scholarly journals Hydraulic impacts of glacier advance over a sediment bed

2006 ◽  
Vol 52 (179) ◽  
pp. 497-527 ◽  
Author(s):  
Geoffrey Boulton ◽  
Sergei Zatsepin
Keyword(s):  
Water Pressure ◽  
Ice Sheet ◽  
Pressure Transducers ◽  
Sediment Bed ◽  
Drainage Time ◽  
Glacier Ice ◽  
Ice Sheet Dynamics ◽  
Poroelastic Model ◽  
Glacier Advance ◽  
The Impact

AbstractA sedimentary sequence of till overlying a gravel aquifer was instrumented with water-pressure transducers prior to a small, anticipated surge of the margin of the glacier Breiðamerkurjökull in Iceland. The records of water pressure at each transducer site show a well-defined temporal sequence of hydraulic regimes that reflect the changing recharge of surface-derived meltwater, the pressure drop along the drainage pathway and the pattern of ice loading. The poroelastic and water-pressure response of glacially overridden sediments to the recharge rate is determined in the frequency domain through an analytic solution. This permits the in situ conductivity, compressibility and consolidation states of subglacial sediments to be derived, and reveals aquifer-scale compressibility that produces an important water-pressure wave associated with the advancing glacier. The model is then used to explore how varying conductivity/compressibility, largely determined by granulometry, can determine drainage states and instabilities that may have a large impact on glacier/ice-sheet dynamics, and how the drainage time of surface water to the bed can determine the frequency response of subglacial groundwater regimes and their influence on subglacial sediment stability. Mismatches between model predictions and specific events in water-pressure records are used to infer processes that are not incorporated in the model: hydrofracturing that changes the hydraulic properties of subglacial sediments; the impact on groundwater pressure of subglacial channel formation; upwelling beyond the glacier margin; and rapid variations in the state of consolidation. The poroelastic model also suggests how seismic methods can be developed further to monitor hydraulic conditions at the base of an ice sheet or glacier.

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 SHaKTI: Subglacial Hydrology and Kinetic Transient Interactions v1.0

2018 ◽  
Author(s):  
Aleah Sommers ◽  
Harihar Rajaram ◽  
Mathieu Morlighem
Keyword(s):  
Water Pressure ◽  
Ice Sheet ◽  
Governing Equations ◽  
Model Formulation ◽  
Seasonal Behavior ◽  
Wide Transition ◽  
Transient Interactions ◽  
Ice Sheet Dynamics ◽  
Hydrology Modeling ◽  
Single Set

Abstract. Subglacial hydrology has a significant influence on ice sheet dynamics, yet remains poorly understood. Complex feedbacks play out between the liquid water and the ice, with constantly changing drainage geometry and flow mechanics. A clear tradition has been established in the subglacial hydrology modeling literature of distinguishing between channelized (efficient) and distributed (inefficient) drainage systems or components. Imposing a distinction that changes the governing physics under different flow regimes, however, may not allow for the full array of drainage characteristics to arise. Here, we present a new subglacial hydrology model: SHaKTI (Subglacial Hydrology and Kinetic Transient Interactions). In this model formulation, a single set of governing equations is applied over the entire domain, with a spatially and temporally varying transmissivity that allows for representation of the wide transition between turbulent and laminar flow, and the geometry of each element is allowed to evolve accordingly to form sheet and channel configurations. The model is implemented as a solution in the Ice Sheet System Model (ISSM). We include steady and transient examples to demonstrate features and capabilities of the model, and we are able to reproduce seasonal behavior of the subglacial water pressure that is consistent with observed seasonal velocity behavior in many Greenland outlet glaciers, supporting the notion that subglacial hydrology may be a key influencer in shaping these patterns.

scholarly journals The Impact of Uncertainties in Ice Sheet Dynamics on Sea-Level Allowances at Tide Gauge Locations

2017 ◽  
Vol 5 (2) ◽  
pp. 21 ◽  
Author(s):  
Aimée Slangen ◽  
Roderik van de Wal ◽  
Thomas Reerink ◽  
Renske de Winter ◽  
John Hunter ◽  
...  
Keyword(s):  
Sea Level ◽  
Tide Gauge ◽  
Ice Sheet ◽  
Ice Sheet Dynamics ◽  
The Impact

scholarly journals Groundwater flow beneath Late Weichselian glacier ice in Nordfjord, Norway

2007 ◽  
Vol 53 (180) ◽  
pp. 84-90 ◽  
Author(s):  
Carolyn A. Moeller ◽  
D.M. Mickelson ◽  
M.P. Anderson ◽  
C. Winguth
Keyword(s):  
Groundwater Flow ◽  
Flow Model ◽  
Water Pressure ◽  
Ice Sheet ◽  
Sheet Thickness ◽  
Overburden Pressure ◽  
Glacier Ice ◽  
Late Weichselian ◽  
Southern Norway ◽  
Basal Melting

AbstractBasal water pressure and water flow patterns are significant factors in controlling the behavior of an ice sheet, because they influence ice-sheet thickness, stability and extent. Water produced by basal melting may infiltrate the subsurface, or occur as sheet or channelized flow at the ice/bed interface. We examine subglacial groundwater conditions along a flowline of the Scandinavian ice sheet through Nordfjord, in the western fjords region of southern Norway, using a steady-state, twodimensional groundwater-flow model. Meltwater input to the groundwater model is calculated by a two-dimensional, time-dependent, thermomechanically coupled ice-flow model oriented along the same flowline. Model results show that the subglacial sediments could not have transmitted all the meltwater out of the fjord during times of ice advance and when the ice sheet was at its maximum position at the edge of the continental shelf. In order for pore-water pressures to remain below the overburden pressure of the overlying ice, other paths of subglacial drainage are necessary to remove excess water. During times of retreat, the subglacial aquifer is incapable of transmitting all the meltwater that was probably generated. Pulses of meltwater reaching the bed could explain nonclimatically driven margin readvances during the overall retreat phase.

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

2020 ◽  
Author(s):  
Emma Lewington ◽  
Stephen Livingstone ◽  
Chris Clark ◽  
Andrew Sole ◽  
Robert Storrar
Keyword(s):  
Large Scale ◽  
Water Pressure ◽  
Pressure Fluctuations ◽  
Ice Sheet ◽  
Drainage System ◽  
Spatial Location ◽  
Variable Pressure ◽  
Ice Sheet Dynamics ◽  
Subglacial Meltwater ◽  
Subglacial Drainage

<p>Despite being widely studied, subglacial meltwater landforms are typically mapped and investigated individually, thus the drainage system as a whole remains poorly understood. Here, we identify and map all visible traces of subglacial meltwater flow across the Keewatin sector of the former Laurentide Ice Sheet from the ArcticDEM, generating significant new insights into the connectedness of the drainage system.</p><p>Due to similarities in spacing, morphometry and spatial location, we suggest that the 100s-1000s m wide features often flanking and connecting sections of eskers (i.e. tunnel valleys, meltwater tracks and esker splays) are varying expressions of the same phenomena and collectively term these features ‘meltwater corridors’. Based on observations from contemporary ice masses, we propose a new formation model based on the pressure fluctuations surrounding a central conduit, in which the esker records the imprint of the central conduit and the wider meltwater corridors the interactions with the surrounding distributed drainage system, or variable pressure axis (VPA).</p><p>We suggest that the widespread aerial coverage of meltwater corridors across the Keewatin sector provides constraints on the extent of basal uncoupling induced by basal water pressure fluctuation and variations in spatial distribution and evolution of the subglacial drainage system, which have important implications for ice sheet dynamics. </p>

scholarly journals Ice-Sheet Dynamics Of Warta Glaciation (SAALE) In The Marginal Zone Of Knyszewicze Area, Northeastern Poland

2015 ◽  
Vol 32 (2) ◽  
pp. 79-90
Author(s):  
Joanna Rychel ◽  
Barbara Woronko ◽  
Mirosław T. Karasiewicz ◽  
Paweł Szymczuk ◽  
Marcin Morawski
Keyword(s):  
Marginal Zone ◽  
Water Pressure ◽  
Ice Sheet ◽  
High Water ◽  
Terminal Moraine ◽  
Pattern Dynamics ◽  
Glaciofluvial Deposits ◽  
Northeastern Poland ◽  
Ice Sheet Dynamics ◽  
Elevation Model

Abstract The paper presents a research on a marginal zone near Knyszewicze in the southern part of Sokółka Hills (northeastern Poland). Terminal moraine hills are arranged amphitheatrically in a lobal pattern. Dynamics of the Knyszewicze frontal ice-sheet lobe during the Saale Glaciation and successive stages of the marginal zone near the village of Knyszewicze were reconstructed based on sedimentary and geomorphological analysis, using a digital elevation model and morpholineaments. Three main phases of the Knyszewicze glacial-lobe activity were identified including accumulation of glaciofluvial deposits, advances of the ice margin and ice-lobe retreat. Moraine hills developed at a stable ice-lobe terminus, initially as short end-moraine fans with the following sequence of lithofacies Gh⇒SGh⇒Sh or Gm⇒Gh⇒Sh. Such a sequence indicates cyclic sheet-floods. During a small but dynamic advance of the ice sheet terminus, these deposits were moved forward and monoclinally folded, then furrowed with sloping faults due to horizontal pressure. Typical thrust-block push moraines developed in this way. Ice sheet advance took place when permafrost was present in the substratum and very high water pressure occurred at glacial terminus. Inside a lobal configuration of moraines, there is a rich inventory of glacial forms with a classic terminal depression in the central part. Based on this landform pattern, their shape, rhythm and glaciotectonic disturbances, the land relief may be referred to as a hill-hole pair. The structure of Horczaki Knoll, deposited on the sub-Quaternary tectonic structure, significantly contributed to a development of this marginal zone.

A coupled model of rapidly-evolving subglacial hydrology with ice dynamics

2021 ◽  
Author(s):  
Michael McPhail ◽  
Ian Hewitt
Keyword(s):  
Large Scale ◽  
Water Pressure ◽  
Ice Sheet ◽  
Drainage System ◽  
Momentum Equation ◽  
Effective Pressure ◽  
Short Term ◽  
Ice Dynamics ◽  
The Impact

<p>The presence of subglacial water can have a significant effect on the motion of an ice sheet. The rate at which the ice slides over the bedrock is mediated by subglacial water pressure. Meltwater on the surface of the sheet can drain through cracks and moulins; drastically increasing the amount of water under the sheet. This source of water fluctuates seasonally and diurnally, much faster than the timescale associated with large-scale glacier evolution. We are interested in the effect that this short-term variation in the subglacial hydrology, and therefore water pressure, has on the long-term behaviour of the ice sheet.<span>  </span>In particular, we are interested in how important it is to resolve the short-timescale variations in ice sliding speed.</p><p> </p><p>We use a mathematical model to study the response of the subglacial drainage system to time-varying surface melt input. By coupling this subglacial hydrology through an effective-pressure-dependent sliding law to the momentum equation for the overlying ice sheet, we study the impact of short-term meltwater fluctuations on the ice velocity.<span>  </span>We study these interactions using a one-dimensional (1D) flowline model representing a confined glacier, allowing us to explore a range of couplings between the ice flow and hydrology.<span>  </span>This enables us to assess the influence of the fluctuating meltwater input on the long-term behaviour of the ice sheet. We find that using a time-averaged effective pressure with an asynchronous coupling to the momentum equation gives a reasonable estimate for the time-averaged ice-sheet velocity, despite the nonlinearity of the governing equations. We use the results to suggest how hydrological coupling might be achieved in larger-scale models where resolving the short-term fluctuations is likely to be infeasible. <span> </span></p>

scholarly journals Evidence for temporally varying “sticky spots” at the base of Trapridge Glacier, Yukon Territory, Canada

1999 ◽  
Vol 45 (150) ◽  
pp. 352-360 ◽  
Author(s):  
Urs H. Fischer ◽  
Garry K. C. Clarke ◽  
Heinz Blatter
Keyword(s):  
Water Pressure ◽  
Strong Support ◽  
Water Film ◽  
High Water ◽  
Yukon Territory ◽  
Basal Resistance ◽  
Model Calculations ◽  
Pressure Transducers ◽  
Glacier Ice ◽  
Trapridge Glacier

AbstractDuring the 1992 summer field season we installed arrays of “plough-meters” and water-pressure transducers beneath Trapridge Glacier. Yukon Territory, Canada, to study hydromechanical coupling at the ice–bed interface. Diurnal signals recorded with two of these ploughmeters appear to correlate with fluctuations in sub-glacial water pressure. These diurnal variations can be explained by changes in basal resistance to sliding as mechanical conditions at the bed vary temporally in response to changes in the subglacial hydrological system. We propose that a lubricating water film, associated with high water pressures, promotes glacier sliding, whereas low pressures cause increased basal drag resulting in “sticky” areas. Using a theoretical model, we analyze the sliding motion of glacier ice over a flat surface having variable basal drag and show that a consistent explanation can be developed. Results from our model calculations provide strong support for the existence of time-varying sticky spots which are associated with fluctuations in subglacial water pressure.

scholarly journals SHAKTI: Subglacial Hydrology and Kinetic, Transient Interactions v1.0

2018 ◽  
Vol 11 (7) ◽  
pp. 2955-2974 ◽  
Author(s):  
Aleah Sommers ◽  
Harihar Rajaram ◽  
Mathieu Morlighem
Keyword(s):  
Water Pressure ◽  
Water Flux ◽  
Ice Sheet ◽  
Mesh Size ◽  
Governing Equations ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Transient Interactions ◽  
Ice Sheet Dynamics

Abstract. Subglacial hydrology has a strong influence on glacier and ice sheet dynamics, particularly through the dependence of sliding velocity on subglacial water pressure. Significant challenges are involved in modeling subglacial hydrology, as the drainage geometry and flow mechanics are constantly changing, with complex feedbacks that play out between water and ice. A clear tradition has been established in the subglacial hydrology modeling literature of distinguishing between channelized (efficient) and sheetlike (inefficient or distributed) drainage systems or components and using slightly different forms of the governing equations in each subsystem to represent the dominant physics. Specifically, many previous subglacial hydrology models disregard opening by melt in the sheetlike system or redistribute it to adjacent channel elements in order to avoid runaway growth that occurs when it is included in the sheetlike system. We present a new subglacial hydrology model, SHAKTI (Subglacial Hydrology and Kinetic, Transient Interactions), in which a single set of governing equations is used everywhere, including opening by melt in the entire domain. SHAKTI employs a generalized relationship between the subglacial water flux and the hydraulic gradient that allows for the representation of laminar, turbulent, and transitional regimes depending on the local Reynolds number. This formulation allows for the coexistence of these flow regimes in different regions, and the configuration and geometry of the subglacial system evolves naturally to represent sheetlike drainage as well as systematic channelized drainage under appropriate conditions. We present steady and transient example simulations to illustrate the features and capabilities of the model and to examine sensitivity to mesh size and time step size. The model is implemented as part of the Ice Sheet System Model (ISSM).

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