scholarly journals Automated detection of basal icequakes and discrimination from surface crevassing

2019 ◽  
Vol 60 (79) ◽  
pp. 167-181 ◽  
Author(s):  
Thomas S. Hudson ◽  
Jonathan Smith ◽  
Alex M. Brisbourne ◽  
Robert S. White
Keyword(s):  
Seismic Energy ◽  
Automated Detection ◽  
Ice Streams ◽  
Glacier Surface ◽  
Ice Dynamics ◽  
Outlet Glacier ◽  
Ice Cap ◽  
Basal Sliding ◽  
Dynamics Models ◽  
Critical Process

ABSTRACTIcequakes at or near the bed of a glacier have the potential to allow us to investigate the interaction of ice with the underlying till or bedrock. Understanding this interaction is important for studying basal sliding of glaciers and ice streams, a critical process in ice dynamics models used to constrain future sea-level rise projections. However, seismic observations on glaciers can be dominated by seismic energy from surface crevassing. We present a method of automatically detecting basal icequakes and discriminating them from surface crevassing, comparing this method to a commonly used spectrum-based method of detecting icequakes. We use data from Skeidararjökull, an outlet glacier of the Vatnajökull Ice Cap, South-East Iceland, to demonstrate that our method outperforms the commonly used spectrum-based method. Our method detects a higher number of basal icequakes, has a lower rate of incorrectly identifying crevassing as basal icequakes and detects an additional, spatially independent basal icequake cluster. We also show independently that the icequakes do not originate from near the glacier surface. We conclude that the method described here is more effective than currently implemented methods for detecting and discriminating basal icequakes from surface crevassing.

scholarly journals Importance of basal processes in simulations of a surging Svalbard outlet glacier

2014 ◽  
Vol 8 (4) ◽  
pp. 1393-1405 ◽  
Author(s):  
R. Gladstone ◽  
M. Schäfer ◽  
T. Zwinger ◽  
Y. Gong ◽  
T. Strozzi ◽  
...  
Keyword(s):  
Steady State ◽  
Inverse Method ◽  
Frictional Heating ◽  
Sensitivity Experiment ◽  
Ice Dynamics ◽  
Outlet Glacier ◽  
Thickness Change ◽  
Ice Cap ◽  
Basal Sliding ◽  
Speed Up

Abstract. The outlet glacier of Basin 3 (B3) of Austfonna ice cap, Svalbard, is one of the fastest outlet glaciers in Svalbard, and shows dramatic changes since 1995. In addition to previously observed seasonal summer speed-up associated with the melt season, the winter speed of B3 has accelerated approximately fivefold since 1995. We use the Elmer/Ice full-Stokes model for ice dynamics to infer spatial distributions of basal drag for the winter seasons of 1995, 2008 and 2011. This "inverse" method is based on minimising discrepancy between modelled and observed surface velocities, using satellite remotely sensed velocity fields. We generate steady-state temperature distributions for 1995 and 2011. Frictional heating caused by basal sliding contributes significantly to basal temperatures of the B3 outlet glacier, with heat advection (a longer-timescale process than frictional heating) also being important in the steady state. We present a sensitivity experiment consisting of transient simulations under present-day forcing to demonstrate that using a temporally fixed basal drag field obtained through inversion can lead to thickness change errors of the order of 2 m year−1. Hence it is essential to incorporate the evolution of basal processes in future projections of the evolution of B3. Informed by a combination of our inverse method results and previous studies, we hypothesise a system of processes and feedbacks involving till deformation and basal hydrology to explain both the seasonal accelerations (short residence time pooling of meltwater at the ice–till interface) and the ongoing interannual speed-up (gradual penetration of water into the till, reducing till strength).

scholarly journals Impact of dust deposition on the albedo of Vatnajökull ice cap, Iceland

2017 ◽  
Vol 11 (2) ◽  
pp. 741-754 ◽  
Author(s):  
Monika Wittmann ◽  
Christine Dorothea Groot Zwaaftink ◽  
Louise Steffensen Schmidt ◽  
Sverrir Guðmundsson ◽  
Finnur Pálsson ◽  
...  
Keyword(s):  
Mass Balance ◽  
Radiative Forcing ◽  
Climate Model ◽  
Dispersion Model ◽  
Dust Deposition ◽  
Glacier Surface ◽  
Outlet Glacier ◽  
Ice Cap ◽  
Weather Stations ◽  
Dust Events

Abstract. Deposition of small amounts of airborne dust on glaciers causes positive radiative forcing and enhanced melting due to the reduction of surface albedo. To study the effects of dust deposition on the mass balance of Brúarjökull, an outlet glacier of the largest ice cap in Iceland, Vatnajökull, a study of dust deposition events in the year 2012 was carried out. The dust-mobilisation module FLEXDUST was used to calculate spatio-temporally resolved dust emissions from Iceland and the dispersion model FLEXPART was used to simulate atmospheric dust dispersion and deposition. We used albedo measurements at two automatic weather stations on Brúarjökull to evaluate the dust impacts. Both stations are situated in the accumulation area of the glacier, but the lower station is close to the equilibrium line. For this site ( ∼  1210 m a.s.l.), the dispersion model produced 10 major dust deposition events and a total annual deposition of 20.5 g m−2. At the station located higher on the glacier ( ∼  1525 m a.s.l.), the model produced nine dust events, with one single event causing  ∼  5 g m−2 of dust deposition and a total deposition of  ∼  10 g m−2 yr−1. The main dust source was found to be the Dyngjusandur floodplain north of Vatnajökull; northerly winds prevailed 80 % of the time at the lower station when dust events occurred. In all of the simulated dust events, a corresponding albedo drop was observed at the weather stations. The influence of the dust on the albedo was estimated using the regional climate model HIRHAM5 to simulate the albedo of a clean glacier surface without dust. By comparing the measured albedo to the modelled albedo, we determine the influence of dust events on the snow albedo and the surface energy balance. We estimate that the dust deposition caused an additional 1.1 m w.e. (water equivalent) of snowmelt (or 42 % of the 2.8 m w.e. total melt) compared to a hypothetical clean glacier surface at the lower station, and 0.6 m w.e. more melt (or 38 % of the 1.6 m w.e. melt in total) at the station located further upglacier. Our findings show that dust has a strong influence on the mass balance of glaciers in Iceland.

scholarly journals A balanced water layer concept for subglacial hydrology in large scale ice sheet models

2012 ◽  
Vol 6 (6) ◽  
pp. 5225-5253 ◽  
Author(s):  
S. Goeller ◽  
M. Thoma ◽  
K. Grosfeld ◽  
H. Miller
Keyword(s):  
Large Scale ◽  
Water Flux ◽  
Ice Sheet ◽  
Water Layer ◽  
Ice Streams ◽  
Ice Dynamics ◽  
Continental Scale ◽  
Basal Sliding ◽  
Subglacial Lakes ◽  
Layer Concept

Abstract. There is currently no doubt about the existence of a wide-spread hydrological network under the Antarctic ice sheet, which lubricates the ice base and thus leads to increased ice velocities. Consequently, ice models should incorporate basal hydrology to obtain meaningful results for future ice dynamics and their contribution to global sea level rise. Here, we introduce the balanced water layer concept, covering two prominent subglacial hydrological features for ice sheet modeling on a continental scale: the evolution of subglacial lakes and balance water fluxes. We couple it to the thermomechanical ice-flow model RIMBAY and apply it to a synthetic model domain inspired by the Gamburtsev Mountains, Antarctica. In our experiments we demonstrate the dynamic generation of subglacial lakes and their impact on the velocity field of the overlaying ice sheet, resulting in a negative ice mass balance. Furthermore, we introduce an elementary parametrization of the water flux–basal sliding coupling and reveal the predominance of the ice loss through the resulting ice streams against the stabilizing influence of less hydrologically active areas. We point out, that established balance flux schemes quantify these effects only partially as their ability to store subglacial water is lacking.

Subglacial Constructions and Investigations At Bondhusbreen, Norway

1979 ◽  
Vol 23 (89) ◽  
pp. 363-379 ◽  
Author(s):  
B. Wold ◽  
G. Østrem
Keyword(s):  
Drainage System ◽  
Hot Water ◽  
Electric Power Station ◽  
Water Drainage ◽  
Diversion Tunnel ◽  
Glacier Surface ◽  
Outlet Glacier ◽  
Ice Cap ◽  
System A ◽  
Tunnel System

Abstract For the construction of a hydro-electric power station in western Norway, a diversion tunnel was made to collect subglacial melt water under an outlet glacier from the Folgefonni ice cap. Many investigations were carried out by glaciologists and engineers before the project could begin, and several unexpected problems arose during the completion of the project. This paper deals with some of the problems and how they were solved. To avoid coarse glacier-carried material from being flushed into the water-collecting tunnel system, a large sedimentation chamber was constructed in the bedrock under the glacier. The dimensions of this huge chamber were decided from sediment-transport studies in the glacier stream and from studies of old bottom deposits in a lake close to the glacier front. Ice-velocity measurements were made on the glacier surface and similar studies were attempted in sub-glacial ice caves made by spraying hot water near the glacier bed, where the ice is 170 m thick. The subglacial water-drainage system was studied from a horizontal tunnel constructed in the bedrock under the glacier. Some preliminary conclusions are drawn from these studies. In future, it will still be possible to undertake subglacial studies because inspection tunnels have been left in the bedrock, and the accessibility is relatively good.

scholarly journals Glaciological observations of Brúarjökull, Iceland, using synthetic aperture radar and thematic mapper satellite data

1995 ◽  
Vol 21 ◽  
pp. 271-276 ◽  
Author(s):  
Dorothy K. Hall ◽  
Richard S. Williams ◽  
Oddur Sigurdsson
Keyword(s):  
Synthetic Aperture Radar ◽  
Thematic Mapper ◽  
Synthetic Aperture ◽  
Glacier Surface ◽  
Outlet Glacier ◽  
Near Surface ◽  
Ice Cap ◽  
Scatter Coefficient ◽  
History Of ◽  
Aperture Radar

The first European Remote Sensing Satellite (ERS-1) synthetic aperture radar (SAR) images offer opportunities for studying glacier surface properties and near-surface features. Analysis of back-scatter values from digital SAR data from 18 January, 7 June, 1 September and 25 October 1993 of Brúarjökull, an outlet glacier on the northeastern margin of the Vatnajökull ice cap, Iceland, that has a history of episodic surges, reveals several back-scatter boundaries that may relate to glacier facies and, inferentially, to mass balance. For example, a strong back-scatter boundary on the 18 January image of the snow-covered glacier, representing a back-scatter coefficient, σ°, difference of 4.34dB, appears to coincide with the position of the transient snow line at the end of the 1990–91 budget year. The boundary is visible on the 7 September 1991 Landsat thematic mapper (TM) image. The terminus is very difficult to define because of back-wasting from the last surge (1963–64) but is most easily delineated on the 1 September 1993 SAR and the 7 September 1991 TM images, in part due to the presence of ice-margin lakes.

scholarly journals Basal conditions at Engabreen, Norway, inferred from surface measurements and inverse modelling

2018 ◽  
Vol 64 (246) ◽  
pp. 555-567
Author(s):  
ANNE M. SOLGAARD ◽  
ALEXANDRA MESSERLI ◽  
THOMAS SCHELLENBERGER ◽  
CHRISTINE S. HVIDBERG ◽  
ASLAK GRINSTED ◽  
...  
Keyword(s):  
Surface Velocity ◽  
Direct Access ◽  
Outlet Glacier ◽  
Basal Friction ◽  
Ice Cap ◽  
Basal Sliding ◽  
Hydrological System ◽  
Surface Measurements ◽  
Essential Input ◽  
Strain Heating

ABSTRACTEngabreen is an outlet glacier of the Svartisen Ice Cap located in Northern Norway. It is a unique glacier due to the Svartisen Subglacial Laboratory which allows direct access to the glacier bed. In this study, we combine both sub- and supraglacial observations with ice-flow modelling in order to investigate conditions at the bed of Engabreen both spatially and temporally. We use the full-Stokes model Elmer/Ice and satellite-based surface-velocity maps from 2010 and 2014 to infer patterns of basal friction. Direct measurements of basal sliding and deformation of lower layers of the ice are used to adjust the ice viscosity and provide essential input to the setup of our model and influence the interpretation of the results. We find a clear seasonal cycle in the subglacial conditions at the higher elevation region of the study area and discuss this in relation to the subglacial hydrological system. Our results also reveal an area with an overdeepening where basal friction is significantly lower than elsewhere on the glacier all year round. We attribute this to either water pooling at the base, or saturated sediments and increased strain heating at this location which softens the ice further.

scholarly journals Analyses of a surging outlet glacier of Vatnajökull ice cap, Iceland

2005 ◽  
Vol 42 ◽  
pp. 23-28 ◽  
Author(s):  
Guðfinna Aðalgeirsdóttir ◽  
Helgi Björnsson ◽  
Finnur Pálsson ◽  
Eyjolfur Magnússon
Keyword(s):  
Mass Balance ◽  
Glacier Surface ◽  
Measured Velocity ◽  
Outlet Glacier ◽  
Ice Cap ◽  
Elevation Changes ◽  
History Of ◽  
Northern Side ◽  
The Difference ◽  
Approximation Type

AbstractMany of the large outlet glaciers of Vatnajökull ice cap, Iceland, have a history of regular surges. The mass transport during surges can be up to 25% of the total ice flux. This is a considerable amount that affects the whole ice cap, the location of the ice divides, the flow field and the size and shape of the ice cap. Data from the surging outlet Dyngjujökull, on the northern side of Vatnajökull, which surged during the period 1998-2000, are presented: surface elevation changes, displacement and total mass tr ansport. The total gain in ice volume in the receiving area, due to the surge, is considerably smaller than the loss in the reservoir area. The difference is mainly due to enhanced melting rates on the larger surface area of the crevassed glacier surface, and increased turbulent fluxes above the surface, but also due to increased frictional melting at the bed during the surge. A two-dimensional vertically integrated numerical flow model, of standard shallow-ice approximation type, is used to show that a modeled glacier that is similar in size to Dyngjujökull and subject to the same mass balance has three times higher velocities than the measured velocity during the quiescent phase. Adding surges in the numerical model, by periodically increasing the sliding velocity, causes the glacier to retreat and oscillate around a smaller state when subject to the same mass-balance regime. Lowering the equilibrium line by 50 m lets the modeled surging glacier oscillate around a size similar to that of the present glacier, indicating that surging is an efficient long-term ablation mechanism.

scholarly journals Observation of recent surges of Vatnajökull, Iceland, by means of ERS SAR interferometry

2003 ◽  
Vol 37 ◽  
pp. 69-76 ◽  
Author(s):  
Andrea Fischer ◽  
Helmut Rott ◽  
Helgi Björnsson
Keyword(s):  
Sar Interferometry ◽  
Surface Velocity ◽  
Outlet Glacier ◽  
Ice Cap ◽  
Glacier Terminus ◽  
New Information ◽  
Basal Sliding ◽  
Velocity Changes ◽  
Extended Area ◽  
In The Beginning

AbstractRecent surges of two outlet glaciers of the Vatnajökull ice cap, Iceland, were observed using European Remote-sensing Satellite (ERS) synthetic aperture radar (SAR) tandem interferograms from12 different dates between December 1995 and January 2000. ERS SAR interferometry provided new information on the temporal and spatial variations in surface velocity during surges, after fieldwork became impossible. The area affected by the surge and therefore by increased basal sliding was delineated. Themigration of flow divides on the ice cap during a surge was described. At Sylgjujökull, a western outlet glacier covering an area of 175 km2, the fully developed surge and its abating phase were studied. Over a period of 4 2 years after December 1995, the ice motion decreased steadily, with initially the highest velocities and subsequently the most pronounced decrease in velocity at the glacier terminus. The surge of Dyngjujökull, a northern outlet glacier covering an area of 1040 km2, reached its maximum in 1999/2000. Slow acceleration over an area of about 200 km2 was first observed between March 1996 and January 1997. The interferogram from January 1999 shows a well-developed surge area, covering 210 km2. This area more than doubled by January 2000, with maximum velocities reaching >7 md–1. Between January 1997 and January 2000, the flow divide between Dyngju- and Skeiðararjökull shifted 16 km to the south. The investigations indicate that a surge cycle on these glaciers spans several years, with slowly increasing motion over an extended area in the beginning, and more pronounced velocity changes during the active surge phase lasting 1–2 years.

scholarly journals A balanced water layer concept for subglacial hydrology in large-scale ice sheet models

2013 ◽  
Vol 7 (4) ◽  
pp. 1095-1106 ◽  
Author(s):  
S. Goeller ◽  
M. Thoma ◽  
K. Grosfeld ◽  
H. Miller
Keyword(s):  
Large Scale ◽  
Water Flux ◽  
Ice Sheet ◽  
Water Layer ◽  
Ice Streams ◽  
Ice Dynamics ◽  
Continental Scale ◽  
Basal Sliding ◽  
Subglacial Lakes ◽  
Layer Concept

Abstract. There is currently no doubt about the existence of a widespread hydrological network under the Antarctic Ice Sheet, which lubricates the ice base and thus leads to increased ice velocities. Consequently, ice models should incorporate basal hydrology to obtain meaningful results for future ice dynamics and their contribution to global sea level rise. Here, we introduce the balanced water layer concept, covering two prominent subglacial hydrological features for ice sheet modeling on a continental scale: the evolution of subglacial lakes and balance water fluxes. We couple it to the thermomechanical ice-flow model RIMBAY and apply it to a synthetic model domain. In our experiments we demonstrate the dynamic generation of subglacial lakes and their impact on the velocity field of the overlaying ice sheet, resulting in a negative ice mass balance. Furthermore, we introduce an elementary parametrization of the water flux–basal sliding coupling and reveal the predominance of the ice loss through the resulting ice streams against the stabilizing influence of less hydrologically active areas. We point out that established balance flux schemes quantify these effects only partially as their ability to store subglacial water is lacking.

scholarly journals Structural controls on englacial esker sedimentation: Skeiðarárjökull, Iceland

2009 ◽  
Vol 50 (51) ◽  
pp. 85-92 ◽  
Author(s):  
Matthew J. Burke ◽  
John Woodward ◽  
Andrew J. Russell ◽  
P. Jay Fleisher
Keyword(s):  
Structural Control ◽  
Preferential Flow ◽  
High Amplitude ◽  
Glacier Surface ◽  
Outlet Glacier ◽  
Structural Controls ◽  
Ice Cap ◽  
Accommodation Space ◽  
Glacier Ice ◽  
Ground Penetrating

AbstractWe have used ground-penetrating radar (GPR) to observe englacial structural control upon the development of an esker formed during a high-magnitude outburst flood (jökulhlaup). The surge-type Skeiðarárjökull, an outlet glacier of the Vatnajökull ice cap, Iceland, is a frequent source of jökulhlaups. The rising-stage waters of the November 1996 jökulhlaup travelled through a dense network of interconnected fractures that perforated the margin of the glacier. Subsequent discharge focused upon a small number of conduit outlets. Recent ice-marginal retreat has exposed a large englacial esker associated with one of these outlets. We investigated structural controls on esker genesis in April 2006, by collecting >2.5km of GPR profiles on the glacier surface up-glacier of where the esker ridge has been exposed by meltout. In lines closest to the exposed esker ridge, we interpret areas of englacial horizons up to ~30m wide and ~10–15m high as an up-glacier continuation of the esker sediments. High-amplitude, dipping horizons define the base of esker materials across many lines. Similar dipping surfaces deeper in the profiles suggest that: (1) the dipping surfaces beneath the esker are englacial tephera bands; (2) floodwaters were initially discharged along structurally controlled englacial surfaces (tephra bands); (3) the rapid increase in discharge resulted in hydrofracturing; (4) establishment of preferential flow paths resulted in conduit development along the tephra bands due to localized excavation of surrounding glacier ice; and (5) sedimentation took place within the new accommodation space to form the englacial structure melting out to produce the esker.

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