| 1. |
- Flink, Anne Elina, et al.
(författare)
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The evolution of a submarine landform record following recent and multiple surges of Tunabreen glacier, Svalbard
- 2015
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 108, s. 37-50
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on the glacial landform record associated with recent surge events of Tunabreen - a calving tidewater glacier in Tempelfjorden, Spitsbergen. Submarine geomorphology and recent terminal fluctuations of Tunabreen's glacier front were studied using high-resolution multibeam-bathymetric data and a range of published and remote-sensing sources, including topographic maps, satellite images and aerial photographs. The retreat moraines in the inner part of Tempelfjorden have been correlated with glacier terminus positions during retreat from the 2004 surge maximum. Glacier surface velocity and ice-front positions derived from high-resolution TerraSAR-X satellite data show ice movements at the glacier front during minor advances of the front in winter when calving is suppressed. This suggests that the moraines have formed annually during quiescent phase winter advances. Tunabreen has experienced three surges since the Little Ice Age (LIA). This is in contrast with most Svalbard surging glaciers which have long quiescent phases and have typically only undergone one or two surges during this time. The landform record in Tempelfjorden is distinguished from previously studied glacier-surge landsystems by four, well-preserved sets of landform assemblages generated by the LIA advance and three subsequent surges, all of which partly modify earlier landform records. Based on the unique landform record in Tempelfjorden, a new conceptual landsystem model for frequently surging glaciers has been put forward improving our understanding of the dynamics of the surging glaciers and, most importantly, how they can be distinguished from the climatically-controlled glaciers in the geological record.
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| 2. |
- How, Penelope, et al.
(författare)
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Calving controlled by melt-under-cutting : detailed calving styles revealed through time-lapse observations
- 2019
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Ingår i: Annals of Glaciology. - : Cambridge University Press (CUP). - 0260-3055 .- 1727-5644. ; 60:78, s. 20-31
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Tidskriftsartikel (refereegranskat)abstract
- We present a highly detailed study of calving dynamics at Tunabreen, a tidewater glacier in Svalbard. A time-lapse camera was trained on the terminus and programmed to capture images every 3 seconds over a 28-hour period in August 2015, producing a highly detailed record of 34 117 images from which 358 individual calving events were distinguished. Calving activity is characterised by frequent events (12.8 events h(-1)) that are small relative to the spectrum of calving events observed, demonstrating the prevalence of small-scale calving mechanisms. Five calving styles were observed, with a high proportion of calving events (82%) originating at, or above, the waterline. The tidal cycle plays a key role in the timing of calving events, with 68% occurring on the falling limb of the tide. Calving activity is concentrated where meltwater plumes surface at the glacier front, and a similar to 5 m undercut at the base of the glacier suggests that meltwater plumes encourage melt-under-cutting. We conclude that frontal ablation at Tunabreen may be paced by submarine melt rates, as suggested from similar observations at glaciers in Svalbard and Alaska. Using submarine melt rate to calculate frontal ablation would greatly simplify estimations of tidewater glacier losses in prognostic models.
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| 3. |
- Lovell, Harold, et al.
(författare)
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Multiple Late Holocene surges of a High-Arctic tidewater glacier system in Svalbard
- 2018
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 201, s. 162-185
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Tidskriftsartikel (refereegranskat)abstract
- Most large tidewater glaciers in Svalbard are known to have surged at least once in the last few hundred years. However, very little information exists on the frequency, timing or magnitude of surges prior to the Little Ice Age (LIA) maximum in ∼1900. We investigate the sediment-landform assemblages produced by multiple advances of the Nathorstbreen glacier system (NGS) in order to reconstruct its Late Holocene surge history. The glacier has recently undergone one of the largest surges ever observed in Svalbard, advancing ∼16 km from 2008 to 2016. We present flow velocities and ice-marginal observations (terminus change, proglacial geomorphological processes) from the later stages of this surge. A first detailed assessment of the development of a glaciotectonic mud apron within the fjord during a surge is provided. Geomorphological and sedimentological examination of the terrestrial moraine areas formed prior to the most recent surge reveals that at least two advances were responsible for their formation, based on the identification of a previously unrecognised ice-contact zone recorded by the distribution of sediment facies in coastal exposures. We distinguish between an outer, older advance to the distal part of the moraine system and an inner, younger advance to a position ∼2 km upfjord. Radiocarbon dating of shells embedded in glaciotectonic composite ridges formed by the onshore bulldozing of marine mud during the outer (older) of the two advances shows that it occurred at some point during the interval 700–890 cal. yr BP (i.e. ∼1160 AD), and not during the LIA as previously assumed. We instead attribute the inner (younger) advance to the LIA at ∼1890. By combining these data with previous marine geological investigations in inner and outer Van Keulenfjorden, we demonstrate that NGS has advanced at least four times prior to the recent 2008–2016 surge: twice at ∼2.7 kyr BP, at ∼1160 AD, and in ∼1890. This represents a unique record of the timing and magnitude of Late Holocene tidewater glacier surges in Svalbard.
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| 4. |
- Sevestre, Heidi, et al.
(författare)
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Tidewater Glacier Surges Initiated at the Terminus
- 2018
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Ingår i: Journal of Geophysical Research - Earth Surface. - : AMER GEOPHYSICAL UNION. - 2169-9003 .- 2169-9011. ; 123:5, s. 1035-1051
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Tidskriftsartikel (refereegranskat)abstract
- There have been numerous reports that surges of tidewater glaciers in Svalbard were initiated at the terminus and propagated up-glacier, in contrast with downglacier-propagating surges of land-terminating glaciers. Most of these surges were poorly documented, and the cause of this behavior was unknown. We present detailed data on the recent surges of two tidewater glaciers, Aavatsmarkbreen and Wahlenbergbreen, in Svalbard. High-resolution time series of glacier velocities and evolution of crevasse patterns show that both surges propagated up-glacier in abrupt steps. Prior to the surges, both glaciers underwent retreat and steepening, and in the case of Aavatsmarkbreen, we demonstrate that this was accompanied by a large increase in driving stress in the terminal zone. The surges developed in response to two distinct processes. (1) During the late quiescent phase, internal thermodynamic processes and/or retreat from a pinning point caused acceleration of the glacier front, leading to the development of terminal crevasse fields. (2) Crevasses allowed surface meltwater and rainwater to access the bed, causing flow acceleration and development of new crevasses up-glacier. Upward migration of the surge coincided with stepwise expansion of the crevasse field. Geometric changes near the terminus of these glaciers appear to have led to greater strain heating, water production, and storage at the glacier bed. Water routing via crevasses likely plays an important role in the evolution of surges. The distinction between internally triggered surges and externally triggered speedups may not be straightforward. The behavior of these glaciers can be understood in terms of the enthalpy cycle model.
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| 5. |
- Vallot, Dorothée, et al.
(författare)
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Effects of undercutting and sliding on calving : a global approach applied to Kronebreen, Svalbard
- 2018
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Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 12, s. 609-625
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we study the effects of basal friction, sub-aqueous undercutting and glacier geometry on the calving process by combining six different models in an offline-coupled workflow: a continuum-mechanical ice flow model (Elmer/Ice), a climatic mass balance model, a simple sub-glacial hydrology model, a plume model, an undercutting model and a discrete particle model to investigate fracture dynamics (Helsinki Discrete Element Model, HiDEM). We demonstrate the feasibility of reproducing the observed calving retreat at the front of Kronebreen, a tidewater glacier in Svalbard, during a melt season by using the output from the first five models as input to HiDEM. Basal sliding and glacier motion are addressed using Elmer/Ice, while calving is modelled by HiDEM. A hydrology model calculates subglacial drainage paths and indicates two main outlets with different discharges. Depending on the discharge, the plume model computes frontal melt rates, which are iteratively projected to the actual front of the glacier at subglacial discharge locations. This produces undercutting of different sizes, as melt is concentrated close to the surface for high discharge and is more diffuse for low discharge. By testing different configurations, we show that undercutting plays a key role in glacier retreat and is necessary to reproduce observed retreat in the vicinity of the discharge locations during the melting season. Calving rates are also influenced by basal friction, through its effects on near-terminus strain rates and ice velocity.
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