scholarly journals Greenland subglacial drainage evolution regulated by weakly connected regions of the bed

2016 ◽  
Vol 7 (1) ◽  
Author(s):  
Matthew J. Hoffman ◽  
Lauren C. Andrews ◽  
Stephen F. Price ◽  
Ginny A. Catania ◽  
Thomas A. Neumann ◽  
...  
Keyword(s):  
Numerical Models ◽  
Water Pressure ◽  
Seasonal Pattern ◽  
Drainage System ◽  
Greenland Ice Sheet ◽  
Late Summer ◽  
Initial Increase ◽  
Ice Dynamics ◽  
Hydrodynamic Coupling ◽  
Subglacial Drainage

Abstract Penetration of surface meltwater to the bed of the Greenland Ice Sheet each summer causes an initial increase in ice speed due to elevated basal water pressure, followed by slowdown in late summer that continues into fall and winter. While this seasonal pattern is commonly explained by an evolution of the subglacial drainage system from an inefficient distributed to efficient channelized configuration, mounting evidence indicates that subglacial channels are unable to explain important aspects of hydrodynamic coupling in late summer and fall. Here we use numerical models of subglacial drainage and ice flow to show that limited, gradual leakage of water and lowering of water pressure in weakly connected regions of the bed can explain the dominant features in late and post melt season ice dynamics. These results suggest that a third weakly connected drainage component should be included in the conceptual model of subglacial hydrology.

The meltwater feedbacks on ice dynamics, influence of melt amplitude, duration and extent.

2021 ◽  
Author(s):  
Basile de Fleurian ◽  
Petra M. Langebroeke ◽  
Richard Davy
Keyword(s):  
Water Pressure ◽  
Ice Sheet ◽  
Drainage System ◽  
Greenland Ice Sheet ◽  
System Model ◽  
Ice Dynamics ◽  
Mountain Glaciers ◽  
Different Characteristics ◽  
Crucial Parameter ◽  
Subglacial Drainage

<p>In recent years, temperatures over the Greenland ice sheet have been rising, leading to an increase in surface melt. This increase however can not be reduced to a simple number. Throughout the recent years we have seen some extreme melt seasons with melt extending over the whole surface of the ice sheet (2012) or melt seasons of lower amplitudes but with a longer duration (2010). The effect of those variations on the subglacial system and hence on ice dynamic are poorly understood and are still mainly deduced from studies based on mountain glaciers.</p><p>Here we apply the Ice-sheet and Sea-level System Model (ISSM) to a synthetic glacier with a geometry similar to a Greenland ice sheet land terminating glacier. The forcing is designed such that it allows to investigate different characteristics of the melt season: its length, intensity or the spatial extension of the melt. Subglacial hydrology and ice dynamics are coupled within ISSM is coupled to a subglacial hydrology model, allowing to study the response of the system in terms of subglacial water pressure and the final impact on ice dynamics. Of particular interest is the evolution of the distribution of the efficient and inefficient component of the subglacial drainage system which directly impacts the water pressure evolution at the base of the glacier.</p><p>We note that the initiation of the melt season and the intensity of the melt at this period is a crucial parameter when studying the dynamic response of the glacier to different melt season characteristics. From those results, we can infer a more precise evolution of the dynamics of land terminating glaciers that are heavily driven by their subglacial drainage system. We also highlight which changes in the melt season pattern would be the most damageable for glacier stability in the future.</p>

A 3D full-Stokes model of Store Glacier, Greenland, with coupling of ice flow, subglacial hydrology, submarine melting and calving

2020 ◽  
Author(s):  
Samuel Cook ◽  
Poul Christoffersen ◽  
Joe Todd ◽  
Donald Slater ◽  
Nolwenn Chauché ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Water Pressure ◽  
Drainage System ◽  
Greenland Ice Sheet ◽  
Pressure System ◽  
Ice Flow ◽  
Tidewater Glaciers ◽  
Iceberg Calving ◽  
Subglacial Drainage

<p>Tidewater glaciers are complex systems, which present numerous modelling challenges with regards to integrating a multitude of environmental processes spanning different timescales. At the same time, an accurate representation of these systems in models is critical to being able to effectively predict the evolution of the Greenland Ice Sheet and the resulting sea-level rise. In this study, we present results from numerical simulations of Store Glacier in West Greenland that couple ice flow modelled by Elmer/Ice with subglacial hydrology modelled by GlaDS and submarine melting represented with a simple plume model forced by hydrographic observations. The simulations capture the seasonal evolution of the subglacial drainage system and the glacier’s response, and also include the influence of plume-induced ice front melting on calving and buttressing from ice melange present in winter and spring.</p><p>Through running the model for a 6-year period from 2012 to 2017, covering both high- and low-melt years, we find inputs of surface meltwater to the subglacial system establishes channelised subglacial drainage with channels >1 m<sup>2</sup> extending 30-60 km inland depending on the amount of supraglacial runoff evacuated subglacially. The growth of channels is, however, not sufficiently fast to accommodate all inputs of meltwater from the surface, which means that basal water pressures are generally higher in warmer summers compared to cooler summers and lowest in winter months. As a result, the simulated flow of Store Glacier is such that velocities peak in warmer summers, though we suggest that higher surface melt levels may lead to sufficient channelisation for a widespread low-water-pressure system to evolve, which would reduce summer velocities. The results indicate that Greenland’s contribution to sea-level rise is sensitive to the evolution of the subglacial drainage system and especially the ability of channels to grow and accommodate surface meltwater effectively. We also posit that the pattern of plume melting encourages further calving by creating an indented calving front with ‘headlands’ that are laterally unsupported and therefore more vulnerable to collapse. We validate our simulations with a three-week record of iceberg calving events gathered using a terrestrial radar interferometer installed near the calving terminus of Store Glacier.</p>

The meltwater feedbacks on ice dynamics, elevation versus lubrication

2020 ◽  
Author(s):  
Basile de Fleurian ◽  
Petra Langebroek ◽  
Paul Halas
Keyword(s):  
Water Pressure ◽  
Ice Sheet ◽  
Drainage System ◽  
Greenland Ice Sheet ◽  
Ice Dynamics ◽  
Ice Surface ◽  
Basal Sliding ◽  
Surface Melt ◽  
The One ◽  
Different Response

<p>In recent years, temperatures over the Greenland ice sheet have been rising leading to an increase in surface melt.  Projections show that this augmentation of surface melt will continue in the future and spread to higher elevations. As it increases, melt leads to two different feedbacks on the dynamic of the Greenland ice sheet. This augmentation of melt lowers the ice surface and changes its overall geometry hence impacting the ice dynamics through ice deformation. The other feedback comes into play at the base of glaciers. Here, the increase of water availability will impact the distribution of water pressure at the base of glaciers and hence their sliding velocity. The first feedback is relatively well known and relies on our knowledge of the rheology and deformation of ice. The lubrication feedback acting at the bed of glaciers is however highly uncertain on time scales longer than a season. Here we apply the  Ice  Sheet  System  Model  (ISSM)  to  a  synthetic  glacier  which  geometry  is  similar to the one of a Greenland ice sheet land terminating glacier. The dynamic contributions from ice deformation and sliding are separated to study their relative evolution. This is permitted by the use of a dynamical subglacial hydrology model that allows to link the basal sliding to the meltwater production through an appropriate friction law. The  model  is  forced  through  a  simple  temperature  distribution  and  a  Positive  Degree  Day  model which allows to apply a large range of different forcing scenarios. Of particular interest is the evolution of the distribution of the efficient and inefficient component of the subglacial drainage system and their different response to the distribution of melt during the year which directly impact the sliding regime at the base of the glacier.</p>

scholarly journals Sensitivity of subglacial drainage to water supply distribution at the Kongsfjord basin, Svalbard

2020 ◽  
Author(s):  
Chloé Scholzen ◽  
Thomas V. Schuler ◽  
Adrien Gilbert
Keyword(s):  
Numerical Models ◽  
Water Pressure ◽  
Drainage System ◽  
Early Summer ◽  
Small Surface ◽  
Svalbard Archipelago ◽  
Tidewater Glaciers ◽  
Hydrological System ◽  
Subglacial Topography ◽  
Subglacial Drainage

Abstract. By regulating the amount, the timing and the location of meltwater supply to the glacier bed, supraglacial hydrology potentially exerts a major control on the evolution of the subglacial drainage system, which in turn modulates sliding. Yet the configuration of the supraglacial hydrological system has received only little attention in numerical models of subglacial hydrology so far. Here we apply the two dimensional subglacial hydrology model GlaDS to a Svalbard glacier basin with the aim of investigating how the spatial distribution of meltwater recharge affects the characteristics of the basal drainage system. We design four experiments with various degrees of complexity in the way that meltwater is delivered to the subglacial drainage model. Our results show significant differences between experiments in the early-summer transition from distributed to channelized drainage, with discrete recharge at moulins favouring channelization and driving earlier rise in basal water pressure. Otherwise, we find that water input configuration only poorly influences subglacial hydrology, which is controlled primarily by subglacial topography. All experiments fail to develop channels of sufficient efficiency to substantially reduce summertime water pressures, which we impute to small surface gradients and short melt seasons. The findings of our study may be extended to most Svalbard tidewater glaciers with similar topography and low meltwater recharge. The absence of efficient channelization implies that the dynamics of tidewater glaciers in the Svalbard archipelago may be sensitive to future long-term trends in meltwater supply.

A numerical study of hydrologically driven glacier dynamics and subglacial flooding

2010 ◽  
Vol 467 (2126) ◽  
pp. 537-558 ◽  
Author(s):  
Sam Pimentel ◽  
Gwenn E. Flowers
Keyword(s):  
Numerical Study ◽  
Water Pressure ◽  
Drainage System ◽  
Greenland Ice Sheet ◽  
Elastic Beam ◽  
Flow Speed ◽  
Water Drainage ◽  
Ice Dynamics ◽  
Outlet Glacier ◽  
Diurnal Variability

A hydrologically coupled flowband model of ‘higher order’ ice dynamics is used to explore perturbations in response to supraglacial water drainage and subglacial flooding. The subglacial drainage system includes interacting ‘fast’ and ‘slow’ drainage elements. The fast drainage system is assumed to be composed of ice-walled conduits and the slow system of a macroporous water sheet. Under high subglacial water pressures, flexure of the overlying ice is modelled using elastic beam theory. A regularized Coulomb friction law describes basal boundary conditions that enable hydrologically driven acceleration. We demonstrate the modelled interactions between hydrology and ice dynamics by means of three observationally inspired examples: (i) simulations of meltwater drainage at an Alpine-type glacier produce seasonal and diurnal variability, and exhibit drainage evolution characteristic of the so-called ‘spring transition’; (ii) horizontal and vertical diurnal accelerations are modelled in response to summer meltwater input at a Greenland-type outlet glacier; and (iii) short-lived perturbations to basal water pressure and ice-flow speed are modelled in response to the prescribed drainage of a supraglacial lake. Our model supports the suggestion that a channelized drainage system can form beneath the margins of the Greenland ice sheet, and may contribute to reducing the dynamic impact of floods derived from supraglacial lakes.

Greenland land-terminating glaciers velocity trends during the last two decades

2021 ◽  
Author(s):  
Paul Halas ◽  
Jeremie Mouginot ◽  
Basile de Fleurian ◽  
Petra Langebroek
Keyword(s):  
Water Pressure ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Melting ◽  
Limited Area ◽  
Ice Dynamics ◽  
Basal Sliding ◽  
Surface Melt ◽  
Ice Sheet Dynamics ◽  
The Impact

<div> <p>Ice losses from the Greenland Ice Sheet have been increasing in the last two decades, leading to a larger contribution to the global sea level rise. Roughly 40% of the contribution comes from ice-sheet dynamics, mainly regulated by basal sliding. The sliding component of glaciers has been observed to be strongly related to surface melting, as water can eventually reach the bed and impact the subglacial water pressure, affecting the basal sliding.  </p> </div><div> <p>The link between ice velocities and surface melt on multi-annual time scale is still not totally understood even though it is of major importance with expected increasing surface melting. Several studies showed some correlation between an increase in surface melt and a slowdown in velocities, but there is no consensus on those trends. Moreover those investigations only presented results in a limited area over Southwest Greenland.  </p> </div><div> <p>Here we present the ice motion over many land-terminating glaciers on the Greenland Ice Sheet for the period 2000 - 2020. This type of glacier is ideal for studying processes at the interface between the bed and the ice since they are exempted from interactions with the sea while still being relevant for all glaciers since they share the same basal friction laws. The velocity data was obtained using optical Landsat 7 & 8 imagery and feature-tracking algorithm. We attached importance keeping the starting date of our image pairs similar, and avoided stacking pairs starting before and after melt seasons, resulting in multiple velocity products for each year.  </p> </div><div> <p>Our results show similar velocity trends for previously studied areas with a slowdown until 2012 followed by an acceleration. This trend however does not seem to be observed on the whole ice sheet and is probably specific to this region’s climate forcing. </p> </div><div> <p>Moreover comparison between ice velocities from different parts of Greenland allows us to observe the impact of different climatic trends on ice dynamics.</p> </div>

scholarly journals Large-scale integrated subglacial drainage around the former Keewatin Ice Divide, Canada reveals interaction between distributed and channelised systems

2020 ◽  
Author(s):  
Emma L. M. Lewington ◽  
Stephen J. Livingstone ◽  
Chris D. Clark ◽  
Andrew J. Sole ◽  
Robert D. Storrar
Keyword(s):  
Spatial Distribution ◽  
Dynamic Response ◽  
Large Scale ◽  
Water Pressure ◽  
Pressure Fluctuations ◽  
Drainage System ◽  
Different Types ◽  
Form Part ◽  
Subglacial Meltwater ◽  
Subglacial Drainage

Abstract. We identify and map traces of subglacial meltwater drainage around the former Keewatin Ice Divide, Canada from ArcticDEM data. Meltwater tracks, tunnel valleys and esker splays exhibit several key similarities, including width, spacing, their association with eskers and transitions to and from different types, which together suggest they form part of an integrated drainage signature. We collectively term these features 'meltwater corridors' and propose a new model for their formation, based on observations from contemporary ice masses, of pressure fluctuations surrounding a central conduit. We suggest that eskers record the imprint of a central conduit and meltwater corridors the interaction with the surrounding distributed drainage system. The widespread aerial coverage of meltwater corridors (5–36 % of the bed) provides constraints on the extent of basal uncoupling induced by basal water pressure fluctuations and variations in spatial distribution and evolution of the subglacial drainage system, which will modulate the ice dynamic response.

scholarly journals Oscillatory subglacial drainage in the absence of surface melt

2014 ◽  
Vol 8 (3) ◽  
pp. 959-976 ◽  
Author(s):  
C. Schoof ◽  
C. A Rada ◽  
N. J. Wilson ◽  
G. E. Flowers ◽  
M. Haseloff
Keyword(s):  
Water Pressure ◽  
Drainage System ◽  
Yukon Territory ◽  
Strongly Correlated ◽  
Pressure Oscillations ◽  
Power Failure ◽  
Multiple Data ◽  
Data Loggers ◽  
Diurnal Cycling ◽  
Subglacial Drainage

Abstract. The presence of strong diurnal cycling in basal water pressure records obtained during the melt season is well established for many glaciers. The behaviour of the drainage system outside the melt season is less well understood. Here we present borehole observations from a surge-type valley glacier in the St Elias Mountains, Yukon Territory, Canada. Our data indicate the onset of strongly correlated multi-day oscillations in water pressure in multiple boreholes straddling a main drainage axis, starting several weeks after the disappearance of a dominant diurnal mode in August 2011 and persisting until at least January 2012, when multiple data loggers suffered power failure. Jökulhlaups provide a template for understanding spontaneous water pressure oscillations not driven by external supply variability. Using a subglacial drainage model, we show that water pressure oscillations can also be driven on a much smaller scale by the interaction between conduit growth and distributed water storage in smaller water pockets, basal crevasses and moulins, and that oscillations can be triggered when water supply drops below a critical value. We suggest this in combination with a steady background supply of water from ground water or englacial drainage as a possible explanation for the observed wintertime pressure oscillations.

Investigating Spatio-temporal Changes in Subglacial Hydrology from Dense Array Seismology.

2020 ◽  
Author(s):  
Ugo Nanni ◽  
Florent Gimbert ◽  
Philippe Roux ◽  
Albanne Lecointre
Keyword(s):  
Water Flow ◽  
Seismic Noise ◽  
Water Pressure ◽  
Noise Analysis ◽  
Drainage System ◽  
Dense Array ◽  
Noise Sources ◽  
Spatio Temporal ◽  
Surrounding Areas ◽  
Subglacial Drainage

<p>Subglacial hydrology strongly modulates glacier basal sliding, and thus likely exerts a major control on ice loss and sea-level rise. However, the limited direct and spatialized observations of the subglacial drainage system make difficult to assess the physical processes involved in its development. Recent work shows that detectable seismic noise is generated by subglacial water flow, such that seismic noise analysis may be used to retrieve the physical properties of subglacial channelized water flow. Yet, investigating the spatial organisation of the drainage system (e.g. channels numbers and positions) together with its evolving properties (e.g. pressure conditions) through seismic observations remains to be done. The objective of this study is to bring new insights on the subglacial hydrology spatio-temporal dynamics using dense array seismic observations.</p><p>We use 1-month long ground motion records at a hundred of sensors deployed on the Argentière Glacier (French Alps) during the onset of the melt season, when the subglacial drainage system is expected to strongly evolve in response to the rapidly increasing water input. We conduct a multi-method approach based on the analysis of both amplitude and phase maps of seismic signals. We observe characteristic spatial patterns, consistent across those independent approaches, which we attribute to the underlying subglacial drainage system.</p><p>The phase-driven approach shows seismic noise sources that focuses in the along-flow direction as the water input increases. We identify this evolution as the development of the main subglacial channel whose position is coherent with the one expected from hydraulic potential calculations. During periods of rapid changes in water input (5 days over 31) and concomitant glacier acceleration the amplitude-driven approach shows spatial pattern highly consistent with the seismic noise sources location. At this time, we suggest that the spatial variations in the amplitude are representative of the water pressure conditions in subglacial channels and surrounding areas. Our spatialized observations therefore reveal the spatio-temporal evolution of the subglacial drainage system together with its changing pressure conditions. We observe, for instance, that channels develop at the very onset of the melt-season and rapidly capture the water from surrounding areas. Such unique observations may allow to better constrain the physics of subglacial water flow and therefore strengthen our knowledge on the dynamics of subglacial environments.</p>

Subglacial water pressure records from a fast-flowing outlet glacier in Greenland

2020 ◽  
Author(s):  
Samuel Doyle ◽  
Bryn Hubbard ◽  
Poul Christoffersen ◽  
Marion Bougamont ◽  
Robert Law ◽  
...  
Keyword(s):  
Water Pressure ◽  
Drainage System ◽  
Greenland Ice Sheet ◽  
Distinct Component ◽  
Outlet Glacier ◽  
Diurnal Cycles ◽  
Close Proximity ◽  
Hydrological System ◽  
Discharge Pressure ◽  
Glacier Motion

<p>Glacier motion is resisted by basal traction that can be reduced significantly by pressurised water at the ice-bed interface. Few records of subglacial water pressure have been collected from fast-flowing, marine-terminating glaciers despite such glaciers accounting for approximately half of total ice discharge from the Greenland Ice Sheet.  The paucity of such measurements is due to the practical challenges in drilling and instrumenting boreholes to the bed, in areas that are often heavily-crevassed, through rapidly-deforming ice that ruptures sensor cables within weeks. Here, we present pressure records and drilling observations from two sites located 30 km from the calving front of Store Glacier in West Greenland, where ice flow averages ~600 m yr<sup>-1</sup>.  In 2018, boreholes were drilled 950 m to the bed near the margin of a large, rapidly-draining supraglacial lake. In 2019, multiple boreholes were drilled ~1030 m to the bed in the centre of the drained supraglacial lake, and in close proximity to a large, active moulin. All boreholes drained rapidly when they intersected or approached the ice-bed interface, which is commonly interpreted as indicating connection to an active subglacial drainage system. Neighbouring boreholes responded to the breakthrough of subsequent boreholes demonstrating hydrological or mechanical inter-connection over a distance of ~70 m. Differences in the time series of water pressure indicate that each borehole intersected a distinct component of the subglacial hydrological system. Boreholes located within 250 m of the moulin reveal clear diurnal cycles either in phase or anti-phase with moulin discharge. Pressure records from boreholes located on the lake margin, however, show smaller amplitude, and less distinct, diurnal cycles superimposed on longer-period (e.g. multiday) variability. We compare these datasets to those in the literature and investigate consistencies and inconsistencies with glacio-hydrological theory.</p>

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