scholarly journals Sliding of temperate basal ice on a rough, hard bed: creep mechanisms, pressure melting, and implications for ice streaming

2016 ◽  
Vol 10 (5) ◽  
pp. 1915-1932 ◽  
Author(s):  
Maarten Krabbendam
Keyword(s):  
Heat Flow ◽  
Power Law ◽  
Basal Layer ◽  
Ice Dynamics ◽  
Basal Ice ◽  
Basal Sliding ◽  
Ductile Flow ◽  
Flow Through ◽  
Pressure Melting ◽  
Power Law Creep

Abstract. Basal ice motion is crucial to ice dynamics of ice sheets. The classic Weertman model for basal sliding over bedrock obstacles proposes that sliding velocity is controlled by pressure melting and/or ductile flow, whichever is the fastest; it further assumes that pressure melting is limited by heat flow through the obstacle and ductile flow is controlled by standard power-law creep. These last two assumptions, however, are not applicable if a substantial basal layer of temperate (T ∼ Tmelt) ice is present. In that case, frictional melting can produce excess basal meltwater and efficient water flow, leading to near-thermal equilibrium. High-temperature ice creep experiments have shown a sharp weakening of a factor 5–10 close to Tmelt, suggesting standard power-law creep does not operate due to a switch to melt-assisted creep with a possible component of grain boundary melting. Pressure melting is controlled by meltwater production, heat advection by flowing meltwater to the next obstacle and heat conduction through ice/rock over half the obstacle height. No heat flow through the obstacle is required. Ice streaming over a rough, hard bed, as possibly in the Northeast Greenland Ice Stream, may be explained by enhanced basal motion in a thick temperate ice layer.

scholarly journals Basal sliding of temperate basal ice on a rough, hard bed: pressure melting, creep mechanisms and implications for ice streaming

2016 ◽  
Author(s):  
Maarten Krabbendam
Keyword(s):  
Heat Flow ◽  
Power Law ◽  
Basal Layer ◽  
Ice Dynamics ◽  
Basal Ice ◽  
Basal Sliding ◽  
Ductile Flow ◽  
Flow Through ◽  
Pressure Melting ◽  
Power Law Creep

Abstract. Basal ice motion is crucial to ice dynamics of ice sheets. The Weertman sliding model for basal sliding over bedrock obstacles proposes that sliding velocity is controlled by pressure melting and/or ductile flow, whichever is the fastest; it further assumes that stoss-side melting is limited by heat flow through the obstacle and ductile flow is controlled by Power Law Creep. These last two assumptions, it is argued here, are invalid if a substantial basal layer of temperate (T ~ Tmelt) ice is present. In that case, frictional melting results in excess basal meltwater and efficient water flow, leading to near-thermal equilibrium. Stoss-side melting is controlled by melt water production, heat advection by flowing meltwater to the next obstacle, and heat conduction through ice/rock over half the obstacle height. No heat flow through the obstacle is required. High temperature ice creep experiments have shown a sharp weakening of a factor 5–10 close to Tmelt, implying breakdown of Power Law Creep and probably caused by a deformation-mechanism switch to grain boundary pressure melting. Ice streaming over a rough, hard bed, as likely in the Northeast Greenland Ice Stream, may be explained by enhanced basal motion in a thick temperate ice layer.

Co-Isotopic Signature of Two Mechanisms of Basal-Ice Formation in Arctic Outlet Glaciers

1988 ◽  
Vol 10 ◽  
pp. 163-166 ◽  
Author(s):  
R. Souchez ◽  
R. Lorrain ◽  
J.L. Tison ◽  
J. Jouzel
Keyword(s):  
Water Pressure ◽  
Isotopic Signature ◽  
Ice Formation ◽  
Basal Ice ◽  
Basal Sliding ◽  
Mechanisms Of Formation ◽  
Pressure Melting

Basal ice is formed by regelation as a consequence of both pressure-melting and freezing-on at the glacier sole.A study of D/H and 18O/16O ratios in basal ice from five Arctic outlet glaciers indicates that a co-isotopic signature exists for these two mechanisms of formation.The dispersed and stratified facies of basal ice present in these glaciers are related respectively to the occurrence of regelation and to freezing-on at the glacier base. Their origin is tentatively connected with the onset of basal sliding and the zone of bed decoupling due to basal water pressure in these Arctic outlet glaciers.

Glaciohydraulic supercooling: a freeze-on mechanism to create stratified, debris-rich basal ice: II. Theory

1998 ◽  
Vol 44 (148) ◽  
pp. 563-569 ◽  
Author(s):  
Richard B. Alley ◽  
Daniel E. Lawson ◽  
Edward B. Evenson ◽  
Jeffrey C. Strasser ◽  
Grahame J. Larson
Keyword(s):  
Water Flow ◽  
Accretion Rate ◽  
Water Discharge ◽  
Steep Slope ◽  
Field Observations ◽  
Ice Accretion ◽  
Flow Paths ◽  
Basal Ice ◽  
Flow Through ◽  
Pressure Melting

AbstractSimple theory supports field observations (Lawson and others, 1998 that subGlaciol water flow out of overdeepenings can cause accretion of layered, debris-bearing ice to the bases of glaciers. The large meltwater flux into a temperate glacier at the onset of summer melting can cause rapid water flow through expanded basal cavities or other flow paths. If that flow ascends a sufficiently steep slope out of an overdeepèning, the water will supercool as the pressure-melting point rises, and basal-ice accretion will occur. Diurnal, occasional or annual fluctuations in water discharge will cause variations in accretion rate, debris content of accreted ice or subsequent diagenesis, producing layers. Under appropriate conditions, net accretion of debris-bearing basal ice will allow debris fluxes that are significant in the glacier sediment budget.

scholarly journals The Dynamics of Ice-Sheet Outlets

1985 ◽  
Vol 31 (108) ◽  
pp. 99-107 ◽  
Author(s):  
N. F. Mcintyre
Keyword(s):  
Landsat Imagery ◽  
Ice Sheet ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Shelves ◽  
Surface Slopes ◽  
Basal Sliding ◽  
Subglacial Topography ◽  
Flow Through ◽  
Pressure Melting

AbstractA comparison of data from aircraft altimetry, Landsat imagery, and radia echo-sounding has shown characteristic surface topographies associated with sheet and stream flow. The transition between the two is abrupt and occurs at a step in the subglacial topography. This marks the onset of basal sliding and high velocities caused by subglacial water; it results in crevassed amphitheatre-like basins round the head of outlet glaciers. It is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase. This abrupt transition appears to be topographically controlled since basal temperatures are at the pressure-melting point well inland of the change in regime. The Marie Byrd Land ice streams exhibit qualitative differences from other ice-sheet outlets, however; the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland. Such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice. The repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers. Acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable. Rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion. This is concentrated towards the heads of outlet glaciers up-stream of the region where significant basal decoupling occurs. This may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls.

Glaciohydraulic supercooling: a freeze-on mechanism to create stratified, debris-rich basal ice: II. Theory

1998 ◽  
Vol 44 (148) ◽  
pp. 563-569 ◽  
Author(s):  
Richard B. Alley ◽  
Daniel E. Lawson ◽  
Edward B. Evenson ◽  
Jeffrey C. Strasser ◽  
Grahame J. Larson
Keyword(s):  
Water Flow ◽  
Accretion Rate ◽  
Water Discharge ◽  
Steep Slope ◽  
Field Observations ◽  
Ice Accretion ◽  
Flow Paths ◽  
Basal Ice ◽  
Flow Through ◽  
Pressure Melting

AbstractSimple theory supports field observations (Lawson and others, 1998 that subGlaciol water flow out of overdeepenings can cause accretion of layered, debris-bearing ice to the bases of glaciers. The large meltwater flux into a temperate glacier at the onset of summer melting can cause rapid water flow through expanded basal cavities or other flow paths. If that flow ascends a sufficiently steep slope out of an overdeepèning, the water will supercool as the pressure-melting point rises, and basal-ice accretion will occur. Diurnal, occasional or annual fluctuations in water discharge will cause variations in accretion rate, debris content of accreted ice or subsequent diagenesis, producing layers. Under appropriate conditions, net accretion of debris-bearing basal ice will allow debris fluxes that are significant in the glacier sediment budget.

scholarly journals The Dynamics of Ice-Sheet Outlets

1985 ◽  
Vol 31 (108) ◽  
pp. 99-107 ◽  
Author(s):  
N. F. Mcintyre
Keyword(s):  
Landsat Imagery ◽  
Ice Sheet ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Shelves ◽  
Surface Slopes ◽  
Basal Sliding ◽  
Subglacial Topography ◽  
Flow Through ◽  
Pressure Melting

AbstractA comparison of data from aircraft altimetry, Landsat imagery, and radia echo-sounding has shown characteristic surface topographies associated with sheet and stream flow. The transition between the two is abrupt and occurs at a step in the subglacial topography. This marks the onset of basal sliding and high velocities caused by subglacial water; it results in crevassed amphitheatre-like basins round the head of outlet glaciers. It is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase. This abrupt transition appears to be topographically controlled since basal temperatures are at the pressure-melting point well inland of the change in regime. The Marie Byrd Land ice streams exhibit qualitative differences from other ice-sheet outlets, however; the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland. Such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice. The repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers. Acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable. Rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion. This is concentrated towards the heads of outlet glaciers up-stream of the region where significant basal decoupling occurs. This may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls.

scholarly journals Changes in glacier dynamics under the influence of proglacial lake formation in Rhonegletscher, Switzerland

2011 ◽  
Vol 52 (58) ◽  
pp. 31-36 ◽  
Author(s):  
Shun Tsutaki ◽  
Daisuke Nishimura ◽  
Takeshi Yoshizawa ◽  
Shin Sugiyama
Keyword(s):  
Flow Velocity ◽  
Water Pressure ◽  
Overburden Pressure ◽  
Ice Dynamics ◽  
Basal Ice ◽  
Marginal Part ◽  
Lake Formation ◽  
Basal Sliding ◽  
Proglacial Lake ◽  
The Impact

AbstarctTo investigate the impact of proglacial lake formation on the dynamics and evolution of glaciers, we measured the ice motion of the terminal part of Rhonegletscher, Switzerland, where a lake formed in 2005. In 2009, the flow velocity near the terminus was >20 m a−1. One of the survey stakes tripled its velocity between 2006 and 2007. Since the lake water pressure was consistently close to the ice overburden pressure, it is likely that the high subglacial water pressure enhanced the basal ice motion. The estimated flow velocity due to ice shearing was negligibly small; almost 100% of the horizontal velocity near the terminus was caused by basal sliding. The longitudinal strain rate was large, 0.064 a–1, indicating that much of the glacier thinning was due to ice dynamics. The region of ice flotation adjacent to the lake expanded between 2008 and 2009 as a result of glacier thinning. Accordingly, a huge uplift of the surface was observed in 2009. It is clear from the vertical ice motion as well as visual observations that the marginal part of the glacier began to float. The ice-thinning rate in the studied area from 2008 to 2009 was 3.4 ma–1, larger than previous estimates.

scholarly journals Co-Isotopic Signature of Two Mechanisms of Basal-Ice Formation in Arctic Outlet Glaciers

1988 ◽  
Vol 10 ◽  
pp. 163-166 ◽  
Author(s):  
R. Souchez ◽  
R. Lorrain ◽  
J.L. Tison ◽  
J. Jouzel
Keyword(s):  
Water Pressure ◽  
Isotopic Signature ◽  
Ice Formation ◽  
Basal Ice ◽  
Basal Sliding ◽  
Mechanisms Of Formation ◽  
Pressure Melting

Basal ice is formed by regelation as a consequence of both pressure-melting and freezing-on at the glacier sole. A study of D/H and 18O/16O ratios in basal ice from five Arctic outlet glaciers indicates that a co-isotopic signature exists for these two mechanisms of formation. The dispersed and stratified facies of basal ice present in these glaciers are related respectively to the occurrence of regelation and to freezing-on at the glacier base. Their origin is tentatively connected with the onset of basal sliding and the zone of bed decoupling due to basal water pressure in these Arctic outlet glaciers.

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