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  • 1
    Online Resource
    Online Resource
    Subglacial sediment distribution from constrained seismic inversion, using MuLTI software: examples from Midtdalsbreen, Norway
    Cambridge University Press (CUP) ; 2019
    In:  Annals of Glaciology Vol. 60, No. 79 ( 2019-09), p. 206-219
    Details
    In: Annals of Glaciology, Cambridge University Press (CUP), Vol. 60, No. 79 ( 2019-09), p. 206-219
    Abstract: Fast ice flow is associated with the deformation of subglacial sediment. Seismic shear velocities, Vs, increase with the rigidity of material and hence can be used to distinguish soft sediment from hard bedrock substrates. Depth profiles of Vs can be obtained from inversions of Rayleigh wave dispersion curves, from passive or active-sources, but these can be highly ambiguous and lack depth sensitivity. Our novel Bayesian transdimensional algorithm, MuLTI, circumvents these issues by adding independent depth constraints to the inversion, also allowing comprehensive uncertainty analysis. We apply MuLTI to the inversion of a Rayleigh wave dataset, acquired using active-source (Multichannel Analysis of Surface Waves) techniques, to characterise sediment distribution beneath the frontal margin of Midtdalsbreen, an outlet of Norway's Hardangerjøkulen ice cap. Ice thickness (0–20 m) is constrained using co-located GPR data. Outputs from MuLTI suggest that partly-frozen sediment (Vs 500–1000 m s −1 ), overlying bedrock (Vs 2000–2500 m s −1 ), is present in patches with a thickness of ~4 m, although this approaches the resolvable limit of our Rayleigh wave frequencies (14–100 Hz). Uncertainties immediately beneath the glacier bed are 〈 280 m s −1 , implying that MuLTI cannot only distinguish bedrock and sediment substrates but does so with an accuracy sufficient for resolving variations in sediment properties.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.1017/aog.2019.13
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2019
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    SSG: 14
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  • 2
    Online Resource
    Online Resource
    Glacier thermal regime linked to processes of annual moraine formation at M idtdalsbreen, southern N orway
    Wiley ; 2013
    In:  Boreas Vol. 42, No. 4 ( 2013-10), p. 896-911
    Details
    In: Boreas, Wiley, Vol. 42, No. 4 ( 2013-10), p. 896-911
    Abstract: Glacier thermal regime is shown to have a significant influence on the formation of ice‐marginal moraines. Annual moraines at the margin of Midtdalsbreen are asymmetrical and contain sorted fine sediment and diamicton layers dipping gently up‐glacier. The sorted fine sediments include sands and gravels that were initially deposited fluvially directly in front of the glacier. Clast‐form data indicate that the diamictons have a mixed subglacial and fluvial origin. Winter cold is able to penetrate through the thin ( 〈 10 m) ice margin and freeze these sediments to the glacier sole. During winter, sediment becomes elevated along the wedge‐shaped advancing glacier snout before melting out and being deposited as asymmetrical ridges. These annual moraines have a limited preservation potential of ∼40 years, and this is reflected in the evolution of landforms across the glacier foreland. Despite changing climatic conditions since the L ittle I ce A ge and particularly within the last 10 years when frontal retreat has significantly speeded up, glacier dynamics have remained relatively constant with moraines deposited via basal freeze‐on, which requires stable glacier geometry. While the annual moraines on the eastern side of M idtdalsbreen indicate a slow steady retreat, the western foreland contains contrasting ice‐stagnation topography, highlighting the importance of local forcing factors such as shielding, aspect and debris cover in addition to changing climate. This study indicates that, even in temperate glacial environments, restricted or localised areas of cold‐based ice can have a significant impact on the geomorphic imprint of the glacier system and may actually be more widespread within both modern and ancient glacial environments than previously thought.
    Type of Medium: Online Resource
    ISSN: 0300-9483 , 1502-3885
    URL: Issue
    URL: Article
    DOI: 10.1111/bor.2013.42.issue-4
    DOI: 10.1111/bor.12008
    Language: English
    Publisher: Wiley
    Publication Date: 2013
    detail.hit.zdb_id: 2028632-6
    detail.hit.zdb_id: 185110-X
    SSG: 14
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  • 3
    Online Resource
    Online Resource
    Formation of the Figge Maar Seafloor Crater During the 1964 B1 Blowout in the German North Sea
    Frontiers Media SA ; 2022
    In:  Earth Science, Systems and Society Vol. 2 ( 2022-6-23)
    Details
    In: Earth Science, Systems and Society, Frontiers Media SA, Vol. 2 ( 2022-6-23)
    Abstract: In 1964, exploration drilling in the German Sector of the North Sea hit a gas pocket at ∼2900 m depth below the seafloor and triggered a blowout, which formed a 550 m-wide and up to 38 m deep seafloor crater now known as Figge Maar. Although seafloor craters formed by fluid flow are very common structures, little is known about their formation dynamics. Here, we present 2D reflection seismic, sediment echosounder, and multibeam echosounder data from three geoscientific surveys of the Figge Maar blowout crater, which are used to reconstruct its formation. Reflection seismic data support a scenario in which overpressured gas ascended first through the lower part of the borehole and then migrated along steeply inclined strata and faults towards the seafloor. The focused discharge of gas at the seafloor removed up to 4.8 Mt of sediments in the following weeks of vigorous venting. Eyewitness accounts document that the initial phase of crater formation was characterized by the eruptive expulsion of fluids and sediments cutting deep into the substrate. This was followed by a prolonged phase of sediment fluidization and redistribution widening the crater. After fluid discharge ceased, the Figge Maar acted as a sediment trap reducing the crater depth to ∼12 m relative to the surrounding seafloor in 2018, which corresponds to an average sedimentation rate of ∼22,000 m 3 /yr between 1995 and 2018. Hydroacoustic and geochemical data indicate that the Figge Maar nowadays emits primarily biogenic methane, predominantly during low tide. The formation of Figge Maar illustrates hazards related to the formation of secondary fluid pathways, which can bypass safety measures at the wellhead and are thus difficult to control.
    Type of Medium: Online Resource
    ISSN: 2634-730X
    URL: Article
    DOI: 10.3389/esss.2022.10053
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2022
    detail.hit.zdb_id: 3106190-4
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  • 4
    Online Resource
    Online Resource
    Pervasive cold ice within a temperate glacier – implications for glacier thermal regimes, sediment transport and foreland geomorphology
    Copernicus GmbH ; 2019
    In:  The Cryosphere Vol. 13, No. 3 ( 2019-03-07), p. 827-843
    Details
    In: The Cryosphere, Copernicus GmbH, Vol. 13, No. 3 ( 2019-03-07), p. 827-843
    Abstract: Abstract. This study suggests that cold-ice processes may be more widespread than previously assumed, even within temperate glacial systems. We present the first systematic mapping of cold ice at the snout of the temperate glacier Midtdalsbreen, an outlet of the Hardangerjøkulen icefield (Norway), from 43 line kilometres of ground-penetrating radar data. Results show a 40 m wide cold-ice zone within the majority of the glacier snout, where ice thickness is 〈10 m. We interpret ice to be cold-based across this zone, consistent with basal freeze-on processes involved in the deposition of moraines. We also find at least two zones of cold ice up to 15 m thick within the ablation area, occasionally extending to the glacier bed. There are two further zones of cold ice up to 30 m thick in the accumulation area, also extending to the glacier bed. Cold-ice zones in the ablation area tend to correspond to areas of the glacier that are covered by late-lying seasonal snow patches that reoccur over multiple years. Subglacial topography and the location of the freezing isotherm within the glacier and underlying subglacial strata likely influence the transport and supply of supraglacial debris and formation of controlled moraines. The wider implication of this study is the possibility that, with continued climate warming, temperate environments with primarily temperate glaciers could become polythermal in forthcoming decades with (i) persisting thinning and (ii) retreat to higher altitudes where subglacial permafrost could be and/or become more widespread. Adversely, the number and size of late-lying snow patches in ablation areas may decrease and thereby reduce the extent of cold ice, reinforcing the postulated change in the thermal regime.
    Type of Medium: Online Resource
    ISSN: 1994-0424
    URL: Article
    DOI: 10.5194/tc-13-827-2019
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2019
    detail.hit.zdb_id: 2393169-3
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  • 5
    Online Resource
    Online Resource
    Image4.TIF
    Frontiers Media SA ; 2022
    In:  Frontiers in Earth Science Vol. 10 ( 2022-3-28)
    Details
    In: Frontiers in Earth Science, Frontiers Media SA, Vol. 10 ( 2022-3-28)
    Abstract: Geophysical surveys provide an efficient and non-invasive means of studying subsurface conditions in numerous sedimentary settings. In this study, we explore the application of three geophysical methods to a proglacial environment, namely ground penetrating radar (GPR), seismic refraction and multi-channel analysis of surface waves (MASW). We apply these geophysical methods to three glacial landforms with contrasting morphologies and sedimentary characteristics, and we use the various responses to assess the applicability and limitations of each method for these proglacial targets. Our analysis shows that GPR and seismic (refraction and MASW) techniques can provide spatially extensive information on the internal architecture and composition of moraines, but careful survey designs are required to optimise data quality in these geologically complex environments. Based on our findings, we define a number of recommendations and a potential workflow to guide future geophysical investigations in analogous settings. We recommend the initial use of GPR in future studies of proglacial environments to inform (a) seismic survey design and (b) the selection of seismic interpretation techniques. We show the benefits of using multiple GPR antenna frequencies (e.g., 25 and 100 MHz) to provide decimetre scale imaging in the near surface (e.g., & lt; 15 m) while also enabling signal penetration to targets at up to ∼40 m depth (e.g., bedrock). This strategy helps to circumvent changes in radar signal penetration resulting from variations in substrate conductivity or abundant scatterers. Our study also demonstrates the importance of combining multiple geophysical methods together with ground-truthing through sedimentological observations to reduce ambiguity in interpretations. Implementing our recommendations will improve geophysical survey practice in the field of glacial geology and allow geophysical methods to play an increasing role in the interpretation of glacial landforms and sediments.
    Type of Medium: Online Resource
    ISSN: 2296-6463
    URL: Article
    URL: Article
    URL: Article
    URL: Article
    URL: Article
    DOI: 10.3389/feart.2022.734682
    DOI: 10.3389/feart.2022.734682.s001
    DOI: 10.3389/feart.2022.734682.s002
    DOI: 10.3389/feart.2022.734682.s003
    DOI: 10.3389/feart.2022.734682.s004
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2022
    detail.hit.zdb_id: 2741235-0
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  • 6
    Online Resource
    Online Resource
    Till genesis at the bed of an Antarctic Peninsula palaeo-ice stream as indicated by micromorphological analysis : Till genesis at the bed of an Antarctic Peninsula palaeo-ice stream
    Wiley ; 2011
    In:  Boreas Vol. 40, No. 3 ( 2011-07), p. 498-517
    Details
    In: Boreas, Wiley, Vol. 40, No. 3 ( 2011-07), p. 498-517
    Type of Medium: Online Resource
    ISSN: 0300-9483
    URL: Issue
    URL: Article
    DOI: 10.1111/bor.2011.40.issue-3
    DOI: 10.1111/j.1502-3885.2010.00199.x
    Language: English
    Publisher: Wiley
    Publication Date: 2011
    detail.hit.zdb_id: 2028632-6
    detail.hit.zdb_id: 185110-X
    SSG: 14
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