Meltwater Availability Research Articles

Estimation of Surface Ice Velocity of Durung Drung Glacier, Western Himalaya using COSI-Corr from Landsat images

Glaciers all over the world have been experiencing recession at varying rates. Alterations in glacial retreat, volume, and mass have direct implications for sea level rise and have implications for the overall health of glaciers. Measuring the surface ice velocity of glaciers presents challenges due to the rugged terrain and harsh climate at high altitudes, making field observations difficult. This study aims to address these challenges by focusing on the calculation of the surface ice velocity of the Durung Drung glacier in Zanskar Valley, Ladakh. Landsat- 7 & 8 panchromatic bands with a resolution of 15 m were used in conjunction with the COSI-Corr module of ENVI image processing software to derive surface ice velocity. The method involved the crosscorrelation of Landsat images from 1999/2000 and 2019/2020. The COSI-Corr module used in this study provided three key outputs: east–west displacement, north–south displacement, and signal-to-noise ratio. These outputs are essential for understanding the movement of the glacier and evaluating the quality of the image correlation. The results indicate that the surface velocity of Durung Drung glacier was 71 ± 6.1 m yr−1 in 1999/2000, which increased (by ∼ 50 %) to 140 ± 7.4 m yr−1 in 2019/2020. An increasing trend in velocity manifests the rising trend in temperature in the western Himalaya. Analysis of CRU TS4 gridded data reveals an increase in temperature while precipitation decreased during 1976–2020. The study recommends that the annual variations in surface ice velocity are a consequence of temperature fluctuations that influence the availability of meltwater.

Surface and subsurface flow of a glacierised catchment in the cold-arid region of Ladakh, Trans-Himalaya

Hydrological assessments of high-altitude catchments in Trans-Himalayan Ladakh are necessary for a better understanding of water availability in the context of irrigated cultivation under conditions of insufficient quantitative information on cryospheric meltwater discharge. In this study, an integrated spatially distributed temperature index model and a coupled surface/subsurface flow model were used to simulate daily, seasonal, and annual surface and subsurface flows to assess the proportion of corresponding source contributors from the Stok catchment. Snow and glacier meltwater discharge secures irrigated agriculture of more than 300 households in this catchment. The models were forced by temperature, precipitation, ice- and snow-covered areas at daily time steps with calibration (2019; 108 days) and validation (2018; 93 days) against the observed discharge. The simulated discharge shows a good agreement with the observed discharge with R2 and RMSE of 0.8 (p < 0.01) and 0.6 m3/s, respectively. The results between 2003 and 2019 show that the snowmelt contribution to the total annual discharge is largest with 65 %, followed by glacier melt and rainfall contributions of approximately 19 % and 16 %, respectively. A reduction in glacierised areas by 4.2 % was observed while snow-covered areas showed high inter-annual variation. Simulated subsurface flow makes up 62 % (mean = 37.2 × 106 m3) of the total discharge with less inter-annual variation. The simulation suggests that while surface flow ceases during the winter period and peaks in August, the annualized mean flow amounts to ∼23.7 × 106 m3. More than 50 % of the melt occurs in the summer months of June, July and August, when the intensity of snowmelt, ice melt, and rainfall reach its maximum. The findings of this study on meltwater availability and surface/subsurface flow is important for irrigated agriculture of Stok village on a local scale, and it might also help to better understand socio-hydrological dynamics and situations of water scarcity in the wider cold-arid region of Ladakh.

Distinct modes of meltwater drainage and landform development beneath the last Barents Sea ice sheet

The flow of glacial ice is impacted by basal meltwater drainage systems that fluctuate on a continuum from distributed, high-pressure environments to channelized, lower pressure networks. Understanding the long-term development of dominant drainage modes and impacts on ice flow and landform development is a crucial step in predicting palaeo and contemporary ice-mass response to changes in climate. The spatial and temporal scales at which different drainage modes operate are largely unknown, and the geomorphological legacy of subglacial meltwater networks that evolve over a glaciation provide composite records of drainage system development. Here, we use high-resolution bathymetric data from shallow banks in the central Barents Sea to map the geomorphological imprint of meltwater drainage beneath the collapsing marine-based Barents Sea Ice Sheet (BSIS). We observe a succession of distinct meltwater landforms that provide relative timing constraints for subglacial drainage modes, indicating that extensive networks of channelized drainage were in operation during deglaciation. Interlinked basins and channels suggest that meltwater availability and drainage system development was influenced by filling and draining cycles in subglacial lakes. Networks of eskers also indicate near-margin meltwater conduits incised into basal ice during late-stage deglaciation, and we suggest that these systems were supplemented by increased inputs from supraglacial melting. The abundance of meltwater during the late stages of BSIS deglaciation likely contributed to elevated erosion of the sedimentary substrate and the mobilisation of subglacial sediments, providing a sediment source for the relatively abundant eskers found deposited across bank areas. A newly discovered beaded esker system over 67 km long in Hopendjupet constrains a fluctuating, but generally decelerating, pace of ice retreat from ∼1,600 m a−1 to ∼620 m a−1 over central Barents Sea bank areas during a 91-year timespan.

Dynamics throughout a complete surge of Iceberg Glacier on western Axel Heiberg Island, Canadian High Arctic

AbstractThis study provides the first comprehensive reconstruction of the dynamics of Iceberg Glacier, located on western Axel Heiberg Island, and reveals detailed observations of a complete surge for the first time in the Canadian Arctic. Historical aerial photographs, declassified intelligence satellite photographs, optical satellite imagery and synthetic aperture radar data were used to quantify changes in terminus position, ice velocity and glacier thickness since the 1950s. A surge initiated at the terminus in 1981 and terminated in 2003, suggesting a 22-year active phase. High surface velocities, reaching ~2300 m a−1 in 1991, were accompanied by a maximum terminus advance of &gt;7 km and a large transfer of mass down-glacier, causing significant median trunk-wide surface elevation changes attaining &gt;3 ± 1 m a−1. We suggest that the retreat from a pinning point, flotation of the terminus, the removal of sea-ice from the ice front, and an increase in subglacial meltwater availability from relatively high air temperatures in 1981 likely contributed to surge initiation. The ensuing quiescent period has seen a continual decrease in surface flow rates to an average centreline velocity of 11.5 m a−1 in 2020–21, a gradual steepening of the glacier surface and a &gt; 2.5 km terminus retreat.

Glacier-specific factors drive differing seasonal and interannual dynamics of Nunatakassaap Sermia and Illullip Sermia, Greenland

ABSTRACT Accelerated ice discharge from marine-terminating outlet glaciers accounted for ~48 percent of ice loss from Greenland between 1992 and 2018, and the northwest has been the largest source of dynamic ice loss. Here, we assess the dynamics of two neighboring northwest Greenland glaciers, Nunatakassaap Sermia (NS) and Illullip Sermia (IS), for 2000 to 2020. Retreat rates at NS far exceeded those at IS, and NS accelerated and thinned substantially following the loss of its ice tongue. This was initially driven by loss of buttressing, followed by feedbacks between thinning, surface slope, and effective pressure, as NS retreated into a deeper and wider section of its fjord. At IS, acceleration and thinning were limited due to its location on a bedrock ridge. At NS, net retreat occurred when seasonal retreat persisted through the winter, whereas at IS it resulted from higher summer retreat rates. The timing of seasonal cycles in frontal positions and ice velocities differed markedly between NS and IS: we suggest that ice velocities respond to seasonal meltwater availability at IS and terminus position variations at NS. Overall, our results demonstrate that the dynamic behavior of NS and IS differs markedly at seasonal to decadal timescales and highlight the importance of glacier-specific factors.

Variations in hydraulic efficiency of the subglacial drainage landsystem control surging and streaming regimes of outlet glaciers

AbstractSurging and streaming of glaciers are modulated by meltwater availability and pressure which controls mechanical coupling at their beds. Using laboratory-scale experimental modelling and palaeoglaciological mapping, we explore how subglacial drainage landsystems control meltwater drainage efficiency and ice flow velocities for terrestrial-based ice lobes resting on flat horizontal and permeable beds. Two end-members regimes, surging and streaming, appear in our experiments. The surge regime is characterised by a rapid increase of drainage efficiency through development of tunnel valleys and their tributaries, thus reducing the duration of ice flow speed-up events by lowering water pressures and increasing ice-bed coupling. Tunnel valleys connected to ice lobe margins, submarginal thrust moraines, reduced ice lobe extensions and ephemeral shear margins are the most distinctive characteristics of this regime. The stream regime is characterised by disconnected channels of smaller dimensions unable to evacuate all the meltwater: this prolonged drainage inefficiency leads to sustained high ice flow velocity and steady shear margins. Small and rectilinear meltwater channels devoid of tributaries, often disconnected from ice lobe margins, and lineation swarms are diagnostic of this regime.

Projected increases in surface melt and ice loss for the Northern and Southern Patagonian Icefields

The Northern Patagonian Icefield (NPI) and the Southern Patagonian Icefield (SPI) have increased their ice mass loss in recent decades. In view of the impacts of glacier shrinkage in Patagonia, an assessment of the potential future surface mass balance (SMB) of the icefields is critical. We seek to provide this assessment by modelling the SMB between 1976 and 2050 for both icefields, using regional climate model data (RegCM4.6) and a range of emission scenarios. For the NPI, reductions between 1.5 m w.e. (RCP2.6) and 1.9 m w.e. (RCP8.5) were estimated in the mean SMB during the period 2005–2050 compared to the historical period (1976–2005). For the SPI, the estimated reductions were between 1.1 m w.e. (RCP2.6) and 1.5 m w.e. (RCP8.5). Recently frontal ablation estimates suggest that mean SMB in the SPI is positively biased by 1.5 m w.e., probably due to accumulation overestimation. If it is assumed that frontal ablation rates of the recent past will continue, ice loss and sea-level rise contribution will increase. The trend towards lower SMB is mostly explained by an increase in surface melt. Positive ice loss feedbacks linked to increasing in meltwater availability are expected for calving glaciers.

Glacier surface velocities in the Jankar Chhu Watershed, western Himalaya, India: Study using Landsat time series data (1992–2020)

This study presents a spatial and temporal surface velocity analysis of 33 glaciers in the Jankar Chhu Watershed (JCW), western Himalaya. The surface velocity was computed using the Co-registration of Optically Sensed Images and Correlation (COSI-Corr) tool on the Landsat images spanning nearly three decades (1992–2020). Long-term (1948–2018) inter-annual and seasonal climatic trends are also evaluated based on the US NCEP/NCAR reanalyzed gridded data. The role of several topographic and climatic parameters was examined to characterize heterogeneity in velocity.Glaciers in the JCW exhibit three distinct spatial velocity patterns. The type-I glaciers show nearly stagnant (<5 m yrˉ1) debris-covered tongues but a maximum velocity of >60 m yrˉ1 in the debris-free accumulation area. The type-II glaciers exhibit active tongues (>50 m yrˉ1) yet have slow movement in the accumulation zone. The type-III glaciers show prolonged (<10 m yrˉ1) yet consistent movement throughout the flow line. Results show that the average surface velocity of studied glaciers was 11.10 ± 4.1 m yrˉ1 in 1992/93, which increased (by ~43%) to 15.87 ± 2.4 m yrˉ1 in 2000/02 and further increased (by ~59%) to 25.25 ± 1.5 m yrˉ1 in 2017/18. Glaciers show seasonal fluctuations in surface velocities with an apparent “summer speedup” of ~19%–200% compared to the winter velocities. Inter-annual velocities show an increasing trend during the observation periods. Analysis of NCEP/NCAR gridded data also reveals that the temperature increased by 0.55 °C while precipitation decreased by 0.73 mm during 1948–2018.Our results indicate that glaciers remain dynamic throughout their length with systematic spatiotemporal variations in surface velocity that points towards the control of several topographical and morphological factors. The spatially heterogeneous pattern in surface velocity is characterized by zones of high activity crevasses with steep gradients (>30°) showing maximum ice movement at higher elevations, while debris-covered tongues in the low elevations having gentle slopes (<2°) are nearly stagnant. Based on our results and evidences from the literatures, we suggest that seasonal variations (i.e., summer speedup) in surface velocity in the JCW are due to seasonal temperature fluctuations that alter meltwater availability to the subglacial processes akin to the other Himalaya glaciers. An increasing trend in annual velocity manifests the rising trend in temperature in the western Himalaya. Local topographic configuration, combined with regional climatic systems, controls the amount and types of precipitation received in areas like ours to sustain glaciers on a millennial-scale.

Surges of Harald Moltke Bræ, north-western Greenland: seasonal modulation and initiation at the terminus

Abstract. Harald Moltke Bræ, a marine-terminating glacier in north-western Greenland, shows episodic surges. A recent surge from 2013 to 2019 lasted significantly longer (6 years) than previously observed surges (2–4 years) and exhibits a pronounced seasonality with flow velocities varying by 1 order of magnitude (between about 0.5 and 10 m d−1) in the course of a year. During this 6-year period, the seasonal velocity always peaked in the early melt season and decreased abruptly when meltwater runoff was maximum. Our data suggest that the seasonality has been similar during previous surges. Furthermore, the analysis of satellite images and digital elevation models shows that the surge from 2013 to 2019 was preceded by a rapid frontal retreat and a pronounced thinning at the glacier front (30 m within 3 years). We discuss possible causal mechanisms of the seasonally modulated surge behaviour by examining various system-inherent factors (e.g. glacier geometry) and external factors (e.g. surface mass balance). The seasonality may be caused by a transition of an inefficient subglacial system to an efficient one, as known for many glaciers in Greenland. The patterns of flow velocity and ice thickness variations indicate that the surges are initiated at the terminus and develop through an up-glacier propagation of ice flow acceleration. Possibly, this is facilitated by a simultaneous up-glacier spreading of surface crevasses and weakening of subglacial till. Once a large part of the ablation zone has accelerated, conditions may favour substantial seasonal flow acceleration through seasonally changing meltwater availability. Thus, the seasonal amplitude remains high for 2 or more years until the fast ice flow has flattened the ice surface and the glacier stabilizes again.

Proglacial landform assemblage in a rapidly retreating cirque glacier due to temperature increase since 1970, Fuegian Andes, Argentina

The general trend of glacial retreat since the Little Ice Age has shown an acceleration during the last decades in Southern Argentine and Chilean Patagonia. The Fuegian Andes climatic records report an irregular mean annual temperature increase since 1970, with acceleration from 2015, and the Chato Glacier, as other regional cirque glaciers, has undergone a rapid ice front retreat. A detailed mapping of the proglacial area of the Chato Glacier allowed the identification of a landform assemblage related to the glacier retreat during the last decades. In this paper morphological and sedimentological features of this peculiar landform assemblage, generated in an intense glacial ablation environment, are described and the causes of their origin are discussed. Among the most remarkable landforms annual moraines, hummocky moraines, esker-like landforms, flutes, kettle ponds, dirt cones, glacifluvial deposits, pronival ramparts and collapsed moraines are found. The multitemporal analysis of the Chato Glacier retreat allowed us to interpret that most of these landforms were generated when the landscape became ice-free after 2005. The Chato Glacier cirque floor gentle slope, the thin-ice thickness and the occurrence of a rocky threshold near the glacier front would have promoted the rapid glacier thinning and the disconnection of dead ice. This context, together with the sediments and meltwater availability, would have favored the development of this landform assemblage which is ephemeral due to its high susceptibility to erosion.

Seasonal ice-speed variations in 10 marine-terminating outlet glaciers along the coast of Prudhoe Land, northwestern Greenland

AbstractWe present a 3-year record of seasonal variations in ice speed and frontal ablation of 10 marine-terminating outlet glaciers along the coast of Prudhoe Land in northwestern Greenland. The glaciers showed seasonal speedup initiated between late May and early June, and terminated between late June and early July. Ice speed subsequently decreased from July to September. The timing of the speedup coincided with the onset of the air temperature rise to above freezing, suggesting an influence of meltwater availability on the glacier dynamics. No clear relationship was found between the speedup and the terminus position or the sea-ice/ice-mélange conditions. These results suggest that the meltwater input to the glacier bed triggered the summer speedup. The excess of summer speed (June–August) over the mean for the rest of the year accounted for 0.5–13% of the annual ice motion. Several glaciers showed seasonal frontal variations, i.e. retreat in summer and advance in winter. This was not due to ice-speed variations, but was driven by seasonal variations in frontal ablation. The results demonstrate the dominant effect of glacier surface melting on the seasonal speedup, and the importance of seasonal speed patterns on longer-term ice motion of marine-terminating outlet glaciers in Greenland.

Equifinality and preservation potential of complex eskers

Eskers are useful for reconstructing meltwater drainage systems of glaciers and ice sheets. However, our process understanding of eskers suffers from a disconnect between sporadic detailed morpho‐sedimentary investigations of abundant large‐scale ancient esker systems, and a small number of modern analogues where esker formation has been observed. This paper presents the results of detailed field and high‐resolution remote sensing studies into two esker systems that have recently emerged at Hørbyebreen, Svalbard, and one at Breiðamerkurjökull, Iceland. Despite the different glaciological settings (polythermal valley glacier vs. active temperate piedmont lobe), in all cases a distinctive planform morphology has developed, where ridges are orientated in two dominant directions corresponding to the direction of ice flow and the shape of the ice margin. These two orientations in combination form a cross‐cutting and locally rectilinear pattern. One set of ridges at Hørbyebreen is a hybrid of eskers and geometric ridges formed during a surge and/or jökulhlaup event. The other sets of ridges are eskers formed time‐transgressively at a retreating ice margin. The similar morphology of esker complexes formed in different ways on both glacier forelands implies equifinality, meaning that care should be taken when interpreting Quaternary esker patterns. The eskers at Hørbyebreen contain substantial ice‐cores with a high ice:sediment ratio, suggesting that they would be unlikely to survive after ice melt. The Breiðamerkurjökull eskers emerged from terrain characterized by buried ice that has melted out. Our observations lead us to conclude that eskers may reflect a wide range of processes at dynamic ice margins, including significant paraglacial adjustments. This work, as well as previous studies, confirms that constraints on esker morphology include: topographic setting (e.g. confined valley or broad plain); sediment and meltwater availability (including surges and jökulhlaups); position of formation (supraglacial, englacial or subglacial); and ice‐marginal dynamics such as channel abandonment, the formation of outwash heads or the burial and/or exhumation of dead ice.

Contrasting Hydrological Controls on Bed Properties During the Acceleration of Pine Island Glacier, West Antarctica

AbstractIn the Amundsen sector of West Antarctica, the flow of glaciers accelerates when intrusion of warm ocean water onto the continental shelf induces strong melting beneath ice shelves and thinning near the glaciers' grounding line. Predicting the future of these glaciers is, however, hindered by a poor understanding of the dynamical processes that may exacerbate, or on the contrary modulate, the inland ice sheet response. This study seeks to investigate processes occurring at the base of Pine Island Glacier through numerical inversions of surface velocities observed in 1996 and 2014, a period of time during which the glacier accelerated significantly. The outputs show that substantial changes took place in the basal environment, which we interpret with models of undrained subglacial till and hydrological routing. The annual basal melt production increased by 25% on average. Basal drag weakened by 15% over nearly two thirds of the region of accelerated flow, largely due to the direct assimilation of locally produced basal meltwater into the underlying subglacial sediment. In contrast, regions of increased drag are found to follow several of the glacier's shear margins and furthermore to coincide with inferred hydrological pathways. We interpret this basal strengthening as signature of an efficient hydrological system, where low‐pressure water channels have reduced the surrounding basal water pressure. These are the first identified stabilization mechanisms to have developed alongside Pine Island ice flow acceleration. Indeed, these processes could become more significant with increased meltwater availability and may limit the glacier's response to perturbation near its grounding line.

Evaluating Glacier Volume Changes since the Little Ice Age Maximum and Consequences for Stream Flow by Integrating Models of Glacier Flow and Hydrology in the Cordillera Blanca, Peruvian Andes

Evaluating the historical contribution of the volume loss of ice to stream flow based on reconstructed volume changes through the Little Ice Age (LIA) can be directly related to the understanding of glacier-hydrology in the current epoch of rapid glacier loss that has disquieting implications for a water resource in the Cordillera Blanca in the Peruvian Andes. However, the accurate prediction of the future glacial meltwater availability for the developing regional Andean society needs more extensive quantitative estimation from long-term glacial meltwater of reconstructed glacial volume. Modeling the LIA paleoglaciers through the mid-19th century (with the most extensive recent period of mountain glacier expansion having occurred around 1850 AD) in different catchments of the Cordillera Blanca allows us to reconstruct glacier volume and its change from likely combinations of climatic control variables and time. We computed the rate and magnitude of centennial-scale glacier volume changes for glacier surfaces between the LIA and the modern era, as defined by 2011 Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model Version 2 (GDEM V2) and 2008 Light Detection and Range (LiDAR) data. The model simulation showed good agreement with the observed geomorphic data and the volume and surface area (V-S) scaling remained within the 25% error range in the reconstructed simulation. Also, we employed a recently demonstrated approach (Baraër, M. et al.) to calculate meltwater contribution to glacierized catchment runoff. The results revealed multiple peaks of both mean annual and dry season discharge that have never been shown in previous research on the same mountain range.

Socio-hydrology of \u201cartificial glaciers\u201d in Ladakh, India: assessing adaptive strategies in a changing cryosphere

The consequences of even small glacier decrease and changes of seasonal snow cover are critical for the functioning of meltwater-dependent mountain agriculture. In order to deal with recurrent water scarcity, different types of ice reservoirs, commonly called “artificial glaciers,” have been introduced in Ladakh and promoted as appropriate adaptive strategies to cope with changes in the cryosphere. The resulting seasonal ice reservoirs increase meltwater availability during the critical period of water scarcity in spring. We examine the efficacy of 14 ice reservoirs through a long-term analysis of their functioning within the environmental and socioeconomic context of Ladakh. Using multi-temporal satellite data (1969–2017), close range photogrammetry, and repeat field measurements (2014 and 2015), we provide an inventory and typology of these ice reservoirs and estimate storage volume of one selected structure, which ranges from 1010 to 3220 m3 of water. We extrapolate this volume to all ice reservoirs and estimate potential irrigation cycles of cropped areas, which vary between less than 0.1 in unfavorable cases and almost 3 in optimal cases and years. Based on interviews and field surveys (2007–2017), we discuss the benefits perceived by local smallholders, such as the reduction of seasonal water scarcity and resulting crop failure risks together with the possibility of growing cash crops. We argue that “artificial glaciers” are remarkably suited to the physical environment. However, their usefulness as a climate change adaptation strategy is questionable because climatic variability, natural hazards, and an incomplete integration into the local socioeconomic setting significantly reduce their efficacy.

Dynamic Hydraulic Conductivity Reconciles Mismatch Between Modeled and Observed Winter Subglacial Water Pressure

The link between subglacial hydrology and basal sliding has prompted work on basal hydrology models with water pressure and drainage capacity as prognostic variables. We find that the Glacier Drainage System model, which belongs to a commonly used family of subglacial hydrology models that include both channelized and distributed drainage components, underpredicts winter water pressure when compared to borehole observations from western Greenland given a wide range of plausible parameter values and inputs. This problem, though previously noted by other modelers, has not been addressed. Possible causes for the discrepancy including idealized model inputs or unconstrained parameters are investigated through a series of modeling experiments on both synthetic and realistic ice sheet geometries. Numerical experiments reveal that englacial storage and hydraulic conductivity in the distributed system are the primary controls on winter water pressure in Glacier Drainage System model. Observations of temperate layer thickness and englacial water content from western Greenland imply an upper bound on englacial storage, suggesting that a reduction in hydraulic conductivity is the most plausible cause of high winter water pressure. We conclude that hydraulic conductivity acts as a proxy for the subgrid‐scale connectivity of the linked cavity system and should therefore change seasonally in correspondence with melt water availability.

Surge glaciers during the Little Ice Age in the Pyrenees

Historical moraine complexes and erosional features are interesting elements to discern the historical climate changes and evolution, with a complex chronologies that help us to understand the dynamics and glacier evolution during the Little Ice Age (LIA). The existence of landforms as crevasses-squeeze ridges, hummocky moraines and flutes, related to different glacier advances and retreats, allows understanding in a better way the LIA glacier evolution in the Pyrenees. The aim of this work is to show how many LIA moraine complexes have traces of fast flow ice; when the surge dynamic happened; his extent and the environmental meaning. Based on glacier landsystem analysis we have established a work hypothesis on the fast flow or surge dynamic glaciers during the LIA, with geomorphological features, as flutes and push and hummocky moraines, at least in 17 LIA glacier complexes. The analysis of morphosquences by fieldwork, photo interpretation and historical sources in 8 selected LIA moraine complexes have been compared with previous climatic reconstructions creating a hypothesis about the response of the LIA glaciers to the short time changes in temperature and moisture.The glacier cirques with fast flow features are found in the highest mountains with summits above 3000 m., mainly northern oriented (88%) and without a significant lithology. The studied complexes (Central Infierno, Eastern Infierno, Oulettes de Gaube, Monte Perdido, Marboré, La Paúl, Literola and Tempestades) show 4 morphological units: a frontal moraine system (U1); a more voluminous moraine (U2); a little push and hummocky moraines complex linking with flutes (U3); and minor arcs up valley (U4). The U3 belongs to a fast flow stage or surging and by morphostratigraphy we can point out that the surge processes were produced between 1820 and 1840, at the end of the LIA. We related it with a possible climatic response to sudden cooling and the increase of winter precipitation with melt-water availability and quick ice melting during the summer, generating hydrodynamic changes in the small glaciers and quick dynamic response.

Grain characteristics of silicic Katla tephra layers indicate a fairly stable eruption environment between 2800 and 8100 years ago

Grain size and shape analyses were performed on silicic to intermediate Katla tephra (SILK) formed 2800–8100 years ago to examine whether the grain characteristics had changed with time, and in such a case, could they reflect changes in the eruption environment and/or changes in chemical composition. No systematic changes with time were observed in the grain shape parameters (elongation, ruggedness and circularity), however, the second oldest tephra layer SILK-A11 does not have the typical elongated grain shape that characterizes the other SILK tephra layers. Chemical analyses indicate that the SILK layers can be divided into three subgroups but no correlation between chemical composition and the grain parameters is observed. Changes in grain size of the SILK tephra layers with time indicate an apparent increase in grain size occurring about 6000 years ago, where largest grains are of category -3 Φ compared to 0 Φ in the older layers, all sampled at similar distance from source. This change in grain size could result from variation in ice thickness in the Katla caldera, with finer grain size between 6000–8200 years ago being due to thicker ice cover and greater availability of meltwater for magma fragmentation. Conversely, the younger coarser grained SILK layers may have formed under a thinner ice cover. A shift of the eruption sites to an area with thinner ice is also a possibility. However, no radical changes in the eruption environment 2800–8100 years ago are demonstrated by variations in grain characteristics, a conclusion further supported by large jökulhlaups from Mýrdalsjökull ice cap during this period

A modeling study of the effect of runoff variability on the effective pressure beneath Russell Glacier, West Greenland

Basal sliding is a main control on glacier flow primarily driven by water pressure at the glacier base. The ongoing increase in surface melting of the Greenland Ice Sheet warrants an examination of its impact on basal water pressure and in turn on basal sliding. Here we examine the case of Russell Glacier, in West Greenland, where an extensive set of observations has been collected. These observations suggest that the recent increase in melt has had an equivocal impact on the annual velocity, with stable flow on the lower part of the drainage basin but accelerated flow above the Equilibrium Line Altitude (ELA). These distinct behaviors have been attributed to different evolutions of the subglacial draining system during and after the melt season. Here we use a high-resolution subglacial hydrological model forced by reconstructed surface runoff for the period 2008 to 2012 to investigate the cause of these distinct behaviors. We find that the increase in meltwater production at low elevation yields a more efficient drainage system compatible with the observed stagnation of the mean annual flow below the ELA. At higher elevation, the model indicates that the drainage system is mostly inefficient and is therefore strongly sensitive to an increase in meltwater availability, which is consistent with the observed increase in ice velocity.

The effects of Antarctic iceberg calving‐size distribution in a global climate model

AbstractIcebergs calved from the Antarctic continent act as moving sources of freshwater while drifting in the Southern Ocean. The lifespan of these icebergs strongly depends on their original size during calving. In order to investigate the effects (if any) of the calving size of icebergs on the Southern Ocean, we use a coupled general circulation model with an iceberg component. Iceberg calving length is varied from 62 m up to 2.3 km, which is the typical range used in climate models. Results show that increasing the size of calving icebergs leads to an increase in the westward iceberg freshwater transport around Antarctica. In simulations using larger icebergs, the reduced availability of meltwater in the Amundsen and Bellingshausen Seas suppresses the sea‐ice growth in the region. In contrast, the increased iceberg freshwater transport leads to increased sea‐ice growth around much of the East Antarctic coastline. These results suggest that the absence of large tabular icebergs with horizontal extent of tens of kilometers in climate models may introduces systematic biases in sea‐ice formation, ocean temperatures, and salinities around Antarctica.