Surface speed and frontal ablation of Kronebreen and Kongsbreen, NW-Svalbard, from SAR offset tracking

Abstract. Kronebreen and Kongsbreen are among the fastest-flowing glaciers on Svalbard and, therefore, important contributors to the total dynamic mass loss from the archipelago. Here, we present a time series of area-wide surface velocity fields from April 2012 to December 2013 based on offset tracking on repeat high-resolution Radarsat-2 Ultrafine data. Surface speeds reached up to 3.2 m d−1 near the calving front of Kronebreen in summer 2013 and 2.7 m d−1 at Kongsbreen in late autumn 2012. Additional velocity fields from Radarsat-1, Radarsat-2 and TerraSAR-X data since December 2007 together with continuous GPS measurements on Kronebreen since September 2008 revealed complex patterns in seasonal and interannual speed evolution. Part of the ice-flow variations seem closely linked to the amount and timing of surface meltwater production and rainfall, both of which are known to have a strong influence on the basal water pressure and hence basal lubrication. In addition, terminus retreat and the associated reduction in back stress appear to have influenced the speed close to the calving front, especially at Kongsbreen in 2012 and 2013. Since 2007, Kongsbreen retreated up to 1800 m, corresponding to a total area loss of 2.5 km2. In 2011 the retreat of Kronebreen of up to 850 m, responsible for a total area loss of 2.8 km2, was triggered after a phase of stable terminus position since ~ 1990. Retreat is an important component of the mass balance of both glaciers, in which frontal ablation is the largest component. Total frontal ablation between April 2012 and December 2013 was estimated to 0.21–0.25 Gt a−1 for Kronebreen and 0.14–0.16 Gt a−1 for Kongsbreen.

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

10.26686/wgtn.17059823 ◽

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

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.

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Surface velocity variations of glaciers on Kenai Peninsula, Alaska, 2014-2019

10.5194/egusphere-egu21-16020 ◽

2021 ◽

Author(s):

Ruitang Yang ◽

Regine Hock ◽

Shichang Kang ◽

Donghui Shangguan ◽

Wanqin Guo

Keyword(s):

Time Series ◽

Velocity Profile ◽

Velocity Fields ◽

Surface Velocity ◽

Spatiotemporal Variations ◽

Outburst Flood ◽

Mean Velocity ◽

Kenai Peninsula ◽

Speed Up ◽

Offset Tracking

We characterize the spatiotemporal variations surface velocity of glaciers on the Kenai Peninsula, Alaska, using intensity offset tracking on a set of repeat-pass Sentinel-1 data and TerraSAR-X data. We derived 92 velocity fields and generated time-averaged annual and seasonal surface velocity maps for the period October 2014 to December 2019, as well as time series surface velocity profiles along centerlines for individual glaciers. We find considerable spatial and seasonal variations in surface velocity in the study area, especially a pronounced average spring speedup of 50% averagely compared to annual mean velocity. Ice velocities varied systematically between glaciers with different terminus types. Generally, the pixel-averaged velocity of tidewater and lake-terminating glaciers are up to 2 and 1.5 times greater than those of the land-terminating glaciers, respectively. For Bear glacier, with the analysis of surface velocity profile and the terminus change, we state this glacier retreat and accelerate. While the time-series result shows the velocity speed-up of the Bear glacier synchronizes well with the ice-damaged lake outburst flood (GLOF) events.

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Longitudinal coupling in ice flow across a subglacial ridge

Annals of Glaciology ◽

10.3189/s026030550001212x ◽

1997 ◽

Vol 24 ◽

pp. 169-174 ◽

Cited By ~ 1

Author(s):

Peter Jansson

Keyword(s):

Numerical Model ◽

Flow Regime ◽

Field Data ◽

Water Pressure ◽

Drastic Change ◽

Surface Velocity ◽

Northern Sweden ◽

Ice Flow ◽

Bedrock Topography ◽

Velocity Variations

A transverse bedrock ridge, or riegel, in the bedrock topography under Storglaciären, northern Sweden, induces a drastic change in flow regime. The part of the glacier located downstream of the riegel exhibits velocity variations correlated to water-pressure variations under this part of the glacier. Similar velocity variations are also observed up-glacier from the riegel despite a lack of significant water-pressure variations there. Field data and a numerical model suggest that the variations in surface velocity observed on the glacier upstream of the riegel are a result of pulling from down-glacier through longitudinal coupling across the riegel.

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RECENT DYNAMICAL FEATURES OF TYNDALL AND GREY GLACIERS, FROM SOUTHERN PATAGONIAN ICEFIELD, BY USING SATELLITE REMOTE SENSING TECHNIQUES

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprs-archives-xlii-3-w12-2020-453-2020 ◽

2020 ◽

Vol XLII-3/W12-2020 ◽

pp. 453-458

Author(s):

A. C. M. Luzardi ◽

C. Cárdenas

Keyword(s):

Remote Sensing ◽

Surface Velocity ◽

Delayed Response ◽

Ice Flow ◽

Temperature Changes ◽

Glacier Terminus ◽

Dynamical Features ◽

Remote Sensing Techniques ◽

Offset Tracking ◽

Sentinel 2

Abstract. Most glaciers in Patagonia have been rapidly shrinking during the past decades in response to ongoing global warming. To extend techniques to monitor their dynamics is crucial to understand individual glacier response to climate change and its consequences. In that context, our study aims to investigate recent dynamic behaviour of two near-site outlet glaciers placed at the Southern Patagonian Icefield (Tyndall and Grey glaciers) with the usage of simple and cheap remote sensing techniques. Sentinel-1 images were used to estimate surface velocity by using the Offset-tracking algorithm, while Sentinel-2 images were used to estimate area change in the ice front. Moreover, climatic variables (e.g., accumulated precipitation and air temperature) were analysed in order to assess its influence on glacier dynamics. Our results indicates that precipitation rather then temperature changes has been playing a major role in both glaciers retreat. While Tyndall tends to stabilize its retreat, Grey exponentially enhances retreat by its east tongue. Additionally, mean ice speed was of 0.448 ± 0.242 m.day−1 for Grey and 0.439 ± 0.245 m.day−1 for Tyndall, which agrees with literature. However, high ice speeds near the ice front indicated by previous work could not be captured here. Our results also suggests that ice flow is a delayed response of precipitation in the accumulation zone, and that may be the cause of decrease in Tyndall’s retreat. Overall, Offset-tracking is an useful tool for studying time series of Patagonian glaciers dynamics. It should be used carefully, however, around high dynamical regions such as the glacier terminus.

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Longitudinal coupling in ice flow across a subglacial ridge

Annals of Glaciology ◽

10.1017/s026030550001212x ◽

1997 ◽

Vol 24 ◽

pp. 169-174 ◽

Cited By ~ 7

Author(s):

Peter Jansson

Keyword(s):

Numerical Model ◽

Flow Regime ◽

Field Data ◽

Water Pressure ◽

Drastic Change ◽

Surface Velocity ◽

Northern Sweden ◽

Ice Flow ◽

Bedrock Topography ◽

Velocity Variations

A transverse bedrock ridge, or riegel, in the bedrock topography under Storglaciären, northern Sweden, induces a drastic change in flow regime. The part of the glacier located downstream of the riegel exhibits velocity variations correlated to water-pressure variations under this part of the glacier. Similar velocity variations are also observed up-glacier from the riegel despite a lack of significant water-pressure variations there. Field data and a numerical model suggest that the variations in surface velocity observed on the glacier upstream of the riegel are a result of pulling from down-glacier through longitudinal coupling across the riegel.

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Basal icequakes during changing subglacial water pressures beneath Gornergletscher, Switzerland

Journal of Glaciology ◽

10.3189/002214308785837110 ◽

2008 ◽

Vol 54 (186) ◽

pp. 511-521 ◽

Cited By ~ 60

Author(s):

Fabian Walter ◽

Nicholas Deichmann ◽

Martin Funk

Keyword(s):

Seismic Activity ◽

Water Pressure ◽

Gps Measurements ◽

Glacier Surface ◽

Ice Flow ◽

Dense Networks ◽

Ice Surface ◽

Hydrological System ◽

Lake Drainage ◽

The Impact

AbstractUsing dense networks of three-component seismometers installed in direct contact with the ice, the seismic activity of Gornergletscher, Switzerland, was investigated during the summers of 2004 and 2006, as subglacial water pressures varied drastically. These pressure variations are due to the diurnal cycle of meltwater input as well as the subglacial drainage of Gornersee, a nearby marginal ice-dammed lake. Up to several thousand seismic signals per day were recorded. Whereas most icequakes are due to surface crevasse openings, about 200 events have been reliably located close to the glacier bed. These basal events tend to occur in clusters and have signals with impulsive first arrivals. At the same time, basal water pressures and ice-surface velocities were measured to capture the impact of the lake drainage on the subglacial hydrological system and the ice-flow dynamics. Contrary to our expectations, we did not observe an increase of basal icequake activity as the lake emptied, thereby raising the subglacial water pressures close to the flotation level for several days. In fact, the basal icequakes were usually recorded during the morning hours, when the basal water pressure was either low or decreasing. During the high-pressure period caused by the drainage of the lake, no basal icequakes were observed. Furthermore, GPS measurements showed that the glacier surface was lowering during the basal seismic activity. These observations lead us to conclude that such icequakes are connected to the diurnal variation in glacier sliding across the glacier bed.

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

10.26686/wgtn.17059823.v1 ◽

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

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.

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Seasonal evolution of basal environment conditions of Russell sector, West Greenland, inverted from satellite observation of surface flow

The Cryosphere ◽

10.5194/tc-15-5675-2021 ◽

2021 ◽

Vol 15 (12) ◽

pp. 5675-5704

Author(s):

Anna Derkacheva ◽

Fabien Gillet-Chaulet ◽

Jeremie Mouginot ◽

Eliot Jager ◽

Nathan Maier ◽

...

Keyword(s):

Time Series ◽

Control Method ◽

Water Pressure ◽

Greenland Ice Sheet ◽

Surface Flow ◽

Surface Velocity ◽

Catchment Scale ◽

Ice Flow ◽

Seasonal Evolution ◽

Bed Topography

Abstract. Due to increasing surface melting on the Greenland ice sheet, better constraints on seasonally evolving basal water pressure and sliding speed are required by models. Here we assess the potential of using inverse methods on a dense time series of surface speeds to recover the seasonal evolution of the basal conditions in a well-documented region in southwest Greenland. Using data compiled from multiple satellite missions, we document seasonally evolving surface velocities with a temporal resolution of 2 weeks between 2015 and 2019. We then apply the inverse control method using the ice flow model Elmer/Ice to infer the basal sliding and friction corresponding to each of the 24 surface velocity data sets. Near the margin where the uncertainty in the velocity and bed topography are small, we obtain clear seasonal variations that can be mostly interpreted in terms of an effective-pressure-based hard-bed friction law. We find for valley bottoms or “troughs” in the bed topography that the changes in modelled basal conditions directly respond to local modelled water pressure variations, while the link is more complex for subglacial “ridges” which are often non-locally forced. At the catchment scale, in-phase variations in the water pressure, surface velocities, and surface runoff variations are found. Our results show that time series inversions of observed surface velocities can be used to understand the evolution of basal conditions over different timescales and could therefore serve as an intermediate validation for subglacial hydrology models to achieve better coupling with ice flow models.

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Dilation of subglacial sediment governs incipient surge motion in glaciers with deformable beds

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2020.0033 ◽

2020 ◽

Vol 476 (2238) ◽

pp. 20200033 ◽

Cited By ~ 1

Author(s):

B. M. Minchew ◽

C. R. Meyer

Keyword(s):

Pore Water ◽

Flow Model ◽

Pore Water Pressure ◽

Water Pressure ◽

Slip Rate ◽

Effective Pressure ◽

Ice Flow ◽

History Of ◽

Glacier Surges ◽

Geographical Clustering

Glacier surges are quasi-periodic episodes of rapid ice flow that arise from increases in slip rate at the ice–bed interface. The mechanisms that trigger and sustain surges are not well understood. Here, we develop a new model of incipient surge motion for glaciers underlain by sediments to explore how surges may arise from slip instabilities within a thin layer of saturated, deforming subglacial till. Our model represents the evolution of internal friction, porosity and pore water pressure within the till as functions of the rate and history of shear deformation, and couples the till mechanics to a simple ice-flow model. Changes in pore water pressure govern incipient surge motion, with less permeable till facilitating surging because dilation-driven reductions in pore water pressure slow the rate at which till tends towards a new steady state, thereby allowing time for the glacier to thin dynamically. The reduction of overburden (and thus effective) pressure at the bed caused by dynamic thinning of the glacier sustains surge acceleration in our model. The need for changes in both the hydromechanical properties of the till and the thickness of the glacier creates restrictive conditions for surge motion that are consistent with the rarity of surge-type glaciers and their geographical clustering.

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