Widespread Moulin Formation During Supraglacial Lake Drainages in Greenland

Hoffman, Matthew J.; Perego, Mauro; Andrews, Lauren C.; Price, S. F.; Neumann, Thomas; Johnson, Jesse V.; Catania, G. A.; Lüthi, Martin P.

doi:10.1002/2017gl075659

Cited by 50 publications

(84 citation statements)

References 87 publications

(173 reference statements)

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“…Rather, the primary impact of lake hydrofracture is in opening surface-to-bed connections. The spatial density of such events has been shown to affect the rate of development of channelized drainage (Banwell et al, 2016) and to act as a key mechanism for the creation of moulins away from crevasse fields or current lake basins (Hoffman et al, 2018), which then drain a significant proportion of the overall surface melt as we find in this study and previous work .…”

Section: Model Sensitivitysupporting

confidence: 74%

Modelling seasonal meltwater forcing of the velocity of land-terminating margins of the Greenland Ice Sheet

Koziol

Arnold²

2018

The Cryosphere

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Abstract. Surface runoff at the margin of the Greenland Ice Sheet (GrIS) drains to the ice-sheet bed, leading to enhanced summer ice flow. Ice velocities show a pattern of early summer acceleration followed by mid-summer deceleration due to evolution of the subglacial hydrology system in response to meltwater forcing. Modelling the integrated hydrologicalice dynamics system to reproduce measured velocities at the ice margin remains a key challenge for validating the present understanding of the system and constraining the impact of increasing surface runoff rates on dynamic ice mass loss from the GrIS. Here we show that a multi-component model incorporating supraglacial, subglacial, and ice dynamic components applied to a land-terminating catchment in western Greenland produces modelled velocities which are in reasonable agreement with those observed in GPS records for three melt seasons of varying melt intensities. This provides numerical support for the hypothesis that the subglacial system develops analogously to alpine glaciers and supports recent model formulations capturing the transition between distributed and channelized states. The model shows the growth of efficient conduit-based drainage up-glacier from the ice sheet margin, which develops more extensively, and further inland, as melt intensity increases. This suggests current trends of decadal-timescale slowdown of ice velocities in the ablation zone may continue in the near future. The model results also show a strong scaling between average summer velocities and melt season intensity, particularly in the upper ablation area. Assuming winter velocities are not impacted by channelization, our model suggests an upper bound of a 25 % increase in annual surface velocities as surface melt increases to 4× present levels.

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Section: Model Sensitivitysupporting

confidence: 74%

Modelling seasonal meltwater forcing of the velocity of land-terminating margins of the Greenland Ice Sheet

Koziol

Arnold²

2018

The Cryosphere

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“…This peak speed then propagated downstream from 33N1 to 28N4 (10:45 UTC), GULL (12:30 UTC), 22N4 (14:46 UTC), 25N1 (16:14 UTC), FOXX (16:45 UTC), and finally at 19N1 (18:44 UTC). GULL had a more muted velocity response and is located on a branch of the predicted subglacial drainage path within Sermeq Avannarleq, suggesting that the propagation of the meltwater from the first two lake drainages induced stresses that triggered the drainage at GULL (Hoffman et al, ). Station 25N1 also has a more muted velocity response, potentially due its location relative to modeled subglacial flow paths.…”

Section: Resultsmentioning

confidence: 99%

“…Without snow cover, supraglacial meltwater retention on bare ice can become potentially important, particularly above~900 m asl, where supraglacial lakes more prevalent (e.g., Koziol et al, 2017;Liang et al, 2012;Morriss et al, 2013). Retention of meltwater within supraglacial lakes can exacerbate spatial differences in meltwater delivery to the bed, resulting in a stronger gradient in ice acceleration and regionally tensile strain rate anomalies, which can trigger additional surface-to-bed connections, potentially including the observed lake drainages on day~182 and 188 in our study area (Figures 4a and 5a; Christoffersen et al, 2018;Hoffman et al, 2018).…”

Section: 1029/2017jf004585mentioning

confidence: 88%

Seasonal Evolution of the Subglacial Hydrologic System Modified by Supraglacial Lake Drainage in Western Greenland

et al. 2018

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The impact of summer surface melt on Greenland Ice Sheet dynamics is modulated by the state of the subglacial hydrologic system. Studies of ice motion indicate that efficiency of the subglacial system increases over the melt season, decreasing the sensitivity of ice motion to surface melt inputs. However, the behavior of the subglacial hydrologic system is complex and some characteristics are still poorly constrained. Here we investigate the coevolution of subglacial hydrology and ice motion in the Pâkitsoq region of western Greenland during the 2011 melt season. We analyze measurements from 11 Global Positioning System stations, from which we derive ice velocity, longitudinal strain rates, and basal uplift, alongside observations of surface ablation and supraglacial lake drainages. We observe ice acceleration after the onset of local surface melting, followed by gradual ice deceleration, consistent with increasing subglacial efficiency. In the study area, supraglacial lake drainages cooccur with a change in regional strain rate patterns and ice deceleration, suggesting that lake drainages contribute to rapid subglacial reorganization. At lower ice surface elevations (below ~900 m above sea level), ice motion is correlated with both total basal uplift and its rate of change, while at higher elevations (~900–1,100 m above sea level), ice motion correlated only with the basal uplift rate. This pattern suggests that continued cavity growth or subglacial sediment dynamics may be important in the apparent increase in subglacial drainage efficiency at higher elevations in the ablation zone. Our results further suggest that transient subglacial behavior is important in the seasonal evolution of ice motion.

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“…The farthest inland location where water reaches the glacier bed is indeed a topic of current studies (e.g. Poinar and others, 2015;Gagliardini and Werder, 2018;Hoffman and others, 2018a). Introducing localised inputs also modifies the local effective pressure (with lower effective pressure at the moulin locations) and the distribution of the efficient channelised drainage system (see supplementary figures).…”

Section: Discussionmentioning

confidence: 97%

SHMIP The subglacial hydrology model intercomparison Project

et al. 2018

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Subglacial hydrology plays a key role in many glaciological processes, including ice dynamics via the modulation of basal sliding. Owing to the lack of an overarching theory, however, a variety of model approximations exist to represent the subglacial drainage system. The Subglacial Hydrology Model Intercomparison Project (SHMIP) provides a set of synthetic experiments to compare existing and future models. We present the results from 13 participating models with a focus on effective pressure and discharge. For many applications (e.g. steady states and annual variations, low input scenarios) a simple model, such as an inefficient-system-only model, a flowline or lumped model, or a porous-layer model provides results comparable to those of more complex models. However, when studying short term (e.g. diurnal) variations of the water pressure, the use of a two-dimensional model incorporating physical representations of both efficient and inefficient drainage systems yields results that are significantly different from those of simpler models and should be preferentially applied. The results also emphasise the role of water storage in the response of water pressure to transient recharge. Finally, we find that the localisation of moulins has a limited impact except in regions of sparse moulin density.

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Widespread Moulin Formation During Supraglacial Lake Drainages in Greenland

Cited by 50 publications

References 87 publications

Modelling seasonal meltwater forcing of the velocity of land-terminating margins of the Greenland Ice Sheet

Modelling seasonal meltwater forcing of the velocity of land-terminating margins of the Greenland Ice Sheet

Seasonal Evolution of the Subglacial Hydrologic System Modified by Supraglacial Lake Drainage in Western Greenland

SHMIP The subglacial hydrology model intercomparison Project

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