Moraine Complex Research Articles

Age and origin of ice‐cored moraines in jotunheimen and breheimen, southern norway: insights from schmidt‐hammer exposure‐age dating

High‐precision chmidt‐hammer exposure‐age dating () is applied to ice‐cored moraine‐ridge complexes at three high‐alpine glaciers in otunheimen and reheimen, southern orway. Local calibration curves were established using moraine ridges dating from the last 50 years and bedrock surfaces deglaciated ∼9700 years ago. ages, with 95% statistical confidence intervals, ranged from 3920 ± 790 years to a negative (futuristic) age of –890 ± 580 years at Gråsubreen, 420 ± 700 to 260 ± 710 years at esle‐Juvbreen and 2250 ± 450 to 1605 ± 410 years at stre Tundradalskyrkjabreen. Negatively skewed ‐value distributions were interpreted as the result of weathered boulders from reworked surfaces. This leads to the interpretation of these ages as maximum estimates of moraine‐ridge age. strem's hypothesis (that the proximal ridges are the oldest and survived being overridden many times) is rejected on the basis of our ages. Although ice‐cored moraine ridges resemble the flow structures of rock glaciers, Barsch's hypothesis (that these ice‐cored moraine complexes are rock glaciers) is also rejected. Instead, the ice‐cored moraine‐ridge complexes are considered to be glaciotectonic structures produced by the interaction of polythermal glaciers and alpine permafrost over the late olocene. All the individual ridges were essentially formed during the ‘ittle ce ge’ glacier advance from material deposited earlier by multiple neoglacial events. The considerable size of the moraine complexes is attributed not only to the accumulation of material from these different events over a long period of time but also to their survival in the landscape during phases of glacier retreat when ice cores do not melt and fluvial and other destructive processes remain ineffective in the permafrost environment.

Dynamics and retreat of the Late Weichselian Kongsfjorden ice stream, NW Svalbard

Terrestrial cosmogenic nuclide dating in combination with detailed landform mapping in the Kongsfjordhallet area, NW Svalbard, have provided new insight on configuration, dynamics, and deglaciation of the Late Weichselian Kongsfjorden ice stream. The minimum Late Weichselian ice surface elevation in Kongsfjorden was >449 m a.s.l. indicating considerably thicker ice and a steeper surface gradient than earlier suggested. For the adjacent inter-ice stream area an even steeper surface slope is reconstructed. The glacial landforms, as well as the surface exposure ages of erratic boulders at different elevations, suggest a gradual lowering of the ice surface. Deglaciation of the higher elevations was probably underway by 20.0 ka. At ca 16.6 ka a large moraine complex (‘the Kongsfjorden moraine’) was deposited close to the fjord mouth. The shape of the moraines, the steep ice surface gradient, as well as the correlation to fine laminated clay lacking ice rafted debris deposited in the trough beyond the moraine suggest that ice dynamics switched from ice-stream behaviour to a slower flowing outlet (tidewater) glacier. A Younger Dryas or Early Holocene advance of local valley glaciers is shown by moraine lobes cross-cutting the Late Weichselian lateral moraines.

A multiple dating-method approach applied to the Sanabria Lake moraine complex (NW Iberian Peninsula, SW Europe)

New evidence in the NW region of the Iberian Peninsula (∼42°N 6°W) of a glacial advance coeval with the global Last Glacial Maximum (LGM) of the Marine Isotope Stage 2 has been identified through a dataset of exposure ages based on 23 10Be concentration measurements carried out on boulder samples taken from a set of latero-frontal moraines. Results span the interval 19.2–15.4 10Be ka, matching the last deglaciation period when Iberia experienced the coldest and driest conditions of the last 25 ka, and are consistent with Lateglacial chronologies established in other mountain regions from SW Europe. The extent of the LGM stade identified in this work is similar to the local maximum ice extent stade recorded and dated as prior to 33 ka using radiocarbon and optically stimulated luminescence. This work showcases how multiple-dating approaches and detailed geomorphological mapping are required to reconstruct realistic palaeoglacier evolution models.

Geomorphology, internal structure, and successive development of a glacier foreland in the semiarid Chilean Andes (Cerro Tapado, upper Elqui Valley, 30°08′ S., 69°55′ W.)

We use geomorphological analysis, sedimentological survey, remote sensing, and ground penetrating radar (GPR) in order to understand the complex landform assemblage found in front of the Cerro Tapado glacier in the upper Elqui River catchment, semiarid Andes of Chile. The geomorphological analysis highlights prominent boundaries dividing the landform assemblage into (from the upper part to the lower part) an upper latero-frontal moraine complex, an upper debris-covered glacier, a lower debris-covered glacier, two rock glaciers, and a lower morainic complex. The sedimentological survey highlights the rather small size of the surface debris (in general <20cm) and the predominance of porphyritic rhyolite. Remote sensing data show that, between 1956 and 2010, considerable (>400m) receding of the glacier occurred, along with downslope displacements (dm–m·y−1) of most of the landform units and a significant evolution of the thermokarst features on the debris-covered glaciers. Considerable surface lowering occurred in the upper part of the assemblage, while localized bulging is seen along the morphological boundaries in the lower units. The GPR profiles highlight spectacular internal structure in the upper debris-covered glacier with up to 80m of buried ice. In the other landform units, the internal structure is less visible and more heterogeneous. The analysis of the radar wave velocity along the GPR profiles reveals the occurrence of air-filled and moist zones in the internal structure. The geomorphological assemblage is fundamentally characterized by its morphological, structural, and dynamical boundaries and defined as a young (probably <2000years) polygenetic construction with landform units having added to/overlapped one another. The rock glaciers do not derive from the present debris-covered glacier but preexist to it.

Quaternary glacial chronology of the Kanas River valley, Altai Mountains, China

The Kanas River originates on the southern slope of Youyi Peak, the largest center of modern glaciation in the Altai Mountains in Central Asia. Glaciers advanced and retreated repeatedly during Quaternary glacial–interglacial cycles in the Kanas River valley, and four moraine complexes and associated glaciofluvial deposits are preserved in the valley. Optically stimulated luminescence (OSL) dating has been used to determine ages of glaciofluvial deposits (sand lenses sandwiched between tills in moraines) using a single aliquot regenerative-dose (SAR) protocol. Based on dating results from this and previous studies (including 14C, electron spin resonance (ESR) and OSL dates) and geomorphic relationships, the innermost moraine complex was concluded to deposit during the Little Ice Age (LIA), the second (Akekule) moraine complex was deposited during the Neoglacial, the third (Kanas) moraine complex was deposited during the last glacial cycle (marine oxygen isotope stage (MIS) 2–4) and the outermost set of moraines is MIS 6 in ages (penultimate glaciation). The Kanas moraine complex could be divided into three subsets (III1, III2 and III3), with inferred ages of MIS 2, mid-MIS 3 and MIS 4, respectively, which is consistent with moraine records from other areas in Central Asia and climate reconstructions from the Guliya ice core. The glaciers in the Kanas valley at their maximum extents during the LIA, Neoglacial, last glaciation and penultimate glaciation were 13.8 km, 32 km, ∼100 km, and ∼120 km long, respectively.

A polyphase glacitectonic model for ice-marginal retreat and terminal moraine development: the Middle Pleistocene British Ice Sheet, northern Norfolk, UK

Recent investigations from modern environments demonstrate that many terminal moraines do not simply record a single glacial maximum, but instead reveal a complex oscillatory pattern of ice-marginal behaviour including polyphase retreat. Within this study, we examine the geomorphology, geology and internal structure of a terminal moraine complex – the ‘Cromer Ridge’ in north Norfolk to reconstruct patterns of ice-marginal behaviour. Previously, this landform was interpreted as the limit of a southern extension of the British Ice Sheet during a Middle Pleistocene glaciation. Evidence presented here reveals a more complicated pattern of ice-marginal behaviour with the ‘Cromer Ridge’ reinterpreted as a ‘complex’ comprising several ridge elements. We propose that the maximum ice extent lay further to the south, with the size and morphology of the largest ridge element (the ‘Cromer Ridge’ as previously defined) a facet of thrust-stacking at an ice-marginal still-stand. We recognise multiple oscillations of the ice-front recorded against a twelve-stage model for the decay of the southern margins of a fast-flowing lobe of North Sea ice. Changes in ice-marginal dynamics are identified by the superimposition and lateral and vertical evolution of glacitectonic styles. Differences between these various states, and switches between ‘shallow’ and ‘deep’ thin-skinned glacitectonics, are strongly influenced by sub-marginal and proglacial water availability. Examination of the evidence for the morphostratigraphic proposals for the glacitectonic assemblage, within the context of the above interpretation, suggests that many of the ‘glacigenic landforms’ are erosional and a MIS 12 age of formation is favoured although several anomalies remain to be explained.

Dynamic behaviour of the northwest Laurentide Ice Sheet and deposition of the latest Pleistocene Jesse Till moraine complex, Banks Island, Canadian Arctic Archipelago

Dynamic behaviour of the northwest Laurentide Ice Sheet and deposition of the latest Pleistocene Jesse Till moraine complex, Banks Island, Canadian Arctic Archipelago

Glacier retreat and landform production on an overdeepened glacier foreland: the debris‐charged glacial landsystem at Kvíárjökull, Iceland

ABSTRACTGlacier recession and landform development in a debris‐charged glacial landsystem characterized by an overdeepening is quantified using digital photogrammetry, digital elevation model (DEM) construction and mapping of the Icelandic glacier Kvíárjökull for the period 1945–2003. Melting of ice‐cores is recorded by surface lowering rates of 0·8 m yr–1 (1945–1964), 0·3 m yr–1 (1964–1980), 0·015 m yr–1 (1980–1998) and 0·044 m yr–1 (1998–2003). The distribution/preservation of pushed and stacked ice‐cored moraine complexes are determined by the location of the long‐term glacial drainage network in combination with retreat from the overdeepening, into which glacifluvial sediment is being directed and where debris‐rich ice masses are being reworked and replaced by esker networks produced in englacial meltwater pathways that bypassed the overdeepening and connected to outwash fans prograding over the snout. Recent accelerated retreat of Kvíárjökull, potentially due to increased mass balance sensitivity, has made the snout highly unstable, especially now that the overdeepening is being uncovered and the snout flooded by an expanding pro‐glacial, and partially supraglacial, lake. This case study indicates that thick sequences of debris‐charged basal ice/controlled moraine have a very low preservation potential but ice‐cored moraine complexes can develop into hummocky moraine belts in de‐glaciated terrains because they are related to the process of incremental stagnation, which at Kvíárjökull has involved periodic switches from transport‐dominant to ablation‐dominant conditions. Glacier recession is therefore recorded temporally and spatially by two suites of landforms relating to two phases of landform production which are likely typical for glaciers occupying overdeepenings: an early phase of active, temperate recession recorded by push moraines and lateral moraines and unconfined pro‐glacial meltwater drainage; and a later phase of incremental stagnation and pitted outwash head development initiated by the increasing topographic constraints of the latero‐frontal moraine arc and the increasing importance of the overdeepening as a depo‐centre. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Radiocarbon chronology of Holocene glacial and climatic events in southeastern Altai (Central Asia)

The geomorphological studies and radiocarbon dating of moraine complexes and the tree line within the North Chuya Ridge, along with active slope processes, soil formation, and peat formation in southeastern Gorny Altai, constrain the age of the main glacial and climatic events in this area at 7 ka to the first half of the 19th century. It is for the first time in the history of Altai studies that 57 absolute dates were obtained for glaciation in a vast but climatically and neotectonically homogeneous area. The new data refute the conventional idea that the Holocene glaciation in this mountain land comprised eight stages of the gradual retreat of the Late Würm (Sartan) glaciation. Also, they evidence that glaciation in the upper parts of the troughs retreated almost completely no later than 7 ka and valley glaciers in southeastern Altai were activated many times in the second half of the Holocene. Data are given on the morphology and age of three moraine generations reflected in the topography. A combination of temperature minima and humidity maxima led to a catastrophically rapid and the largest (up to 5–6 km) ice advance at the Akkem Stage (4.9–4.2 ka). In addition to the radiocarbon data, the time limits of the Historical stage (2.3–1.7 ka) were defined more precisely using dendrochronological and archaeological data from Scythian burials of Pazyryk culture in SE Altai. The moraines closest to the present-day glaciers formed at the Aktru Stage (late 13th–middle 19th century). During warm interglacials, the glaciers waned considerably or retreated completely and the zone of recent glaciation was reforested. As a result of progressive aridization in the Holocene, the glaciers in southeastern Altai waned at each successive stage, and their mass balance was not positive during the greatest temperature minimum of the last millennium (middle 19th century).

Holocene glacier fluctuations and climate changes in the southeastern part of the Russian Altai (South Siberia) based on a radiocarbon chronology

This study investigates glacier dynamic and climatic variations in the southeastern part of the Russian Altai (SE Altai) during the last 7000 years. Recent glacier retreats and ice melting in moraines has led to exhumation of organic material allowing the possibility of radiocarbon dating. We report here 57 new radiocarbon dates from wood remains buried by moraines and from proglacial forefields, from peat layers and lacustrine sediments that cover moraines, from dead trees at the upper tree limit, and from rock glaciers on trough slopes from six glacial valleys in the North Chuya Range, SE Altai. Such a numerous dataset for the vast but unified in neotectonic and climatic conditions area is presented for the first time the history of research in the Altai.Together with 62 previously published radiocarbon ages, mainly of fossil soils and peat layers in the foot of the ranges in SE Altai, they form the basis for understanding the relative magnitudes and timing of the most important glacial and climatic events of SE Altai. New data refute the traditional concept of the Russian Altai Holocene glaciations as a consecutive retreat of the late Würm glaciers and argue their complete degradation at the head of trough valleys at least 7000 cal. years BP. Moraine complexes of three Holocene glacial stages are morphologically expressed in trough valleys of the North Chuya range. They correlate with three identified periods of glacial advances: from 4900 to 4200 cal. years BP (Akkem stage), from 2300 to 1700 cal. years BP (Historical stage) and in the 13th–19th centuries (Little Ice Age (LIA) or Aktru stage). The coincident extremes of lowering temperature and increasing precipitation during the Akkem stage led to abrupt glacier advances and forming of the most remote moraine complexes downstream in the valleys. Following glacier advances had distinctly smaller magnitudes. In addition to the radiocarbon data, the time limits of the Historical stage were defined more precisely using dendrochronological and archaeological data from Scythian burials of Pazyryk culture in SE Altai. Repeated forest regrowth in the presently glaciatiated area indicates significant retreat or even complete glacier degradation during interstage warming. The decreases of glacier length in the following stages argues for intensification of aridity in the SE Altai during the second half of the Holocene. The thermal minimum in the middle of 19th century, the greatest in the last millennium, did not positively influence the mass balance of glaciers, which also supports this conclusion.

OSL and ESR dating of glacial deposits and its implications for glacial landform evolution in the Bogeda Peak area, Tianshan range, China

The Bogeda Peak area is the largest center of modern glaciation in the eastern Tianshan range in China. Four moraine complexes and associated fluvioglacial deposits are well preserved in the valleys, indicating multiple Quaternary glaciations in this region. Optically stimulated luminescence (OSL) and electron spin resonance (ESR) dating were used to determine the ages of the glacial tills and associated sediments in the Gubanbogeda and Heigou valleys. A total of eighteen samples were collected from moraines and fluvioglacial deposits. Fourteen samples were dated using OSL with a single-aliquot regenerative-dose (SAR) protocol, and the other four samples were analyzed by ESR dating of germanium (Ge) centers in quartz grains, which are sensitive to both sunlight and grinding. The results indicate that the fluvioglacial deposits are more suitable for OSL dating than the tills. Most ages show good agreement with the geological setting and field investigations, and the OSL and ESR ages are consistent with each other for the samples collected from the fourth set of moraines. Based on the ages as well as geomorphic and stratigraphic, the first and second moraine complexes of the Bogeda Peak area were deposited during the Little Ice Age (LIA) and Neoglaciation respectively. The low and high glacial terraces of the third set of moraines in the Gubanbogeda and Heigou valleys were deposited during marine oxygen isotope stages (MIS) 2 and 4. The fourth set of moraines has MIS 6 ages associated with the penultimate glaciation.

Integrated electrical resistivity tomography (ERT) and self-potential (SP) techniques for assessing hydrological processes within glacial lake moraine dams

AbstractMoraine dams can be inherently unstable, but effective assessment strategies remain poorly identified. We integrate electrical resistivity tomography (ERT) with electrical self-potential (SP) and lake-level measurements to investigate the structure of, and hydrological processes within, a moraine-dam complex adjacent to Miage glacier, Italy. This complex separates two meltwater lakes characterized by an efficient subterranean hydraulic connection. Our ERT data reveal a continuous free surface within the complex, whose morphology reflects the topography of the moraine complex akin to unconfined groundwater aquifers. SP data were corrected for spatial changes in the thickness of the upper unsaturated layer using principles of electrography. The residual streaming-potential map is consistent with Darcian flow of lake waters through the moraine complex, characterized by a negative-to-positive potential change from &lt;-30 mV to &gt;+70 mV. These electrical signatures are consistent with those generated by water seepage through earth dams in various non-glacial settings. Integrated electrical geophysical methods thus provided an inexpensive and unobtrusive evaluation of the hydrological properties of and processes within the moraine complex. Since spatio-temporal patterns of subsurface water flow critically affect the strengths of moraine sediments, such methods promise to be powerful in assessing the long-term stability of moraine-dammed glacial lakes.

Stratigraphic architecture and sedimentology of a Late Pleistocene subaqueous moraine complex, southwest Ireland

AbstractGlacigenic sediments exposed in coastal cliffs cut through undulatory terrain fronting the Last Glacial Maximum laterofrontal moraine at Waterville on the Iveragh Peninsula, southwest Ireland, comprise three lithofacies. Lithofacies 1 and 2 consist of interdigitated, offlapping and superimposed ice‐proximal subaqueous outwash and stacked sequences of cohesionless and cohesive subaqueous debris flows, winnowed lag gravels and coarse‐grained suspension deposits. These are indicative of sedimentation in and around small grounding line fans that prograded from an oscillating glacier margin into a proglacial, interlobate lake. Lithofacies 3 comprises braided river deposits that have undergone significant syn‐sedimentary soft‐sediment deformation. Deposition was likely related to proglacial outwash activity and records the reduction of accommodation space for subaqueous sedimentation, either through the lowering of proglacial water levels or due to basin infilling. The stratigraphic architecture and sedimentology of the moraine at Waterville highlight the role of ice‐marginal depositional processes in the construction of morphostratigraphically significant ‘end moraine’ complexes in Great Britain and Ireland. Traditional ‘tills’ in these moraines are often crudely stratified diamictons and gravelly clinoforms deposited in ice‐proximal subaqueous and subaerial fans. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Geophysical surveys of the sediments of Loch Ness, Scotland: implications for the deglaciation of the Moray Firth Ice Stream, British–Irish Ice Sheet

AbstractWe present results from three geophysical campaigns using high‐resolution sub‐bottom profiling to image sediments deposited in Loch Ness, Scotland. Sonar profiles show distinct packages of sediment, providing insight into the loch's deglacial history. A recessional moraine complex in the north of the loch indicates initial punctuated retreat. Subsequent retreat was rapid before stabilisation at Foyers Rise formed a large stillstand moraine. Here, the calving margin produced significant volumes of laminated sediments in a proglacial fjord‐like environment. Subsequent to this, ice retreated rapidly to the southern end of the loch, where it again deposited a sequence of proglacial laminated sediments. Sediment sequences were then disturbed by the deposition of a thick gravel layer and a large turbidite deposit as a result of a jökulhlaup from the Spean/Roy ice‐dammed lake. These sediments are overlain by a Holocene sheet drape. Data indicate: (i) a former tributary of the Moray Firth Ice Stream migrated back into Loch Ness as a major outlet glacier with a calving margin in a fjord‐like setting; (ii) there was significant sediment supply to the terminus of this outlet glacier in Loch Ness; and (iii) that jökulhlaups are important for sediment supply into proglacial fjord/lake environments and may compose &gt;20% of proglacial sedimentary sequences. Copyright © 2011 John Wiley &amp; Sons, Ltd.

In-situ cosmogenic 10Be production rate at Lago Argentino, Patagonia: Implications for late-glacial climate chronology

When calculated with the commonly accepted average Northern Hemisphere production rate, 10Be dates of surface boulders on moraines in the Lago Argentino area of Patagonia are younger than minimum-limiting 14C ages for the same landforms. This disagreement could result from the lack of a regional 10Be production-rate calibration site. To assess this possibility, we here present high-precision measurements of 10Be in samples collected from surface boulders on the Herminita and Puerto Bandera moraine complexes deposited alongside Lago Argentino on the eastern flank of the Andes at 50°S in Patagonia. Together with maximum- and minimum-limiting 14C ages for the two moraine systems, these measurements confine the local 10Be production rate to between 3.60 and 3.82 atoms/g/yr (midpoint = 3.71 ± 0.11 atoms/g/yr) when using a time-dependent scaling method that incorporates a high-resolution geomagnetic model. This range includes upper and lower error bounds of acceptable production rates derived from both the Herminita and the Puerto Bandera sites. The upper limit of this range is more than 12% below the average Northern Hemisphere production rate, as calculated using the same scaling method, given in Balco et al. [Quat. Geochron 3 (2008) 174–195]. Other scaling models yield production rates with similarly large offsets from the Balco et al. (2008) rate. On the other hand, the range of acceptable production rate values determined from Patagonia overlaps at 1σ with, and encompasses, the production rate recently derived in Macaulay valley in the Southern Alps of New Zealand [A. Putnam et al., Quat. Geochron. 5 (2010a) 392–409]. Within uncertainties (i.e., overlap at 1 sigma) this Patagonian production rate range also agrees with a recently determined production rate from low-elevation sites in northeastern North America and northern Norway. When the Macaulay production rate is used to calculate Patagonian exposure dates, 14C and 10Be chronologies are mutually compatible for late-glacial moraine systems. Both chronologies then indicate that outlet glaciers of the Southern Patagonian Icefield achieved a late-glacial maximum in the western reaches of Lago Argentino at 13,000 cal. yr BP at the end of the Antarctic Cold Reversal (14,500–12,900 cal. yr BP). Outlet glaciers subsequently receded to near present-day ice margins during the Younger Dryas stadial (12,900–11,700 cal. yr BP). This general retreat was interrupted about 12,200 cal. yr BP when Upsala Glacier constructed an interlobate complex of moraine ridges on Herminita Peninsula. Mountain glaciers in Patagonia and New Zealand, on both sides of the South Pacific Ocean, exhibited a coherent pattern of late-glacial ice-margin fluctuations.

The hydrology of the proglacial zone of a high-Arctic glacier(Finsterwalderbreen, Svalbard): Sub-surface water fluxes and complete water budget

Summary Proglacial areas receive fluxes of glacial meltwater in addition to their own hydrological inputs and outputs, while in high latitudes the seasonal development of the active layer also affects their hydrology. This paper supplements a previous study of the surface and atmospheric water fluxes in the proglacial area of the Svalbard glacier Finsterwalderbreen (77° N), by focusing on the sub-surface water fluxes of the active layer, and bringing together all the components of the proglacial water balance over a complete annual cycle. Particular attention is given to the transitional zone between the moraine complex and the flat sandur. Sub-surface water in the moraine complex (sourced mainly from snowmelt, lake drainage and active-layer thawing), is exchanged with sub-surface water from the sandur (sourced mainly from glacier-derived snow- and ice-melt), across a largely distinct boundary. Hydraulic head and specific discharge were monitored in a transect of wells spanning this boundary. A hydraulic gradient from the moraine complex to the sandur is maintained throughout the melt season, although this is reversed first briefly when glacial runoff floods the sandur, and then diurnally from mid-melt-season, as peak daily flow in the proglacial channel network drives sub-surface water in the sandur towards the moraine complex. It is estimated that the active layer does not freeze up until mid-December at this location, so that sub-surface water flow may be maintained for months after the cessation of surface runoff. However, the magnitude of sub-surface flow is very small: the total, annual flux from the moraine complex to the sandur is 11 mm, compared with 1073 mm of total, annual runoff from the whole catchment (glacier included). Furthermore, when considering the water balance of the entire proglacial area, there are unlikely to be significant, seasonal storage changes in the active layer.

Paired bedrock and boulder 10Be concentrations resulting from early Holocene ice retreat near Jakobshavn Isfjord, western Greenland

We measured in situ cosmogenic 10Be in 16 bedrock and 14 boulder samples collected along a 40-km transect outside of and normal to the modern ice margin near Sikuijuitsoq Fjord in central-west Greenland (69°N). We use these data to understand better the efficiency of glacial erosion and to infer the timing, pattern, and rate of ice loss after the last glaciation. In general, the ages of paired bedrock and boulder samples are in close agreement ( r 2 = 0.72). Eleven of the fourteen paired bedrock and boulder samples are indistinguishable at 1 σ; this concordance indicates that subglacial erosion rates are sufficient to remove most or all 10Be accumulated during previous periods of exposure, and that few, if any, nuclides are inherited from pre-Holocene interglaciations. The new data agree well with previously-published landscape chronologies from this area, and suggest that two chronologically-distinct land surfaces exist: one outside the Fjord Stade moraine complex (∼10.3 ± 0.4 ka; n = 7) and another inside (∼8.0 ± 0.7 ka; n = 21). Six 10Be ages from directly outside the historic (Little Ice Age) moraine show that the ice margin first reached its present-day position ∼7.6 ± 0.4 ka. Early Holocene ice margin retreat rates after the deposition of the Fjord Stade moraine complex were ∼100–110 m yr −1. Sikuijuitsoq Fjord is a tributary to the much larger Jakobshavn Isfjord and the deglaciation chronologies of these two fjords are similar. This synchronicity suggests that the ice stream in Jakobshavn Isfjord set the timing and pace of early Holocene deglaciation of the surrounding ice margin.

The formation of Alpine lateral moraines inferred from sedimentology and radar reflection patterns: a case study from Gornergletscher, Switzerland

Abstract Studies on the formation of alpine lateral moraines are rare; consequently, their internal structure and their modes of formation are relatively poorly understood. We present here sedimentological and ground-penetrating radar (GPR) data from a lateral moraine complex where an exposure allows radar facies to be compared to the field evidence. The moraine, which is slightly asymmetric with a slightly steeper distal slope, consists of alternating clast- and matrix-supported stratified diamicts and intercalated sorted sediment units which are all subparallel to the moraine surface. They are interpreted as subaerial debris flows and fluvial sediments, respectively. The GPR, using frequencies of 50, 100 and 200 MHz, allows tracing of very similar subparallel reflectors to c. 10 m into the subsurface. These are interpreted to represent the diamict units while the thickness of the sorted sediment units is below GPR resolution. Our data suggests that a two or three frequency approach supplemented by common-midpoint (CMP) measurements works well in glaciated high-mountain environments. Based on our sedimentological and GPR data we develop a conceptual framework for the formation of successive lateral moraines which involves ice-contact fan sedimentation, followed by collapse and incremental reworking of the proximal side during glacier retreat.

New findings concerning the Pleistocene Glaciation of the Leh Basin, Ladakh (34°03′ N/77°38′ E)

Like for most parts of High Asia, researches concerning the Pleistocene landscape evolution of the Leh Basin (34°03′ N/77°38′ E) have also left contradictions. To push this topic, three up to now unexplored Ladakh Range tributaries of the Leh Basin (Stagmo-, Arzu- and Nang-Valley) have been investigated. U-shaped profiles, transfluence passes, moraine mantled and glacially rounded peaks and ridges, roches moutonnees, glacial flank polishings and ground moraines document the former glaciation of the study area. The ice fillings of these tributaries reached a minimum thickness up to 540 m. Even at the valley outlets and on the orographic right side of the Leh Basin, the glaciation was more than 350 m thick. Based on these empirically extracted results, theoretical snow line considerations lead to the conclusion that the whole Leh Basin was filled up by a former Indus-Valley glacier. An ice injection limited to the nourishment areas of the Ladakh Range valleys could not have caused the reconstructed ice cover (down to 3236 m a.s.l.), which is proved by extended ground moraine complexes. Only an Indus ice stream network (most likely during the LGP), nourished by inflowing glaciers of the Ladakh- and Stok Range, explains the widespread existence of the glacial sediments at the outlets of the investigated valleys.

Cosmogenic radionuclide chronology of pre-last glacial cycle moraines in the Western Arthur range, Southwest Tasmania

Cosmogenic 10Be and 26Al exposure ages of 12 boulders from two moraine complexes in the Western Arthur Range of southwest Tasmania, which previously were considered to have been deposited during the Last Glacial Maximum, predate the Last Glacial Cycle. Zero-erosion minimum exposure ages range from 95 ka to 232 ka based on weighted mean 10Be and 26Al ages per boulder. For a reasonable choice of erosion rates, 10Be boulder ages range from 105 to 326 ka, respectively. Although a direct association of moraine construction to a specific marine isotope stage (MIS) glaciation is not definitive, erosion-corrected exposure ages indicate glacial advances commensurate with MIS-6 and -10, although the latter advance may be attributable to MIS-8 if the erosion rate correction is an over-estimate. Given the relatively close proximity of the dated moraines to their source cirques, this new cosmogenic glacial chronology implies a very limited extent for any younger glacial advances that occurred in the Western Arthur Range during the Last Glacial Cycle (post MIS-5) including the global LGM.