. The extent of land reached a minimum in the middle Oligocene, with widespread deposition of calcareous sediments in the surrounding seas. Development of the Australian-Pacific plate boundary started in the Early Miocene. Associated tectonic deformation caused subsidence west of the Alpine Fault, with deposition of marine sediments. Meanwhile, to the east, there was progressive emergence of the land and the formation of ranges and basins, with concomitant erosion and deposition. Uplift by folding and faulting continues to the present day throughout much of the central part of the map area, while to the east, subsidence occurs beneath parts of the Canterbury Plains and offshore. Glacial-interglacial climatic fluctuations in the late Neogene resulted in the widespread deposition of unconsolidated Quaternary sediments. Metallic mineral occurrences are mostly restricted to South Westland, where hard-rock and alluvial gold deposits and mineral-rich beach sands have been worked. Pounamu/greenstone is a locally important non-metallic mineral in South Westland. Coal, clay and sand have been extracted from the Cretaceous-Cenozoic sedimentary sequence of Canterbury, and there is potential for hydrocarbons to be discovered in this sequence beneath the Canterbury Plains or offshore. There are vast resources of limestone and aggregate in Canterbury. Shallow groundwater resources are substantial and are widely utilised in the low-rainfall areas east of the Southern Alps. Deeper groundwater resources are not well known but may be needed for future urban and rural development. The Aoraki map area is vulnerable to significant geological hazards, particularly earthquakes associated with the Alpine Fault and other active faults, with potential for strong ground shaking, landsliding, liquefaction and ground rupture. Slope instability, including rock avalanches, rockfalls and debris flows, is a major hazard in hill and mountain terrain. Erosion, flooding and sedimentation hazards exist near watercourses. Low-lying areas along the coast and lake shores are potentially at risk from tsunamis.
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Recent theoretical investigations suggest that the rate of river incision into bedrock depends nonlinearly on sediment supply, challenging the common assumption that incision rate is simply proportional to stream power. Our measurements from laboratory abrasion mills support the hypothesis that sediment promotes erosion at low supply rates by providing tools for abrasion, but inhibits erosion at high supply rates by burying underlying bedrock beneath transient deposits. Maximum erosion rates occur at a critical level of coarse-grained sediment supply where the bedrock is only partially exposed. Fine-grained sediments provide poor abrasive tools for lowering bedrock river beds because they tend to travel in suspension. Experiments also reveal that rock resistance to fluvial erosion scales with the square of rock tensile strength. Our results suggest that spatial and temporal variations in the extent of bedrock exposure provide incising rivers with a previously unrecognized degree of freedom in adjusting to changes in rock uplift rate and climate. Furthermore, we conclude that the grain size distribution of sediment supplied by hill-slopes to the channel network is a fundamental control on bedrock channel gradients and topographic relief.
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A talus slope with a predominantly rectilinear profile extending between 4260 and 4450 m was studied in the North Andean Paramo de Piedras Blancas, in Venezuela. The talus presented a well developed longitudinal sorting of debris, the mean size of which increased downslope; the particles were also laterally sorted into large- stone stripes, gravelly sand tongues, and areas with fragments of an intermediate size. The debris belonged to two lithologies, which influenced particle shape and particle size. Analysis by the dispersion angle technique revealed that particle orientation was significantly correlated with talus texture and mean particle size, with a high percentage of fragments showing a strong downslope orientation in gravelly sand tongues, but no preferred alignment in stone stripes. -from Author
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Within-valley moraine asymmetry and clast from trends are assessed for the Jardalen cirque complex, western Norway. Various statistical analyses of the data indicate that moraine asymmetry is linked to both basin asymmetry (specifically the free face area feeding unequal quantities of frost shattered debris to the glacier surface) and the reworking of pre-existing regolith or sediments on lower valley slopes and valley floors. This reworking is also responsible for the larger volumes and asymmetry of latero-frontal moraines. The asymmetry of latero-frontal moraines is strongly correlated with basin asymmetry at the sub-basin scale but not at the whole basin scale, indicating that the volume of reworked regolith and pre-existing sediments may be the most significant source of debris once glaciers expand beyond their cirque basins. The RA (clast roundness) and C40 (clast shape) indices reveal some inheritance of clast forms which are unrelated to the most recent episode of glacial activity, supporting the regolith reworking hypothesis. The variability in sediment reworking is manifest in a range of clast form gradients form moraines from the different cirque sub-basins but strong clast form gradients are used in conjunction with moraine asymmetry to suggest that moraine debris includes proportionately more actively (subglacially) transported clasts in a down-glacier direction and proportionately more pre-existing regolith and sediment due to reworking by transverse ice flow in the former glacier snout.
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Clast shape data from a range of different glacial environments at several high-arctic valley glaciers in Svalbard are presented. These data add to the growing body of reference information about clast shape in modern glacial environments and is used to explore the role of lithology in clast morphogenesis and to evaluate the different methodological approaches to the analysis of clast shape data. The following conclusions are drawn: (1) it is possible to distinguish clasts transported subglacially from those moved supraglacially; (2) it is not possible to differentiate among different types of subglacial sediment or to distinguish them collectively from glaciofluvial samples; (3) lithology has some influence on clast shape, although not as much as previously suggested; and (4) covariant plots of the RA (percentage of angular and very angular clasts) versus C 40 (percentage of clasts with c to a axial ratio ≤0.4) index give superior data visualization and discriminate more effectively among different glacial sediments than sphericity and roundness plots.
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Analysis of the shape of sedimentary particles can provide information about their transport history and aid facies differentiation and the characterization of depositional environments. Triangular (Sneed and Folk) diagrams, employing ratios of the three orthogonal particle axes, have been advocated as the most appropriate method for unbiased presentation of primary particle shape data. A spreadsheet method for the production of these diagrams is described. Clast data-sets from a range of environments are presented using this method. An alternative use of the spreadsheet for the presentation of sedimentary fabric shape is suggested.
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The nature and origin of the outermost 'Little Ice Age' moraine in front of a NE-flowing glacier (Storbreen, Jotunheimen) are investigated by analysing the variability along the length of the moraine of a range of characteristics (cross-profile form, surface composition, clast form and quartz sand grain characteristics). Concentrated application of a range of techniques in relation to a single moraine has enabled inferences to be made about glacial transport paths of debris in the moraine and processes of moraine-building. Moraine form is consistent within lateral and latero-terminal sections. Origin is attributed to a combination of some pushing of valley-side debris and dumping of glacially-transported material, in which the ratio of modified subglacial to unmodified supraglacial/englacial debris increases downglacier. A larger southern than northern side of the outer moraine is attributed to a difference in the quantity of debris being supplied from headwall areas, which are steep and heavily-eroded on the southern side but low-angled and vegetated on the northern side.