Increased summer ice velocities on the Greenland ice sheet are driven by meltwater input to the s... more Increased summer ice velocities on the Greenland ice sheet are driven by meltwater input to the subglacial environment. However, spatial patterns of surface input and partitioning of meltwater between different pathways to the base remain poorly understood. To further our understanding of surface drainage, we apply a supraglacial hydrology model to the Paakitsoq region, West Greenland for three contrasting melt seasons. During an average melt season, crevasses drain ~47% of surface runoff, lake hydrofracture drains ~3% during the hydrofracturing events themselves, while the subsequent surface-to-bed connections drain ~21% and moulins outside of lake basins drain ~15%. Lake hydrofracture forms the primary drainage pathway at higher elevations (above ~850 m) while crevasses drain a significant proportion of meltwater at lower elevations. During the two higher intensity melt seasons, model results show an increase (~5 and ~6% of total surface runoff) in the proportion of runoff drained...
A key challenge in modelling coupled ice flow – subglacial hydrology is initializing the st... more A key challenge in modelling coupled ice flow – subglacial hydrology is initializing the state and parameters of the system. We address this problem by presenting a workflow for initializing these values at the start of a summer melt season. The workflow depends on running a subglacial hydrology model for the winter season, when the system is not forced by meltwater inputs, and ice velocities can be assumed constant. Key parameters of the winter run of the subglacial hydrology model are determined from an initial inversion for basal drag using a linear sliding law. The state of the subglacial hydrology model at the end of winter is incorporated into an inversion of basal drag using a non-linear sliding law which is a function of water pressure. We demonstrate this procedure in the Russell Glacier Area, and compare the output of the linear sliding law with two non-linear sliding laws. Additionally, we compare the winter output of a recent subglacial hydrology model to radar obs...
Supraglacial ponds on debris-covered glaciers present a mechanism of atmosphere/glacier energy tr... more Supraglacial ponds on debris-covered glaciers present a mechanism of atmosphere/glacier energy transfer that is poorly studied, and only conceptually included in mass-balance studies of debris-covered glaciers. This research advances previous efforts to develop a model of mass and energy balance for supraglacial ponds by applying a free-convection approach to account for energy exchanges at the subaqueous bare-ice surfaces. We develop the model using field data from a pond on Lirung Glacier, Nepal, that was monitored during the 2013 and 2014 monsoon periods. Sensitivity testing is performed for several key parameters, and alternative melt algorithms are compared with the model. The pond acts as a significant recipient of energy for the glacier system, and actively participates in the glacier’s hydrologic system during the monsoon. Melt rates are 2-4 cm d-1 (total of 98.5 m3 over the study period) for bare ice in contact with the pond, and <1 mmd-1 (total of 10.6m3) for the satura...
We use a simple energy-conservation model and a model based on Röthlisberger’s theory for steady-... more We use a simple energy-conservation model and a model based on Röthlisberger’s theory for steady-state water flow in a subglacial conduit to model water movement between lakes in the Adventure subglacial trench region of East Antarctica during a 1996–98 jökulhlaup. Using available field evidence to constrain the models suggests that water flow would likely be accommodated in a tunnel with a cross-sectional area of 36 m2 and a value for k (the reciprocal of Manning’s roughness parameter) larger than the 12.5 m1/3 s−1 previously calculated. We also use Nye’s theory for time-dependent conduit water flow to model the temporal evolution of conduit discharge, cross-sectional area, water pressure and lake draining and filling during the flood. We initially assume one source and one sink lake. We perform sensitivity tests on the input parameter set, matching modeled source- and sink-lake depth changes with measured surface elevation data. Using a simple function for vertical ice deformation...
Supraglacial meltwater lakes trigger ice-shelf break-up and modulate seasonal ice-sheet flow, and... more Supraglacial meltwater lakes trigger ice-shelf break-up and modulate seasonal ice-sheet flow, and are thus agents by which warming is transmitted to the Antarctic and Greenland ice sheets. To characterize supraglacial lake variability we perform a comparative analysis of lake geometry and depth in two distinct regions, one on the pre-collapse (2002) Larsen B ice shelf, Antarctica, and the other in the ablation zone of Paakitsoq, a land-terminating region of the Greenland ice sheet. Compared to Paakitsoq, lakes on the Larsen B ice shelf cover a greater proportion of surface area (5.3% cf. 1%), but are shallower and more uniform in area. Other aspects of lake geometry (e.g. eccentricity, degree of convexity (solidity) and orientation) are relatively similar between the two regions. We attribute the notable difference in lake density and depth between ice-shelf and grounded ice to the fact that ice shelves have flatter surfaces and less distinct drainage basins. Ice shelves also posses...
Earth Surface Processes and Landforms, Mar 1, 2003
Digital elevation models (DEMs) of the bed and surface of the polythermal Midre Lovénbreen, Svalb... more Digital elevation models (DEMs) of the bed and surface of the polythermal Midre Lovénbreen, Svalbard, are used to identify changes in glacier geometry between 1977 and 1995. The calculated mean annual mass balance (− 0· 61 m water equivalent (we) a− 1) is more negative than that derived from field measurements (− 0· 35 m we a− 1), although the error associated with this value (±0· 7 ma− 1) suggests that the difference may be accounted for by errors. However, similar discrepancies between DEM-based and field-based ...
High Mountain Asia (HMA) hosts the largest glacier concentration outside of polar regions. It is ... more High Mountain Asia (HMA) hosts the largest glacier concentration outside of polar regions. It is also distinct glaciologically as it forms one of two major surge clusters globally, and many glaciers there contradict the globally observed glacier recession trend. Surging glaciers are critical to our understanding of HMA glacier dynamics, threshold behaviour and flow instability, and hence have been the subject of extensive research, yet many dynamical uncertainties remain. Using the cloud-based geospatial data platform, Google Earth Engine (GEE) and GEE-developed tool, GEEDiT, to identify and quantify trends in the distribution and phenomenological characteristics of surging glaciers synoptically across HMA, we identified 137 glaciers as surging between 1987–2019. Of these, 55 were newly identified, 15 glaciers underwent repeat surges, and 18 were identified with enhanced glaciological hazard potential, most notably from Glacier Lake Outburst Floods (GLOFs). Terminus position time se...
This paper describes the development and testing of a distributed surface energy-balance model us... more This paper describes the development and testing of a distributed surface energy-balance model used to calculate rates of surface melting at Haut Glacier d’Arolla, Valais, Switzerland. The model uses a digital elevation model (DEM) of the glacier surface and surrounding topography together with meterological data collected at a site in front of the glacier to determine hourly or daily totals of the energy-balance components and hence of melting over the entire surface of the glacier with a spatial resolution of 20 m. The model can also be used to determine temporal and spatial variations in snow depth, snow-line position and glacier surface albedo. Calculations from the model are compared with observations made along the glacier centre line 1990, and in general the model performs very well. The correlation coefficients between calculated and measured snow-line elevation, albedo and ablation are 0.99, 0.85 and 0.81, respectively. The main source of error between modelled and measured...
ABSTRACT Glaciers can be divided into distinct surface zones (or facies) such as new snow, firn, ... more ABSTRACT Glaciers can be divided into distinct surface zones (or facies) such as new snow, firn, slush, and glacier ice, which can then be quantitatively linked to the mass balance state of a glacier. Due to similarities in reflective properties, persistent difficulty is had identifying the snow line and accumulation area rather than the more distinct glacier ice-firn line. Yet, it is the snow line rather than the firn line which provides a sensitive indicator of how a given year&#39;s climate influences a glacier. As small icecaps and glaciers contribute significantly to current sea level rise and will continue to do so in the coming decades, it would be highly beneficial to develop a technique which measures a glacier mass balance proxy - the glacier accumulation area ratio - using widespread, high resolution multispectral imagery. In situ glacier surface spectra (350-2300 nm) were measured on Midtre Lovénbreen (Svalbard) in August 2010 and Langjökull (Iceland) in August 2011 using an ASD field spectroradiometer. The full-spectrum reflectance measurements allow simulation of various airborne and spaceborne multispectral sensors including the Airborne Thematic Mapper, Landsat ETM+, MODIS or MERIS, and ESA&#39;s forthcoming Sentinel 2. Published studies have applied methods such as spectral band ratios, normalized indices, thresholding, principal component analysis, unsupervised classification, supervised classification, and spectral mixing analysis to classify glacier surfaces. The work presented here uses the collected in situ surface reflectance data to inform interpretation of ISODATA classification schemes of airborne and satellite multispectral imagery, can provide end member points for spectral mixing studies, and gives a starting point from which to further develop useful analysis strategies for remote imagery. Future research directions could integrate elevation and intensity data from airborne LiDAR campaigns. While spectra and classifications of airborne/satellite multispectral imagery match reasonably for Svalbard data, this is not the case between in situ measurements from Svalbard and imagery from Iceland. This paper will investigate not only the potential causes of differing spectral properties of glacier surfaces in Svalbard and Iceland, but also use the in situ spectra to evaluate classification techniques and inform more effective and reliable strategies for remotely measuring a glacier&#39;s accumulation area.
Increased summer ice velocities on the Greenland ice sheet are driven by meltwater input to the s... more Increased summer ice velocities on the Greenland ice sheet are driven by meltwater input to the subglacial environment. However, spatial patterns of surface input and partitioning of meltwater between different pathways to the base remain poorly understood. To further our understanding of surface drainage, we apply a supraglacial hydrology model to the Paakitsoq region, West Greenland for three contrasting melt seasons. During an average melt season, crevasses drain ~47% of surface runoff, lake hydrofracture drains ~3% during the hydrofracturing events themselves, while the subsequent surface-to-bed connections drain ~21% and moulins outside of lake basins drain ~15%. Lake hydrofracture forms the primary drainage pathway at higher elevations (above ~850 m) while crevasses drain a significant proportion of meltwater at lower elevations. During the two higher intensity melt seasons, model results show an increase (~5 and ~6% of total surface runoff) in the proportion of runoff drained...
A key challenge in modelling coupled ice flow – subglacial hydrology is initializing the st... more A key challenge in modelling coupled ice flow – subglacial hydrology is initializing the state and parameters of the system. We address this problem by presenting a workflow for initializing these values at the start of a summer melt season. The workflow depends on running a subglacial hydrology model for the winter season, when the system is not forced by meltwater inputs, and ice velocities can be assumed constant. Key parameters of the winter run of the subglacial hydrology model are determined from an initial inversion for basal drag using a linear sliding law. The state of the subglacial hydrology model at the end of winter is incorporated into an inversion of basal drag using a non-linear sliding law which is a function of water pressure. We demonstrate this procedure in the Russell Glacier Area, and compare the output of the linear sliding law with two non-linear sliding laws. Additionally, we compare the winter output of a recent subglacial hydrology model to radar obs...
Supraglacial ponds on debris-covered glaciers present a mechanism of atmosphere/glacier energy tr... more Supraglacial ponds on debris-covered glaciers present a mechanism of atmosphere/glacier energy transfer that is poorly studied, and only conceptually included in mass-balance studies of debris-covered glaciers. This research advances previous efforts to develop a model of mass and energy balance for supraglacial ponds by applying a free-convection approach to account for energy exchanges at the subaqueous bare-ice surfaces. We develop the model using field data from a pond on Lirung Glacier, Nepal, that was monitored during the 2013 and 2014 monsoon periods. Sensitivity testing is performed for several key parameters, and alternative melt algorithms are compared with the model. The pond acts as a significant recipient of energy for the glacier system, and actively participates in the glacier’s hydrologic system during the monsoon. Melt rates are 2-4 cm d-1 (total of 98.5 m3 over the study period) for bare ice in contact with the pond, and <1 mmd-1 (total of 10.6m3) for the satura...
We use a simple energy-conservation model and a model based on Röthlisberger’s theory for steady-... more We use a simple energy-conservation model and a model based on Röthlisberger’s theory for steady-state water flow in a subglacial conduit to model water movement between lakes in the Adventure subglacial trench region of East Antarctica during a 1996–98 jökulhlaup. Using available field evidence to constrain the models suggests that water flow would likely be accommodated in a tunnel with a cross-sectional area of 36 m2 and a value for k (the reciprocal of Manning’s roughness parameter) larger than the 12.5 m1/3 s−1 previously calculated. We also use Nye’s theory for time-dependent conduit water flow to model the temporal evolution of conduit discharge, cross-sectional area, water pressure and lake draining and filling during the flood. We initially assume one source and one sink lake. We perform sensitivity tests on the input parameter set, matching modeled source- and sink-lake depth changes with measured surface elevation data. Using a simple function for vertical ice deformation...
Supraglacial meltwater lakes trigger ice-shelf break-up and modulate seasonal ice-sheet flow, and... more Supraglacial meltwater lakes trigger ice-shelf break-up and modulate seasonal ice-sheet flow, and are thus agents by which warming is transmitted to the Antarctic and Greenland ice sheets. To characterize supraglacial lake variability we perform a comparative analysis of lake geometry and depth in two distinct regions, one on the pre-collapse (2002) Larsen B ice shelf, Antarctica, and the other in the ablation zone of Paakitsoq, a land-terminating region of the Greenland ice sheet. Compared to Paakitsoq, lakes on the Larsen B ice shelf cover a greater proportion of surface area (5.3% cf. 1%), but are shallower and more uniform in area. Other aspects of lake geometry (e.g. eccentricity, degree of convexity (solidity) and orientation) are relatively similar between the two regions. We attribute the notable difference in lake density and depth between ice-shelf and grounded ice to the fact that ice shelves have flatter surfaces and less distinct drainage basins. Ice shelves also posses...
Earth Surface Processes and Landforms, Mar 1, 2003
Digital elevation models (DEMs) of the bed and surface of the polythermal Midre Lovénbreen, Svalb... more Digital elevation models (DEMs) of the bed and surface of the polythermal Midre Lovénbreen, Svalbard, are used to identify changes in glacier geometry between 1977 and 1995. The calculated mean annual mass balance (− 0· 61 m water equivalent (we) a− 1) is more negative than that derived from field measurements (− 0· 35 m we a− 1), although the error associated with this value (±0· 7 ma− 1) suggests that the difference may be accounted for by errors. However, similar discrepancies between DEM-based and field-based ...
High Mountain Asia (HMA) hosts the largest glacier concentration outside of polar regions. It is ... more High Mountain Asia (HMA) hosts the largest glacier concentration outside of polar regions. It is also distinct glaciologically as it forms one of two major surge clusters globally, and many glaciers there contradict the globally observed glacier recession trend. Surging glaciers are critical to our understanding of HMA glacier dynamics, threshold behaviour and flow instability, and hence have been the subject of extensive research, yet many dynamical uncertainties remain. Using the cloud-based geospatial data platform, Google Earth Engine (GEE) and GEE-developed tool, GEEDiT, to identify and quantify trends in the distribution and phenomenological characteristics of surging glaciers synoptically across HMA, we identified 137 glaciers as surging between 1987–2019. Of these, 55 were newly identified, 15 glaciers underwent repeat surges, and 18 were identified with enhanced glaciological hazard potential, most notably from Glacier Lake Outburst Floods (GLOFs). Terminus position time se...
This paper describes the development and testing of a distributed surface energy-balance model us... more This paper describes the development and testing of a distributed surface energy-balance model used to calculate rates of surface melting at Haut Glacier d’Arolla, Valais, Switzerland. The model uses a digital elevation model (DEM) of the glacier surface and surrounding topography together with meterological data collected at a site in front of the glacier to determine hourly or daily totals of the energy-balance components and hence of melting over the entire surface of the glacier with a spatial resolution of 20 m. The model can also be used to determine temporal and spatial variations in snow depth, snow-line position and glacier surface albedo. Calculations from the model are compared with observations made along the glacier centre line 1990, and in general the model performs very well. The correlation coefficients between calculated and measured snow-line elevation, albedo and ablation are 0.99, 0.85 and 0.81, respectively. The main source of error between modelled and measured...
ABSTRACT Glaciers can be divided into distinct surface zones (or facies) such as new snow, firn, ... more ABSTRACT Glaciers can be divided into distinct surface zones (or facies) such as new snow, firn, slush, and glacier ice, which can then be quantitatively linked to the mass balance state of a glacier. Due to similarities in reflective properties, persistent difficulty is had identifying the snow line and accumulation area rather than the more distinct glacier ice-firn line. Yet, it is the snow line rather than the firn line which provides a sensitive indicator of how a given year&#39;s climate influences a glacier. As small icecaps and glaciers contribute significantly to current sea level rise and will continue to do so in the coming decades, it would be highly beneficial to develop a technique which measures a glacier mass balance proxy - the glacier accumulation area ratio - using widespread, high resolution multispectral imagery. In situ glacier surface spectra (350-2300 nm) were measured on Midtre Lovénbreen (Svalbard) in August 2010 and Langjökull (Iceland) in August 2011 using an ASD field spectroradiometer. The full-spectrum reflectance measurements allow simulation of various airborne and spaceborne multispectral sensors including the Airborne Thematic Mapper, Landsat ETM+, MODIS or MERIS, and ESA&#39;s forthcoming Sentinel 2. Published studies have applied methods such as spectral band ratios, normalized indices, thresholding, principal component analysis, unsupervised classification, supervised classification, and spectral mixing analysis to classify glacier surfaces. The work presented here uses the collected in situ surface reflectance data to inform interpretation of ISODATA classification schemes of airborne and satellite multispectral imagery, can provide end member points for spectral mixing studies, and gives a starting point from which to further develop useful analysis strategies for remote imagery. Future research directions could integrate elevation and intensity data from airborne LiDAR campaigns. While spectra and classifications of airborne/satellite multispectral imagery match reasonably for Svalbard data, this is not the case between in situ measurements from Svalbard and imagery from Iceland. This paper will investigate not only the potential causes of differing spectral properties of glacier surfaces in Svalbard and Iceland, but also use the in situ spectra to evaluate classification techniques and inform more effective and reliable strategies for remotely measuring a glacier&#39;s accumulation area.
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Papers by Neil Arnold