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Recent surges of Dan Zhur (Donjek) Glacier have formed lakes at the glacier terminus that have drained catastrophically, resulting in hazards to people and infrastructure downstream. Here we use air photos and satellite imagery to describe lake formation, and the timing of filling and draining, since the 1930s. Between the 1930s and late 1980s, lakes were typically small (1 [km.sup.2]) and drain rapidly through or under the glacier by breaking a terminal ice dam. For the past two surges, since 2001, the lakes formed during or immediately after a surge in an increasingly larger basin between the Neoglacial maximum moraine and an increasingly smaller maximum terminus extent. Most recently, the 2012-2014 surge created a lake that drained in summer 2017, refilled, and drained again in both summer 2018 and summer 2019. The 2019 lake was 2.2 [km.sup.2], the largest on record, and drained entirely within 2 days. While a lake is unlikely to form again before the next expected surge in the mid-2020s, future surges of Dan Zhur Glacier are still likely to create terminal lakes, necessitating continued monitoring for surge activity and lake formation. Key words: glacier surge, remote sensing, glacier lake outburst flood, Yukon, St. Elias Mountains. Résumé: Les surges récentes du glacier Dan Zhùr (Donjek) ont formé des lacs au front du glacier qui se sont vidangés de manière catastrophique, posant un danger pour les humains et les infrastructures en aval. Nous utilisons des photographies aériennes et l'imagerie satellitaire pour décrire la formation des lacs et le moment de leur remplissage et de leur vidange depuis les années 1930. Entre cette décennie et la fin des années 1980, les lacs étaient typiquement petits (1 [km.sup.2]) et se vidangent rapidement à travers ou sous le glacier en brisant une obturation glaciaire frontale. Pour les deux dernières surges, depuis 2001, les lacs se sont formés durant ou immédiatement après une surge dans un bassin de plus en plus grand entre la moraine du maximum néoglaciaire et l'étendue maximumde plusen plus restreintedufront.Lasurgela plus récentede 2012-2014 aentraîné la formation d'un lac qui s'est vidangé à l'été 2017, puis s'est rempli et vidangé à nouveau aux étés 2018 et 2019. Le lac de 2019 faisait 2,2 [km.sup.2], soit le plus grand lac observé, et s'est complètement vidangé en deux jours. S'il est peu probable qu'un autre lac se forme avant la prochaine surge prévue au milieu de la décennie 2020, les surges futures du glacier Dan Zhùr sont toujours susceptibles de créer des lacs frontaux, nécessitant ainsi une surveillance continue de l'activité de surge et de la formation de lacs. [Traduit par la Rédaction] Mots-clés : surge glaciaire, télédétection, débâcle de lac glaciaire, Yukon, St. Elias Mountains., Introduction Glacier-dammed lakes pose a threat to downstream infrastructure and communities because glacial lake outburst floods can occur rapidly with little or no warning. Surge-type glaciers pose a unique set [...]

On 4 August 2010, about one fifth of the floating ice tongue of Petermann Glacier (also known as "Petermann Gletscher") in northwestern Greenland calved (Figure 1). The resulting "ice island" had an area approximately 4 times that of Manhattan Island (about 253±17 square kilometers). The ice island garnered much attention from the media, politicians, and the public, who raised concerns about downstream implications for shipping, offshore oil and gas operations, and possible connections to Arctic and global warming. Does this event signal a change in the glacier's dynamics? Or can it be characterized as part of the glacier's natural variability? Understanding the known historical context of this event allows scientists and the public to judge its significance.

In Greenland, 87% of the glacierized area terminates in the ocean, but mass lost at the ice‐ocean interface, or frontal ablation, has not yet been fully quantified. Using measurements and models we calculate frontal ablation of Greenland's 213 outlet and 537 peripheral glaciers and find a total frontal ablation of 481.8 ± 24.0 for 2000–2010 and 510.2 ± 18.6 Gt a−1 for 2010–2020. Ice discharge accounted for ∼90% of frontal ablation during both periods, while mass loss due to terminus retreat comprised the remainder. Only 16 glaciers were responsible for the majority (>50%) of frontal ablation from 2010 to 2020. These estimates, along with the climatic‐basal balance, allow for a more complete accounting of Greenland Ice Sheet and peripheral glacier mass balance. In total, Greenland accounted for ∼90% of Northern Hemisphere frontal ablation for 2000–2010 and 2010–2020. Plain Language Summary: We estimate the mass of ice lost from all Greenland glaciers that entered the ocean during each of the last two decades. This ice loss at the front of these marine‐terminating glaciers is called frontal ablation and is approximately equal to the mass of icebergs entering the ocean. Frontal ablation is important because 87% of glacier area in Greenland ends in the ocean, through 750 outlets, and previous work has only approximated frontal ablation. This study quantifies it for the first time, helping to close the mass budget for the Greenland Ice Sheet and better partition its mass balance into components. We find that Greenland accounts for ∼90% of all Northern Hemisphere frontal ablation and, of that contribution, just 17 glaciers for 2000–2010 and 16 glaciers for 2010–2020 account for more than half of total Greenland frontal ablation. Key Points: Frontal ablation of the Greenland Ice Sheet averaged 510.2 ± 18.6 Gt a−1 for 2010–2020, ∼90% of which came from ice dischargeThe frontal ablation we measured is larger than the total mass loss from the ice sheet, indicating a positive climatic‐basal balanceOnly 16 glaciers account for 50% of the total frontal ablation from the Greenland Ice Sheet [ABSTRACT FROM AUTHOR]

Knowledge of frontal ablation from marine-terminating glaciers (i.e., mass lost at the calving face) is critical for constraining glacier mass balance, improving projections of mass change, and identifying the processes that govern frontal mass loss. Here, we discuss the challenges involved in computing frontal ablation and the unique issues pertaining to both glaciers and ice sheets. Frontal ablation estimates require numerous datasets, including glacier terminus area change, thickness, surface velocity, density, and climatic mass balance. Observations and models of these variables have improved over the past decade, but significant gaps and regional discrepancies remain, and better quantification of temporal variability in frontal ablation is needed. Despite major advances in satellite-derived large-scale datasets, large uncertainties remain with respect to ice thickness, depth-averaged velocities, and the bulk density of glacier ice close to calving termini or grounding lines. We suggest ways in which we can move toward globally complete frontal ablation estimates, highlighting areas where we need improved datasets and increased collaboration. [ABSTRACT FROM AUTHOR]

Links between proglacial lakes and glacier dynamics are poorly understood but are necessary to predict how mountain glaciers will react to a warmer, wetter climate, where such lakes are expected to increase both in number and volume. Here, we examine a long-term (~120 year) record of terminus retreat, thinning and surface velocities from in-situ and remote sensing observations at the terminus of Kaskawulsh Glacier, Yukon, Canada, and determine the impact of a local proglacial hydrological reorganisation on glacier dynamics. After an initial deceleration during the late 1990s, terminus velocities increased at a rate of 3 m a−2 from 2000–12, while proglacial Slims Lake area increased simultaneously. The rapid drainage of the lake in May 2016 substantially altered the velocity profile, decreasing annual velocities by 48% within 3 km of the terminus between 2015 and 2021, at an average rate of ~ 12.5 m a−2. A key cause of the rapid drop in glacier motion was a reduction in flotation of the lower part of the glacier terminus after lake drainage. This has important implications for glacier dynamics and provides one of the first assessments of the impacts of a rapid proglacial lake drainage event on local terminus velocities. [ABSTRACT FROM AUTHOR]

Supraglacial drainage networks play an integral role in both glacier dynamics and run-off timing, and mapping them provides insight into their role in glacial systems. Here we present a reproducible approach for semi-automated mapping of supraglacial hydrologic features, which complements existing work in automated and manual mapping by providing clear definitions for identification of features. This framework uses a digital terrain model (DTM) to identify potential flow routes on the glacier surface, which are then classified using a set of standardized rules based on the DTM and an orthomosaic. We found that the normalized difference water index calculated from digital imagery was influenced by image brightness and introduce a new approach using average RGB values to correct for this. Using this framework we mapped supraglacial drainage networks at Nàłùdäy and Thores Glacier, Canada. The framework was easier to implement with high-resolution (0.5 m) imagery and DTMs, compared to data with lower resolution (10 m), due to the increased detail in topography and feature boundaries at high-resolution. Lower-resolution data captured larger streams (>2 pixels wide), however, indicating that the framework can still be used at this resolution. Mapping supraglacial hydrology using standardized methods opens possibilities for investigating many questions relating to changes in supraglacial hydrology over time. [ABSTRACT FROM AUTHOR]

Speckle tracking of ALOS PALSAR fine beam data from 2007-2011 are used to determine the surface motion of major ice masses on Baffin Island and Bylot Island in the southern Canadian Arctic Archipelago. Glacier velocities are low overall, with peaks of ~100 m [a.sup.-1] and means of ~20-60 m [a.sup.-1] common along the main trunk of many outlet glaciers. Peak velocities on Penny and Bylot Island ice caps tend to occur near the mid-sections of their primary outlet glaciers, while the fastest velocities on all other glaciers usually occur near their termini due to relatively large accumulation areas draining through narrow outlets. Estimates of ice thickness at the fronts of tidewater-terminating glaciers are combined with the velocity measurements to determine a regional dynamic discharge rate of between ~17 Mt [a.sup.-1] and ~108 Mt [a.sup.-1], with a mid-point estimate of ~55 Mt [a.sup.-1], revising downward previous approximations. These velocities can be used as inputs for glacier flow models, and provide a baseline dataset against which future changes in ice dynamics can be detected. Le suivi speckle des donnees de faisceau fin ALOS PALSAR, prelevees entre 2007 et 2011, est utilise pour determiner le mouvement de surface des grandes masses de glace sur les iles de Baffin et de Bylot dans le sud de l'archipel arctique canadien. Les vitesses des glaciers sont generalement faibles avec des pointes d'environ 100 m [a.sup.-1] et des moyennes de 20 a 60 m [a.sup.-1] frequentes le long du tronc principal de nombreux glaciers emissaires. Les vitesses de pointe des champs de glace de Penny et de Bylot tendent a etre pres des sections medianes de leurs glaciers emissaires primaires, alors que les vitesses les plus rapides sur tous les autres glaciers sont enregistrees pres du front en raison des aires d'accumulation relativement grandes qui s'ecoulent a travers d'etroites decharges. Des estimations de l'epaisseur de la glace aux fronts de glaciers de maree sont combinees aux mesures de vitesse afin de determiner un taux regional de decharge dynamique entre ~17 Mt [a.sup.-1] et ~108 Mt [a.sup.-1], avec une estimation du taux median de ~55 [a.sup.-1], ce qui revise les estimations anterieures a la baisse. Ces vitesses peuvent etre utilisees comme donnees d'entree pour les modeles d'ecoulement glaciaire et ainsi fournir un ensemble de donnees de reference pour detecter les futurs changements dans la dynamique glaciaire. [Traduit par la Redaction], Introduction The southern Canadian Arctic Archipelago (CAA), consisting of Baffin Island and Bylot Island (Fig. 1), contain ~40 000 [km.sup.2] of glacier ice (Gardner et al. 2012). Recent studies indicate [...]

The physical, sedimentological, mineralogical and elemental geochemical properties of sediment cores AMD1803‐02BC and 01PC from the Cape Norton Shaw Inlet were investigated to reconstruct glacial sediment discharges from southeastern Manson Icefield and document the impact of ice–ocean interactions on the sediment dynamics and opening of the North Water Polynya (NOW) in northwestern Baffin Bay since the last deglaciation. Laminated glaciomarine sediments rich in quartz and feldspar are observed prior to 11 cal. ka BP and were probably deposited by hyperpycnal currents triggered by the local retreat of the southern margin of the Innuitian Ice. Detrital proxies suggest that Early Holocene sediment dynamics were mainly influenced by sea ice and iceberg rafting and meltwater discharges related to the deglaciation of eastern Smith (~11 to 10.65 cal. ka BP) and Jones (~10.7 cal. ka BP) sounds. This also provides an upper limit to the timing of formation of the NOW. The high detrital carbonate contents during 8.8 to 6.6 cal. ka BP confirm that enhanced carbonate‐rich sediment export from Nares Strait to northern Baffin Bay occurred during and after the deglaciation of Kennedy Channel (8.8 to 8.2 cal. ka BP). Canadian Shield sediment inputs have dominated since 6.6 cal. ka BP, indicating that sedimentation is mainly influenced by Cape Norton Shaw glacier discharges. The lower level of sedimentation recorded in core 01PC during the Middle to Late Holocene suggests an accelerated landward retreat of the Cape Norton Shaw glaciers in response to warmer marine conditions. During the Neoglacial period, higher sedimentation rates and detrital proxies in the cores suggest increased glacial erosional processes, probably associated with the long‐term declines in boreal summer insolation and glacier growth. Finally, mineralogical and grain‐size data in core 02BC support the idea that increased Arctic atmospheric temperatures have had an important influence on the glacial dynamics during the industrial period. [ABSTRACT FROM AUTHOR]

Substrate properties and hydrological conditions at the base of Haut Glacier d'Arolla, Switzerland, are nonuniform. The thickness and grain size of subglacial sediment vary on length scales less than one ice thickness, whereas hydrological conditions vary seasonally and on length scales of about one ice thickness transverse to ice motion. There is a close relationship between the annually averaged velocity field and this nonuniformity of bed conditions. Basal motion dominates in an area with large water-level variations in boreholes, whereas ice deformation contributes significantly to total movement elsewhere. Localized enhanced basal motion occurs primarily in summer, especially during a July 'spring event,' but this motion is barely discernible in annually averaged surface velocity measurements, because transverse coupling suppresses surface expression of the basal motion discontinuity. These results highlight the need to include representations of bed nonuniformity in models of glacier flow and to consider ice deformation and basal motion as interdependent processes.