scholarly journals A subglacial hydrological model dedicated to glacier sliding

2013 ◽  
Vol 7 (4) ◽  
pp. 3449-3496 ◽  
Author(s):  
B. de Fleurian ◽  
O. Gagliardini ◽  
T. Zwinger ◽  
G. Durand ◽  
E. Le Meur ◽  
...  
Keyword(s):  
Hydrological Model ◽  
Water Pressure ◽  
Computational Cost ◽  
Ice Streams ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Wide Range ◽  
Hydrological System ◽  
Speed Up ◽  
Model Components

Abstract. The flow of glaciers and ice-streams is strongly influenced by the presence of water at the interface between ice and bedrock. In this paper, a hydrological model evaluating the subglacial water pressure is developed with the final aim of estimating the sliding velocities of glaciers. The global model fully couples the subglacial hydrology and the ice dynamics through a water-dependent friction law. The hydrological part of the model follows a double continuum approach which relies on the use of porous layers to compute water heads in inefficient and efficient drainage systems. This method has the advantage of a relatively low computational cost that would allow its application to large ice bodies such as Greenland or Antarctica ice-streams. The hydrological model has been implemented in the finite element code Elmer/Ice, which simultaneously computes the ice flow. Herein, we present an application to the Haut Glacier d'Arolla for which we have a large number of observations, making it well suited to the purpose of validating both the hydrology and ice flow model components. The selection of hydrological, under-determined parameters from a wide range of values is guided by comparison of the model results with available glacier observations. Once this selection has been performed, the coupling between subglacial hydrology and ice dynamics is undertaken throughout a melt season. Results indicate that this new modelling approach for subglacial hydrology is able to reproduce the broad temporal and spatial patterns of the observed subglacial hydrological system. Furthermore, the coupling with the ice dynamics shows good agreement with the observed spring speed-up.

scholarly journals A double continuum hydrological model for glacier applications

2014 ◽  
Vol 8 (1) ◽  
pp. 137-153 ◽  
Author(s):  
B. de Fleurian ◽  
O. Gagliardini ◽  
T. Zwinger ◽  
G. Durand ◽  
E. Le Meur ◽  
...  
Keyword(s):  
Hydrological Model ◽  
Water Pressure ◽  
Computational Cost ◽  
Ice Streams ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Wide Range ◽  
Hydrological System ◽  
Speed Up ◽  
Model Components

Abstract. The flow of glaciers and ice streams is strongly influenced by the presence of water at the interface between ice and bed. In this paper, a hydrological model evaluating the subglacial water pressure is developed with the final aim of estimating the sliding velocities of glaciers. The global model fully couples the subglacial hydrology and the ice dynamics through a water-dependent friction law. The hydrological part of the model follows a double continuum approach which relies on the use of porous layers to compute water heads in inefficient and efficient drainage systems. This method has the advantage of a relatively low computational cost that would allow its application to large ice bodies such as Greenland or Antarctica ice streams. The hydrological model has been implemented in the finite element code Elmer/Ice, which simultaneously computes the ice flow. Herein, we present an application to the Haut Glacier d'Arolla for which we have a large number of observations, making it well suited to the purpose of validating both the hydrology and ice flow model components. The selection of hydrological, under-determined parameters from a wide range of values is guided by comparison of the model results with available glacier observations. Once this selection has been performed, the coupling between subglacial hydrology and ice dynamics is undertaken throughout a melt season. Results indicate that this new modelling approach for subglacial hydrology is able to reproduce the broad temporal and spatial patterns of the observed subglacial hydrological system. Furthermore, the coupling with the ice dynamics shows good agreement with the observed spring speed-up.

Basal processes beneath an Arctic glacier and their geomorphic imprint after a surge, Elisebreen, Svalbard

2005 ◽  
Vol 64 (2) ◽  
pp. 125-137 ◽  
Author(s):  
Poul Christoffersen ◽  
Jan A. Piotrowski ◽  
Nicolaj K. Larsen
Keyword(s):  
Flow Instability ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Water System ◽  
Water Drainage ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Glacier Ice ◽  
Water Saturated ◽  
Arctic Glacier

AbstractThe foreground of Elisebreen, a retreating valley glacier in West Svalbard, exhibits a well-preserved assemblage of subglacial landforms including ice-flow parallel ridges (flutings), ice-flow oblique ridges (crevasse-fill features), and meandering ridges (infill of basal meltwater conduits). Other landforms are thrust-block moraine, hummocky terrain, and drumlinoid hills. We argue in agreement with geomorphological models that this landform assemblage was generated by ice-flow instability, possibly a surge, which took place in the past when the ice was thicker and the bed warmer. The surge likely occurred due to elevated pore-water pressure in a thin layer of thawed and water-saturated till that separated glacier ice from a frozen substratum. Termination may have been caused by a combination of water drainage and loss of lubricating sediment. Sedimentological investigations indicate that key landforms may be formed by weak till oozing into basal cavities and crevasses, opening in response to accelerated ice flow, and into water conduits abandoned during rearrangement of the basal water system. Today, Elisebreen may no longer have surge potential due to its diminished size. The ability to identify ice-flow instability from geomorphological criteria is important in deglaciated terrain as well as in regions where ice dynamics are adapting to climate change.

scholarly journals Ice dynamics of the Haupapa/Tasman Glacier measured at high spatial and temporal resolution, Aoraki/Mount Cook, New Zealand

2021 ◽  
Author(s):  
◽  
Edmond Lui
Keyword(s):  
New Zealand ◽  
Surface Area ◽  
Water Pressure ◽  
Seasonal Pattern ◽  
Anthropogenic Sources ◽  
Oblique View ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Glacier Terminus ◽  
Area Loss

<p>Glaciers are among the clearest of signals for anthropogenic climate change and their retreat is considered symptomatic of the observed warming since the start of the 20th century from anthropogenic sources (Mann et al., 2004). New Zealand has 3,100 mountain glaciers, with those in the Southern Alps experiencing losses of 34% since 1977 and a decline in volume of 51 km3 in 1994 to 41 km3 in 2010 (NIWA, 2011). The direct impact of increasing atmospheric temperatures on glaciers is well understood (Chinn, 2012) through its effects on the melt and accumulation rates (Kirkbride, 2010; Purdie, 2011; Chinn, 1997; Oerlemans, 2001). However lake calving glaciers such as the Tasman Glacier exhibit different behaviour and are suggested to be at least partially decoupled from climate forcing (Benn et al., 2007).  Here, I present a temporally and spatially complete study of Haupapa/Tasman Glacier, Aoraki/Mt. Cook over three years to investigate the ice dynamics at the terminus. I used oblique photogrammetry at high resolution for data acquisition and adapted computer vision algorithms for correcting this oblique view to a real-world geometry. This technique has been rarely used (Murray et al., 2015; Messerli and Grinsted, 2015; Ahn and Box, 2010; Harrison et al., 1986 and Flotron, 1973) but owing to its cost-effectiveness and high data yields, it is becoming an increasingly powerful methodology favoured by glaciologists.  During the 3 year study period, Tasman Glacier terminus retreat rate Ur was 116 ± 19 m a⁻¹ (2013-2014), 83 ± 18 m a⁻¹ (2014-2015) and 204 ± 20 (2015-2016). A strong seasonal pattern was evident in the calving events. Three major calving events occurred over the study, one occurring in the summer of 2013 and two in the summer of 2016. The latter two events are responsible for the elevated Ur in 2015-2016. These events were characterised as distinct large-magnitude calving (usually as a large tabular iceberg) which continued to drift and break up in the lake for weeks to months. Three large calving events accounted for 47% of the total surface area loss for the 38 month study period with the remaining surface area loss from 2nd order calving including notching at the waterline and the spalling of lamallae of ice from surface fractures, and ice-cliff melt. During the spring/summer months of 2014 and 2015 there was no large buoyancy driven calving event such as those seen in 2013 and 2016, but there were many smaller-magnitude calving events. Smaller-magnitude events were less frequent in winter months as compared to summer months. Ice flow in winter has been shown to be less than in summer (Horgan et al, 2015). While seasonal temperatures and changes to the basal water pressure are linked to these observations, it is also likely that the relatively faster ice flow in summer/autumn could be influencing the rate of 1st and 2nd order calving mechanisms. Overall, the calving rates were calculated as 171 ± 18 m a⁻¹ (2013-2014), 136 ± 17 m a⁻¹ (2014-2015) and accelerated to 256 ± 20 m a⁻¹ in the last year (2015-2016). My results show that almost half of the ice loss at the terminus comes from large, infrequent calving events and that retreat rates for 2015-2016 were high compared to the historic record but the area loss is lower than it has been because of the relatively narrow terminus.</p>

scholarly journals Signature of ice streaming in Bjørnøyrenna, Polar North Atlantic, through the Pleistocene and implications for ice-stream dynamics

2009 ◽  
Vol 50 (52) ◽  
pp. 17-26 ◽  
Author(s):  
Karin Andreassen ◽  
Monica Winsborrow
Keyword(s):  
Barents Sea ◽  
Extensional Flow ◽  
Three Dimensional ◽  
Ice Streams ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Ice Stream ◽  
Geomorphic Features ◽  
Common Behaviour ◽  
Fast Flow

AbstractThe geomorphology of palaeo-ice-stream beds and the internal structure of underlying tills can provide important information about the subglacial conditions during periods of fast flow and quiescence. This paper presents observations from three-dimensional seismic data, revealing the geomorphology of buried beds of the Bjørnøyrenna (Bear Island Trough) ice stream, the main drainage outlet of the former Barents Sea ice sheet. Repeated changes in ice dynamics are inferred from the observed successions of geomorphic features. Megablocks, aligned in long chains parallel to inferred ice-stream flowlines, and forming dipping plates that are thrust one on top of another, are taken as evidence for conditions of compressive ice flow. Mega-scale glacial lineations (MSGL) and pull-apart of underlying sediment blocks suggest extensional flow. The observed pattern of megablocks and rafts overprinted by MSGL indicates a change in ice dynamics from a compressional to an extensional flow regime. Till stiffening, due to subglacial freezing, is the favoured mechanism for creating switches in sub-ice-stream conditions. The observed pattern of geomorphic features indicates that periods of slowdown or quiescence were commonly followed by reactivation and fast flow during several glaciations, suggesting that this may be a common behaviour of marine ice streams.

scholarly journals Constraining subglacial processes from surface velocity observations using surrogate-based Bayesian inference

2021 ◽  
pp. 1-19
Author(s):  
Douglas Brinkerhoff ◽  
Andy Aschwanden ◽  
Mark Fahnestock
Keyword(s):  
Probability Distributions ◽  
Water Pressure ◽  
Model Development ◽  
Computational Cost ◽  
Hydrologic Model ◽  
Surface Velocity ◽  
Small Scale ◽  
Model Parameters ◽  
Stress Regime ◽  
Ice Dynamics

Abstract Basal motion is the primary mechanism for ice flux in Greenland, yet a widely applicable model for predicting it remains elusive. This is due to the difficulty in both observing small-scale bed properties and predicting a time-varying water pressure on which basal motion putatively depends. We take a Bayesian approach to these problems by coupling models of ice dynamics and subglacial hydrology and conditioning on observations of surface velocity in southwestern Greenland to infer the posterior probability distributions for eight spatially and temporally constant parameters governing the behavior of both the sliding law and hydrologic model. Because the model is computationally expensive, characterization of these distributions using classical Markov Chain Monte Carlo sampling is intractable. We skirt this issue by training a neural network as a surrogate that approximates the model at a sliver of the computational cost. We find that surface velocity observations establish strong constraints on model parameters relative to a prior distribution and also elucidate correlations, while the model explains 60% of observed variance. However, we also find that several distinct configurations of the hydrologic system and stress regime are consistent with observations, underscoring the need for continued data collection and model development.

scholarly journals Glacier Speed-Up Events and Subglacial Hydrology on the Lower Franz Josef Glacier, New Zealand

2021 ◽  
Author(s):  
◽  
Laura M. Kehrl
Keyword(s):  
New Zealand ◽  
Water Pressure ◽  
Drainage System ◽  
Temporal Variations ◽  
Ice Flow ◽  
Speed Up ◽  
Glacier Velocity ◽  
Glacier Flow ◽  
Flow Velocities ◽  
Subglacial Drainage

<p>The contribution of glacier mass loss to future sea level rise is still poorly constrained (Lemke and others, 2007). One of the remaining unknowns is how water inputs influence glacier velocity. Short-term variations in glacier velocity occur when a water input exceeds the capacity of the subglacial drainage system, and the subglacial water pressure increases. Several studies (Van de Wal and others, 2008; Sundal and others, 2011) have suggested that high ice-flow velocities during these events are later offset by lower ice-flow velocities due to a more efficient subglacial drainage system. This study combines in-situ velocity measurements with a full Stokes glacier flowline model to understand the spatial and temporal variations in glacier flow on the lower Franz Josef Glacier, New Zealand. The Franz Josef Glacier experiences significant water inputs throughout the year (Anderson and others, 2006), and as a result, the subglacial drainage system is likely well-developed. In March 2011, measured ice-flow velocities increased by up to 75% above background values in response to rain events and by up to 32% in response to diurnal melt cycles. These speed-up events occurred at all survey locations across the lower glacier. Through flowline modelling, it is shown that the enhanced glacier flow can be explained by a spatially-uniform subglacial water pressure that increased during periods of heavy rain and glacier melt. From these results, it is suggested that temporary spikes in water inputs can cause glacier speed-up events, even when the subglacial hydrology system is well-developed (cf. Schoof, 2010). Future studies should focus on determining the contribution of glacier speed-up events to overall glacier motion.</p>

scholarly journals Fracture-induced softening for large-scale ice dynamics

2013 ◽  
Vol 7 (5) ◽  
pp. 4501-4544 ◽  
Author(s):  
T. Albrecht ◽  
A. Levermann
Keyword(s):  
Large Scale ◽  
Ice Sheet ◽  
Damage Threshold ◽  
Fracture Density ◽  
Ice Streams ◽  
Model Framework ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Ice Shelves ◽  
Linear Threshold

Abstract. Floating ice shelves can exert a retentive and hence stabilizing force onto the inland ice sheet of Antarctica. However, this effect has been observed to diminish by fracture-coupled dynamic processes within the protective ice shelves leading to accelerated ice flow and hence to a sea-level contribution. In order to better understand the role of fractures in ice dynamics we apply a large-scale continuum representation of fractures and related fracture growth into the prognostic Parallel Ice Sheet Model (PISM). To this end we introduce a higher-order accuracy advection scheme for the transport of the two-dimensional fracture density across the regular computational grid. Dynamic coupling of fractures and ice flow is attained by a reduction of effective ice viscosity proportional to the inferred fracture density. This formulation implies the possibility of a non-linear threshold behavior due to self-amplified fracturing in shear regions triggered by small variations in damage threshold. As a result of prognostic flow simulations, flow patterns with realistically large across-flow velocity gradients in fracture-weakened regions as seen in observations are reproduced. This model framework is expandable to grounded ice streams and accounts for climate-induced effects on fracturing and hence on the ice-flow dynamics. It further allows for an enhanced fracture-based calving parameterization.

PoLIM: an open source 2D higher-order thermomechanically coupled mountain glacier flow model

2020 ◽  
Author(s):  
Yuzhe Wang ◽  
Tong Zhang
Keyword(s):  
Flow Model ◽  
Order Approximation ◽  
Water Pressure ◽  
Computational Cost ◽  
Higher Order ◽  
Thermomechanical Coupling ◽  
High Mountain ◽  
Climate Data ◽  
Mountain Glacier ◽  
Ice Flow

&lt;p&gt;The worldwide glacier is retreating and is expected to continue shrinking in a warming climate. Understanding the dynamics of glaciers is essential for the knowledge of sea-level rise, water resources in high mountain and arid regions, and the potential glacier hazards. Over the past decades, various 3D higher-order and full-Stokes ice flow models including thermomechanical coupling have been developed, and some have opened their source codes. However, such 3D modeling requires detailed datasets about surface and bedrock topography, variable climatic conditions, and high computational cost. Due to difficulties in measuring glacier thickness, only a small minority of glaciers around the globe have ice thickness observations. It is also a challenge to downscale the climate data (e.g., air temperature, precipitation) to the glacier surface, particularly, in rugged high-mountain terrains. In contrast to 3D models, flowline models only require inputs along the longitudinal profile and are thus computationally efficient. They continue to be useful tools for simulating the evolution of glaciers and studying the particular phenomena related to glacier dynamics. In this study, we present a two-dimensional thermomechanically coupled ice flow model named PoLIM (Polythermal Land Ice Model). The velocity solver of PoLIM is developed based on the higher-order approximation (Blatter-Pattyn type). It includes three critical features for simulating the dynamics of mountain glaciers: 1) an enthalpy-based thermal model to describe the heat transfer, which is particularly convenient to simulate the polythermal structures; 2) a drainage model to simulate the water transport in the temperate ice layer driven by gravity; 3) a subglacial hydrology model to simulate the subglacial water pressure for the coupling with the basal sliding law. We verify PoLIM with several standard benchmark experiments (e.g., ISMIP-HOM, enthalpy, SHMIP) in the glacier modeling community. PoLIM shows a good performance and agrees well with these benchmark results, indicating its reliable and robust capability of simulating the thermomechanical behaviors of glaciers.&lt;/p&gt;

Dynamics of tidewater surge-type glaciers in northwest Svalbard

2012 ◽  
Vol 58 (207) ◽  
pp. 110-118 ◽  
Author(s):  
Damien Mansell ◽  
Adrian Luckman ◽  
Tavi Murray
Keyword(s):  
Active Phase ◽  
Surface Flow ◽  
Alos Palsar ◽  
Glacier Surface ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Compressive Stresses ◽  
Flow Speeds ◽  
Iceberg Calving ◽  
Speed Up

AbstractThe evolution of ice dynamics through surges of four tidewater-terminating glaciers in northwest Svalbard is investigated by remote sensing. A 20 year time series of glacier surface flow speeds and frontal positions is presented covering the recent surges of Monacobreen, Comfortlessbreen, Blomstrandbreen and Fjortende Julibreen. Surface flow speeds were derived using feature tracking between pairs of ERS SAR and ALOS PALSAR images, while frontal positions were taken from the same imagery, as well as more frequent but lower-spatial-resolution Envisat Wide Swath Mode images. During all four surges, increased ice flow caused the tidewater margin to advance while the calving flux was initially reduced to near zero due to compressive stresses limiting crevasse propagation. As ice speed decreased, the terminus continued to advance, until the glacier’s speed had returned to its pre-surge flow rate. Only at this time did the terminus start to retreat and peak iceberg calving flux was established. We conclude that terminus advance closely tracks glacier speed-up, that there is little mass loss through calving during the most active phase of the surge, and that seasonal cycles of terminus positions diminish during the active surge phase.

scholarly journals Influence of subglacial Vostok lake on the regional ice dynamics of the Antarctic ice sheet: a model study

2004 ◽  
Vol 50 (171) ◽  
pp. 583-589 ◽  
Author(s):  
Frank Pattyn ◽  
Bert De Smedt ◽  
Roland Souchez
Keyword(s):  
Three Dimensional ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Surface Flattening ◽  
Subglacial Lake ◽  
Model Study ◽  
Speed Up ◽  
Order Stress ◽  
The Antarctic

AbstractWe applied a newly developed three-dimensional, time-dependent, thermomechanical icesheet model including higher-order stress gradients, to simulate the ice flow across subglacial Vostok lake, East Antarctica. Simulations of both ‘lake’ and ‘no lake’ conditions (by treating the ice/lake interface as a stress-free surface, similar to an ice shelf) demonstrate the effects of the subglacial lake, such as pronounced surface flattening and ice-flow turning, on the overall ice dynamics in the vicinity, although subglacial lake dynamics are not treated explicitly. When buoyancy forces and hydrostatic equilibrium of the ice above the lake are taken into account, the along-lake surface slope is preserved and the ice-flow pattern is in accord with sparse observations. Model experiments point to a local ice speed-up in the northern part of the lake, which can be associated with the onset of an enhanced ice-flow feature, more precisely the onset of the Totten Glacier catchment.

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