Supraglacial Moraines Research Articles

Migrating boulders on the surface of Alpine valley glaciers

ABSTRACT Boulders in the ablation areas of Alpine valley glaciers were found to not travel along with the ice in a passive manner only. Many show an additional but smaller component of movement towards the south. We investigate this phenomenon and its governing processes using field observations and measurements from terrestrial and aerial photographs of glaciers in the Swiss Alps. We found that large boulders can migrate from their medial moraine due to cyclic formation of classical glacier tables and also a similar process that produces ice tails. The main driving factors behind boulder migration are the size (and shape) of the boulder, ablation, radiation, and surface slope. On glaciers roughly oriented to the east or west, these processes result in a sorting of boulders from the supraglacial moraine towards the southern side, i.e. towards the sun. Future studies complementing our approach using a differential global positioning system should be able to better distinguish between the velocity components of ice flow and boulder migration, determine the precise azimuth of the latter, and investigate the potential influence on photogrammetric feature tracking.

Sedimentological and mineralogical characteristics of active glacial sediments in the Indian Himalaya regions

ABSTRACT Glaciated sediments are a significant source to know the glacier environment processes. Glacial meltwater streams draining from the Himalayan glaciers carry with a different type of sediment sizes, because of the supraglacial, englacial, and subglacial debris, as well as formation of sediments from erosion by the movement of the ice. This study examines mineralogical and textural characteristics of sediments transported in the selected Indian Himalayan glacier meltwater streams. The results indicate that various sedimentological diversity occurring within proximity of active glaciations due to glacio-hydrological processes. Sedimentological and mineralogical characteristics suggest that sediments of the proglacial area are polygenic in nature. A comparative change in feldspar/quartz among bedrock, sand, and clay suggested that the active geochemical weathering regime at a low-temperature environment maturing the sand composition. The less clay fraction in glacier sediment indicates limited generation of clay minerals in the glacier environment. Change in clay composition from supraglacial moraine to proglacial environment indicated a chemical alteration in glaciated valley assisted by low slope glacio-fluvial environment.

The January 2018 to September 2019 surge of Shisper Glacier, Pakistan, detected from remote sensing observations

This study analysed the actively surging Shisper Glacier in the Karakoram region of Pakistan using earth observation data from Landsat 8 OLI and Planet images. Changes in the surface glacier velocity, supraglacial moraines and debris cover were assessed using Landsat 8 data at monthly time-steps from January 2018 to May 2019. High resolution data from Planet Labs was used to precisely detect the snout advance and ice-dammed lake expansion. Downstream cross-section profiles of the valley were generated using a moderate resolution digital elevation model to assess the inundation in the event of rapid ice-dammed lake drainage. Correlation Image Analysis Software working on the principle of normalized cross-correlation was used to generate time series monthly surface velocity profiles for Shisper Glacier. Manual digitization at 1:30000 scale was used to delineate supraglacial moraines and supraglacial debris cover. The glacier surface velocity profiles indicate that the ablation zone of the glacier continues to be in an active surge phase resulting in advance of the snout and expansion of the ice-dammed lake. Surface glacier velocities are as high as 48 m d−1. Between 18 December 2018 and 8 May 2019, the glacier snout advanced at ~6 m d−1 with a total overall advance of 860 m. The lake formed due to damming of an outflow stream from Mochowar Glacier expanded to its maximum area (29.69 ha) in May 2019 before drainage started on 23 June 2019. Our estimates indicate that the peak discharge in case of rapid drainage could vary between 5033 m3 s−1 and 6167 m3 s−1 and potentially affect infrastructure downstream.

Accumulation mechanisms of micrometeorites in an ancient supraglacial moraine at Larkman Nunatak, Antarctica

AbstractWe report the discovery of a large accumulation of micrometeorites (MMs) in a supraglacial moraine at Larkman Nunatak in the Grosvenor Mountains of the Transantarctic Range in Antarctica. The MMs are present in abundances of ~600 particles kg−1 of moraine sediment and include a near‐complete collection of MM types similar to those observed in Antarctic blue ice and within bare‐rock traps in the Antarctic. The size distribution of the observed particles is consistent with those collected from snow collections suggesting the moraine has captured a representative collection of cosmic spherules with significant loss of only the smallest particles (<100 μm) by wind. The presence of microtektites with compositions similar to those of the Australasian strewn field suggests the moraine has been accumulating for 780 ka with dust‐sized debris. On the basis of this age estimate, it is suggested that accumulation occurs principally through ice sublimation. Direct infall of fines is suggested to be limited by snow layers that act as barriers to accumulation and can be removed by wind erosion. MM accumulation in many areas in Antarctica, therefore, may not be continuous over long periods and can be subject to climatic controls. On the basis of the interpretation of microtektites as Australasian, Larkman Nunatak deposit is the oldest known supraglacial moraine and its survival through several glacial maxima and interglacial periods is surprising. We suggest that stationary ice produced by the specific ice flow conditions at Larkman Nunatak explains its longevity and provides a new type of record of the East Antarctic ice sheet.

GEOMORPHOLOGY AND SEDIMENTOLOGY OF UNION GLACIER AREA, ELLSWORTH MOUNTAINS, OCCIDENTAL ANTARCTICA

The work aims to investigate the geomorphological and sedimentological aspects of Union Glacier area (79°45’00’’S; 82°30’00’’W), southern sector of Ellsworth Mountains. Geomorphological cartography based on 15 m ASTER (2010) satellite imagery and field works were carried out during the Brazilian expedition (2011/2012) enabled the identification of morainic formations: ice-cored hummock moraines, supraglacial moraines, and recession moraines in the interior of the valleys. With the exception of the latter one, all types of moraines have been developed on the blue-ice areas. The evidence for paleo wet-based glacial conditions is reconstructed from a range of geomorphological record, including exposed abrasion marks, striations and glaciotectonic deformation. This type of deformation is represented by lee sides of oversteepening bedrock promontories which follow the tributaries of glaciers ice flow. Glacial sediments were collected from the moraines for granulometric and morphometric analyses. They show the prevalence of sandy gravel and sand texture, low quantity of fine fractions, and absence of attributes such as striated and faceted clasts, which indicate, on the other side, low-sediment transport capacity from the ice sheet bottom. It is inferred that the moraine debris are originated from local sources. Weathering action and constant katabatic winds are possibly the major agents of transport and alteration of the exposed sediments. The geomorphological features reveal an ancient thicker ice sheet, and sedimentary characteristics of the morainic formations reveal a latter thinner ice sheet in this sector of Ellsworth Mountains.

Detailed dynamic, geometric and supraglacial moraine data for Glaciar Pio XI, the only surge-type glacier of the Southern Patagonia Icefield

ABSTRACTIn contrast to the general trend for glaciers of the Southern Patagonia Icefield, Glaciar Pio XI has experienced a large cumulative frontal advance since 1945. In an effort to better understand this advancing behaviour, this paper presents a synoptic analysis of frontal fluctuations (1998–2014), ice velocities (1986–2014), ice-surface elevations (1975–2007) and supraglacial moraines (1945–2014) derived from geospatial datasets. These analyses reveal changes in the ice flow of Glaciar Pio XI's freshwater calving northern terminus and tidewater calving southern terminus over recent decades. Between 1986 and 2000, ice flow speed generally accelerated reaching peaks of >15 m d−1 at the frontal edge of the southern terminus. Following this period, flow speed decreased, reducing to <1 m d−1 for the central part of the southern terminus in 2014, despite advancing to a neoglacial maximum. From 2000 to 2014 the reduction in speed was accompanied by a shift in maximum velocity away from the southern terminus, towards the central glacier trunk. As a result, the northern terminus, which accelerated during this period, represented the new primary flow path in 2014. Notably, the moraine maps presented highlight surges occurring around 1981 and again between 1997 and 2000, marked by arcuate moraine features on the southern terminus.

Pattern of retreat and related morphological zones of Gangotri Glacier, Garhwal Himalaya, India

Gangotri, one of the longest valley glaciers of the Garhwal Himalaya has attracted global attention due to rapid rate of retreat. It is characterized by supraglacial moraines, supraglacial lakes, intensive crevasses, active and inactive tributary glaciers which were mainly responsible for the enhanced recession rate of the glacier. However, contrary to the generally accepted notion of “Global Warming”, the Gangotri Glacier has been experiencing diminishing rates of retreat during last five decades. High retreat rate of 38 m/y observed in 1970s has been reduced in 1980s and maintaining the similar trend in the recent decades with reduced rate of retreat around 10 m/y in 2015. The measurement of Equilibrium Line Altitude (ELA) and ablation area over the last few decades also explained that the response of Gangotri Glacier is not in pace with the global warming trend.Glacial (Gl) and glacio-fluvial (Gf) features have been identified as the marker morphological zones which provides information about pattern of retreat and ELA. The sediment size decreases whereas sorting, roundness and percentage of matrix increases from Gl-Gf zone. The glacial zone contains the primary sediments and provides information about the pattern of retreat and ELA. The glacio-fluvial outwash plain exhibits modification of glacial signatures and often contains secondary sediments.Further, different rate of fluctuation observed in different glaciers indicate that the glaciers are not uniformly responding with change in climatic conditions, especially with respect to global warming. Such observations and present study suggest that fluctuation of a glacier is not only controlled by global warming induced temperature but also governed by characteristics of the glacier and local morphological factors. Hence, the analysis of the pattern of retreat, ELA and retreat related morphological zones, provide real information and precise glacial history of the area.

A new concept for glacial geological investigations of surges, based on High-Arctic examples (Svalbard)

Svalbard is a key area for the investigation of glacial surges, and almost two centuries worth of field observations exists from this region. Studies have shown that the course of a surge and the associated formation of landforms are strongly influenced by basinal factors, and that the broad range of variables involved can hamper interpretations and comparisons. Based on a review of surges in Svalbard, a new concept for glacial geological investigations has been developed that combines ice-flows, ice-front movements, and morphostratigraphy. The concept is comprised of the following four elements: 1) classification based on the configuration and characteristics of the receiving basin, 2) division of the surge cycle into six stages, 3) guidelines for morphological mapping, and 4) use of an allostratigraphic approach for interpreting ice-front movements. In this context, delineation of the active phase is critical, which include the history of terminus movements, and four main categories of receiving basins are recognized. These are (A) terrestrial basins with deformable substrates, (B) terrestrial basins with poorly deformable substrates, (C) shallow water basins, and (D) deep water basins. The ice-front movement history is reconstructed by coupling information from the proglacial moraines (syn-surge), the supraglacial moraines (post-surge), and the associated traces of meltwater to the surge stages (I–VI). This approach has revealed a critical relationship between the termination of the active phase and three morphological elements, namely, the maximum ice-front position, the maximum moraine extent and the youngest proglacial moraine, which are unique for each of the basins A–D. The concept is thus a novel and more precise approach for mapping the active phase and the active phase duration, as shown by the ∼12-year long surge of Fridtjovbreen, where stage I was 30 months (inception), stage II was 54 months (ice-front advance), stage III was 12 months (stillstand), and stage IV was 48 months (retreat during active flow). The glacier has been in quiescent phase (stages V/VI) since 2002.

Carbon dioxide flux in the ablation area of Koxkar glacier, western Tien Shan, China

AbstractAccelerating loss of glacial mass caused by rising global temperatures has significant implications. The global cycle of the greenhouse gas CO2 is also associated with mineral weathering and glaciation. In glaciated areas, most estimates of atmospheric CO2 consumption are confined to chemical ionic mass balance or analog modeling methods. We applied the gradient method to the surface of Koxkar glacier, western Tien Shan, China, for a 5 month period during 2012. The overall net glacier-system CO2 exchange (NGE) rate was measured as -0.05 and -0.07mmol m–2 s–1 for regions of exposed ice and supraglacial moraine, respectively. This suggests that atmospheric CO2 drawdown may occur during ice melting because of consumption of H+ by CO2 hydrolysis that occurs in solutions. Using the degree-day model to calculate glacier ablation in bare-ice regions and considering characteristics of the NGE rate in the supraglacial debris region with the support of GIS, the daily NGE rate was estimated to be -1.23 ± 0.17μmmol m–2 d–1 between Julian days 125 and 268 of 2012. These findings present a new approach for modeling the dynamics of glacial CO2 sinks undergoing melting, and develop an understanding of the mechanism of atmospheric CO2 exchange.

Sub‐debris melt rates on southern inylchek glacier, central tian shan

.Melt rates of glacier surfaces are strongly influenced by the existence of a debris cover. Dependent on thickness and other physical parameters, the debris layer can enhance or reduce ablation as compared to bare ice conditions. Supraglacial moraines appear very frequently on Central Asian glaciers, greatly affecting water yield from these high mountain regions. In summer 2005, a network of 22 ablation stakes was drilled into locations with varying debris thicknesses on southern Inylchek Glacier in the central Tian Shan. Mean ablation rates varied from 2.8 to 6.7 cm/day, strongly correlated with moraine thickness. Parallel observation of air temperature allowed the application of a simple degree‐day approach and the calculation of ablation rates. Efforts to improve calculations of melt rates by incorporating relative air humidity to account for latent heat fluxes failed. This proves that air temperature is already a very good melt indicator. Ice albedo measurements show that reflectivity might be controlled by the occurrence of evaporation or condensation, but this topic needs further investigation.

Glaciological results of the 2005 expedition to Inylchek Glacier, Central Tian Shan

Like many other glaciers in Central Asia, Southern Inylchek glacier in the Kyrgyz Tian Shan is covered by supraglacial moraine, which drastically influences melt rates and complicates the estimation of ablation. The quantification of sub-debris melt from simple parameters is still an unsolved problem, but also essential to predict future yield from high mountains. Snow cover and glacier ice are the main water storages for the surrounding arid lowlands and a better understanding of ablation processes is the prerequisite for a sustainable water resources management. Another interesting feature of Southern Inylchek glacier is the existence of an ice dammed lake in a tributary valley, which is drained regularly by outburst floods. Improvements in predicting these floods would lower the risk potential for the downstream population. The main objectives of a group of glaciologists which participated in an expedition to the glacier in 2005 were to investigate melt rates on debris covered glacier parts and to quantify the ice flux into the glacier lake. The results of their field experiments are reported in this paper.

Cirque infills in the Khibiny Mountains, Kola Peninsula, Russia — palaeoglaciological interpretations and modern analogues in East Antarctica

AbstractWe report here on cirque infills mapped in the Khibiny Mountains, Kola Peninsula, Russia. Cirque infills are morainic deposits located near the headwalls of valleys and cirques. Their location and shape, often with concave margins towards the valley side, indicate that they were deposited by ice flowing up‐valley, into the mountains, rather than by local glaciers. We suggest that they formed during the last deglaciation, when Khibiny was a nunatak and Fennoscandian ice sheet lobes extended into valleys and cirques of the massif. The formation of cirque infills is probably more related to ice sheet dynamic factors, occurring when the ice margin retreated from the cirques, than to climate‐driven interruption in the ice‐marginal retreat. Glacial conditions similar to those prevalent when the Khibiny cirque infills were formed, occur today in Antarctica where the ice sheets engulf nunatak ranges. In Heimefrontfjella, Antarctica, the formation of supraglacial moraines at the head of cirques are linked to blue‐ice conditions, indicating locally low accumulation rates, a dry continental climate and sublimation dominated ablation. We suggest that these Antarctic moraines are modern analogues of cirque infills on the Kola Peninsula, and possibly, that the cirque infills may be used as palaeoenvironmental indicators. Copyright © 2007 John Wiley & Sons, Ltd.

Supraglacial moraines in Scharffenbergbotnen, Heimefrontfjella, Dronning Maud Land, Antarctica – significance for reconstructing former blue ice areas

The ice surface of the glacier in the 7 km long valley Scharffenbergbotnen in Heimefrontfjella, Dronning Maud Land, is characterized by blue ice fields and is partly covered by supraglacial moraine complexes. The debris cover of the supraglacial moraines is generally less than 50 cm thick and rests on glacial ice, and most of the surface morphology of ridges and numerous sink holes reflects irregularities in the underlying ice. The debris consists of angular to sub-angular clasts of local bedrock. We interpret the moraines to have an entirely supraglacial history, where colluvium and pre-existing moraines were brought into Scharffenbergbotnen primarily from the south/south-west by an advancing glacier during the last ice maximum in the region. The debris cover of the supraglacial moraines extends up to 200–250 m above the present ice surface on surrounding slopes in Scharffenbergbotnen, and generally to less than 100 m above the present ice surface on slopes outside the valley. We interpret this as marking the ice surface elevation in the area during the last ice maximum (probably LGM). The deposition of supraglacial moraines in the valley at that time, and their survival in the area until the present day, indicate that a local ablation centre and probably blue ice fields were present in Scharffenbergbotnen at LGM, and has been a persistent feature since. In a wider context, we argue that supraglacial moraines constitute a hitherto unexploited resource when reconstructing the former extent of blue ice areas.

A sedimentological and isotopic study of the origin of supraglacial debris bands: Kongsfjorden, Svalbard

AbstractDebris bands associated with supraglacial moraines and associated basal deposits have been logged and sampled for their ice and debris at three glaciers in northwest Spitsbergen, Svalbard. Physical properties, including sediment concentrations, sediment particle-size distributions, clast macro-fabrics, and oxygen isotope compositions, indicate that all transverse and some longitudinal debris bands originate from the basal zone of these glaciers. Transverse supraglacial bands are composed of extensive stratified-facies basal ice that is enriched in 18O and which contains polymodal debris with spatially consistent clast fabrics. These properties suggest initial formation as basal ice and subsequent elevation into an englacial position by thrusting rather than formation as crevasse fills. The formation of longitudinal debris bands results from laterally compressive folding in response to the convergence of multiple flow units into a narrow glacier tongue. In common with transverse debris bands, longitudinal bands appear to be composed of stratified basal ice. The bands exposed at the surface of austre Brøggerbreen comprise two subfacies, strongly suggesting that the glacier was at least partially warm-based in the past, when the basal ice formed.

Narrowband-to-broadband albedo conversion for glacier ice and snow based on aircraft and near-surface measurements

This article presents albedo measurements of snow and glacier ice at Vatnajökull (Iceland) and the Kangerlussuaq transect (Greenland). Radiative fluxes were measured in the broadband and in four narrowbands, namely, Thematic Mapper (TM) Bands 2 and 4, and Advanced Very High Resolution Radiometer (AVHRR) Bands 1 and 2. The incoming fluxes were measured near the ground and the outgoing fluxes from a helicopter. Extracts of the data collected over snow, ice, supraglacial moraines, supraglacial lakes, and tundra are discussed. Using the data sets from Iceland and Greenland, and data sets with entirely ground-based albedo measurements from the Morteratschgletscher (Switzerland) and Scharffenbergbotnen (Antarctica), new equations for narrowband-to-broadband (NTB) conversion were developed. They have a residual standard deviation of 0.011 for TM and 0.008 for AVHRR and can be applied without having to classify the surface. The helicopter data are also used to develop criteria for distinguishing different types of surfaces, which are needed for the application of Bidirectional Reflectance Distribution Functions (BRDFs). Snow can be distinguished from ice by defining a threshold for a single narrowband albedo. The ratio of the albedos in TM4 and TM2, and to a lesser extent, the ratio of the albedos in AVHRR2 and AVHRR1, may serve as a proxy for the surface characteristics of glacier ice in terms of concentrations of water, debris, and dust.

Controls on the major-ion chemistry of the Dokriani glacier meltwaters, Ganga basin, Garhwal Himalaya, India

AbstractA detailed study of the major-ion chemistry of the Dokriani glacier meltwaters, feeding the Bhagirathi river, Ganga basin, Garhwal Himalaya, India, has been carried out to assess the role of active glaciers in the higher chemical-denudation rate (CDR) in this area. The CDR of the Dokriani glacier catchment is 321.6 t km-2 a-1, higher than in other glacierized catchments of the world, indicating intense chemical erosion in the glacierized catchments of the Himalaya. The dominance of Ca2+, HCO3- and SO42- in meltwaters throughout the 6 month (May–October) ablation period suggests that the chemical weathering is dominated by coupled reactions involving sulphide oxidation and carbonate dissolution. Good positive correlation between SO42- and suspended-sediment concentration during July and August (r2 = 0.72 and 0.67, respectively) suggests that the southwest monsoonal rainfall enhances the weathering of supraglacial moraine and contributes significant amounts of sulphate to the high meltwater discharges. The sulphate flux, as a proportion of combined (SO42- + HCO3-) flux, also increased from 45% at 2 m3 s-1 to 63% at 10 m3 s-1.

Controls on the major-ion chemistry of the Dokriani glacier meltwaters, Ganga basin, Garhwal Himalaya, India

AbstractA detailed study of the major-ion chemistry of the Dokriani glacier meltwaters, feeding the Bhagirathi river, Ganga basin, Garhwal Himalaya, India, has been carried out to assess the role of active glaciers in the higher chemical-denudation rate (CDR) in this area. The CDR of the Dokriani glacier catchment is 321.6 t km-2 a-1, higher than in other glacierized catchments of the world, indicating intense chemical erosion in the glacierized catchments of the Himalaya. The dominance of Ca2+, HCO3- and SO42- in meltwaters throughout the 6 month (May–October) ablation period suggests that the chemical weathering is dominated by coupled reactions involving sulphide oxidation and carbonate dissolution. Good positive correlation between SO42- and suspended-sediment concentration during July and August (r2 = 0.72 and 0.67, respectively) suggests that the southwest monsoonal rainfall enhances the weathering of supraglacial moraine and contributes significant amounts of sulphate to the high meltwater discharges. The sulphate flux, as a proportion of combined (SO42- + HCO3-) flux, also increased from 45% at 2 m3 s-1 to 63% at 10 m3 s-1.

Flux of debris transported by ice at three Alaskan tidewater glaciers

AbstractThe stability of a tidewater terminus is controlled by glacial dynamics, calving processes and sedimentary processes at the grounding line. An investigation of grounding-line sediment dynamics and morainal-bank sediment budgets in Glacier Bay, Alaska, U.S.A., has yielded data that enable us to determine the debris fluxes of Grand pacific, Margerie and Muir Glaciers. Debris flux ranges from 105to 106m3a−1, one to two orders of magnitude lower than the glacifluvial sediment fluxes (106−107m3a−1). Combined, these fluxes represent the highest yields known for glacierized basins. Large debris fluxes reflect the combined effects of rapid glacier flow, driven by the maritime climate of southeast Alaska, and highly erodible bedrock. Englacial-debris distribution is affected by valley width and relief, both of which control the availability of sediment. The number of tributaries controls the distribution and volume of debris in englacial and supraglacial moraines. At the terminus, iceberg-rafting removes up to two orders of magnitude more sediment from the ice-proximal environment than is deposited by melt-out or is dumped during calving events. Rough estimates of the sediment flux by deforming beds suggests that soft-bed deformation may deliver up to an order of magnitude more sediment to the terminus than is released from within the glacier ice.

Flux of debris transported by ice at three Alaskan tidewater glaciers

AbstractThe stability of a tidewater terminus is controlled by glacial dynamics, calving processes and sedimentary processes at the grounding line. An investigation of grounding-line sediment dynamics and morainal-bank sediment budgets in Glacier Bay, Alaska, U.S.A., has yielded data that enable us to determine the debris fluxes of Grand pacific, Margerie and Muir Glaciers. Debris flux ranges from 105 to 106 m3 a−1, one to two orders of magnitude lower than the glacifluvial sediment fluxes (106−107 m3 a−1). Combined, these fluxes represent the highest yields known for glacierized basins. Large debris fluxes reflect the combined effects of rapid glacier flow, driven by the maritime climate of southeast Alaska, and highly erodible bedrock. Englacial-debris distribution is affected by valley width and relief, both of which control the availability of sediment. The number of tributaries controls the distribution and volume of debris in englacial and supraglacial moraines. At the terminus, iceberg-rafting removes up to two orders of magnitude more sediment from the ice-proximal environment than is deposited by melt-out or is dumped during calving events. Rough estimates of the sediment flux by deforming beds suggests that soft-bed deformation may deliver up to an order of magnitude more sediment to the terminus than is released from within the glacier ice.

Glacier disequilibrium in the Convoy Range, Transantarctic Mountains, Antarctica

Field work for a geological map of the Convoy Range included mapping glaciers, moraines and surficial deposits. A range of glaciological indicators, including supraglacial and other moraines and margin morphology, has been used to assess the present equilibrium of the glaciers. Fields of rafted supraglacial moraine have accumulated over long periods of time at specific low-gradient, low-velocity locations. As the glacier regime changes, the shape of the moraine field distorts, signalling a change in flow pattern. By reversing the ice flow vectors directed at the moraine field, the directions from whence the debris came are shown. Unsorting the contortions of supraglacial moraine fields reveals the nature of the changes in glacier regime. Moraine-field configurations all suggest that local glaciers are expanding in response to higher local precipitation, estimated to have occurred between 2000 and 8000 year BP, most likely coincident with the world-wide “climatic optimum” of about 6000 year BP.Ice-cliff morphology, fresh terminal moraines and boulder trains indicate that larger local glaciers are currently receding from a Holocene maximum, while the margin of the large Mackay Ice Sheet outlet glacier shows no evidence of recent recession and is probably close to its Holocene maximum. In contrast, areas of present snow cover are expanding, superimposing a recent positive balance (decades to hundreds of years), which has yet to reverse a general recession of mid- to high-altitude glaciers. Local hollows in some névé areas imply that glacier flow is not in equilibrium with snow accumulation.