Fast-flowing outlet glaciers on Svalbard ice caps

Dowdeswell, Julian A.; Collin, R. L.

doi:10.1130/0091-7613(1990)018<0778:ffogos>2.3.co;2

Cited by 43 publications

(33 citation statements)

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“…Their velocity gradient, expressed through the decreasing distance between interferometric fringes, increases toward the coastal ice margin, and phase coherence breaks down close to the terminus of each (Figure 9). This pattern of steadily increasing velocity within approach to the ocean (Figure 11) is typical of many tidewater outlet glaciers and ice streams in both the Antarctic and Arctic [e.g., Bentley, 1987;Dowdeswell and Collin, 1990]. These ice streams are the major locations of iceberg calving from the Academy of Sciences Ice Cap (Figures 4b and 4c).…”

Section: Velocity Structure From Sar Interferometrymentioning

confidence: 99%

Form and flow of the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian High Arctic

et al. 2002

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[ 1 ] The 5,575-km 2 Acad emy of Sciences Ice Cap is the largest in the Russia n Arctic. A 100-M Hz airbo rne radar, digital Landsat imagery, and satelli te syntheti c apertu re radar (SAR) interfero metry are used to investig ate its form and flow, incl uding the propor tion of mass lost throu gh iceberg calvi ng. The ice cap was covered by a 10-km -space d grid of radar fli ght paths , and the centr al porti on was covered by a grid at 5-km inte rvals: a total of 1,657 km of radar data. Digit al elevation model s (DEM s) of ice surfa ce elevation, ice thickness, and bed elevat ion data sets wer e produce d (cell size 500 m). The DEMs wer e used in the selec tion o f a deep ice core dril l site. To tal ice cap volum e is 2,1 84 km 3 ( $ 5.5 mm sea level equiva lent). The ice cap has a single dome reachi ng 749 m. Maxi mum ice thic kness is 819 m. About 200 km, or 42%, of the ice margin is mari ne. About 50% of the ice cap bed is below sea level. The central divide of the ice cap and severa l maj or drain age basins, in the south an d east of the ice cap and of up to 975 km 2 , are delimited from satel lite ima gery. The re is no eviden ce of past surge ac tivity on the ice cap. SAR interfero metric frin ges and phase-unwrapped velociti es for the whole ice cap indicate slow flow in the interior and much of the margin, punctu ated by four fast flowin g featu res with late ral shear zones and maxi mum veloci ty of 140 m y r À 1 . These ice streams extend back into the slower moving ice to wi thin 5 -10 km of the ice cap crest. They have lengths of 17 -37 km a nd widths of 4 -8 km. Mass flux from these ice streams is $ 0.54 km 3 yr À 1 . Tabular icebergs up to $ 1.7 km long are produce d. Total iceberg flux from the ice cap is $ 0.65 km 3 yr À 1 and probably represe nts $ 40% of the overal l mass loss , with the rema inder coming from surfa ce mel ting. Drivin g stre sses are general ly low est (<40 kP a) close to the ice cap divides and in severa l of the ice stre ams. Ice stream motion is likely to incl ude a signifi cant basal compo nent and may involve deformabl e marine sedim ents.

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Section: Velocity Structure From Sar Interferometrymentioning

confidence: 99%

Form and flow of the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian High Arctic

et al. 2002

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“…Such deep and often overdeepened channels (Frazerbreen and Franklinbreen in Fig. 5) are explained by convergent ice flow draining large zones of the ice-cap accumulation area (Dowdeswell and Collin, 1990). For Bragebreen and Gimlebreen, the reconstruction suggests deep troughs which arise from a very positive AMB.…”

Section: Ice Thickness and Bedrock Elevationmentioning

confidence: 99%

Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard

et al. 2017

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Abstract. The basal topography is largely unknown beneath most glaciers and ice caps, and many attempts have been made to estimate a thickness field from other more accessible information at the surface. Here, we present a two-step reconstruction approach for ice thickness that solves mass conservation over single or several connected drainage basins. The approach is applied to a variety of test geometries with abundant thickness measurements including marine-and landterminating glaciers as well as a 2400 km 2 ice cap on Svalbard. The input requirements are kept to a minimum for the first step. In this step, a geometrically controlled, non-local flux solution is converted into thickness values relying on the shallow ice approximation (SIA). In a second step, the thickness field is updated along fast-flowing glacier trunks on the basis of velocity observations. Both steps account for available thickness measurements. Each thickness field is presented together with an error-estimate map based on a formal propagation of input uncertainties. These error estimates point out that the thickness field is least constrained near ice divides or in other stagnant areas. Withholding a share of the thickness measurements, error estimates tend to overestimate mismatch values in a median sense. We also have to accept an aggregate uncertainty of at least 25 % in the reconstructed thickness field for glaciers with very sparse or no observations. For Vestfonna ice cap (VIC), a previous ice volume estimate based on the same measurement record as used here has to be corrected upward by 22 %. We also find that a 13 % area fraction of the ice cap is in fact grounded below sea level. The former 5 % estimate from a direct measurement interpolation exceeds an aggregate maximum range of 6-23 % as inferred from the error estimates here.

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“…Vestfonna (VSF) is characterised by a varied surface topography with two main ridges and strongly pronounced fastoutlet glaciers (Dowdeswell and Collin, 1990, Fig. 1).…”

Section: Research Area and Observational Datamentioning

confidence: 99%

“…Therefore, understanding the response of fast flowing features to changing climate is crucial in order to make reliable projections Rignot et al, 2011;Shepherd et al, 2012;Dunse et al, 2012). Observations dating back several decades show multiple modes of fast ice flow behaviour including permanently fast flowing outlet glaciers or ice streams, networks of ice streams that switch between fast and slow flow (Boulton and Jones, 1979), pulsing glaciers (Mayo, 1978), short-term velocity variations of fast tidewater glaciers (Meier and Post, 1987), and surging glaciers (Kamb, 1987;Dowdeswell and Collin, 1990;Dunse et al, 2012;Gladstone et al, 2014;Sund et al, 2009Sund et al, , 2011Sund et al, , 2014 that show occasional massive accelerations of a factor 10 or higher compared to their quiescent state. The underlying processes behind this range of behaviours are not yet fully understood and need to be addressed.…”

Section: Introductionmentioning

confidence: 99%

“…It is instead dominated by fast flowing outlet glaciers that extend from the coast to regions close to the ice divide. All of the fast outlet glaciers on Vestfonna are thought to be topographically controlled and several of them are believed to have surge-type behaviour (Dowdeswell and Collin, 1990). We will especially focus on the recent speed-up of Franklinbreen , one of the major outlet glaciers on Vestfonna, and simulate ice flow with the Elmer/Ice finite element Full Stokes ice dynamic model (Gagliardini et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Assessment of heat sources on the control of fast flow of Vestfonna ice cap, Svalbard

et al. 2014

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Abstract. Understanding the response of fast flowing ice streams or outlet glaciers to changing climate is crucial in order to make reliable projections of sea level change over the coming decades. Motion of fast outlet glaciers occurs largely through basal motion governed by physical processes at the glacier bed, which are not yet fully understood. Various subglacial mechanisms have been suggested for fast flow but common to most of the suggested processes is the requirement of presence of liquid water, and thus temperate conditions.We use a combination of modelling, field, and remote observations in order to study links between different heat sources, the thermal regime and basal sliding in fast flowing areas on Vestfonna ice cap. A special emphasis lies on Franklinbreen, a fast flowing outlet glacier which has been observed to accelerate recently. We use the ice flow model Elmer/Ice including a Weertman type sliding law and a Robin inverse method to infer basal friction parameters from observed surface velocities. Firn heating, i.e. latent heat release through percolation of melt water, is included in our model; its parameterisation is calibrated with the temperature record of a deep borehole. We found that strain heating is negligible, whereas friction heating is identified as one possible trigger for the onset of fast flow. Firn heating is a significant heat source in the central thick and slow flowing area of the ice cap and the essential driver behind the ongoing fast flow in all outlets.Our findings suggest a possible scenario of the onset and maintenance of fast flow on the Vestfonna ice cap based on thermal processes and emphasise the role of latent heat released through refreezing of percolating melt water for fast flow. However, these processes cannot yet be captured in a temporally evolving sliding law. In order to simulate correctly fast flowing outlet glaciers, ice flow models not only need to account fully for all heat sources, but also need to incorporate a sliding law that is not solely based on the basal temperature, but also on hydrology and/or sediment physics.

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Fast-flowing outlet glaciers on Svalbard ice caps

Cited by 43 publications

References 0 publications

Form and flow of the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian High Arctic

Form and flow of the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian High Arctic

Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard

Assessment of heat sources on the control of fast flow of Vestfonna ice cap, Svalbard

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