Article

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

June 2013
Earth-Science Reviews 121(3):96-116

DOI:10.1016/j.earscirev.2013.02.005

Authors:

Sven Lukas

Lund University

Douglas Benn

University of St Andrews

Clare M. Boston

University of Portsmouth

Martin S. Brook

University of Auckland

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Implications of a rapidly thinning ice margin for annual moraine formation at Gornergletscher, Switzerland

Article

Full-text available

May 2023
QUATERNARY SCI REV

Late Pleistocene glaciation in the headwaters of the Ceremuşul Alb valley (Maramureş Mountains, Romania)

Article

Full-text available

Apr 2023

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.

A model of ice-marginal sediment-landform development at Lake Tekapo, Southern Alps, New Zealand

Article

Full-text available

Jun 2022

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.

Sedimentary evidence of glacial entrainment at Patriot Hills and Union Glacier moraines, Ellsworth Mountains, West Antarctica

Article

Full-text available

Apr 2022
AN ACAD BRAS CIENC

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.

The lowest elevation Pleistocene glaciers in the Carpathians — The geomorphological and sedimentological record of glaciation in the Polonyna Rivna and Borzhava massifs (Ukraine Carpathians)

Article

Dec 2021
GEOMORPHOLOGY

The Polonyna Rivna (1480 m asl) and Borzhava (1682 m asl) ranges represent medium-high mountain massifs located in the north-western part of the Ukrainian Carpathians, where the legacy of the Pleistocene glaciation has long been unexplored. Based on the first detailed mapping of glacial landforms and sedimentological analysis, we document the presence of freshly-shaped outer moraines and glacial cirques and reconstruct the extent and ice-surface geometry of the six very small (0.09–0.78 km² area) palaeoglaciers. The specific feature of the area is the presence of extensive mountain-top plateaus that play an important role as additional areas for snowblow accumulation. The equilibrium line altitudes (ELAs) calculated from hypsometry of reconstructed local Last Glacial Maximum (LLGM) using the area x altitude balance ratio (AABR) 1.6 method is exceptionally low at 1138 m asl in the Polonyna Rivna and 1230 m asl in the Borzhava range. Excluding the topographic effect produced by additional snow accumulation the ELA shift upwards between 120 and 180 m which corresponds to 25–53% of the glacier elevation range. The resulted climatic ELA (1282–1352 m asl) together with the mean cirque floor altitude (1194 m asl) and mean elevation of the glacier fronts (994 m asl) represent the lowest values in the entire Carpathian arc. Our data indicate glacier-friendly conditions in the mountain massifs exceeding 1400 m asl in the windward NW part of the Ukrainian Carpathians where due to relatively cold air temperatures and orographic induced precipitation local topolimatic factors dictated the development of marginal glaciation.

The Lowest Elevated Pleistocene Glaciers in the Carpathians – Geomorphological and Sedimentological Record of Glaciation in the Polonyna Rivna and Borzhava Massifs (Ukraine Carpathians)

Article

Jan 2021

Multiple mechanisms of minor moraine formation in the Schwarzensteinkees foreland, Austria

Chapter

Apr 2020

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.

Sub-annual moraine formation at an active temperate Icelandic glacier

Article

Full-text available

Feb 2020
EARTH SURF PROC LAND

This paper presents detailed geomorphological and sedimentological investigations of small recessional moraines at Fjallsjökull, an active temperate outlet of Öræfajökull, southeast Iceland. The moraines are characterised by striking sawtooth or hairpin planforms, which are locally superimposed, giving rise to a complex spatial pattern. We recognise two distinct populations of moraines, namely a group of relatively prominent moraine ridges (mean height ~1.2 m) and a group of comparatively low-relief moraines (mean height ~0.4 m). These two groups often occur in sets/systems, comprising one pronounced outer ridge and several inset smaller moraines. Using a representative subsample of the moraines, we establish that they form by either (i) submarginal deformation and squeezing of subglacial till or (ii) pushing of extruded tills. Locally, proglacial (glaciofluvial) sediments are also incorporated within the moraines during pushing. For the first time, to our knowledge, we demonstrate categorically that these moraines formed sub-annually using repeat uncrewed aerial vehicle (UAV) imagery. We present a conceptual model for sub-annual moraine formation at Fjallsjökull that proposes the sawtooth moraine sequence comprises (i) sets of small squeeze moraines formed during melt-driven squeeze events and (ii) larger push moraines formed during winter re-advances. We suggest the development of this process-form regime is linked to a combination of elevated temperatures, high surface meltwater fluxes to the bed, and emerging basal topography (a depositional overdeepening). These factors result in highly saturated subglacial sediments and high porewater pressures, which induces submarginal deformation and ice-marginal squeezing during the melt season. Strong glacier recession during the summer, driven by elevated temperatures, allows several squeeze moraines to be emplaced. This process-form regime may be characteristic of active temperate glaciers receding into overdeepenings during phases of elevated temperatures, especially where their englacial drainage systems allow efficient transfer of surface meltwater to the glacier bed near the snout margin.

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

Article

Full-text available

Dec 2019
BOREAS

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

Different generation of controlled moraines in the glacier foreland of Midtdalsbreen, Norway

Thesis

Full-text available

Sep 2019

Xavier Allègre

A series of small mounds (< 3m) were sampled in the foreland of Midtdalsbreen outlet glacier, southern Norway. These landforms were interesting, especially at site number 1 because they were located very close to a higher Little Ice Age (LIA) moraine (> 5 m), thereby informing the dynamic of the glacier after the LIA at this location.

Rates of rockwall slope erosion in the upper Bhagirathi catchment, Garhwal Himalaya

Article

Full-text available

Aug 2019

Rockwall slope erosion is defined for the upper Bhagirathi catchment using cosmogenic 10Be concentrations in sediment from medial moraines on Gangotri glacier. Beryllium‐10 concentrations range from 1.1±0.2 to 2.7±0.3x104 at/g SiO2, yielding rockwall slope erosion rates from 2.4±0.4 to 6.9±1.9 mm/a. Slope erosion rates are likely to have varied over space and time and responded to shifts in climate, geomorphic and/or tectonic regime throughout the late Quaternary. Geomorphic and sedimentological analyses confirm that the moraines are predominately composed of rockfall and avalanche debris mobilized from steep relief rockwall slopes via periglacial weathering processes. Slope erosion affects sediment flux and storage of snow and ice at the catchment head on diurnal to millennial timescales, and more broadly influences catchment configuration and relief, glacier dynamics and microclimates. The slope erosion rates exceed the averaged catchment‐wide and exhumation rates of Bhagirathi and the Garhwal region on geomorphic timescales (103−105 years), supporting the view that erosion at the headwaters can outpace the wider catchment. The 10Be concentrations of medial moraine sediment for the upper Bhagirathi catchment and the catchments of Chhota Shigri in Lahul, northern India and Baltoro glacier in Central Karakoram, Pakistan show a tentative relationship between 10Be concentration and rainfall. As such there is more rapid slope erosion in the monsoon‐influenced Lesser and Greater Himalaya compared to the semi‐arid interior of the orogen. Rockwall slope erosion in the three study areas, and more broadly across the NW Himalaya is likely governed by individual catchment dynamics that vary across space and time.

Synsedimentary glacitectonic deformation within a glacilacustrine-esker sequence, Teesdale, Northern England

Article

Full-text available

Aug 2019
P GEOLOGIST ASSOC

Emrys Phillips

In glacial sedimentology there has been a recent improvement in the understanding of both progressive and polyphase deformation of glacigenic sequences, and the role played by water during these complex deformation histories. However, the processes occurring during the detachment and transport of sediment blocks during ice-marginal glaciotectonic thrusting remain poorly understood. This lack of understanding is addressed in detail through a macro- and microscale study of the deformation structures in the glacigenic sequence exposed at Hayberries, Teesdale, County Durham (UK), where esker sands and gravels and associated tills truncate and overlie a sequence of rhythmically bedded glacilacustrine sands, silts and clays. Thrusts within the glacilacustrine and glacifluvial sediments appear to be relatively sharp, planar structures. However, orientated thin sections reveal that these bedding-parallel detachments are marked by a thin layer of massive to foliated sand. The geometry of both meso and small-scale folds and sense of displacement on the thrusts is consistent with both brittle and ductile structures having formed in response to ice-push from the N/NW. Detailed analysis of the thin sections reveals that initial folding and thrusting was followed by the liquefaction and injection of a massive, matrix poor sand along the propagating thrust. Evidence for liquefaction and injection (sand-filled veins) increases towards the NW consistent with fluid flow and sediment injection accompanying SE-directed ice-push. These results suggest that the introduction of pressurised meltwater and sediment along the thrusts during deformation may facilitate decoupling and displacement along these detachments by thrust gliding.

Sedimentation during Marine Isotope Stage 3 at the eastern margins of the Glacial Lake Humber basin, England: SEDIMENTATION DURING MARINE ISOTOPE STAGE 3

Article

Full-text available

Sep 2018

The stratigraphic sequence at North Cave, on the eastern margins of the Lake Humber basin, records the deposition of a fluvioperiglacial fan (LFs 1–4), with early sedimentation (LF1) dating to Marine Isotope Stage (MIS) 3 (optically stimulated luminescence date range 41.8–38.6 ka and ¹⁴C dates 41.6–49 ka BP). Three phases of permafrost and ice wedge development during MIS 3 are evident and indicate possible fan abandonment and hence periods of reduced nival runoff. Involution structures dated to 11.1 ka with large boulders and fine‐grained sorted circles in LF4b are interpreted as periglacially cryoturbated littoral deposits with boulders derived from anchor ice, initially deposited at the margins of Lake Humber up to an altitude of 8 m OD during MIS 2. The style and age of fluvioperiglacial fan deposition at North Cave is compatible with several mid‐Devensian sites around Britain characterized by significant nival melt and run‐off from steeply incised valleys in permafrozen cuesta landscapes. This phase of fluvioperiglacial fan aggradation to near or below 0 m OD is recorded around the glacial lakes Humber and Fenland basins and indicates that no glacial lakes existed at that time.

The historical emergence of a geometric and sinuous ridge network at the Hørbyebreen polythermal glacier snout, Svalbard and its use in the interpretation of ancient glacial landforms

Article

Mar 2022
GEOMORPHOLOGY

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.

Rock Glacier Characteristics Under Semiarid Climate Conditions in the Western Nyainqêntanglha Range, Tibetan Plateau

Article

Full-text available

Jan 2022

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.

Timing and flow pattern of the Orta Glacier (European Alps) during the Last Glacial Maximum

Article

Full-text available

Jan 2020
BOREAS

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.

New statistical methods for the comparison and characterisation of particle shape

Article

May 2019

This paper presents novel methods for robust statistical testing of particle shape data. Shape (the relative lengths of three orthogonal axes) is a key property of sedimentary particles, providing information on provenance, transport history and depositional environment. However, the usefulness of shape data, including the ability to make robust comparisons between samples, has been constrained by the absence of a satisfactory definition of the mean shape for a sample of particles. Such a definition is proposed and used to develop confidence regions for the population mean shape using both parametric (theoretical) and computational (bootstrap) methods. These techniques are based on a transform that permits multivariate statistical methods for the analysis of compositional data to be extended to shape. These techniques are validated with reference to a dataset of 169 clast samples and found to perform well. A statistical test on the mean – using the multivariate extension of Student's t‐test, Hotelling's T² – is presented. The benefits of the methods presented are demonstrated with reference to a case study.

Glacier dynamics during a phase of Late Quaternary warming in Patagonia reconstructed from sediment-landform associations

Article

Full-text available

Jul 2019
GEOMORPHOLOGY

The geomorphological record in glaciated landscapes can provide important information for the study of the response of glaciers to rapid climate change. This study presents a new reconstruction of the glacial history of the northern Monte San Lorenzo ice cap, southern South America, during a period of accelerated warming and deglaciation following the Antarctic Cold Reversal (14.5–12.8 ka). We present a detailed geomorphological map of the valleys to the north of Monte San Lorenzo. Sediment-landform assemblages identified include lateral and terminal moraine ridges, flutes, deltas, ice-contact fans, palaeoshorelines, kame terraces and outwash plains. We map 14 primary ice-limits, 7 of which are newly identified, and 7 of which are from previous studies, mapped here in greater detail. We devise landsystem models to formalise and document spatial and temporal changes in glacial processes and environments. Our new geomorphological mapping and landsystem reconstructions provide an important insight into the response of temperate Patagonian glaciers to rapidly-warming climate.

Formation of crevasse-squeeze ridges at Trygghamna, Svalbard

Article

May 2023
EARTH SURF PROC LAND

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 gla- cier 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 bed- rock. Our findings confirm previous CSR formation theories; basal sediments are squeezed into bottom-up crevasses during surges, which are subsequently trans- ported 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.

Craig Rhos-y-felin: no wedges and no quarry

Preprint

Full-text available

Apr 2023

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.

Reconstructing the pattern of late Quaternary climate through sediment-landform assemblages in the Dhauli Ganga valley (upper Ganga catchment), India

Article

Apr 2023
GEOMORPHOLOGY

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.

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

Article

Full-text available

Mar 2023

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.

Late Pleistocene glaciation in the Eastern Carpathians – A regional overview

Article

Feb 2023
CATENA

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

Late Quaternary Climate and Landform Evolution in Dhauli Ganga Valley (Upper Ganga Catchment), Central Himalaya, India

Article

Jan 2023

Late Pleistocene Glaciation in the Eastern Carpathians - a Regional Overview

Article

Jan 2022

The status of the "Little Ice Age" in southern Norway: Relative-age dating of Neoglacial moraines with Schmidt Hammer and lichenometry

Article

Jun 1984
BOREAS

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.

Glaciofluvial sequences recording the Birrfeld Glaciation (MIS 5d–2) in the Bern area, Swiss Plateau

Article

Full-text available

Dec 2022

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.

Early Pleistocene complex cut-and-fill sequences in the Alps

Article

Full-text available

Dec 2022

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.

Effects of catchment characteristics and hydro-meteorological scenarios on sediment connectivity in glacierised catchments

Article

Full-text available

Jan 2022
GEOMORPHOLOGY

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.

Luminescence dating of a late Middle Pleistocene glacial advance in eastern England

Article

Full-text available

Nov 2021

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.

The impact of local topoclimatic factors on marginal Pleistocene glaciation in the Northern Romanian Carpathians

Article

Mar 2022
CATENA

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.

Evolution of the Białka valley Pleistocene moraine complex in the High Tatra Mountains

Article

Dec 2021
CATENA

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.

Re-interpretation of ‘hummocky moraine’ in the Gaick, Scotland, as erosional remnants: Implications for palaeoglacier dynamics

Article

Full-text available

Jun 2021
P GEOLOGIST ASSOC

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.

Glacial landforms and sediments (landsystem) of the Smoking Hills area, Northwest Territories, Canada: Implications for regional Pliocene – Pleistocene Laurentide Ice Sheet dynamics

Article

Jun 2021
QUATERNARY SCI REV

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.

Fourier Shape Analysis, FSA: Freeware for quantitative study of particle morphology

Article

Aug 2020
J VOLCANOL GEOTH RES

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.

The glacial geomorphology of western Dronning Maud Land, Antarctica

Article

Full-text available

Dec 2020
J MAPS

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 glacial landsystem of Fjallsjökull, Iceland: Spatial and temporal evolution of process-form regimes at an active temperate glacier

Article

Full-text available

Apr 2020
GEOMORPHOLOGY

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.

Schmidt-hammer exposure-age dating (SHD) of sorted stripes on Juvflye, Jotunheimen (central South Norway): Morphodynamic and palaeoclimatic implications

Article

Jan 2020
GEOMORPHOLOGY

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.

Origin and age of The Hillocks and implications for post‐glacial landscape development in the upper Lake Wakatipu catchment, New Zealand

Article

Full-text available

Nov 2019

Ambiguous landscape histories can arise from equivocal or incomplete geomorphological, sedimentological or geochronological evidence. In this study, we apply quantitative analyses to robustly assess the origin and age of a field of rounded mounds, known as ‘The Hillocks’. Using clast analysis, the sediment is shown to be consistent with a landslide origin but inconsistent with other glacial sediments in the region. Cosmogenic 10Be exposure age dating suggests The Hillocks formed ~8 ka. Ground‐penetrating radar reveals that the deposit rests upon deltaic foreset beds; combined with topographical data, we calculate a deposit volume of ~15–27 M m3, consistent with the estimated volume of the proposed source area. Overall, our data support a rock avalanche origin, indicating that by 8 ka the valley was ice‐free at The Hillocks’ location, and the level of Lake Wakatipu was lower than 340 m asl by this time. The Dart River delta shoreline was situated somewhere between The Hillocks and the present day shoreline at that time, and has prograded at a maximum average rate of 1 m a−1 since ~8 ka. These findings are significant given the lack of landforms by which to constrain glacial or post‐glacial landscape histories in this region of New Zealand.

Mountain glacier-to-rock glacier transition

Article

Full-text available

Jul 2019
GLOBAL PLANET CHANGE

In many of the world's high mountain systems, glacier recession in response to climate change is accompanied by a paraglacial response whereby glaciers are undergoing a transition to rock glaciers. We hypothesise that this transition has important implications for hydrological resources in high mountain systems and the surrounding lowlands given the insulating effects that debris cover can have on glacier ice. Despite this, however, little is known about how this transition occurs nor how quickly, which glaciers are liable to transition, the factors driving this process and the water supply implications that follow. This paper assesses the role of glacier and rock glacier textural properties from a deglaciating region of the Himalayas to begin to address some of these issues. We investigated six landsystems on the spectrum from glaciers-to-rock glaciers in the Khumbu Himal, Nepal, and sampled for clast shape and roundness during 2016 and 2017. Kite aerial photography was additionally used to capture aerial images of an ongoing glacier-to-rock glacier transitional landform (Chola Glacier) to elucidate the surface geomorphic features of a fully transitioned landform. This image data, processed using a structure-from-motion multi-view stereo photogrammetry approach, revealed the presence of a spatially coherent ridge-and-furrow surface morphology in the lower reaches of Chola Glacier, which is potentially indicative of an ongoing glacier-to-rock glacier transition. We show that glacier-derived and slope-derived clast roundness significantly statistically different (Kolmogorov–Smirnov two-sample test: Dmax = 0.62, two-tail p < .001; n = 1650) and suggest that sediment connectivity (i.e. linkage between sediment sources and downslope landforms) is one of the drivers of the transition process. Consequently, we hypothesise that the presence of well-developed lateral moraines along glacier margins serves to reduce this connectivity and thus the likelihood of glacier-to-rock glacier transition occurring. Understanding such processes has implications for predicting the geomorphological evolution of deglacierizing mountains under future climate warming and the water supply consequences that follow.

Temperate glaciation on a Snowball Earth: Glaciological and palaeogeographic insights from the Cryogenian Yuermeinak Formation of NW China

Article

Full-text available

May 2019
PRECAMBRIAN RES

Ubiquitous glaciation was the hallmark of the Cryogenian Period (ca. 720 – 635 Ma), therefore understanding the character, behaviour, extent and configuration of Cryogenian ice bodies is a fundamental requirement in reconstructing climates and environments from the period. Unfortunately, despite abundant evidence for glaciation, there is a strong preservational bias towards basinal glaciogenic sedimentary strata and against subglacial strata. In particular subglacially striated surfaces, owing to their fragile millimetre-thickness, are very rare and represent only a tiny proportion of the global Cryogenian outcrop area. Thermal regime is one of the most important controls of glacial behaviour and subglacially striated surfaces are one of the very few means of determining an ancient temperate thermal regime. In this context we present sedimentological and detrital zircon detail of a fortuitously preserved Cryogenian (Marinoan) outcrop in the Aksu-Wushi area of the Tarim Craton, NW China. The Yuermeinak Formation preserves not only a subglacially striated surface and palaeotopography but also a thin, locally preserved, subglacial tillite. Together these indicate grounded ice. The remaining formation reveals glacial retreat and deposition of predominantly supraglacially-sourced debris within a dynamic, open-water, ice-proximal proglacial environment. A palaeogeographic reconstruction is proposed in which the Aksu-Wushi area developed from a deeper-water basinal environment, without clear evidence for glaciation, during the early Cryogenian, to an area of mountainous uplift with nearby grounded glacial ice, during the latter Cryogenian. Combining detrital zircon data of this study with published data it is further proposed that this development was linked to an active margin setting, either through expansion of an Andean-type mountain range to the north of the study area or flank-uplift of a back-arc basin.

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

Article

Full-text available

Mar 2019
QUATERNARY SCI REV

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

COMPARISON BETWEEN GLACIAL SEDIMENTS IN SOUTHWEST WALES AND SOUTHWEST CORNWALL AND IMPLICATIONS FOR THE LAST GLACIAL MAXIMUM

Thesis

Full-text available

Feb 2019

Sophie Morris

This dissertation looks at sediments in regions of southwest Wales and southwest Cornwall. Similarities are held between sediments at Hunts Bay, Wales, and sediments found in situ at an exposed section of cliff face in Porth Nanven, Cornwall, which could be indicative of glacial process occurring in southwest Cornwall. Recent research suggested that glaciers may have extended much further south than previously thought in the Last Glacial Maximum, due to a niche-glacier system from the Last Glacial Maximum being identified at Rosemergy, Cornwall (Harrison, Knight & Rowan 2015). Clast fabric analysis and stereonet projections of Rotherslade, Hunts Bay and Porth Nanven were carried out and compared to identify whether the conclusion could be drawn that glacial processes occurred in Porth Nanven and Hunts Bay and that Rotherslade remained unglaciated in the Last Glacial Maximum, and the implications of this conclusion. Results suggest that Porth Nanven and Hunts Bay experienced glaciation and Rotherslade did not, which calls for a revision of British and Irish Ice Sheet limits.

GEM-2 Western Arctic Project, Smoking Hills 2018 Report of Activities: a multi-disciplinary study of Cretaceous, Neogene and Quaternary stratigraphy, and bocannes and their associated mineralogy and hydrochemistry.

Technical Report

Dec 2018

This report provides a rationale and scientific basis for three multi-disciplinary research projects undertaken during the Smoking Hills fieldwork campaign of July, 2018 (Fig. 1.1). It summarizes their field sample collections and observations and discusses their future research plans. The first activity concerns the age and environment of deposition of Cretaceous strata (145-66 Ma) in the Canadian Arctic mainland. This study will provide new insights into the tectonostratigraphic evolution of the offshore Canada Basin and the regional Mackenzie-Beaufort and Sverdrup basins. This study is also expected to provide insight into Cretaceous climates of the Canadian Arctic. The second activity concerns the study of bocannes, areas of burning shale/mudrock for which the Smoking Hills is aptly named. It aims to collect samples of minerals from within the burning vents and also to study the chemistry of ponds and streams draining from these features and associated bedrock. The final activity is focused on kimberlite (diamond) indicator minerals and tries to draw comparisons between those found in deposits in the Smoking Hills with those previously recovered in related deposits on Banks Island. This activity will also examine sediments from mapped areas of Neogene fluvial Beaufort Formation (<23-2.58 Ma), and from Quaternary glacial deposits (<2.58 Ma).

Glacial geomorphology of the Gaick, Central Grampians, Scotland

Article

Full-text available

Jul 2019
J MAPS

The Gaick is an enigmatic glaciated landscape in the Central Grampians, Scotland, dominated by an expansive dissected plateau. Previous studies have postulated widely differing interpretations of the glacial landforms and current understanding of the glacial events in this area is partly restricted by the absence of detailed glacial geomorphological mapping. To address this issue, we present a comprehensive 1: 46,000-scale glacial geomorphological map, covering an area of ~520 km2. A combination of detailed field mapping and interpretation of aerial photographs and Digital Surface Models (DSMs) has revealed a variety of glacial, periglacial and fluvial landforms, including an abundance of moraines and meltwater channels within valleys. We also identify a glacial sediment-landform assemblage, dissected glaciogenic material, that has not previously been reported in the Scottish Highlands. The geomorphological map provides the necessary foundation for elucidating the extent, dynamics and timing of former glaciation in the area.

Multiple Late Holocene surges of a High-Arctic tidewater glacier system in Svalbard

Article

Oct 2018
QUATERNARY SCI REV

Most large tidewater glaciers in Svalbard are known to have surged at least once in the last few hundred years. However, very little information exists on the frequency, timing or magnitude of surges prior to the Little Ice Age (LIA) maximum in ∼1900. We investigate the sediment-landform assemblages produced by multiple advances of the Nathorstbreen glacier system (NGS) in order to reconstruct its Late Holocene surge history. The glacier has recently undergone one of the largest surges ever observed in Svalbard, advancing ∼16 km from 2008 to 2016. We present flow velocities and ice-marginal observations (terminus change, proglacial geomorphological processes) from the later stages of this surge. A first detailed assessment of the development of a glaciotectonic mud apron within the fjord during a surge is provided. Geomorphological and sedimentological examination of the terrestrial moraine areas formed prior to the most recent surge reveals that at least two advances were responsible for their formation, based on the identification of a previously unrecognised ice-contact zone recorded by the distribution of sediment facies in coastal exposures. We distinguish between an outer, older advance to the distal part of the moraine system and an inner, younger advance to a position ∼2 km upfjord. Radiocarbon dating of shells embedded in glaciotectonic composite ridges formed by the onshore bulldozing of marine mud during the outer (older) of the two advances shows that it occurred at some point during the interval 700–890 cal. yr BP (i.e. ∼1160 AD), and not during the LIA as previously assumed. We instead attribute the inner (younger) advance to the LIA at ∼1890. By combining these data with previous marine geological investigations in inner and outer Van Keulenfjorden, we demonstrate that NGS has advanced at least four times prior to the recent 2008–2016 surge: twice at ∼2.7 kyr BP, at ∼1160 AD, and in ∼1890. This represents a unique record of the timing and magnitude of Late Holocene tidewater glacier surges in Svalbard.

Rock glaciers and the geomorphological evolution of deglacierizing mountains

Article

Jan 2019
GEOMORPHOLOGY

Rock glaciers are an important geomorphic element of glaciated mountain landscapes, but our understanding of their distribution and ages, controls on their development, and their importance in regional mountain hydrology and mountain geomorphic evolution is incomplete. In part, this incomplete knowledge arises through problems associated with identifying rock glaciers on a morphological basis alone, amplified by the multiple ways in which rock glaciers can form in different glacial, periglacial, and paraglacial settings. This study focuses on rock glaciers as a paraglacial mountain landscape element and considers the relationships between rock glaciers and glacial, periglacial, and paraglacial processes. New geomorphic and sedimentary data on different rock glaciers from the Khumbu region of Nepal are presented. These data show that even within a single region, rock glaciers may have varied origins and thus likely ages and different climatic and environmental controls. We argue that rock glaciers in deglacierizing mountains may have a long residence time in the landscape, unlike many other glacially influenced mountain landforms, and can undergo significant morphodynamic changes as glaciated landscapes transition into paraglacial landscapes.

Depositional Processes

Chapter

Mar 2022

Jane K. Hart

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.

Sediment supply from lateral moraines to a debris-covered glacier in the Himalaya

Article

Full-text available

May 2019

Debris-covered glaciers in the Himalaya play an important role in the high-altitude water cycle. The thickness of the debris layer is a key control of the melt rate of those glaciers, yet little is known about the relative importance of the three potential sources of debris supply: the rockwalls, the glacier bed and the lateral moraines. In this study, we hypothesize that mass movement from the lateral moraines is a significant debris supply to debris-covered glaciers, in particular when the glacier is disconnected from the rockwall due to downwasting. To test this hypothesis, eight high-resolution and accurate digital elevation models from the lateral moraines of the debris-covered Lirung Glacier in Nepal are used. These are created using structure from motion (SfM), based on images captured using an unmanned aerial vehicle between May 2013 and April 2018. The analysis shows that mass transport results in an elevation change on the lateral moraines with an average rate of -0.31±0.26 m year−1 during this period, partly related to sub-moraine ice melt. There is a higher elevation change rate observed in the monsoon (-0.39±0.74 m year−1) than in the dry season (-0.23±0.68 m year−1). The lower debris aprons of the lateral moraines decrease in elevation at a faster rate during both seasons, probably due to the melt of ice below. The surface lowering rates of the upper gullied moraine, with no ice core below, translate into an annual increase in debris thickness of 0.08 m year−1 along a narrow margin of the glacier surface, with an observed absolute thickness of approximately 1 m, reducing melt rates of underlying glacier ice. Further research should focus on how large this negative feedback is in controlling melt and how debris is redistributed on the glacier surface.

Formy i osady glacjalne w dolinie Małej Płoszanki (Karpaty Wschodnie, Ukraina) Glacial landforms and sediments in the Mala Ploshanka valley (Eastern Carpathians, Ukraine)

Chapter

Full-text available

Feb 2019

The Borzhava range (1682 m) is a prominent mountain range within the NW part of the Ukrainian Carpathians, where the traces of Pleistocene glaciation are poorly recognized and which is still lacking detailed geomorphological case studies. In this paper, we present the result of detailed geomorphological mapping, remote sensing data analysis and sedimentological analysis, which provide first evidence of glacial activity in the Borzhava range (1679 m). Detailed geomorphological studies were conducted in the middle and upper part of the Mala Ploshanka valley (NE part of the range) where the glacial landforms and sediments are particularly well-preserved. According to obtained results, the maximal ice extent (ca. 1 km long) documented by preserved frontal moraines reached an elevation of 1075 m a.s.l. Amphitheatre-shaped and relatively deep Yama glacial cirque was cut out in the headwaters of the Mala Ploshanka valley. Its vast floor lies at a considerably low altitude (1250 – 1300 m) in comparison with the surrounding mountain ranges. Our data support a cirque-valley glaciation on the NE slopes of Borzhava range during the last glaciation. Results of clast-shape (C40) and roundness (RA ) analysis show clearly distinct characteristics between the controlled samples of slope environment (slope covers, alluvial sediments) and moraine deposits in the study area. Most of the sandstone clasts within the moraine sediments in the terminal and cirque part of the former glacier system were actively transported (subglacially modified), however, some samples in the middle of the studied valley indicate also passively-transported conditions.

Boulder shapes and grain-size distributions of debris as indicators of transport paths through a glacier and till genesis

Article

Full-text available

Jan 1978

Geoffrey Boulton

A simple device for measuring the primary axes of clasts.

Article

Full-text available

Jan 1979

Richard A. Shakesby

Describes a plywood box that proved twice as speedy in measuring the principal axes of clasts as the conventional technique using callipers.-K.Clayton

Application of a critical wedge taper model to the Tertiary transpressional fold-thrust belt on Spitsbergen, Svalbard

Article

Full-text available

Oct 1999

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.

Discriminating glacier thermal and dynamic regimes in the sedimentary record

Article

Full-text available

Apr 2012
SEDIMENT GEOL

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.

Modification of Clasts in Lodgement Tills by Glacial Erosion

Article

Full-text available

Jan 1982
J GLACIOL

Martin Sharp

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

Pebble Shape (and Size!)

Article

Full-text available

Jan 1991

Werner Illenberger

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.

The influence of rock mass strength on the form and evolution of deglaciated valley slopes in the English Lake District

Article

Full-text available

May 2002

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 characteristics '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.

Moraine-mound formation by englacial thrusting: The Younger Dryas moraines of Cwm Idwal, North Wales

Article

Full-text available

Jan 2000

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.

Graphical representation of particle shape using triangular diagrams: an Excel spreadsheet method

Article

Full-text available

Dec 2000
EARTH SURF PROC LAND

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.

20th century mass balance and thermal regime change at Scott Turnerbreen, Svalbard

Article

Full-text available

Jan 1999

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.

Formation, Meltout Processes and Landscape Alteration of High-Arctic Ice-Cored Moraines—Examples From Nordenskiöld Land, Central Spitsbergen

Article

Full-text available

Jul 2005

The debris-covered ice-margins of three largely cold-based glaciers in central Spitsbergen were investigated to reconstruct their formation and degradation. Clast shapes indicate dominant englacial and supraglacial transport with a smaller subglacial component. Emplacement of material is inferred to have been through meltout along flowlines due to the relatively uniform and continuous debris cover along the glacier margins; no evidence of thrusting has been found. Degradation of all three belts is rapid and involves debris flows at unstable places—e.g., the margins of meltwater channels. Resultant exposure of underlying ice initiates or accelerates melting, thereby leading to further debris flows. Hence, once degradation starts, a self-reinforcing cycle that removes material from the glacier commences. Landform preservation potential on millennial time scales in a high-arctic, continuous permafrost environment is thus limited. This work has implications for the interpretation of Pleistocene landform associations that use modern analogues from Svalbard.

Lateral Moraines of Glacier De Tsidjiore Nouve: Form, Development, and Implications

Article

Jan 1983

R. J. Small

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.

Modification of Clasts in Lodgement Tills by Glacial Erosion

Article

Jan 1982

Martin J Sharp

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.

Engineering classifications and index properties of intact rock. Tech Rep AFWL-TR 65-116. Air Force Weapons Laboratory, Kirtland Air Force Base

Article

Jan 1966

Spät- und postglaziale Gletscherschwankungen im Mont Blanc-Gebiet

Article

Jan 1987

W. Wetter

The Precambrian

Article

Zur Stereometrie von Geröllen

Article

Jan 1977

M. Behrens

Geology of the Aoraki area

Chapter

Jan 2007

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.

Sediment and rock strength controls on river incision into bedrock

Article

Dec 2001

Dietrich W.E. Sklar L.S.

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.

Talus texture and particle morphology in a North Andean paramo

Article

Apr 1986
Z GEOMORPHOL

Francisco Perez

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

Glacial debris transport and moraine deposition: A case study of the Jardalen cirque complex, Sogn-og-Fjordane, western Norway

Article

Jun 1999
Z GEOMORPHOL

David J. A. Evans

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 morphology

Article

Jan 2004

D.I. Benn

Geologischer Atlas der Schweiz 1:25000

Article

Jan 1953

P. Bearth

Modification of clast shape in high-arctic glacial environments

Article

May 1997

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.

Modification of Clast Shape in High-Arctic Glacial Environments

Article

Jan 1997

Matthew R. Bennett

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.

Graphical representation of particle shape using triangular diagrams: An Excel spreadsheet method

Article

Dec 2000

The research project – a case study of Quaternary glacial sediments

Chapter

Oct 2004

Variability in Neoglacial Moraine Morphology and Composition, Storbreen, Jotunheimen, Norway: Within-Moraine Patterns and Their Implications

Article

Jan 1989

Richard A. Shakesby

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.

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

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