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Clast shape analysis and clast transport paths in glacial environments: A critical review of methods and the role of lithology
... (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) (1993,1994), and refined subsequently (Hambrey and Glasser, 2012;Lukas et al., 2013), to establish provenance and transport of glacial material. We characterised clasts of multiple lithologies collected from moraine exposures on the basis of their shape and morphology. ...
... These forms are common within cold-based glacial regimes (e.g., Tonkin et al., 2017) and those receiving abundant material via marginal rockfalls and talus (Benn and Ballantyne, 1993). In contrast, Rounded (R) and Well Rounded (WR) forms typically signify extensive modification by water and the subglacial entrainment of pre-existing fluvial material (Lukas et al., 2013). The ratio of Very Angular to Angular clasts in a sample is expressed as the RA value, while the RWR value corresponds to the ratio of Rounded to Well Rounded clasts. ...
... That RA ratios for the lateral moraines (Exposures I-IIa,b) are slightly elevated relative to the RWR ratios is unsurprising given the higher degree of entrainment and supraglacial transport of hillslope material along the glacier margins (Kirkbride, 2002). Sneed and Folk (1958) clast shapes after Ballantyne (1993, 1994) and Lukas et al. (2013) According to Lukas et al. (2013), mixed lithologies can impact the apparent validity of till C 40 analyses since different rock types might be more susceptible to modification. Recognising that the clast shape and roundness samples here are mixed to varying degrees, this consideration is relevant to our analysis. ...
Within the North Atlantic region, climatic perturbations such as Heinrich Stadial 1 (HS1) and the Younger Dryas stadial (YD) have traditionally been viewed as anomalous periods of extreme cooling linked to abrupt changes in the poleward oceanic transport of heat. While there is considerable geologic data to support strong cooling during stadial winters, recent work in mid- and high-latitude regions fringing the North Atlantic suggests that this thermal signal did not extend to stadial summers, contrary to previously inferred palaeoecological and ice core proxies. Some directly dated glacial records from Britain, Ireland, and Scandinavia, for instance, document the large-scale retreat of terrestrial ice masses during both HS1 and the YD, coincident with meltwater pulses from the European continent and consequent weakening of Atlantic meridional overturning circulation. Similar patterns of stadial deglaciation have been reported from Greenland and north-east North America. Together, these datasets support the emerging model of stadials as periods of anomalous seasonality imposed on the strongly maritime North Atlantic climate. In this study, we present a geologic record of ice sheet behaviour from the Maumturk Mountains in western Ireland during the last glacial termination, constrained with cosmogenic 10Be surface-exposure dating. Coupled with glacio-geomorphologic and sedimentologic characterisation of moraine landforms, our record describes a temperate ice mass undergoing sustained active retreat during the first half of HS1, synchronous with increased European meltwater discharge into the North Atlantic.
... In analyses of glacially transported clasts the majority fall in the sub-angular and sub-rounded categories. Glaciofluvial sands and gravels contain more rounded and sub-rounded stones and fewer sub-angular ones (Lukas et al., 2013;Evans, 2018;Benn and Lukas, 2021). Fluvially transported clasts contain more rounded clasts, and clasts on wave-washed beaches tend to be well rounded. ...
... On the edge of a facet near the blunt end of the boulder, there are two pronounced concave fracture scars. Overall, the surface characteristics of this boulder suggest that it is a discrete erratic that has been transported for much if not all of the time in a subglacial position (Benn and Ballantyne, 1994;Lukas et al., 2013;Benn and Lukas, 2021). ...
... On the matter of clast morphology in the debitage, Ixer and Bevins (2010, 2011a, b, 2013 have consistently failed to differentiate between sharp-edged fragments, cobbles and larger clasts and have concentrated on material that might be related to existing or destroyed bluestone monoliths. So-called hammer stones, mauls and packing stones have not received adequate attention, although some of them are made of igneous rock and look like glacial clasts (Cleal et al., 1995). ...
There has been considerable dispute over the mode of transport of the Stonehenge bluestones from their multiple sources in West Wales. For a century most archaeologists have accepted that the stones were transported by humans, but a number of earth scientists have taken the view that they were entrained and transported to Salisbury Plain by glacier ice. There is remarkably little evidence in support of either theory, and for this reason any new description of a possible glacial clast found at or near the stone monument is of potentially great importance. A small bullet-shaped boulder of welded tuff was found in a Stonehenge excavation in 1924, and apart from a brief examination by geologists from the Institute of Geological Sciences (IGS) around 1970, it has been stored out of sight and out of mind. Its geological source is uncertain. Following a detailed examination of its shape and surface characteristics it is now proposed that it has been subjected to glacial transport and that it has had a long and complex history. It is also proposed that the abundant weathered and abraded bluestone boulders and slabs at Stonehenge were also glacially transported, along with many of the cobbles and stone fragments found in the sediments of the local landscape. The elaborate archaeological narrative of bluestone quarrying and human transport to Stonehenge must now be re-examined.
... The ratio between the three axes was determined and plotted on a ternary diagram (following Sneed & Folk 1958) (Table 1, Fig. 3B). The shape and roundness of clasts have been used before in the reconstruction of glacial pathways (Benn & Ballantyne 1994;Benn 2013;Lukas et al. 2013) and in our study we integrated parts of this methodology to look for correlations between clast shape and luminescence profiles; a summary of the size and shape of the samples is given in Table 1. ...
... Boulton 1970;Benn & Ballantyne 1994;Alley et al. 1997). The mechanisms are usually studied through the use of modern analogues (Benn & Ballantyne 1993;Lukas et al. 2013). Unfortunately, there are few modern analogues for sediments eroded and transported by continental ice sheets. ...
... To more closely identify where the exposure took place other indicators need to be employed. There are several studies using clast shape analysis to reconstruct pathways through the ice (Benn & Ballantyne 1993, 1994Bennett et al. 1997;Lukas et al. 2013). Combining the new information about exposure to daylight with clast shape analysis may provide a more informed view of the transport processes taking place in a glacier or ice sheet. ...
The dating of moraine deposits can present challenges to standard geochronological methods; terrestrial cosmogenic nuclide (TCN), sediment luminescence and radiocarbon dating may suffer from problems of incomplete resetting (by inheritance, intermittent cover/exposure, transport under unfavourable conditions) and/or a lack of suitable (organic) material. Rock surface luminescence burial dating (RSLBD) offers an alternative approach with considerable potential in dating moraines. In RSLBD, large cobbles/boulders are targeted, rather than smaller grains usually used in luminescence dating. The age limit of RSLBD is much higher than that of radiocarbon dating, and rocks are much more readily available than organic material. In contrast to TCN dating, the effect of exposure prior to deposition can be measured. In this study, we sampled a broad selection of primarily granitic boulders of various sizes and shapes (e.g. different degrees of roundness and sphericity) from the Vimmerby Moraine, a prominent and accessible feature in southern Sweden dated using TCN to 14.4±0.9 ka. Our study was designed to test whether morphological characteristics can be used to discriminate in favour of the most light-exposed boulders and minimize measurements of non-exposed boulders. As expected, not all RSLBD ages can be attributed to the same depositional event, but the majority of the resulting ages provide a mean age of 13.0±1.5 ka, consistent with the cosmogenic nuclide dating of the Vimmerby Moraine. Despite the apparently successful TCN study, the luminescence–depth profiles measured in the buried surfaces of the sampled clasts indicate that >50% of these moraine boulders were exposed to light (and cosmic radiation) before final deposition, implying some (presumably small) TCN inheritance; seven of the 16 boulders identified as light exposed were sufficiently bleached to be useful for RSLBD. These results and their implications in regard to transport and deposition of the sampled cobbles are critically discussed and evaluated.
... A lithofacies code was applied to summarise these observations more effectively (Evans and Benn, 2021). To better constrain the genetic origin of diamictic units found in the moraines, clast shape and roundness samples were collected from these sediments (Lukas et al., 2013;Benn and Lukas, 2021a, and references therein). The sampling was carried out according to standardised methods outlined in Benn and Lukas (2021a) and was constrained to a single lithology throughout. ...
... In concordance, no signs of squeezing of the till or deformation structures such as folded sediment units that relate to ice-marginal push were found in this diamict. A subglacial origin of LF1 is corroborated by the dominance of striated and facetted clasts that point to an active transport of these particles at the ice-bed interface (Boulton, 1978;Benn and Ballantyne, 1994;Lukas et al., 2013). The abundance of serpentinite clasts in this lithofacies provides further evidence for subglacial entrainment and transport, as serpentinite bedrock lenses are exclusively situated beneath Gornergletscher (Bearth, 1953). ...
... This also explains the absence of finer grain fractions within LF2, as these were washed out during the gradual melting of the ice margin (e.g., Lukas et al., 2005). Clasts within LF2 are largely angular meta-granites, providing further evidence for supraglacial entrainment and transport as metagranite largely crops out in the steep headwalls surrounding the glacier snout (Bearth, 1953;Boulton, 1978;Benn and Ballantyne, 1994;Lukas et al., 2013). ...
... Analyses of clast morphology (clast shape and roundness) are commonly used in glaciated environments to distinguish between different erosional, transportation and depositional clast histories (Benn & Ballantyne, 1993, 1994Glasser et al., 2009;Brook & Lukas, 2012). Clast morphology analysis (Lukas et al., 2013) was used in this study to confim the glacial origin of the mapped sediments. Moraine clasts commonly display a higher proportion of blade and elongate shapes and stronger rounding when compared to clasts of scree and gravitational mass movements sediments, but are much more angular compared to fluvial environments. ...
... The C 40 index (percentage of clasts with c/a axial ratio ≤ 0.4) was subsequently calculated for each sample site. The RA ratio (the percentage of angular and very angular clasts in any sample) and RWR ratio (the percentage of rounded to well-rounded clasts; Lukas et al., 2013) were calculated for each site. In order to distinguish the transportation and depositional clast histories co-variance plots using both RA-C 40 and RWR-C 40 were presented (Benn & Ballantyne, 1994;Lukas et al., 2013) and compared with clast morphology data from the surrounding Rodna Mountains, where metamorphic clast lithology dominates (Kłapyta et al., 2021a, Supplementary Data 2). ...
... The RA ratio (the percentage of angular and very angular clasts in any sample) and RWR ratio (the percentage of rounded to well-rounded clasts; Lukas et al., 2013) were calculated for each site. In order to distinguish the transportation and depositional clast histories co-variance plots using both RA-C 40 and RWR-C 40 were presented (Benn & Ballantyne, 1994;Lukas et al., 2013) and compared with clast morphology data from the surrounding Rodna Mountains, where metamorphic clast lithology dominates (Kłapyta et al., 2021a, Supplementary Data 2). ...
The Late Pleistocene Jupania palaeoglacier (area 0.85 km2, 1.7 km long) was reconstructed in the headwaters of the Ceremuşul Alb/Bilyj Cheremosh valley (Maramureş Mountains). The study area represents one of the most inaccessible natural areas in the Romanian part of the Eastern Carpathians where the legacy of the
Pleistocene glaciation has recently been discovered. Based on mapping of glacial landforms and deposits, we reconstruct glacier dimension and ice-surface geometry, as well as estimate equilibrium line altitude (ELA) during the maximal ice extent (MIE). Well-preserved terminal moraines mark the extent of glacier front
at ~1400 m a.s.l. Sedimentological analysis documents that the lateral moraines are sometimes overbuilt by 1-1.5 m thick colluvial deposits. The ELA for the Jupania palaeoglacier calculated with the Area-Altitude-Balance-Ratio (AABR) 1.6 was 1630 m. However, the gentle-sloping mountain-top could serve as an important
snow contribution area to glacier mass balance; therefore, the ELA could potentially exist even higher at 1676 m. The resulting climatic ELA (1630-1676 m) in the south-eastern part of the Maramureş Mountains fits well with the rising trend of ELA towards the southeast observed between Chornohora (ELA = 1516 m) and Rodna Mountains (ELA = 1697 m). The SE rising trend of the ELA corresponds well with the dominant palaeowind
direction suggested in the Carpathian region and supports the prevalence of zonal circulation pattern in Central Eastern Europe during the culmination of the last glaciation.
... 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. ...
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.
... 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). ...
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.
... 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. ...
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.
... 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. ...
... 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 . ...
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.
... 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. ...
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 characterized by striking sawtooth or hairpin planforms, which are locally superimposed, giving rise to a complex spatial pattern. We recognize 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. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd
... Specifically, this entailed sediment logging and descriptions using a lithofacies approach, augmented by clast shape analyses (cf. Lukas et al., 2013;Evans & Benn, 2021). Clast shape indices include clast roundness, quantified using the RA (percentage of A and VA clasts) and the average roundness (AvgR; cf. ...
... The degree of clast modification is then related to glacial debris transport pathways by employing the Type II RA-C 40 covariance plot (Lukas et al., 2013) for anisotropic (foliated) lithologies, similar to those of the crystalline schists of the Sc arişoara plateau. ...
Reconstructing the extent, style, timing and drivers of past mountain glaciation is crucial in both understanding past atmospheric circulation and predicting future climate change. Unlike in high‐elevation mountains situated in maritime and continental climates, less is known of past glaciation in mid‐altitude mountains, located in transitional climates, such as the Southern Carpathians of Romania. Despite these mountains harbouring a rich glacial geomorphology, this has never been systematically mapped according to well‐established morphological criteria, nor confidently related to former styles of glaciation. Therefore, filling this gap is important for not only accurately identifying glacial extents but also for establishing past glaciation styles and relating them to past ice dynamics and climate. Here, we devise the first glacial landsystem model for the Southern Carpathians, to enhance our understanding of the glaciation style and dynamics of past mountain glaciers in temperate‐continental climates. We present a geomorphological map, from which we infer the spatial and temporal evolution of glacial, periglacial and paraglacial landforms. We then assess the links between the mountain geomorphology and glaciation style and dynamics to construct a glacial landsystem model for debris‐charged plateau icefields and cirque glaciers in temperate‐continental mountain settings.
... 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. ...
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.
... 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. ...
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.
... 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). ...
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.
... The absence of finer-grained material may have been caused by meltwater winnowing (e.g., Winkler, 2020;Boston et al., 2023). Lithology may also have played a role since most Class 3 moraines are composed of granite, which has a high resistance to erosion (Lukas et al., 2013;Matmon et al., 2020). At Lough Ouler (Fig. 5e), Class 3 moraines are composed of shale and schists and, although they are still boulder-dominant, there is a larger volume of intra-boulder sedimentary material (matrix). ...
In Ireland, the Nahanagan Stadial (NS) was characterised by cirque glacier, plateau icefield and mountain ice cap expansion and is named after the cirque glacier type‐site of Lough Nahanagan in the Wicklow Mountains. This period is broadly equivalent to the Younger Dryas Stadial and Greenland Stadial‐1 (GS‐1: ~12.9–11.7 ka). Here, we provide the first evaluation of the full extent of NS glaciation in the Wicklow Mountains by combining solar radiation modelling, mapping of glacial geomorphology, ¹⁰ Be and ²⁶ Al cosmogenic surface exposure dating, 3D glacier reconstructions and analysis of snowblow and avalanching potential. We identify seven sites that hosted cirque glaciers at this time. Glacier extent was very restricted, with most glaciers only partially filling their cirques. Equilibrium line altitudes (ELAs) ranged from 470 ± 5 m a.s.l. (Lough Nahanagan) to 721 ± 5 m a.s.l. (Lough Cleevaun), with an average ELA of 599 m a.s.l. Higher snowblow and avalanching contributions at sites with lower ELAs demonstrate local topoclimatic influence on glacier growth and preservation alongside regional climate. The Wicklow Mountains provides a good example of marginal cirque glaciation during GS‐1 and the importance of local topography and microclimate for sustaining glaciers in some mountain areas of Britain and Ireland.
... For the diamicts of unit 1 (7.0-3.8 m), several characteristics indicate a glacial origin, namely the variable degree of rounding of gravel clasts, which points to different sediment transport pathways, and the mixed clast petrography indicating a large Alpine source area (e.g. Dreimanis & Schlüchter 1985;Kjaer 1999;Lukas et al. 2013). More specifically, the three gravel petrography samples show a similar lithological spectrum with ≥15% of crystalline pebbles. ...
The present‐day landscape of the northern Alpine foreland is marked by the cumulated impact of weathering during interglacial, and of erosion and deposition during glacial periods of the Quaternary. Direct traces of the earliest phases of ice advance, as well as thorough studies thereof, exist only sporadically. Here, a succession of diamictic deposits, which has been interpreted as the infill of an Early Pleistocene overdeepened basin, is investigated with a combined sedimentological‐geotechnical approach including analysis via μCT scans, and standard tests of the water uptake, consistency, and compaction properties. The diamicts are exposed along a 4.5‐m‐deep profile, and are subdivided into a yellowish‐brown lower unit with a variable, carbonaceous, silty to sandy matrix, and a reddish‐brown upper unit that is free from carbonate and appears largely homogeneous. Although the lower unit is rather loose and surficially bioturbated, it contains microstructures indicative of subglacial deformation, which are lacking in the compact and clay‐rich upper unit. The lower part is interpreted as a secondary glacial deposit (i.e. it has been affected by limited sorting in water) that was overridden and sheared by a glacier briefly after deposition, and recently bioturbated. The upper part is less sorted, more massive and compact, and thus likely of a primary glacial nature. It is further characterized by a strong pedogenetic overprint typical of prolonged warm periods. This suggests that it is separated from the overlying glacifluvial gravel, which has an equivalent petrographic composition, by a full interglacial at least. Thus, the combination of geotechnical testing and CT‐based micromorphology offers a new, practical and cost‐effective approach to the characterization of glacially derived sediments.
... The ridges possibly link to low, indistinct mounds at the headwall foot. The few sandstone and conglomerate boulders and cobbles found on the surface were subangular and subrounded, which would be more typical of glacial rather than slope action (e.g., Lukas et al., 2013). The coarse surface texture and surface weathering of the clasts meant that any striations would not have been preserved. ...
A glacial origin for cirque-like hollows cut into the western escarpment of the Usk valley near Abergavenny, South Wales has become widely accepted. Associated supposed extensive moraine ‘festoons’ have been depicted merging and contemporaneous with Last Glacial Maximum (LGM) deposits formed by ice occupying the adjacent Usk valley. We re-interpret these festoons as the product mainly of rock slope failures (RSFs) emanating from the hollows. A cirque glacier origin is preferred to account for a compact double-ridge feature in one of the hollows. The equilibrium-line altitude (ELA) of the reconstructed glacier (357 m) is > 60 m lower than all similarly small, presumed Younger Dryas Stadial (YDS; c., 12.9–11.7 ka) glaciers elsewhere in South Wales. To test whether this glacier nevertheless might date from the YDS, we apply three approaches to reconstruct annual palaeo-precipitation amounts at the ELA, two based on relationships between accumulation and ablation for modern glaciers and the third on a simple degree-day model (DDM) using likely climatic characteristics for this event. The DDM can be tailored to represent the recognised large-amplitude YDS annual temperature range rather than the much smaller one experienced by modern glaciers, making it our preferred approach. Although conditions along the Usk valley escarpment during the LGM would have been well suited to cirque glacier formation, the DDM approach, using the large-amplitude annual temperature ranges, suggests that a YDS age might also be possible. The results have implications for re-assessing the likely ages of some former small glaciers in South Wales.
... The clast analysis was done for units 1 and 8 of the outwash terrace. The longest 'a', intermediate 'b', and smallest 'c' axis were measured for ~50 randomly picked lithoclasts from a 1 × 1 m 2 sampling grid (Bennett et al., 1997;Hambrey et al., 2008;Lukas et al., 2013). Due to inaccessibility, the remaining six litho-units were not sampled, however field observation shows that texturally these units are identical having upward fining characteristics and similar clast size (pebble-cobble) and lithologies. ...
The geomorphological disposition of (para/peri) glacial landforms, elemental geochemistry, and optical chronology of the relict lake sediment in the Southern Zanskar ranges, northwest Himalaya are used to understand the relationship between glacial dynamics and the lake sedimentation during the mid-Holocene climate variability. Following the Last Glacial Maxima (LGM), pulsating deposition of outwash gravels until the early Holocene overwhelmed the Zanskar valley. The obstruction of Tsarap Chu (chu = river) by alluvial fans during the mid-Holocene led to the development of Padum Lake. In the present study, cirque glacier moraines representing three minor glacial advances were mapped along with sedimentological details and dated using Optically Stimulated Luminescence (OSL) dating technique. The oldest cirque glacier advance - Padum Cirque moraine-3 (PDCm-3) is dated to 11.4 ± 0.9 ka. The succeeding advance (PDCm-2) is dated to 5.3 ± 0.6 and 4.8 ± 0.8 ka whereas, the younger cirque glacier advance (PDCm-1) remains undated. The mid to late Holocene climate variability inferred using major and trace element geochemistry of the relict Padum lake sediments supported by optical chronology indicates six centennial to millennial-scale climatic phases. The prominent warmer phases are represented by decreased mineralogical fine grain flux (low K/Ti, Fe/Si, and Al/Si) with a corresponding increased coarse grain flux (higher Ti/Al and Sr/Al ratios). These phases are dated between 5.9 and 5.5 ka (phase-I), 3.8 and 3.4 ka (phase-IV), and 2.8 and 2.5 ka (phase-VI). The increased mineralogical finer fraction (higher K/Ti, Fe/Si, and Al/Si) between 5.5 and 5.1 ka (phase-II) and 3.4 and 2.8 ka (phase-V) indicate reduced meltwater flux during cooler phases. The intervening phase-III (5.1–3.8 ka) is characterized by increased mineralogical coarse grain flux (decreasing K/Ti, Fe/Si, Al/Si) suggesting gradual warming. The oscillatory climate at millennial scale was further used to understand glacier dynamics. The PDCm-2 advance in the lake record corresponds to the first major cooling (5.5 and 5.1 ka; phase-II) and continued until ~3.8 ka. Using geochemical data of lake record, a major recession is inferred after 3.8 ka that persisted until around 3.4 ka (phase-IV). Similarly, the undated younger cirque glacier advance (PDCm-1) is assigned to the second cooling event (3.4 and 2.8 ka; phase-V). Thereafter, the cirque glaciers receded, most likely under increasing dryness and fluctuating climate (2.8–2.5 ka, phase-VI). After ~2.6 ka, the development of ice-wedge pseudomorphs indicates the onset of permafrost conditions that degraded after ~2.5 ka implying an increase in air temperature. The lake sedimentation terminates with the deposition of multiple younger alluvial fan facies. The climate variability shows a close correspondence with regional climate records suggesting that marginal glacier advancements were triggered by enhanced moisture via atmospheric rivers and cooler winter temperatures. The study highlights the potential of relict lake sediment in association with para- and peri-glacial landforms to reconstruct the pattern of minor glacier responses to climate variability during the Holocene.
... The clast shape is presented as the C40 index (percentage of clasts with c: a axis ratio ≤0.4) (Benn & Ballantyne, 1994). According to Lukas et al. (2013), all samples should consist of the same lithology. Due to the small bulk samples and high similarities between different lithologies, several lithologies were examined and included in the same analysis. ...
Crevasse‐squeeze ridges (CSRs) are landforms that have been unequivocally linked to surge‐type glaciers. The formation of CSRs has been discussed since they were first defined in the mid‐1980s. Here, we describe geometric CSR networks from the terrestrial glacier forefields of two glaciers in Trygghamna, Western Svalbard. No glacier surges have been observed in Trygghamna; however, the presence of the CSRs signifies past surge activity. Detailed geomorphological maps were constructed, and the spatial context of these landforms described. Cross‐sections of several CSRs highlight ridge architecture, structure and relationships to surrounding landforms and sediments. Most CSRs are symmetrical in cross‐profile, orientated perpendicular or oblique to the ice‐flow direction. Like previous investigations, we observe these ridge networks on top of till and flutes. Additionally, we, for the first time, document CSRs deposited directly on non‐glaciogenic subsurfaces, namely, beach gravels and bedrock. Our findings confirm previous CSR formation theories; basal sediments are squeezed into bottom‐up crevasses during surges, which are subsequently transported englacially until surge termination and are finally released by melt out from stagnant ice. Consequently, a network of CSRs is the product of a significant reorganisation and down‐glacier transport of basal sediment, exemplifying how single surges are agents of glacial sediment redistribution. These formation processes are illustrated in a refined schematic model. The results further contemporary understanding of CSRs in terrestrial surge‐type glacier settings and may also apply to landforms and sediments in certain marine settings and palaeoglacial environments.
... In their discussion of megalith extraction at Carn Goedog, Parker Pearson et al (2019) claim that there was megalith quarrying "on an industrial scale" of large spotted dolerite natural pillars, and they list Stonehenge bluestones 33, 37, 49, 65 and 67 as having originated at Carn Goedog. Even if that claim is justiYied, those are not sharp-edged tall pillars or columns which have been quarried; they are small unremarkable stones, faceted and with heavily abraded edges, and apparently deeply weathered, best described as typical glacial erratics (Lukas et al, 2013). Out of 43 known bluestones at Stonehenge, there are only seven "ideal" elongated pillars --six of them in the remnants of the bluestone horseshoe, bearing signs of shaping or dressing. ...
This article challenges the claims made by Parker Pearson et al (2022a) that there is a Neolithic bluestone quarry at Craig Rhos-y-felin and that rock wedges used in the quarrying process have been discovered. The current authors suggest that the evidence for monolith quarrying at Rhos-y-felin and Carn Goedog does not withstand scrutiny, and field research at the Rhos-y-felin site suggests a long history of crag disintegration and rockfall debris accumulation, with Late Devensian glacial and fluvioglacial deposits overlain by Holocene colluvium and other slope materials. The engineering features listed by the archaeologists are disputed, and it is suggested that the radiocarbon evidence from the site also falsifies the quarrying hypothesis. The present authors do, however, accept that there is evidence of a long history of intermittent occupation by hunting and gathering parties, and it is proposed that they might have used Rhos-y-felin as a source for sharp-edged disposable cutting and scraping tools. The use of rhyolite rock wedges in Neolithic quarrying makes no sense from a rock mechanics standpoint, and after examining the fractures in which the wedges were found, it is pointed out that not one of them would have been of use in the extraction of a viable stone monolith or orthostat. Finally, the current authors point out that the "Stonehenge narrative" involving quarries at Rhos-y-felin and Carn Goedog, a "lost stone circle" at Waun Mawn, and stone transport to Salisbury Plain is seriously damaged by recent research publications and should be abandoned. It is a matter of regret that Parker Pearson et al have ignored two detailed Rhos-y-felin papers written by the present authors and published in 2015.
... The clast form attributes such as shape (relative dimensions of the three orthogonal axes of a clast) and roundness (degree of curvature of clast edges) were determined in the field. For shape, the longest 'a', intermediate 'b', and smallest 'c' axis were measured for approximately 50 randomly picked lithoclasts from a 1 × 1 m 2 sampling grid (Bennett et al., 1997;Hambrey et al., 2008;Lukas et al., 2013). The three axes define three basic shapesblocks or spheres with high b/a and c/a axial ratios; slabs or discs with b/a high and c/a low; and elongated clasts or rods with b/a low and c/a. ...
The present study focuses on the reconstruction of the pattern of late Quaternary climate variability through sediment-landform assemblages in the monsoon-dominated Dhauli Ganga valley. The South Tibet Detachment System (STDS) is a major litho-tectonic boundary that divides the Dhauli Ganga valley into two broad geomorphic entities. Towards the north of STDS, the valley is wide and “U” shaped, and the rivers have a braid-meandering channel, implying that the valley was carved by glacial sculpturing in the past. Whereas in the south, deep gorges indicate the dominance of fluvial processes. Based on the stratigraphic position and optical chronologies, the lithified moraines were assigned to Marine Isotopic Stage-3 (MIS-3) they were followed by a major deglaciation event represented by moderately lithified outwash gravels. Following this, a second glacier advance of lesser magnitude is dated 21.3 ± 2.2 ka, corresponding to the Last Glacial Maximum (LGM). A gradual recession of the LGM moraines led to the formation of a proglacial lake which probably persisted until around the onset of a pulsating deglaciation stage represented by outwash gravels dated between 13.4 ± 1.6 and 9.4 ± 0.8 ka. This was also the period when the valleys were overwhelmed by a high sediment water ratio, as indicated by temporary impoundments dated between 15.0 ± 1 ka and 10.0 ± 1 ka. Alluvial fan and debris flow sedimentation overwhelm the valley after around 9 ka and continues till the present.
... Sources for these ice margin positions are listed in Table 1. and bedding plane dip and strike, as described in Evans & Benn (2021) (Figure 2). Samples for clast shape and roundness analysis were also collected at each section and compared with supraglacial and fluvial control samples, using the approach described by Lukas et al. (2013). Each sample contained 50 mica schist clasts, and the data were plotted and analysed in Triplot (Graham & Midgley, 2000). ...
Topography exerts a strong control on how glaciers respond to changes in climate. Increased understanding of this role is important for both refining model predictions of future rates of glacier recession and for reconstructing climatic change from the glacial geological record. In this paper, we examine the geomorphological and sedimentological evidence in the foreland of Fingerbreen, a temperate outlet of the plateau icefield Østre Svartisen. The aim is to investigate the relationship between processes of landform generation and the changing influence of topography as recession progressed. The Fingerbreen foreland is dominated by bouldery Little Ice Age moraines and extensive areas of striated bedrock. A heavily fluted zone occurs in the central part of the foreland that is cross‐cut by annual transverse and sawtooth moraines. Systematic investigations of the structural architecture of moraines at various locations in the foreland provide evidence for a range of moraine‐forming processes, which can be linked to the topographic setting (e.g. deposition on a reverse bedrock slope) and drainage conditions. This includes push and bulldozing of proglacial sediments and squeezing of sub‐glacial sediments and submarginal freeze‐on of sediment slabs. We also identify variations in moraine spacing as a result of topography. This research demonstrates the importance of topography when interpreting moraine records in the context of climate and glacier dynamics.
... The extent of the most recent glacial advance was recognised using the distribution of mapped outer moraine ridges (lateral and frontal moraines) and glacial till covers with large (greater than 1 m) boulders and hummocky relief. The identification of glacial landforms in selected massifs (Polonyna Rivna, Borzhava, Svydovets, Chornohora, Rodna and Cȃlimani Mountains) was additionally based on modern sedimentological techniques (Lukas et al., 2013) which show that in the Eastern Carpathians moraine clasts of various lithologies (sandstone, metamorphic and volcanic) display strong rounding in contrast to nonglacial sediments which feature a dominance of angular clasts (Kłapyta et al., 2021a(Kłapyta et al., , b, 2022a. ...
The Eastern Carpathians are the northeasternmost sector of the European Alpine Mountain system and comprise 14 formerly glaciated massifs that stretch over 300 km into the territories of Ukraine and Romania. In this study we provide a regional overview on Late Pleistocene glaciation in the Eastern Carpathians integrating recently published and new geomorphological data which include mapped glacial landforms and glacier reconstruction of the maximal ice extent (MIE) which is assigned to the global Last Glacial Maximum (LGM). Thus we obtain a complete inventory of glaciation in the Eastern Carpathians, including the documentation of 214 glacial cirques and 147 small mountain glaciers with a total area of 153.2 km2. The estimated LGM equilibrium line altitude (ELA) shows a strong rise of 2.4 m/km from the northwest (1270 m asl) to the southeast (1870 m asl), as well as a consistent eastward rise on several W-E transects (2–3.4 m/km). Similar patterns are shown by the palaeoglaciation level and the cirque floor altitude trend, which mimic the pattern of modern temperature-precipitation ELA (tpELA) in the region. Reconstructed palaeoglacial trends reflect dominant W-NW precipitation-wind regime and an enhanced zonal North Atlantic circulation pattern in the far interior of Europe in full glacial climate. This is consistent with both regional palaeoclimatic simulations and wind regime proxies which indicate that the pattern of LGM circulation was similar to the present circulation, although the magnitude may have increased during glacial conditions. Additionally, based on the wide array of glacial landscapes inventoried in this study, ranging from traces of small niche/cirques to about 7 km long valley glaciers, we propose a quantitative approach to define the distinct stages of glacial landscape development based on the relationship between the Pleistocene ELA and mountain hypsometry
... The clast form attributes such as shape (relative dimensions of the three orthogonal axes of a clast) and roundness (degree of curvature of clast edges) were determined in the field. For shape, the longest 'a', intermediate 'b', and smallest 'c' axis were measured for approximately 50 randomly picked lithoclasts from a 1 × 1 m 2 sampling grid (Bennett et al., 1997;Hambrey et al., 2008;Lukas et al., 2013). The three axes define three basic shapesblocks or spheres with high b/a and c/a axial ratios; slabs or discs with b/a high and c/a low; and elongated clasts or rods with b/a low and c/a. ...
... The extent of the most recent glacial advance was recognised using the distribution of mapped outer moraine ridges (lateral and frontal moraines) and glacial till covers with large (greater than 1 m) boulders and hummocky relief. The identification of glacial landforms in selected massifs (Polonyna Rivna, Borzhava, Svydovets, Chornohora, Rodna and Cȃlimani Mountains) was additionally based on modern sedimentological techniques (Lukas et al., 2013) which show that in the Eastern Carpathians moraine clasts of various lithologies (sandstone, metamorphic and volcanic) display strong rounding in contrast to nonglacial sediments which feature a dominance of angular clasts (Kłapyta et al., 2021a(Kłapyta et al., , b, 2022a. ...
... 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. ...
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 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. ...
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.
... 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). ...
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.
... 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. ...
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.
... 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. ...
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 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). ...
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.
... 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. ...
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. ...
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.
... (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.) percentage of clasts with a C:A axis ratio of <0.4; Benn and Ballantyne, 1993); b) clast roundness (Powers, 1953), 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 (AvR), based upon a numerical classification of Powers roundness as VA ¼ 0 to WR ¼ 5 (cf. Spedding and Evans, 2002;Evans, 2010). ...
The Smoking Hills area in the western Canadian Arctic was purported to contain a regionally rare Quaternary stratigraphic section with multiple, local ice cap-derived tills and a long chronology constrained by palaeomagnetic markers. We present a fundamental revision of previous glacial and magnetostratigraphic interpretations based on detailed sedimentological and structural analyses of the main stratigraphic section and many new exposures, cosmogenic nuclide isochron burial dating, and a systematic reconstruction of the geomorphology and landscape evolution using a glacial landsystem approach. We demonstrate that the Smoking Hills area was fully glaciated during the last (Wisconsinan) glaciation. Previously reported tills ascribed to multiple glaciations represent instead a complex facies sequence of glacitectonic thrust stacking of Laurentide Ice Sheet (LIS) sourced diamictons, glacilacustrine and glacifluvial deposits, together with previously unidentified, poorly-consolidated Cretaceous bedrock rafts and deformed intraclasts. Much of this sedimentation and glacitectonic activity dates to the last (Wisconsinan) glaciation and can be reconciled with a polythermal ice sheet marginal landsystem signature, wherein ice-cored moraine belts are developed over subglacial bedforms (flutings) arranged in discrete flowsets. The flowsets record the complex interaction of ice streams nourished by ice flowing from three main sources: Great Bear Lake to the south, Amundsen Gulf (Franklin Bay) to the east and Liverpool Bay (Mackenzie Valley) to the southwest. Decoupling of the ice margins of these three ice sources gave rise to interlobate ice-dammed lake development over the lower Horton River area during final deglaciation. A cosmogenic ²⁶Al/¹⁰Be isochron burial age of 2.9 ± 0.3 Ma (1σ, n = 4) from the lowermost glacial diamicton and glacitectonite sequence provides evidence of perhaps the earliest continental glaciation of this region. This deposit postdates, or is perhaps a later re-advance of the same initial glaciation that produced widespread glacitectonic disturbance of bedrock in preglacial valley networks and early glacifluvial and glacilacustrine deposits containing an ice wedge pseudomorph. Subsequent glaciations have largely removed or cannibalised pre-existing records to construct complex till and glacitectonite stacks that contain reworked organics with non-finite radiocarbon ages. One site preserves buried “old” glacier ice in which prominent ice wedges had formed during an interglacial permafrost phase and were then deformed down-flow by the LIS during the Wisconsinan glaciation.
... 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). ...
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. ...
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). ...
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). ...
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.
Deception Island, situated in the South Shetland Archipelago, Maritime Antarctica, has unique characteristics such as a young and active stratovolcano, which dates back approximately 0.75 Ma. Recently, the island has witnessed glacier retreat, leading to more frequent occurrences of ice-free areas with exposed soil. This phenomenon highlights the intricate interactions between volcanic activity and regional climate warming, reflecting in the formation of the sedimentation environment. This study focuses on the sedimentary characteristics of four subaerial profiles distributed along coastal areas. Sediment samples were collected during the OPERANTAR XXXVI expedition, and underwent a range of analyses including granulometric, morphoscopic, geochemical, isotopic and statistical examinations. The granulometric and morphoscopic analyses suggest that sediments are transported and reworked over relatively short distances from their original source, reflecting rapid sedimentation processes. Iron (Fe) was identified as the most abundant element, likely linked to both tephra deposits from volcanic activity and the early stages of chemical weathering. The isotopic analyses suggest contributions from both local (autochthonous) and distant (allochthonous) sources, primarily involving Antarctic lichens and animal excrement, which are transported by meltwater flows. In conclusion, the sedimentation dynamics on Deception Island are primarily influenced by the volcanic eruptions that occurred between 1967 and 1970. However, glacial and periglacial processes are significant as well, with meltwater flows, liquid precipitation and sediments contributions from glaciers and permafrost, playing a critical role in developing fluvio-glacial deposits in the region. This study enhances the understanding of the complex environmental interactions at Deception Island in the context of ongoing climate change.
The Babia Góra (1725 m a.s.l.) is the highest and most prominent mountain massif in the Western Flysch Carpathians (WFC). Its monoclinal flysch structure, combined with tectonically controlled high local relief, has led to the development of a striking pattern of rock slope failures (RSFs), particularly along the steep, anti-dip
northern slope cuesta. This study integrates field geomorphological, geophysical, and sedimentological data,
along with Schmidt-hammer relative age dating, to provide a detailed account of the development and relative chronology of ancient RSFs in this area. The northern slope of Babia Góra exhibits all major types of RSFs, including rock slope deformations, rock slides and rock avalanches, with a total volume of approximately 418 M m3. The inventory encompasses 125 RSFs, which affect 45 % of the northern slope, and up to 77 % of the
sandstone cuesta slope. Among these, multi-temporal rock slides with long-runout, flow-like tongues represent the largest mass movement complexes in the range and rank among the largest in the WFC. Morphotectonic analysis suggests that the primary mechanism of gravitational failure involved backward rotation along listricshaped structures, with vertical displacements ranging from 6 to 90 m, although the depth of gravitational
disintegration may exceed 150 m. The Schmidt-hammer weathering index provides evidence for the multitemporal
activity of RSFs, identifying five distinct phases of RSF activity. The oldest of these phases corresponds to the timing of local deglaciation and periglacial processes.
The Hudson Mountains are situated in the eastern Amundsen Sea sector of the West Antarctic Ice Sheet, adjacent to Pine Island Glacier. They form a volcanic field of 17 stratovolcanoes and parasitic vents, preserved as nun-ataks. Two former tributaries of Pine Island Glacier (Larter and Lucchitta glaciers) flow through the mountains. Here we present a detailed study of the glacial geology of the area. We describe field observations and measurements of geomorphological features from 15 of the nunataks, meltwater ponds found on the surface of three nunataks and supraglacial features (ice dolines) from two sites near the present grounding line. Together these provide constraints on the past ice sheet extent, flow pathways and thermal regime, and enhance our understanding of the present hydrological regime-all of which are important as context for the observed modern ice sheet behaviour. We find evidence suggesting that all nunataks in the Hudson Mountains were covered by ice during the Last Glacial Maximum (defined here as 26.5-19 ka; Clark et al., 2009) and have since deglaciated. Faceted and polished erratic cobbles and boulders of exotic lithologies (syenites, alkali granites, granites, granodiorites, tonalites and gabbros) are numerous and perched on nunatak surfaces. A marked difference between the dominant erratic lithologies on nunataks adjacent to Pine Island Glacier (granite) and Lucchitta Glacier (granodiorite-tonalite) indicates that the ice sheet was transporting clasts from at least two distinct upstream source regions. The similarity in degree of weathering suggests, however, that all the erratics were transported by one phase of (warm-based) glaciation; their presence on or close to the summits of all except one nunatak indicates that the ice sheet during that time was at least 700 m thicker than present. These results are consistent with ice sheet model simulations which suggest that all nunataks in the Hudson Mountains were completely submerged by the Last Glacial Maximum ice sheet.
The sediment fills of large terrestrial basins offer an opportunity to study and reconstruct regional-scale landscape history over time. An example of such a basin is the Upper Rhine Graben in central Europe, whose proximal, southern part has so far only sporadically been investigated sedimentologi-cally. Three new drillings in close proximity have recovered the upper ∼ 40-60 m of the Quaternary sedimentary infill near the eastern graben margin north of Freiburg, Germany. Grain sizes, the rounding and shape of clasts, and the petrographic composition of the deposits have been determined and statistically analysed. The cored intervals consist of glaciofluvial gravels derived from and deposited by the Rhine system. While no consistent trends of the morphometric properties could be found, we succeeded in distinguishing two subunits within the topmost stratigraphic unit (Neuenburg Formation, Fm) based on compositional (i.e. gravel petrographic) data. An upper subunit (Hartheim Subforma-tion, Sfm) enriched in lithologies representative of the Alpine orogen could be separated from a lower subunit (Nambsheim Sfm) that is enriched in lithologies of an outer-Alpine origin. We correlate these findings with a shift in the pattern of meltwater discharge from the Rhine glacier lobe that may have delivered more Alpine material into the study region during the last than during the penultimate glacia-tion and highlight the value of quantitative approaches and appropriate statistical evaluation for gravel petrographic studies.
Glaciers response to climate change and their contribution to sea level partly depends on subglacial processes. These processes are recorded in the resultant till. Recent technical developments that can help our understanding of the bed include: in situ sensors, geophysical techniques and detailed velocity changes (from GPS, satellite, TLS, UAV and time lapse cameras). The subglacial environment is dominated by changes in pore water pressure which change in space and time. The resultant sedimentological characteristics of different tills are discussed along with in situ and experimental results for sedimentation styles, rates and till fabric development.
Describes a plywood box that proved twice as speedy in measuring the principal axes of clasts as the conventional technique using callipers.-K.Clayton
The Tertiary opening of the North Atlantic Ocean involved major and long-lived overall dextral transpression between the Svalbard and Greenland plates. On Spitsbergen, this tectonic event is manifest as a 100-200-km-wide contractional fold-thrust belt in the form of an east-pinching prism. This belt can be subdivided into (1) a western, basement-involved hinterland province that reveals more complex deformation, including thrust, transcurrent, and normal faulting, and (2) an eastern thin-skinned fold-thrust belt with structures oriented subparallel (north-northwest-south-southeast) to the transform plate boundary. The time-space distribution and interaction of different structural styles of Tertiary deformation evident on Spitsbergen support a model with linked, long-term and short-term (episodic) dynamic growth of a composite contractional and transcurrent fold-thrust wedge. The growth of a narrow, high-taper (critical-supercritical) contractional wedge occurred during northward-directed crustal shortening (stage 1) in an oblique, dextral transcurrent setting. Crustal thickening in the form of thrust uplift and basin inversion and strike-slip duplexing during the main contractional event (stages 2 and 3) created an unstable, supercritical wedge of basement and cover rocks in the hinterland. At the same time, a broader and more homogeneous frontal part of the wedge developed eastward by in-sequence imbrication in order to reduce the taper angle. Local erosion and lateral wedge extrusion (stages 3 and 4) modified the oversteepened hinterland wedge to a critical taper angle. Continued tectonic activity in the hinterland caused renewed internal imbrication of the frontal wedge, where deformation was accommodated by tear faulting and out-of-sequence thrusting (stage 4). Adjustment toward a stable taper geometry included local extension (stage 5) and erosion and sedimentation. In a transpressional fold-thrust belt, as on Spitsbergen, out-of-plane (orogen oblique to parallel) transport in the hinterland may cause local and lateral supercritical and subcritical wedge tapers. Hinterland geometries could trigger adjustments in a frontal thrust wedge in a decoupled situation, and/or orogen oblique or parallel motions in a coupled situation. Changing kinematics may thus be expected along strike in such an orogen.
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.
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
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.
Synopsis
Selby established the fact that on many rock slopes a condition of ‘strength–equilibrium’ exists in which slope gradients are in adjustment with the mass strength of the underlying rock. An established assessment technique, the rock mass strength (RMS) classification, can be used to quantify rock slope condition and, in combination with slope gradient, determine the status of rock slopes with respect to a statistically-defined ‘strength–equilibrium envelope’. This technique has been applied to 59 glacial valley slopes in the English Lake District, an area with characteristic ‘U-shaped’ glacial valleys, deglaciated around 11 ka bp . Overall, two-thirds of the slopes examined plot within the limits of the strength-equilibrium envelope, whilst the remainder are ‘understeepened’ or ‘oversteepened’ with respect to their RMS. ‘U-shaped’ valleys possess slopes that are yet to respond measurably to post-glacial erosion or readjust significantly. Evidently, slopes in similar deglaciated environments with tectonic, climatic and relief characteristics comparable with those of the Lake District need more than 11 ka (and probably much more) to evolve into strength-equilibrium. The implication is that even if slopes plot within the strength-equilibrium envelope they are in a pseudo-equilibrium condition, indicating that the Selby strength-equilibrium theorem is inapplicable to landscapes deglaciated c. 11 ka bp .
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
Moraines in six cirques in Northern Scotland are shown to be asymmetrically developed, being larger below north- or east-facing valley sides. Moraine asymmetry is strongly correlated with the distribution of free faces in the valleys, a relationship that is interpreted as the result of variation in slope retreat rates. Analysis of clast form and roundness demonstrates that following initial release from bedrock, debris entered both passive high-level glacial transport and tractive transport at the ice-bed interface. The importance of glacier velocities and medial moraines on debris flux is discussed. Consideration is also given to the implications of process asymmetry to long term landform development.
This paper deals with the statistical analysis of the uniaxial compressive strength and of the elastic modulus of jointed rock masses under different confining pressures. Properties of the rock masses with different joint fabric, with and without gouge have been considered in the analysis. A large amount of experimental data of jointed rock masses from the literature has been compiled and used for this statistical analysis. The uniaxial compressive strength of a rock mass has been represented in a nondimensional form as the ratio of the compressive strength of the jointed rock to the intact rock. In the case of the elastic modulus, the ratio of elastic modulus of jointed rock to that of intact rock at different confining pressures is used in the analysis. The effect of the joints in the rock mass is taken into account by a joint factor. The joint factor is defined as a function of joint frequency, joint orientation, and joint strength. Several empirical relationships between the strength and deformation properties of jointed rock and the joint factor have been arrived at via statistical analysis of the experimental data. A comparative study of these relationships is presented. The effect of confining pressure on the elastic modulus of the jointed rock mass is also considered in the analysis. These empirical relationships are incorporated in a nonlinear FEM code to carryout the equivalent continuum analysis of jointed rock masses. The method presented in this paper recognizes that the jointed rock mass will act both as an elastic material and a discontinuous mass. The results obtained by the model with equivalent properties of the jointed rock mass predict fairly well the behavior of jointed rock mass.
Glacier thermal regime is shown to have a significant influence on the formation of ice-marginal moraines. Annual moraines at the margin of Midtdalsbreen are asymmetrical and contain sorted fine sediment and diamicton layers dipping gently up-glacier. The sorted fine sediments include sands and gravels that were initially deposited fluvially directly in front of the glacier. Clast-form data indicate that the diamictons have a mixed subglacial and fluvial origin. Winter cold is able to penetrate through the thin (<10 m) ice margin and freeze these sediments to the glacier sole. During winter, sediment becomes elevated along the wedge-shaped advancing glacier snout before melting out and being deposited as asymmetrical ridges. These annual moraines have a limited preservation potential of ∼40 years, and this is reflected in the evolution of landforms across the glacier foreland. Despite changing climatic conditions since the Little Ice Age and particularly within the last 10 years when frontal retreat has significantly speeded up, glacier dynamics have remained relatively constant with moraines deposited via basal freeze-on, which requires stable glacier geometry. While the annual moraines on the eastern side of Midtdalsbreen indicate a slow steady retreat, the western foreland contains contrasting ice-stagnation topography, highlighting the importance of local forcing factors such as shielding, aspect and debris cover in addition to changing climate. This study indicates that, even in temperate glacial environments, restricted or localised areas of cold-based ice can have a significant impact on the geomorphic imprint of the glacier system and may actually be more widespread within both modern and ancient glacial environments than previously thought.
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ID - 552
Clast shape measurements have developed into a standard method for reconstructing the transport histories of sediments in glacial environments. The majority of studies use the ‘RA-C40’ covariance approach, with some researchers routinely including clasts of varying lithologies within their samples. The corollary is that variable lithological properties may control clast form and roundness, rather than debris-transport mechanisms. Despite this, the role of lithology on clast shape in glacial environments has rarely been analysed. Furthermore, some studies have reported difficulties in using the RA-C40 co-variance plot in discriminating clasts that have undergone subglacial transport, and clasts that have been modified by fluvial activity. Results from a glacierized valley in a temperate alpine setting indicate that detailed analysis of clast shape where samples are of uniform lithology, although time consuming, is a useful tool in the investigation of deposits in glaciated environments. Copyright © 2012 John Wiley & Sons, Ltd.
The complex record of glaciogenic landforms and sediments in Britain
relating to the last British-Irish Ice Sheet provides the opportunity to
reconstruct former ice extents, ice dynamics, retreat patterns and
examine their links to climate change. Yet in Scotland, as in the rest
of Britain, a previously fragmentary approach to palaeo-glaciological
research has limited our understanding of glacier dynamics and their
relationship with climate, particularly during the Last
Glacial-Interglacial Transition. The Monadhliath Mountains in central
Scotland have received little research attention during the last
century. The few examples of research include work by British Geological
Survey officers in the early 1900s and J.R. Young in the 1970s. These
studies focussed primarily on the geomorphology and sedimentology of
isolated valleys and therefore this PhD research provides the first
systematic mapping of the region as a whole. Results of remote and
field mapping demonstrate that two coalescent plateau icefields occurred
over the south-west and central sector of the Monadhliath Mountains
during the Younger Dryas. Together these icefields cover an area of
around 270 km2. Equilibrium Line Altitudes (ELAs) calculated for the
icefield are of comparable magnitude to those reconstructed for nearby
Younger Dryas ice masses, such as in Drumochter and Creag Meagaidh, but
indicate slightly lower precipitation in the Monadhlaith Mountains. ELAs
of individual outlet glaciers rise steeply from west to east, indicating
a strong precipitation gradient across the plateau.
Lateral moraines are prominent features of glaciated landscapes in high-mountain environments and key landforms in glacier and palaeoclimatic reconstructions, yet, compared to smaller moraines, they have been little studied and several aspects are not well understood. We here present detailed sedimentological results from the lateral moraines of Findelengletscher in SW Switzerland to gain new insights into the formation of these landforms. The lateral moraines studied here stand up to 140 m above the valley floor, are over 3 km long and strongly asymmetrical in cross-profile, with distal slopes between 29 and 36° and proximal slopes that are commonly 41–64°, but locally reach angles of up to 80°. Recorded lithofacies comprise loose clast and matrix-supported, stratified diamicts and intercalated sorted sediments in the distal slopes and near the crestline; overconsolidated matrix-supported, massive and weakly stratified diamicts and streaked-out sorted sediment lenses in the core and proximal slopes; and partly intercalated dark-brown layers overlain by loose and consolidated diamicts exposed in near-vertical walls in the proximal flank. These are interpreted as supraglacial debris flow units with intercalated fluvial ‘wash’ horizons; glaciotectonised and subglacial traction till with boudinaged and streaked-out sediment lenses; and palaeosoils overlain by sediment produced by overtopping of the former moraine surface during a subsequent advance of the glacier. Clast shape analysis and process observations reveal that the dominant mode of transport is subglacial and glaciofluvial, and that the main mode of sediment delivery to the moraines is by debris flows after the material has been transferred from the bed via englacial debris bands and meltout at the surface. This differs from previous studies that found that a supraglacial source was dominant. Sedimentary structures, clast fabric and process observations during the 1979/1980 readvance of Findelengletscher strongly suggest that proximal layers of reworked pre-existing sediments and/or basal traction zone till have been plastered onto the moraine core in several locations, causing a high degree of overconsolidation and strongly-clustered fabric eigenvalues (S1 ≤ 0.94) with clustering parallel to the moraine crestline. This suggests that a combination of basal-lateral drag and lateral plastering produces the observed proximal stability and ensures a high preservation potential. We develop a conceptual model that describes Alpine lateral moraines as structurally complex landforms that do not just record a single event as often surmised, and we discuss implications for palaeo-glacier reconstruction and the application of numerical dating methods.
The term ‘weathering’ has been in use for a very long time but it has come to mean different things to different people and hence, as scientific short-hand, it no longer functions. Here we question the tenets underpinning the most common usage of the term and note that the climate-process linkage implicit to the term is often missing and amounts to misdirection. Rather than climate as the primary driver behind specific weathering processes, it is argued that rock properties constitute the dominant control. Further, a case is made for reconsideration of our present bipartite (mechanical/chemical) division of weathering processes and of the weathering processes currently deemed to be ‘those that occur’. As process studies become evermore reductionist in nature, so the functionality of the term comes more and more into question. The linkage between process and landform, the scaling-up attribute, is seen as a current weakness and one that will become more confusing as reductionist approaches continue. As a ‘way forward’ it is suggested that weathering, stripped of specific preconceived notions of specific processes, be envisaged as a function of energy transfer and be investigated in that light. Identification of new processes as well as restructuring of known processes, particularly when considering weathering on other planets, is a potential outcome of such an approach. With a process foundation rooted in energy transfer, ‘rock decay’ provides a better umbrella term and liberates researchers from the inescapable conceptual baggage implicit to the term ‘weathering’.
The relationship between supraglacial lateral moraines and lateral dump moraines at Arolla, Switzerland, is discussed. 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 sediments 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.-Author
A systematic relationship exists between the texture of a rock type and the shapes of fragments produced by fracturing it. In visually isotropic rocks, the percentage of Zingg blades and spheres produced is directly dependent upon the texture, with aphanitic and glassy rocks producing the most blades and coarse-textured rocks producing the most spheres. The proportions of rods and discs are less predictable, perhaps because their basic specification are the same, as suggested by Smalley's random fracture theory. Weak anisotropy, still visible in hand specimen, has little effect on the shape of crushed fragments. This study shows the proportions of clast shape that should be produced by the initial breakup of various types of bedrock. Marked deviations from the observed trends may be characteristic of the environment in which the pebbles were later fractured and abraided.
Counts of 626 cobbles from Wisconsin till collected at random showed that not over 3 to 4 per cent of the cobbles show prominent glacial striation or shaping, these characteristics being about ten times as abundant among the limestone cobbles as among the other sedimentary, metamorphic, and igneous rocks. Detailed measurements and evaluation of shapes and markings were made on 300 selected glacial cobbles. These showed a dominance of tabular forms with a tendency toward pointed pentagonal profiles and practically all these were smoothed and rounded on the edges. The dominant striation pattern is a subparallel one which is almost universally parallel to the long axis of the cobble.
Krundalen, a valley occupied by three eastern outlet glaciers of the Jostedalsbre ice cap, contains three groups of moraines, two of which are outside the dated neoglacial (`Little Ice Age', LIA) limits. Exposures in the outermost moraine ridge display three sedimentary units. Detailed sedimentological analyses reveal that the lower two units formed during a temporary stillstand of the ice margin inferred to have occurred because of a topographically controlled stabilization of the ice margin during glacier retreat following the Younger Dryas. A climatically controlled readvance during which the upper unit was deposited, partly eroding pre-existing sediments, followed. Continuation of this readvance led to the whole sequence being pushed up to form the present moraine. The sedimentological results including clast shape measurements imply a temperate glacier thermal regime at the time of moraine formation. The glacial palaeoenvironment was characterized by frequent oscillations and an abundant supply of glaciogenic sediment. The age of this landform can at present not be determined by numerical dating. However, the moraine is likely to have been formed in the early Holocene, during Jondal Event 2 (JE) from c. 10 550—10 450 cal. yr BP. The average equilibrium-line altitude lowering calculated for this event is c. 440 m, 340 m for the Erdalen Event 1 (EE, 10 100—10 050 cal. yr BP) moraines and c. 190 m for the LIA moraines farther upvalley. Precipitation calculated for these stages compared with present values is 160—175% (JE), 165—175% (EE) and 110% (LIA). Summer air temperatures were slightly higher than today's during the JE, much higher during the EE and are indistinguishable from present values during the LIA. The existence of a potential JE-equivalent and the extent of the EE are reported and used for glacier reconstruction for the first time in Krundalen. The sedimentological data implies that the JE did not simply consist of a single readvance but was more complex. It is argued that glacial sedimentology linked with methods of glacier reconstruction provides a powerful tool to gain insights into the dynamics and functioning of formerly glaciated areas.
Abstract Using data from the Scottish Highlands and northwest Iceland, the present study indicates that bedrock strength properties are an important control on the morphology of glacial valleys. Results indicate that on closely jointed metasedimentary bedrock of low rock mass strength, broad U-shaped valleys are developed, whilst steeper sided, narrower cross-profiles have been developed on igneous bedrock of high rock mass strength. Findings suggest it is the interplay of the mass strength of the subglacial bedrock and the dynamic properties of the eroding glacier that control valley morphological development. The implication is that realistic models of topographic development beneath ice sheets need to consider the rock mass strength properties of the eroded bedrock as well as the glaciological variables.
Although there is an established relationship between geological structure and the morphology of certain glacial erosional landforms, the role of lithology is less clear. This is particularly true of the surface wear characteristics of glaciated bedrock. In order to examine this relationship, the surface wear characteristics of eight recently deglaciated metamorphic bedrock slabs in the Kongsfjorden area of Svalbard were mapped and recorded using detailed "micromaps." Features recorded included lee-side fracture surfaces, lee-side cavities, and the location and depth of open joints and quartz veins. On schist, glacial erosion is.favored by situations where ice movement is parallel to the trend of the bedrock foliation. In these situations, cavities may be elongated in the direction of ice flow. On more homogeneous lithologies such as marble, cavity formation is suppressed and more uniform glacially abraded rock surfaces develop. On all the metamorphic rocks examined, glacial abrasion is favored in situations where bedrock foliation is normal to ice flow. The structure of the parent bedrock, especially the orientation of foliation, exerts a strong influence on the surface wear characteristics of glaciated bedrock slabs and on the location of subglacial cavities. Geological structure therefore has the potential to influence rates of ice flow across bedrock surfaces.
Subglacial erosion beneath glaciers occurs predominantly by abrasion and plucking, producing distinct erosional forms. The controls on the relative importance of abrasion vs. plucking are poorly understood. On the one hand, glacial conditions that favour or suppress cavity formation (ice velocity, ice thickness, and water pressure) are thought to favour plucking or abrasion, respectively. Conversely, bedrock properties are also known to control landforms, but this has rarely been analysed quantitatively. In this study we compare landforms and bedrock properties of sandstone and quartzite at the bed of a palaeo-ice stream near Ullapool in NW Scotland. The boundary between the rock types is at right angles to the westward palaeo-ice flow, and palaeoglacial conditions on both rock types were similar. We report quantitative parameters for bedrock properties (Schmidt hammer hardness and joint spacing) and use morphometric parameters to analyse the landforms. Torridon sandstone is soft but thick-bedded and with a wide joint spacing. Erosional bedforms include roche moutonnées with smoothed tops and concave stoss sides, whalebacks, and elongate p-forms, indicating a high proportion of abrasion over plucking. Cambrian quartzite is hard but thin-bedded with narrow joint spacing. Erosional landforms are angular to subangular with abundant plucked lee faces, suggesting a high proportion of plucking over abrasion. Hardness and joint spacing thus exert a strong control on subglacial erosional landforms and the mechanisms that formed them. Thus glacial conditions (ice velocity, ice thickness) can only be inferred from glacial erosional landforms if the effects of bedrock properties of the substrate are considered.
A data chart is presented for detailed field description of sediment successions containing glacial diamicts and associated sediments. The design is based on field experience from modern glacial environments in Greenland and Iceland and ancient deposits in Denmark. The data chart proposes an integrated scheme that provides a synthesis of existing approaches to sediment description in the field. Three examples of the use of the data chart and logging technique illustrate its wide variability in comparison with the limited sedimentology practised by many scientists working with ancient glacial diamicts. It is concluded that the data chart might be a useful approach for recognition of the various possible types of glacial diamicts, but it does not assume to be a complete approach; it is the object of continuing discussion and can be extended or modified.
Physical and elastic properties of NX-size rock core from 27 localities were investigated in order to develop an engineering classification system for intact rock, and also to develop index properties related to important physical and engineering characteristics. Thirteen rock types are represented. Laboratory tests were conducted on these rocks as follows: unit weight, Shore scleroscope hardness, Schmidt hammer hardness, abrasion hardness, absorption, sonic-velocity stress-strain under cyclic loading to 5,000 psi, uniaxial stress-strain to failure, and point-load tensile strength. A total of 257 specimens with L/D ratios of 2:1 were tested. Statistical studies were conducted with the IBM 7094 computer to determine correlation and regression relationships for selected pairs of variables. A system of engineering classification is proposed in which rocks are classified on the basis of their strength and modulus properties either obtained directly from laboratory tests, or approximately from index properties recommended herein. Application of the proposed engineering classification system to data obtained by others is shown by individual charts for each of several different rock types. Five charts are presented for estimating the strength or modulus properties for intact rock from the numerical indices obtained by either the Schmidt hammer, the Shore scleroscope, or the sonic pulse velocity, all used in conjunction with the unit weight of the rock.
This paper discusses spatial distribution, characteristics and transport of the supraglacial debris cover at Pasterze Glacier, Austria (c. 17.6 km2, 47°05'N, 12°44'E). Research is based on field work, laboratory analyses, long-term monitoring data as well as semi-historic maps and orthophotos. The south-western part of the 3.6 km2 large glacier tongue is mantled by a pronounced debris cover (1.2 km2). The total debris-covered area has increased by 0.8 km2 during the last 38 years. Thicknesses of the debris cover increase significantly towards the glacier margin. Mean debris thickness along a longitudinal profile follows a power function decreasing from 47.3 cm close to the glacier terminus to 7.5 cm 3.8 km up-glacier. Sedimentological analyses of debris characteristics along a longitudinal profile revealed a tendency towards more slabby clasts and finer sediments further down-glacier attributed presumably to increased exposure to weathering. The mean annual debris load for the period 2001-2006 varied between 895 t.a−1 close to the terminus, 1025 t.a−1 at the central part and 745 t.a−1 at the upper part of the glacier tongue. During the period 1970-2006 the efficiency of supraglacial debris transport was up to sixfold reduced due to decreased velocities. It is likely that Pasterze Glacier will continue to transform from a 'clean' glacier into a debris-covered glacier and finally into an ice-cored moraine: a presumably typical fate for comparable alpine valley glaciers caused by ongoing climate warming and subsequent glacier shrinkage.
German
Dieser Beitrag beschäftigt sich auf Basis von Gelände-, Labor- und Langzeitbeobachtungsdaten sowie von semi-historischen Karten und Orthofotos mit verschiedenen Aspekten betreffend der supraglazialen Schuttdecke (Räumliche Verteilung, Materialeigenschaft und Sedimenttransport) der Pasterze, des größten Gletschers Österreichs (c.17,6 km2, 47°05'N, 12°44'E). Das södwestliche Drittel der 3,6 km2 großen Gletscherzunge ist von einer geschlossenen supraglazialen Schuttdecke bedeckt. Die räumliche Ausdehnung sämtlicher schuttbedeckter Flächen auf der Pasterzenzunge nahm in den letzten 38 Jahren um rund 0,8 km2 zu. Statistisch signifikante Zunahmen der Schuttmächtigkeiten wurden zum Gletscherrand sowie zum Gletscherende hin registriert. Sedimentologische Analysen der Materialeigenschaft entlang eines 4 km langen Längsprofils weisen auf Tendenzen von zunehmend plattigen Klasten sowie feineren Feinsedimenten gegen Gletscherende hin, welche möglicherweise verwitterungsbedingt erklärbar sind. Die mittlere jährliche Sedimenttransportrate för die Periode 2001-2006 variiert zwischen 895 t.a−1 nahe dem Gletscherende, 1025 t.a−1 im zentralen Bereich und 745 t.a−1 im oberen Bereich der Gletscherzunge. Bedingt durch die Verlangsamung der Gletscherbewegung reduzierte sich im Zeitraum 1970-2006 die Effizienz des Sedimenttransports durch die Pasterze auf ein Sechstel. Es kann als sehr wahrscheinlich angesehen werden, dass die Pasterzenzunge sich weiter von einem schuttfreien zu einem schuttbedeckten Gletscher und schließlich zu einem massiv schuttbedeckten, langsam abschmelzenden Toteiskörper entwickeln wird; einem Schicksal welches auch vergleichbare Talgletscher - bedingt durch Klimaerwärmung und folgendem Gletscherröckgang - ausgeliefert sind.