scholarly journals Short-term variations in flow velocity of Glaciar Soler, Patagonia, Chile

1992 ◽  
Vol 38 (128) ◽  
pp. 152-156 ◽  
Author(s):  
Renji Naruse ◽  
Hiroshi Fukami ◽  
Masamu Aniya
Keyword(s):  
Flow Velocity ◽  
Water Pressure ◽  
Water Discharge ◽  
Time Lag ◽  
Maximum Flow ◽  
Sliding Velocity ◽  
Short Term ◽  
Ice Flow ◽  
Glacier Terminus ◽  
Basal Sliding

AbstractShort-term variations in ice-flow velocity were obtained at intervals of a few hours and a few days in the ablation area of Glaciar Soler, Patagonia, Chile, in November 1985. A maximum flow rate was measured at about four times the minimum value. A good correlation, with a time lag of 7.5 h, was found between the ice-flow velocity in the lower reaches and the amount of water discharge from the glacier terminus. It was concluded, therefore, that the velocity variations should have resulted from the variations in basal sliding velocity which is strongly controlled by the subglacial water pressure.

scholarly journals Short-term variations in flow velocity of Glaciar Soler, Patagonia, Chile

1992 ◽  
Vol 38 (128) ◽  
pp. 152-156 ◽  
Author(s):  
Renji Naruse ◽  
Hiroshi Fukami ◽  
Masamu Aniya
Keyword(s):  
Flow Velocity ◽  
Water Pressure ◽  
Water Discharge ◽  
Time Lag ◽  
Maximum Flow ◽  
Sliding Velocity ◽  
Short Term ◽  
Ice Flow ◽  
Glacier Terminus ◽  
Basal Sliding

AbstractShort-term variations in ice-flow velocity were obtained at intervals of a few hours and a few days in the ablation area of Glaciar Soler, Patagonia, Chile, in November 1985. A maximum flow rate was measured at about four times the minimum value. A good correlation, with a time lag of 7.5 h, was found between the ice-flow velocity in the lower reaches and the amount of water discharge from the glacier terminus. It was concluded, therefore, that the velocity variations should have resulted from the variations in basal sliding velocity which is strongly controlled by the subglacial water pressure.

scholarly journals Variations in the Sliding of a Temperate Glacier

1974 ◽  
Vol 13 (69) ◽  
pp. 349-369 ◽  
Author(s):  
Steven M. Hodge
Keyword(s):  
Water Discharge ◽  
Ice Flow ◽  
Sliding Speed ◽  
Temporary Storage ◽  
State Of Stress ◽  
Basal Sliding ◽  
Internal Deformation ◽  
Pressure Melting ◽  
Glacier Flow ◽  
Basal Shear

Detailed measurements of the positions of stakes along the center-line of the lower Nisqually Glacier were made over a period of two years. Variations in the basal sliding speed were calculated from the measured changes in surface speed, surface slope, and thickness, using the glacier flow model of Nye (1952) and allowing for the effect of the valley walls, longitudinal stress gradients, and uncertainties in the flow law of ice. The flow is predominantly by basal sliding and has a pronounced seasonal variation of approximately ±25%. Internal deformation contributes progressively less to the total motion with distance up-glacier. Neither the phase nor the magnitude of the seasonal velocity fluctuations can be accounted for by seasonal variations in the state of stress within the ice or at the bed, and the variations do not correlate directly with the melt-water discharge from the terminus. A seasonal wave in the ice flow travels down the glacier at a speed too high for propagation by internal deformation or the pressure melting/enhanced creep mechanism of basal sliding.The rate of sliding appears to be determined primarily by the amount of water in temporary storage in the glacier. The peak in sliding speed occurs, on the average, at the same time as the maximum liquid water storage of the South Cascade Glacier. The data support the idea that glaciers store water in the fall, winter and spring and then release it in the summer. This temporary storage may be greatest near the equilibrium line. The amount of stored water may increase over a period of years and be released catastrophically as a jökulhlaup. Any dependence of sliding on the basal shear stress is probably masked by the effect of variations in the hydrostatic pressure of water having access to the bed.

Variations in the Sliding of a Temperate Glacier

1974 ◽  
Vol 13 (69) ◽  
pp. 349-369 ◽  
Author(s):  
Steven M. Hodge
Keyword(s):  
Water Discharge ◽  
Ice Flow ◽  
Sliding Speed ◽  
Temporary Storage ◽  
State Of Stress ◽  
Basal Sliding ◽  
Internal Deformation ◽  
Pressure Melting ◽  
Glacier Flow ◽  
Basal Shear

Detailed measurements of the positions of stakes along the center-line of the lower Nisqually Glacier were made over a period of two years. Variations in the basal sliding speed were calculated from the measured changes in surface speed, surface slope, and thickness, using the glacier flow model of Nye (1952) and allowing for the effect of the valley walls, longitudinal stress gradients, and uncertainties in the flow law of ice. The flow is predominantly by basal sliding and has a pronounced seasonal variation of approximately ±25%. Internal deformation contributes progressively less to the total motion with distance up-glacier. Neither the phase nor the magnitude of the seasonal velocity fluctuations can be accounted for by seasonal variations in the state of stress within the ice or at the bed, and the variations do not correlate directly with the melt-water discharge from the terminus. A seasonal wave in the ice flow travels down the glacier at a speed too high for propagation by internal deformation or the pressure melting/enhanced creep mechanism of basal sliding. The rate of sliding appears to be determined primarily by the amount of water in temporary storage in the glacier. The peak in sliding speed occurs, on the average, at the same time as the maximum liquid water storage of the South Cascade Glacier. The data support the idea that glaciers store water in the fall, winter and spring and then release it in the summer. This temporary storage may be greatest near the equilibrium line. The amount of stored water may increase over a period of years and be released catastrophically as a jökulhlaup. Any dependence of sliding on the basal shear stress is probably masked by the effect of variations in the hydrostatic pressure of water having access to the bed.

Seasonal to multi-annual speedup and slowdown of Greenland outlet glaciers inferred from time-dependent remote sensing observations

2020 ◽  
Author(s):  
Lizz Ultee ◽  
Bryan Riel ◽  
Brent Minchew
Keyword(s):  
Time Series ◽  
Flow Velocity ◽  
Ice Sheet ◽  
Surface Air Temperature ◽  
Greenland Ice Sheet ◽  
Time Dependent ◽  
Surface Velocity ◽  
Short Term ◽  
Ice Flow

<p>The rate of ice flux from the Greenland Ice Sheet to the ocean depends on the ice flow velocity through outlet glaciers. Ice flow velocity, in turn, evolves in response to multiple geographic and environmental forcings at different timescales. For example, velocity may vary daily in response to ocean tides, seasonally in response to surface air temperature, and multi-annually in response to long-term trends in climate. The satellite observations processed as part of the NASA MEaSUREs Greenland Ice Sheet Velocity Map allow us to analyse variations in ice surface velocity at multiple timescales. Here, we decompose short-term and long-term signals in time-dependent velocity fields for Greenland outlet glaciers based on the methods of Riel et al. (2018). Patterns found in short-term signals can constrain basal sliding relations and ice rheology, while the longer-term signals hint at decadal in/stability of outlet glaciers. We present example velocity time series for outlets including Sermeq Kujalleq (Jakobshavn Isbrae) and Helheim Glacier, and we highlight features indicative of dynamic drawdown or advective restabilization. Finally, we comment on the capabilities of a time series analysis software under development for glaciological applications.</p>

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 Instruments and Methods: Direct measurement of sliding at the glacier bed

1994 ◽  
Vol 40 (136) ◽  
pp. 595-599 ◽  
Author(s):  
W. Blake ◽  
Urs H. Fischer ◽  
C.R. Bentley ◽  
Garry K. G. Clarke
Keyword(s):  
Water Pressure ◽  
Pressure Fluctuations ◽  
Yukon Territory ◽  
Diurnal Variations ◽  
Sliding Velocity ◽  
Total Flow ◽  
Glacier Surface ◽  
Basal Sliding ◽  
Sediment Deformation ◽  
Opening And Closing

AbstractSliding at the base of Trapridge Glacier, Yukon Territory, Canada, was measured using a “drag spool”. We describe this simple and inexpensive instrument as well as its installation and operation. From 1990 to 1992 seven sites were instrumented with drag spools. At six of the sites basal sliding, during the period of observation, accounted for 50-70% of the total flow observed at the glacier surface. The contribution from ice creep is known to be small, so most of the remaining surface motion must be attributed to subglacial sediment deformation. For the seventh site the observed sliding rate was ~ 90% of the total flow, an indication that the sliding contribution varies spatially across the bed. Diurnal variations in the response of one of our instruments appear to be correlated to subglacial water-pressure fluctuations and are interpreted in terms of changes in sliding velocity rather than the opening and closing of basal cavities.

Glacier sliding set by self-regulating feedback between friction and drainage efficiency

2020 ◽  
Author(s):  
Adrien Gilbert ◽  
Florent Gimbert ◽  
Kjetil Thøgersen ◽  
Thomas Schuler ◽  
Andreas Kääb
Keyword(s):  
Climate Change ◽  
Water Supply ◽  
Numerical Models ◽  
Water Pressure ◽  
Water Discharge ◽  
Coupled System ◽  
Dynamical Response ◽  
Main Process ◽  
Friction Laws ◽  
Basal Sliding

&lt;p&gt;Glacier basal sliding accommodates most of glacier motion and is the main process behind glacier dynamic variability, able to substantially modulate glacier response to climate change. In particular, it controls glacier instabilities, surges, ice stream development and flow speeds of most glaciers on Earth. Paradoxically, glacier sliding remains one of the least understood processes in glacier physics due to the difficulty of accessing and observing the sub-glacial environment. In numerical models, sliding of glaciers is traditionally determined by friction laws interlinking basal shear stress, sliding velocity and water pressure. However, assessing the effects of water pressure on sliding remains a challenge due to the sparsity of appropriate data to validate coupled ice-flow/subglacial-hydrology models. We unify here the description of subglacial cavities transient dynamic for basal friction and sub-glacial hydrology and show how it interacts as a self-regulating coupled system. Our results are in striking agreement with observation from a unique multi-decadal record of basal sliding and water discharge in Argenti&amp;#232;re Glacier (French Alps). We show that sliding speed of hard-bedded glaciers is set by the drainage efficiency necessary to accommodate the melt water supply rather than being driven by water pressure. We suggest that liquid water supply at the glacier base rather water pressure should be used to develop friction laws that include the effect subglacial hydrology. This will make glacier dynamical response to climate change more predictable.&lt;/p&gt;

scholarly journals Streaming flow of an Antarctic Peninsula palaeo-ice stream, both by basal sliding and deformation of substrate

2011 ◽  
Vol 57 (204) ◽  
pp. 596-608 ◽  
Author(s):  
Benedict T.I. Reinardy ◽  
Robert D. Larter ◽  
Claus-Dieter Hillenbrand ◽  
Tavi Murray ◽  
John F. Hiemstra ◽  
...  
Keyword(s):  
Flow Velocity ◽  
Antarctic Peninsula ◽  
Outer Shelf ◽  
Inner Shelf ◽  
Ice Flow ◽  
Transparent Layer ◽  
Basal Sliding ◽  
Fast Ice ◽  
Fast Flow ◽  
Streaming Flow

AbstractAcoustic sub-bottom profiler surveys on the northeast Antarctic Peninsula shelf indicate that parts of the seabed are underlain by an acoustically transparent layer that is thin on the inner shelf and becomes thicker and more extensive towards the outer shelf. Sedimentological and geophysical data are combined to construct a bed model where streaming ice flow, by both deformation and basal sliding, took place within cross-shelf troughs. The model suggests only limited deformation contributed to fast flow on the inner shelf, i.e. in the onset zone of ice streaming, where the bed was predominantly underlain by a stiff till. Thus, fast ice flow in this area might have been by basal sliding, with deformation confined to discontinuous patches of soft till <40 cm thick. Towards the middle and outer shelf, extensive, thick sequences of soft till suggest a change in the dominant subglacial process towards widespread deformation. This downstream change from basal sliding to subglacial deformation is manifest in the transition from stiff-till dominance to soft-till dominance, while a downstream increase in ice flow velocity is evident from the complex geomorphic imprint on the inner shelf evolving to the more restricted set of bedforms on the outer shelf.

scholarly journals The Effect of the Subglacial Water Pressure on the Sliding Velocity of a Glacier in an Idealized Numerical Model

1981 ◽  
Vol 27 (97) ◽  
pp. 407-421 ◽  
Author(s):  
Almut Iken
Keyword(s):  
Steady State ◽  
Numerical Model ◽  
Water Pressure ◽  
Small Drop ◽  
Sliding Velocity ◽  
Short Term ◽  
State Size

AbstractIn order to interpret observed short-term variations of the sliding velocity of a glacier the effect of a variable subglacial water pressure on the sliding velocity has been studied using an idealized numerical model. In particular the transient stages of growing or shrinking water-filled cavities at the ice-bedrock interface were analysed. It was found that the sliding velocity was larger when cavities were growing than when they had reached the steady-state size for a given water pressure. The smallest sliding velocities occurred while cavities were shrinking. When cavitation is substantial a small drop of water pressure below the steady-state value (e.g. by 0.5 bar) can temporarily cause backward sliding. A limiting water pressure at which sliding becomes unstable is derived. The consequences of more realistic assumptions than those of the model are discussed.

scholarly journals Glacier hydromechanics: early insights and the lasting legacy of three works by Iken and colleagues

2010 ◽  
Vol 56 (200) ◽  
pp. 1069-1078 ◽  
Author(s):  
Gwenn E. Flowers
Keyword(s):  
Shear Stress ◽  
Vertical Velocity ◽  
Water Pressure ◽  
Ice Sheets ◽  
Strong Correlations ◽  
Velocity Measurements ◽  
Short Term ◽  
Ice Flow ◽  
Alpine Glaciers ◽  
Basal Shear

AbstractThe association between basal hydrology and glacier sliding has become nearly synonymous with the early work of Almut Iken and colleagues. Their research published in theJournal of Glaciologyfrom 1981 to 1986 made an indelible impact on the study of glacier hydromechanics by documenting strong correlations between basal water pressure and short-term ice-flow variations. With a passion for elucidating the physics of glacier-bed processes, Iken herself made fundamental contributions to our theoretical and empirical understanding of the sliding process. From the theoretical bound on basal shear stress, to the inferences drawn from detailed horizontal and vertical velocity measurements, the work of Iken and colleagues continues to inform the interpretation of data from alpine glaciers and has found increasing relevance to observations from the ice sheets.

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