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A.j. Russell - One of the best experts on this subject based on the ideXlab platform.
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Jökulhlaup‐related Ice Fracture and Supraglacial Water Release During the November 1996 Jökulhlaup, Skeiðarárjökull, Iceland
Geografiska Annaler Series A-physical Geography, 2020Co-Authors: Richard I Waller, A.j. Russell, T A G P Van Dijk, Oskar KnudsenAbstract:During the initial stages of the November 1996 Jokulhlaup at Skeiðararjokull, Iceland, floodwaters burst onto the glacier surface via a series of fractures. This supraglacial drainage led to the formation of a number of distinct ice surface depressions, one of which is investigated in detail. The morphology and structural characteristics of this feature are described, as well as the sedimentology of an associated assemblage of debris-filled fractures. This work suggests that debris-charged subglacial floodwaters travelled up to the glacier surface, where supraglacial flow occurred initially via an extensive network of fractures, orientated parallel to the glacier margin. Supraglacial discharge became progressively more focused into a series of discrete outlets, leading to the mechanical erosion of a number of depressions on the glacier surface. The associated transfer of subglacially derived floodwaters to high levels within the glacier resulted in the rapid entrainment of large volumes of sediment which may influence the patterns, processes and products of ice-marginal sedimentation in the future.
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Controls on the development of supraglacial floodwater outlets during jökulhlaups
IAHS-AISH publication, 2020Co-Authors: Matthew J Roberts, Fiona S. Tweed, A.j. Russell, Oskar KnudsenAbstract:Recent field observations have revealed that Jokulhlaups with a near-instantaneous rise to peak discharge can generate temporary hydraulic pressures capable of forcing floodwater through the surface of glaciers. This paper identifies and explains the controls on the development of supraglacial Jokulhlaup outlets. Field evidence is presented from two recent Icelandic Jokulhlaups, which produced multiple supraglacial outbursts. Subglacial hydraulic pressure increase is identified as the principal control on supraglacial outlet development during Jokulhlaups. A near-instantaneous rise to peak subglacial water pressure can produce supraglacial outbursts by hydrofracturing. Pressure increases below the hydrofracturing threshold, but above ice overburden pressure, can back-feed pre-existing drainage, resulting in outbursts from moulins and crevasses. Hydrofracture outbursts can route water to areas of the glacier not normally inundated by floods, and can control the spatial distribution of ice block release.
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Tunnel channel formation during the November 1996 jökulhlaup, Skeiðarárjökull, Iceland
Annals of Glaciology, 2020Co-Authors: A.j. Russell, Andrew R G Large, Andrew R. Gregory, P. Jay Fleisher, Tim HarrisAbstract:AbstractDespite the ubiquity of tunnel channels and valleys within formerly glaciated areas, their origin remains enigmatic. Few modern analogues exist for event-related subglacial erosion. This paper presents evidence of subglacial meltwater erosion and tunnel channel formation during the November 1996 jökulhlaup, Skeiðarárjökull, Iceland. The jökulhlaup reached a peak discharge of 45 000 to 50 000 m3 s–1, with flood outbursts emanating from multiple outlets across the entire 23 km wide glacier snout. Subsequent retreat of the southeast margin of Skeiðarárjökull has revealed a tunnel channel excavated into the surrounding moraine sediment and ascending 11.5m over a distance of 160 m from a larger trough to join the apex of an ice-contact fan formed in November 1996. The tunnel channel formed via hydro-mechanical erosion of 14 000m3 to 24 000 m3 of unconsolidated glacier substrate, evidenced by copious rip-up clasts within the ice-contact fan. Flow reconstruction provides peak discharge estimates of 680±140m3 s–1. The tunnel channel orientation, oblique to local ice flow direction and within a col, suggests that local jökulhlaup routing was controlled by (a) subglacial topography and (b) the presence of a nearby proglacial lake. We describe the first modern example of tunnel channel formation and illustrate the importance of pressurized subglacial jökulhlaup flow for tunnel channel formation.
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A new cycle of jökulhlaups at Russell Glacier, Kangerlussuaq, West Greenland
Journal of Glaciology, 2020Co-Authors: A.j. Russell, J.l. Carrivick, Thomas Ingeman-nielsen, M. WilliamsAbstract:Jokulhlaups in 2007 and 2008 from an ice-dammed lake at the northern margin of Russell Glacier, West Greenland, marked the onset of a renewed Jokulhlaup cycle after 20 years of stability. We present a record of successive ice-dammed lake drainage events and associated ice-margin dynamics spanning 25 years. Robust calculations of lake volumes and peak discharges are made, based on intensive field surveys and utilizing high-spatial-resolution orthophotographs of the lake basin and ice margin. These data enable identification of controls on the behaviour of the ice-dammed lake and provide the first field-based examination of controls on Jokulhlaup magnitude and frequency for this system. We find that Russell Glacier Jokulhlaups have a much higher peak discharge than predicted by the Clague-Mathews relationship, which we attribute to an unusually short englacial/subglacial routeway and the presence of a thin ice dam that permits incomplete sealing of Jokulhlaup conduits between lake drainage events. Additionally, we demonstrate that the passage of Jokulhlaups through an interlinked system of proglacial bedrock basins produces significant attenuation of peak discharge downstream. We highlight that improved understanding of Jokulhlaup dynamics requires accurate information about ice-dammed lake volume and ice-proximal Jokulhlaup discharge.
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Discharge magnitude and frequency as a control on proglacial fluvial sedimentary systems
IAHS-AISH publication, 2020Co-Authors: Philip M Marren, A.j. Russell, Oskar KnudsenAbstract:Recent work on active, inactive and Quaternary proglacial outwash plains or sandur, subjected to contrasting magnitude and frequency regimes has yielded new insights into the controls on sandur evolution. This paper provides a review of recent research on magnitude and frequency in proglacial systems. The primary objective of this paper is to demonstrate that sandur influenced by repeated high magnitude flooding (Jokulhlaups) are dominated by large-scale bar systems (Jokulhlaup bars), which are unrelated to normal, low magnitude-high frequency flows which occur between floods. Jokulhlaup bars scale to flood-channel widths, and their upper surfaces are topographically higher than, and unaffected by, between-flood flows. Large gravel bars are distinctive from large bars in sandy braided rivers, where the dominant discharge is less than bankfull, and large bars grow by amalgamation of smaller bars.
Oskar Knudsen - One of the best experts on this subject based on the ideXlab platform.
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Jökulhlaup‐related Ice Fracture and Supraglacial Water Release During the November 1996 Jökulhlaup, Skeiðarárjökull, Iceland
Geografiska Annaler Series A-physical Geography, 2020Co-Authors: Richard I Waller, A.j. Russell, T A G P Van Dijk, Oskar KnudsenAbstract:During the initial stages of the November 1996 Jokulhlaup at Skeiðararjokull, Iceland, floodwaters burst onto the glacier surface via a series of fractures. This supraglacial drainage led to the formation of a number of distinct ice surface depressions, one of which is investigated in detail. The morphology and structural characteristics of this feature are described, as well as the sedimentology of an associated assemblage of debris-filled fractures. This work suggests that debris-charged subglacial floodwaters travelled up to the glacier surface, where supraglacial flow occurred initially via an extensive network of fractures, orientated parallel to the glacier margin. Supraglacial discharge became progressively more focused into a series of discrete outlets, leading to the mechanical erosion of a number of depressions on the glacier surface. The associated transfer of subglacially derived floodwaters to high levels within the glacier resulted in the rapid entrainment of large volumes of sediment which may influence the patterns, processes and products of ice-marginal sedimentation in the future.
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Controls on the development of supraglacial floodwater outlets during jökulhlaups
IAHS-AISH publication, 2020Co-Authors: Matthew J Roberts, Fiona S. Tweed, A.j. Russell, Oskar KnudsenAbstract:Recent field observations have revealed that Jokulhlaups with a near-instantaneous rise to peak discharge can generate temporary hydraulic pressures capable of forcing floodwater through the surface of glaciers. This paper identifies and explains the controls on the development of supraglacial Jokulhlaup outlets. Field evidence is presented from two recent Icelandic Jokulhlaups, which produced multiple supraglacial outbursts. Subglacial hydraulic pressure increase is identified as the principal control on supraglacial outlet development during Jokulhlaups. A near-instantaneous rise to peak subglacial water pressure can produce supraglacial outbursts by hydrofracturing. Pressure increases below the hydrofracturing threshold, but above ice overburden pressure, can back-feed pre-existing drainage, resulting in outbursts from moulins and crevasses. Hydrofracture outbursts can route water to areas of the glacier not normally inundated by floods, and can control the spatial distribution of ice block release.
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Discharge magnitude and frequency as a control on proglacial fluvial sedimentary systems
IAHS-AISH publication, 2020Co-Authors: Philip M Marren, A.j. Russell, Oskar KnudsenAbstract:Recent work on active, inactive and Quaternary proglacial outwash plains or sandur, subjected to contrasting magnitude and frequency regimes has yielded new insights into the controls on sandur evolution. This paper provides a review of recent research on magnitude and frequency in proglacial systems. The primary objective of this paper is to demonstrate that sandur influenced by repeated high magnitude flooding (Jokulhlaups) are dominated by large-scale bar systems (Jokulhlaup bars), which are unrelated to normal, low magnitude-high frequency flows which occur between floods. Jokulhlaup bars scale to flood-channel widths, and their upper surfaces are topographically higher than, and unaffected by, between-flood flows. Large gravel bars are distinctive from large bars in sandy braided rivers, where the dominant discharge is less than bankfull, and large bars grow by amalgamation of smaller bars.
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volcanoes and climate the triggering of preboreal Jokulhlaups in iceland
International Journal of Earth Sciences, 2020Co-Authors: Brigitte Van Vlietlanoe, Oskar Knudsen, Agust Guðmundsson, Herve Guillou, Jessica Langlade, Celine Liorzou, Gilles Chazot, Philippe NonnotteAbstract:The Early Holocene (12–8.2 cal ka) deglaciation and pulsed warming was associated in Iceland with two major generations of Jokulhlaups around the Vatna ice-cap (Vatnajokull), at ca 11.4–11.2 cal ka and ca 10.4–9.9 cal ka, and major tephra emissions from the Grimsvotn and Barðarbunga subglacial volcanoes. The earliest flood events were recorded inland during the Middle Younger Dryas and their deposits were overlain by the Early Preboreal Vedde Ash (11.8 cal ka). The first Holocene flood events (ca 11.4–11.2 cal ka) are issued from a glacial advance. The second, and major, set of floods was partly driven by the Erdalen cold events and advances (10.1–9.7 10Be ka) initially issued from the Barðarbunga (10.4, 10.1–9.9 ka) and Grimsvotn volcanoes (Saksunarvatn tephra complex, ca. 10.2–9.9 cal ka). These floods were also fed by the residual glacio-isostatic depressions below the Vatnajokull that enabled the storage of meltwaters in large subglacial lakes or aquifers until ca. 9.3 cal ka. This storage was enhanced by ice-damming and permafrost, especially during the twinned Erdalen events. Due to the glacio-isostatic rebound, the general slope was nearly flat, and the valley was partly filled with sediments until ca 10.8 cal ka. Temporary lacustrine deposits in this valley resulted from the very broad splay of waters as for the ca 11.2 cal ka and ca 10.1–9.9 cal ka flood, due to regional permafrost. These floods had a potential duration of several months as they were mostly fed by climate-driven meltwater. The maximal volume evacuated by these events did not greatly exceed 1 × 106 m3 s−1 from the flood-affected transverse profile of the valleys that remain partly filled with sediments.
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an unusual Jokulhlaup resulting from subglacial volcanism solheimajokull iceland
Quaternary Science Reviews, 2010Co-Authors: A.j. Russell, Oskar Knudsen, Fiona S. Tweed, Matthew J Roberts, Tim Harris, Magnus T Gudmundsson, Philip M MarrenAbstract:Jokulhlaups (glacial outburst floods) are frequent in glaciated terrain. Jokulhlaups exhibiting a sudden rise to peak discharge have not been subject to detailed investigation. A volcanically-generated flood burst from Solheimajokull, Iceland in July 1999. This paper accounts for the causes, characteristics and impacts of this flood. Pre- and post-flood fieldwork was carried out at Solheimajokull allowing the reconstruction of mean flow velocities and peak discharge. Flood onset was rapid, rising to a peak discharge of 4.4 x 103 m3s−1 (± 1.2 x 103 m3s−1) within one hour. High basal water pressures resulted in floodwater bursting through the glacier surface. Ice rip-up clasts containing glacial diamict provided evidence of floodwater contact with the glacier bed. Within the glacier, Jokulhlaup sedimentation occurred within hydrofractures and conduits generating complex hydrofracture fills and esker ridges. In the proglacial zone, regions of flow expansion associated with rapid reductions in sediment transport capacity controlled the locations of major Jokulhlaup sedimentation. A large fan composed of material of up to boulder size was deposited at the glacier snout. Two ice-marginal basins filled and drained during the Jokulhlaup. One of the basins, Jokulsargil, emptied rapidly during the flood, via ice-dam flotation, accentuating peak Jokulhlaup discharge. High rates of downstream peak discharge attenuation during the July 1999 Jokulhlaup provides an analogy with flash flood hydrographs in semi-arid regions and the catastrophic failure of man-made dams. The July 1999 Jokulhlaup was initially triggered by the subglacial volcanic eruption, but the characteristics of the flood were accentuated by within-event meltwater storage and release. This unusual Jokulhlaup provides an important addition to our understanding of the spectrum of distinctive Jokulhlaup characteristics.
Fiona S. Tweed - One of the best experts on this subject based on the ideXlab platform.
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Controls on the development of supraglacial floodwater outlets during jökulhlaups
IAHS-AISH publication, 2020Co-Authors: Matthew J Roberts, Fiona S. Tweed, A.j. Russell, Oskar KnudsenAbstract:Recent field observations have revealed that Jokulhlaups with a near-instantaneous rise to peak discharge can generate temporary hydraulic pressures capable of forcing floodwater through the surface of glaciers. This paper identifies and explains the controls on the development of supraglacial Jokulhlaup outlets. Field evidence is presented from two recent Icelandic Jokulhlaups, which produced multiple supraglacial outbursts. Subglacial hydraulic pressure increase is identified as the principal control on supraglacial outlet development during Jokulhlaups. A near-instantaneous rise to peak subglacial water pressure can produce supraglacial outbursts by hydrofracturing. Pressure increases below the hydrofracturing threshold, but above ice overburden pressure, can back-feed pre-existing drainage, resulting in outbursts from moulins and crevasses. Hydrofracture outbursts can route water to areas of the glacier not normally inundated by floods, and can control the spatial distribution of ice block release.
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controls on Jokulhlaup transported buried ice melt out at skeiðararsandur iceland implications for the evolution of ice marginal environments
Geomorphology, 2020Co-Authors: David J Blauvelt, A.j. Russell, Fiona S. Tweed, Andrew R G Large, John F Hiemstra, Bernd Kulessa, David J A Evans, Richard I WallerAbstract:Abstract High-magnitude Jokulhlaups, glacier margin position and ice-thickness have been identified as key controls on sandur evolution. Existing models however have focused primarily on observations made during short windows of time and often do not account for the subsequent modification of proglacial landsystems by repeated Jokulhlaups or post-depositional modification due to melt out over decadal time-scales. Digital Elevation Models (DEMs) were used to reconstruct the development of large depressions on Skeiðararsandur, an outwash plain in southeast Iceland. These depressions measure up to 1 km in width and up to 13 m in depth and are associated with ice bodies up to 1 km in length and up to 150 m in height emplaced during a high-magnitude Jokulhlaup in 1903 and subsequently buried by Jokulhlaups in 1913 and 1922. The continued melting of the Harðaskriða ice bodies over a century following their emplacement, together with subsequent repeated burial, by high-magnitude Jokulhlaups demonstrates that Jokulhlaups may continue to serve as important controls on sandur evolution on a decadal to centennial timescale (101–102 years). The Harðaskriða depressions developed only following the retreat of the glacier margin after 1945, which highlights the controls of margin position on the evolution of the sandur. Margin position and thickness of the glacier profile was seen to affect not only the distribution and thickness of sediment emplaced during jokulhaups but also the rate and pattern of melt in the decades following the decoupling of the margin from the sandur. The Jokulhlaup landsystem model signatures identified at this site may provide a useful analogue for interpreting landforms and strata emplaced by glacier margin fluctuations, Jokulhlaups and melt out generated by retreating continental Pleistocene ice sheets.
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Discussion of ‘Field evidence and hydraulic modeling of a large Holocene jökulhlaup at Jökulsá á Fjöllum channel, Iceland’ by Douglas Howard, Sheryl Luzzadder-Beach and Timothy Beach, 2012
Geomorphology, 2013Co-Authors: J.l. Carrivick, A.j. Russell, Fiona S. Tweed, Philip M Marren, Petteri Alho, E. Lucy Rushmer, Paul A Carling, Kate E H Staines, Robert A DullerAbstract:Abstract This paper discusses Howard et al. (2012) who reconstruct the peak discharge of a glacial outburst flood, or ‘Jokulhlaup’, for part of the Jokulsa a Fjollum in north-central Iceland. They propose that this flood was the largest on Earth. We consider that the magnitude of the Jokulhlaup proposed by Howard et al. (2012) warrants much more robust field evidence and demands more carefully parameterised hydraulic modelling. For these reasons we firstly (i) present their study in the context of previous research (ii) highlight issues with attributing landforms and sediments to Jokulhlaups, and (iii) consider uncertainty regarding the timing and magnitude of Jokulhlaups along the Jokulsa a Fjollum. We argue herein that whilst a range of landforms and sediments that are attributable to Jokulhlaups can be observed along the Jokulsa a Fjollum, these are not necessarily diagnostic of Jokulhlaups. Secondly, we critically discuss (iv) the major underlying assumptions of their study, and (v) their calculations and subsequent interpretations. These assessments lead us to consider that the proposal by Howard et al. (2012) of the largest flood on Earth is highly unrealistic, especially when due consideration is given to a possible source area and a trigger mechanism.
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discussion of field evidence and hydraulic modeling of a large holocene Jokulhlaup at jokulsa a fjollum channel iceland by douglas howard sheryl luzzadder beach and timothy beach 2012
Geomorphology, 2013Co-Authors: J.l. Carrivick, A.j. Russell, Fiona S. Tweed, Philip M Marren, Lucy E Rushmer, Petteri Alho, Paul A Carling, Kate E H Staines, Robert A DullerAbstract:This paper discusses Howard et al. (2012) who reconstruct the peak discharge of a glacial outburst flood, or ‘Jokulhlaup’, for part of the Jokulsa a Fjollum in north-central Iceland. They propose that this flood was the largest on Earth.Weconsider that the magnitude of the Jokulhlaup proposed by Howard et al. (2012) warrants much more robust field evidence and demands more carefully parameterised hydraulic modelling. For these reasons we firstly (i) present their study in the context of previous research (ii) highlight issues with attributing landforms and sediments to Jokulhlaups, and (iii) consider uncertainty regarding the timing and magnitude of Jokulhlaups along the Jokulsa a Fjollum. We argue herein that whilst a range of landforms and sediments that are attributable to Jokulhlaups can be observed along the Jokulsa a Fjollum, these are not necessarily diagnostic of Jokulhlaups. Secondly, we critically discuss (iv) the major underlying assumptions of their study, and (v) their calculations and subsequent interpretations. These assessments lead us to consider that the proposal by Howard et al. (2012) of the largest flood on Earth is highly unrealistic, especially when due consideration is given to a possible source area and a trigger mechanism.
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The role of multiple glacier outburst floods in proglacial landscape evolution: The 2010 Eyjafjallajökull eruption, Iceland
Geology, 2013Co-Authors: Stuart Dunning, A.j. Russell, Matthew J Roberts, Robert A Duller, Andrew R G Large, John Woodward, Anne-sophie Mériaux, Fiona S. TweedAbstract:The 2010 Eyjafjallajokull eruption in Iceland provided a unique opportunity to quantify the evolution of proglacial geomorphology during a series of volcanogenic Jokulhlaups (glacial outburst floods) (>140 events). Time-lapse imagery and repeat terrestrial laser scans before and directly after the eruption show that the Jokulhlaup of 14 April 2010 composed 61% of the 57 × 106 m3 total discharge of the combined events, and had the highest peak discharge for the two main flood events, but only deposited 18% of the total volume of sediment in front of Gigjokull glacier. The majority of sediments (67% of a total volume of 17.12 × 106 m3) were deposited by the 15 April 2010 Jokulhlaup, and this was followed by extensive reworking by a series of smaller Jokulhlaups over the following 29 days that deposited 15% of the total sediment. The geomorphological and sedimentary signatures of the two largest Jokulhlaups associated with the onset of the eruption have either been reworked by later floods or are buried by later flood deposits. Consequently, the ice-proximal, posteruption landscape cannot be used to reconstruct the characteristics or magnitudes of either of the two largest Jokulhlaups. The findings support a complex-response model in which peak discharge and the bulk of the sediment transported is decoupled by changing routing mechanisms and water:sediment ratios during the eruption.
J.l. Carrivick - One of the best experts on this subject based on the ideXlab platform.
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A new cycle of jökulhlaups at Russell Glacier, Kangerlussuaq, West Greenland
Journal of Glaciology, 2020Co-Authors: A.j. Russell, J.l. Carrivick, Thomas Ingeman-nielsen, M. WilliamsAbstract:Jokulhlaups in 2007 and 2008 from an ice-dammed lake at the northern margin of Russell Glacier, West Greenland, marked the onset of a renewed Jokulhlaup cycle after 20 years of stability. We present a record of successive ice-dammed lake drainage events and associated ice-margin dynamics spanning 25 years. Robust calculations of lake volumes and peak discharges are made, based on intensive field surveys and utilizing high-spatial-resolution orthophotographs of the lake basin and ice margin. These data enable identification of controls on the behaviour of the ice-dammed lake and provide the first field-based examination of controls on Jokulhlaup magnitude and frequency for this system. We find that Russell Glacier Jokulhlaups have a much higher peak discharge than predicted by the Clague-Mathews relationship, which we attribute to an unusually short englacial/subglacial routeway and the presence of a thin ice dam that permits incomplete sealing of Jokulhlaup conduits between lake drainage events. Additionally, we demonstrate that the passage of Jokulhlaups through an interlinked system of proglacial bedrock basins produces significant attenuation of peak discharge downstream. We highlight that improved understanding of Jokulhlaup dynamics requires accurate information about ice-dammed lake volume and ice-proximal Jokulhlaup discharge.
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assessment of hydro morphodynamic modelling and geomorphological impacts of a sediment charged Jokulhlaup at solheimajokull iceland
Journal of Hydrology, 2015Co-Authors: Mingfu Guan, N G Wright, Andy P Sleigh, J.l. CarrivickAbstract:Understanding of complex flood-riverbed interaction processes in large-scale (field) outburst floods remains incomplete, not least due to a lack of well-constrained field data on hydraulics and sediment transport, but also because consensus on an appropriate model framework has yet to be agreed. This study presents a novel full 2D hydro-morphodynamic model containing both bedload and suspended load capability. Firstly, the model design is presented with an emphasis on its design to simulate rapidly-varied sediment-laden outburst floods and also the associated geomorphological impacts. Secondly, the model is applied to a large-scale (field) glacier outburst flood or ‘Jokulhlaup’ at Solheimajokull, Iceland. For this real-world event, model scenarios with only water and with inclusion of sediment with different parameter setups were performed. Results indicated that grain size specifications affected resultant geomorphological changes, but that the sensitivity of the simulated riverbed changes to the empirical bedload transport formulae were insignificant. Notably, a positive feedback occurred whereby the Jokulhlaup led to significant net erosion of the riverbed, producing an increase in flow conveyance capacity of the river channel. Furthermore, bulking effects of sediment entrainment raised the peak discharge progressively downstream, as well as the flood volume. Effects of geomorphological changes on flood water level and flow velocity were significant. Overall, despite the increased computational effort required with inclusion of sediment transport processes, this study shows that river morphological changes cannot be ignored for events with significant in-channel erosion and deposition, such as during outburst floods.
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discussion of field evidence and hydraulic modeling of a large holocene Jokulhlaup at jokulsa a fjollum channel iceland by douglas howard sheryl luzzadder beach and timothy beach 2012
Geomorphology, 2013Co-Authors: J.l. Carrivick, A.j. Russell, Fiona S. Tweed, Philip M Marren, Lucy E Rushmer, Petteri Alho, Paul A Carling, Kate E H Staines, Robert A DullerAbstract:This paper discusses Howard et al. (2012) who reconstruct the peak discharge of a glacial outburst flood, or ‘Jokulhlaup’, for part of the Jokulsa a Fjollum in north-central Iceland. They propose that this flood was the largest on Earth.Weconsider that the magnitude of the Jokulhlaup proposed by Howard et al. (2012) warrants much more robust field evidence and demands more carefully parameterised hydraulic modelling. For these reasons we firstly (i) present their study in the context of previous research (ii) highlight issues with attributing landforms and sediments to Jokulhlaups, and (iii) consider uncertainty regarding the timing and magnitude of Jokulhlaups along the Jokulsa a Fjollum. We argue herein that whilst a range of landforms and sediments that are attributable to Jokulhlaups can be observed along the Jokulsa a Fjollum, these are not necessarily diagnostic of Jokulhlaups. Secondly, we critically discuss (iv) the major underlying assumptions of their study, and (v) their calculations and subsequent interpretations. These assessments lead us to consider that the proposal by Howard et al. (2012) of the largest flood on Earth is highly unrealistic, especially when due consideration is given to a possible source area and a trigger mechanism.
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Discussion of ‘Field evidence and hydraulic modeling of a large Holocene jökulhlaup at Jökulsá á Fjöllum channel, Iceland’ by Douglas Howard, Sheryl Luzzadder-Beach and Timothy Beach, 2012
Geomorphology, 2013Co-Authors: J.l. Carrivick, A.j. Russell, Fiona S. Tweed, Philip M Marren, Petteri Alho, E. Lucy Rushmer, Paul A Carling, Kate E H Staines, Robert A DullerAbstract:Abstract This paper discusses Howard et al. (2012) who reconstruct the peak discharge of a glacial outburst flood, or ‘Jokulhlaup’, for part of the Jokulsa a Fjollum in north-central Iceland. They propose that this flood was the largest on Earth. We consider that the magnitude of the Jokulhlaup proposed by Howard et al. (2012) warrants much more robust field evidence and demands more carefully parameterised hydraulic modelling. For these reasons we firstly (i) present their study in the context of previous research (ii) highlight issues with attributing landforms and sediments to Jokulhlaups, and (iii) consider uncertainty regarding the timing and magnitude of Jokulhlaups along the Jokulsa a Fjollum. We argue herein that whilst a range of landforms and sediments that are attributable to Jokulhlaups can be observed along the Jokulsa a Fjollum, these are not necessarily diagnostic of Jokulhlaups. Secondly, we critically discuss (iv) the major underlying assumptions of their study, and (v) their calculations and subsequent interpretations. These assessments lead us to consider that the proposal by Howard et al. (2012) of the largest flood on Earth is highly unrealistic, especially when due consideration is given to a possible source area and a trigger mechanism.
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Jokulhlaup influenced topography and geomorphology at kverkfjoll iceland
Journal of Maps, 2012Co-Authors: J.l. Carrivick, David R TwiggAbstract:Abstract Please click here to download the map associated with this article. High magnitude Jokulhlaups (glacial outburst floods) are known to have drained along the Jokulsa a Fjollum river from the northern margin of Vatnajokull, Iceland during the Holocene. However, little is known of the number, age, source and flow characteristics of these Jokulhlaups. Ongoing research therefore seeks to quantitatively analyse Jokulhlaups from Kverkfjoll, which is a discrete source of meltwater into the Jokulsa a Fjollum. To this end a high-resolution digital elevation model was produced and extensive geomorphological mapping and sedimentary analyses were accomplished in the field. The digital elevation model was produced by digital photogrammetry of scanned aerial photographs with the ERDAS Imagine Orthobase software. Processing incorporated twenty-nine ground control points, which were surveyed with a differential global positioning system. Ground control points allow photographic distortion to be removed and the el...
Robert A Duller - One of the best experts on this subject based on the ideXlab platform.
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landscape reaction response and recovery following the catastrophic 1918 katla Jokulhlaup southern iceland
Geophysical Research Letters, 2014Co-Authors: Robert A Duller, A.j. Russell, N H Warner, Chris Mcgonigle, Silvio De Angelis, Nigel P MountneyAbstract:One of the largest recorded glacier outburst floods (Jokulhlaups) occurred in 1918, generated by the last major subglacial eruption of Katla volcano in southern Iceland. Using digitized historical topographic surveys and field observations from the main proglacial outwash plain (Mýrdalssandur), we document the reaction of Mýrdalssandur to the 1918 event and subsequent response and recovery. Our analysis highlights the longevity of elevated topography, over the recovery period, and the complete reorganization of the main perennial meltwater channel system, both of which will affect and condition the flow routing and impact of future Jokulhlaups. The Jokulhlaup deposited approximately 2 km3 of sediment onto Mýrdalssandur immediately after the event and extended the coastline by several kilometers. However, 80% of this material by volume has since been removed by surface and subsurface water flow on the main sandur and by marine reworking at the coast. By 2007, the surface elevation at specific locations on the outwash plain and the position of the coastline were similar to those in 1904, indicating near-complete recovery of the landscape. Despite this, the Mýrdalssandur coastline has experienced net advance over the past 1000 years. Using our calculated characteristic landscape response and recovery values following the 1918 event (60 years and 120 years) we deduce that the landscape has been in a dominant state of transience, with regard to forcing frequency and timescale of recovery, over the past 1000 years, which has facilitated long-term landscape growth.
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discussion of field evidence and hydraulic modeling of a large holocene Jokulhlaup at jokulsa a fjollum channel iceland by douglas howard sheryl luzzadder beach and timothy beach 2012
Geomorphology, 2013Co-Authors: J.l. Carrivick, A.j. Russell, Fiona S. Tweed, Philip M Marren, Lucy E Rushmer, Petteri Alho, Paul A Carling, Kate E H Staines, Robert A DullerAbstract:This paper discusses Howard et al. (2012) who reconstruct the peak discharge of a glacial outburst flood, or ‘Jokulhlaup’, for part of the Jokulsa a Fjollum in north-central Iceland. They propose that this flood was the largest on Earth.Weconsider that the magnitude of the Jokulhlaup proposed by Howard et al. (2012) warrants much more robust field evidence and demands more carefully parameterised hydraulic modelling. For these reasons we firstly (i) present their study in the context of previous research (ii) highlight issues with attributing landforms and sediments to Jokulhlaups, and (iii) consider uncertainty regarding the timing and magnitude of Jokulhlaups along the Jokulsa a Fjollum. We argue herein that whilst a range of landforms and sediments that are attributable to Jokulhlaups can be observed along the Jokulsa a Fjollum, these are not necessarily diagnostic of Jokulhlaups. Secondly, we critically discuss (iv) the major underlying assumptions of their study, and (v) their calculations and subsequent interpretations. These assessments lead us to consider that the proposal by Howard et al. (2012) of the largest flood on Earth is highly unrealistic, especially when due consideration is given to a possible source area and a trigger mechanism.
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Discussion of ‘Field evidence and hydraulic modeling of a large Holocene jökulhlaup at Jökulsá á Fjöllum channel, Iceland’ by Douglas Howard, Sheryl Luzzadder-Beach and Timothy Beach, 2012
Geomorphology, 2013Co-Authors: J.l. Carrivick, A.j. Russell, Fiona S. Tweed, Philip M Marren, Petteri Alho, E. Lucy Rushmer, Paul A Carling, Kate E H Staines, Robert A DullerAbstract:Abstract This paper discusses Howard et al. (2012) who reconstruct the peak discharge of a glacial outburst flood, or ‘Jokulhlaup’, for part of the Jokulsa a Fjollum in north-central Iceland. They propose that this flood was the largest on Earth. We consider that the magnitude of the Jokulhlaup proposed by Howard et al. (2012) warrants much more robust field evidence and demands more carefully parameterised hydraulic modelling. For these reasons we firstly (i) present their study in the context of previous research (ii) highlight issues with attributing landforms and sediments to Jokulhlaups, and (iii) consider uncertainty regarding the timing and magnitude of Jokulhlaups along the Jokulsa a Fjollum. We argue herein that whilst a range of landforms and sediments that are attributable to Jokulhlaups can be observed along the Jokulsa a Fjollum, these are not necessarily diagnostic of Jokulhlaups. Secondly, we critically discuss (iv) the major underlying assumptions of their study, and (v) their calculations and subsequent interpretations. These assessments lead us to consider that the proposal by Howard et al. (2012) of the largest flood on Earth is highly unrealistic, especially when due consideration is given to a possible source area and a trigger mechanism.
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The role of multiple glacier outburst floods in proglacial landscape evolution: The 2010 Eyjafjallajökull eruption, Iceland
Geology, 2013Co-Authors: Stuart Dunning, A.j. Russell, Matthew J Roberts, Robert A Duller, Andrew R G Large, John Woodward, Anne-sophie Mériaux, Fiona S. TweedAbstract:The 2010 Eyjafjallajokull eruption in Iceland provided a unique opportunity to quantify the evolution of proglacial geomorphology during a series of volcanogenic Jokulhlaups (glacial outburst floods) (>140 events). Time-lapse imagery and repeat terrestrial laser scans before and directly after the eruption show that the Jokulhlaup of 14 April 2010 composed 61% of the 57 × 106 m3 total discharge of the combined events, and had the highest peak discharge for the two main flood events, but only deposited 18% of the total volume of sediment in front of Gigjokull glacier. The majority of sediments (67% of a total volume of 17.12 × 106 m3) were deposited by the 15 April 2010 Jokulhlaup, and this was followed by extensive reworking by a series of smaller Jokulhlaups over the following 29 days that deposited 15% of the total sediment. The geomorphological and sedimentary signatures of the two largest Jokulhlaups associated with the onset of the eruption have either been reworked by later floods or are buried by later flood deposits. Consequently, the ice-proximal, posteruption landscape cannot be used to reconstruct the characteristics or magnitudes of either of the two largest Jokulhlaups. The findings support a complex-response model in which peak discharge and the bulk of the sediment transported is decoupled by changing routing mechanisms and water:sediment ratios during the eruption.
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architectural analysis of a volcaniclastic Jokulhlaup deposit southern iceland sedimentary evidence for supercritical flow
Sedimentology, 2008Co-Authors: A.j. Russell, Robert A Duller, Nigel P Mountney, Nigel C CassidyAbstract:The 1918 eruption of the glacially capped Katla volcano, southern Iceland, generated a violent Jokulhlaup, or glacial outburst flood, inundating a large area of Mýrdalssandur, the proglacial outwash plain, where it deposited ca 1 km3 of volcaniclastic sediment. The character of the 1918 Jokulhlaup is contentious, having been variously categorized as a turbulent water flow, a hyperconcentrated flow or as a debris flow, based on localized outcrop analysis. In this study, outcrop-based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi-stationary antidunes and down-current migrating antidunes, and from regular based bedsets, associated with transient chute-and-pool bedforms, all of which are associated with turbulent, transcritical to supercritical water flow conditions. Antidune wavelengths range from 24 to 96 m, corresponding to flow velocities of 6 to 12 m sec−1 and average flow depths of 5 to 19 m. This range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts. Architectural analysis of the 1918 Jokulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 Jokulhlaup that could not have been achieved through localized outcrop analysis. The observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions. The physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes; sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations, regarding modes of deposition and formative flow hydraulics, are to be made.
