201 results on '"Hubbard, Bryn"'
Search Results
2. Hydrology of debris-covered glaciers in High Mountain Asia
- Author
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Miles, Katie E., Hubbard, Bryn, Irvine-Fynn, Tristram D.L., Miles, Evan S., Quincey, Duncan J., and Rowan, Ann V.
- Published
- 2020
- Full Text
- View/download PDF
3. Continuous borehole optical televiewing reveals variable englacial debris concentrations at Khumbu Glacier, Nepal
- Author
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Miles, Katie E., Hubbard, Bryn, Miles, Evan S., Quincey, Duncan J., Rowan, Ann V., Kirkbride, Martin, and Hornsey, Josephine
- Published
- 2021
- Full Text
- View/download PDF
4. Seawater softening of suture zones inhibits fracture propagation in Antarctic ice shelves
- Author
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Kulessa, Bernd, Booth, Adam D., O’Leary, Martin, McGrath, Daniel, King, Edward C., Luckman, Adrian J., Holland, Paul R., Jansen, Daniela, Bevan, Suzanne L., Thompson, Sarah S., and Hubbard, Bryn
- Published
- 2019
- Full Text
- View/download PDF
5. Chapter 4 - Glacial deposits, remnants, and landscapes on Amazonian Mars: Using setting, structure, and stratigraphy to understand ice evolution and climate history
- Author
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Koutnik, Michelle, Butcher, Frances E.G., Soare, Richard J., Hepburn, Adam J., Hubbard, Bryn, Brough, Stephen, Gallagher, Colman, Mc Keown, Lauren E., and Pathare, Asmin
- Published
- 2024
- Full Text
- View/download PDF
6. Provenance and transport of supraglacial debris revealed by variations in debris geochemistry on Khumbu Glacier, Nepal Himalaya.
- Author
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Kirkbride, Martin P., Sherriff, Sophie C., Rowan, Ann V., Egholm, David L., Quincey, Duncan J., Miles, Evan, Hubbard, Bryn, and Miles, Katie
- Subjects
GLACIERS ,GLACIAL Epoch ,ANALYTICAL geochemistry ,PROVENANCE (Geology) ,ICE ,CHEMICAL fingerprinting ,HOLOCENE Epoch - Abstract
The origin of supraglacial debris covers is often conceptualised as the formation of a surface lag by melt‐out of englacial debris from slow‐moving ice, where complexity arises from feedback between debris thickness and sub‐debris ice melt. Here, we examine the origin of a debris cover from the perspective of debris provenance and changing tributary supply in a high‐elevation compound valley glacier. Geochemical analysis of 11 major elements in 21 debris samples from six tributaries of Khumbu Glacier (Nepal) shows unambiguous statistical differentiation of debris sources reflecting lithological differences between tributary catchments. Twenty‐four samples from transects across the ablation area are partitioned according to their source areas using the FR2000 sediment unmixing model. We estimate the age of ice at each transect using a higher order ice flow model. The results show greater proportions of debris from lateral tributaries in downglacier locations that have experienced longer flowline histories. More recently, ice from the Main Himalayan Divide (Western Cwm) has become relatively more important. This suggests a change in the state of the lower glacier's structure depending on the relative ice discharges of lateral and divide sources. Ice flux from lower elevation tributaries was more important probably prior to a weakening of the Indian Summer Monsoon at around 1420 CE. The lower elevation tributaries lie within the range of late Holocene equilibrium line altitude variation and therefore respond most sensitively to climatic drivers of the glacier's flow structure. Negative glacier mass balance since around 1900 CE caused tributary glaciers to detach and high‐elevation catchments to re‐establish as the dominant ice source to Khumbu Glacier. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
7. Former extent of glacier-like forms on Mars
- Author
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Brough, Stephen, Hubbard, Bryn, and Hubbard, Alun
- Published
- 2016
- Full Text
- View/download PDF
8. Basal ice facies and their formation in the western Alps
- Author
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Hubbard, Bryn Pugh
- Subjects
551.31 ,Glaciers - Published
- 1992
9. Characterising ice slabs in firn using seismic full waveform inversion, a sensitivity study.
- Author
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Pearce, Emma, Booth, Adam D., Rost, Sebastian, Sava, Paul, Konuk, Tuğrul, Brisbourne, Alex, Hubbard, Bryn, and Jones, Ian
- Subjects
SEISMIC wave velocity ,ICE ,SEISMIC surveys ,ICE shelves ,ATMOSPHERIC models ,HYDROLOGIC models - Abstract
The density structure of firn has implications for hydrological and climate modelling, and ice-shelf stability. The structure of firn can be evaluated from depth models of seismic velocity, widely obtained with Herglotz–Wiechert inversion (HWI), an approach that considers the slowness of refracted seismic arrivals. However, HWI is strictly appropriate only for steady-state firn profiles and the inversion accuracy can be compromised where firn contains ice layers. In these cases, full waveform inversion (FWI) may yield more success than HWI. FWI extends HWI capabilities by considering the full seismic waveform and incorporates reflected arrivals. Using synthetic firn density profiles, assuming both steady- and non-steady-state accumulation, we show that FWI outperforms HWI for detecting ice slab boundaries (5–80 m thick, 5–80 m deep) and velocity anomalies within firn. FWI can detect slabs thicker than one wavelength (here, 20 m, assuming a maximum frequency of 60 Hz) but requires the starting velocity model to be accurate to ±2.5%. We recommend for field practice that the shallowest layers of velocity models are constrained with ground-truth data. Nonetheless, FWI shows advantages over established methods, and should be considered when the characterisation of firn ice slabs is the goal of the seismic survey. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
10. Field-based research directions for investigating the interior of high-elevation debris-covered glaciers.
- Author
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Miles, Katie E., Hubbard, Bryn, Miles, Evan S., Quincey, Duncan J., and Rowan, Ann V.
- Subjects
- *
GLACIERS - Abstract
The debris that covers the ablation areas of high-elevation debris-covered glaciers contributes to the distinctive features and processes occurring both on and within such glaciers. Despite recent advances, knowledge of the subsurface environments of high-elevation debris-covered glaciers is still extremely limited. In particular, targeted field-based data are needed to parameterise and refine the projections of these glaciers in numerical models. Here, we outline the current understanding of the internal properties of high-elevation debris-covered glaciers based on direct field-based methods and suggest future research directions for field-based studies. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
11. Characterising sediment thickness beneath a Greenlandic outlet glacier using distributed acoustic sensing: preliminary observations and progress towards an efficient machine learning approach.
- Author
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Booth, Adam D., Christoffersen, Poul, Pretorius, Andrew, Chapman, Joseph, Hubbard, Bryn, Smith, Emma C., de Ridder, Sjoerd, Nowacki, Andy, Lipovsky, Bradley Paul, and Denolle, Marine
- Subjects
CONVOLUTIONAL neural networks ,MACHINE learning ,GLACIERS ,SEISMIC tomography ,DATA compression ,SEDIMENTS ,SEISMOLOGY - Abstract
Distributed Acoustic Sensing (DAS) is increasingly recognised as a valuable tool for glaciological seismic applications, although analysing the large data volumes generated in acquisitions poses computational challenges. We show the potential of active-source DAS to image and characterise subglacial sediment beneath a fast-flowing Greenlandic outlet glacier, estimating the thickness of sediment layers to be 20–30 m. However, the lack of subglacial velocity constraint limits the accuracy of this estimate. Constraint could be provided by analysing cryoseismic events in a counterpart 3-day record of passive seismicity through, for example, seismic tomography, but locating them within the 9 TB data volume is computationally inefficient. We describe experiments with data compression using the frequency-wavenumber (f-k) transform ahead of training a convolutional neural network, that provides a ~300-fold improvement in efficiency. In combining active and passive-source and our machine learning framework, the potential of large DAS datasets could be unlocked for a range of future applications. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
12. A synthetic study of acoustic full waveform inversion to improve seismic modelling of firn.
- Author
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Pearce, Emma, Booth, Adam D., Rost, Sebastian, Sava, Paul, Konuk, Tuğrul, Brisbourne, Alex, Hubbard, Bryn, and Jones, Ian
- Subjects
SEISMIC wave velocity ,ICE shelves ,SURFACE waves (Seismic waves) ,SEISMIC waves ,HYDROLOGIC models ,ATMOSPHERIC models ,VELOCITY - Abstract
The density structure of firn has implications for hydrological and climate modelling and for ice shelf stability. The firn structure can be evaluated from depth models of seismic velocity, widely obtained with Herglotz-Wiechert inversion (HWI), an approach that considers the slowness of refracted seismic arrivals. However, HWI is appropriate only for steady-state firn profiles and the inversion accuracy can be compromised where firn contains ice layers. In these cases, Full Waveform Inversion (FWI) can be more successful than HWI. FWI extends HWI capabilities by considering the full seismic waveform and incorporates reflected arrivals, thus offering a more accurate estimate of a velocity profile. We show the FWI characterisation of the velocity model has an error of only 1.7% for regions (vs. 4.2% with HWI) with an ice slab (20 m thick, 40 m deep) in an otherwise steady-state firn profile. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
13. Internal structure of a Himalayan debris-covered glacier revealed by borehole optical televiewing.
- Author
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Miles, Katie E., Hubbard, Bryn, Miles, Evan S., Quincey, Duncan J., and Rowan, Ann V.
- Subjects
GLACIERS ,ALPINE glaciers ,MORAINES - Abstract
Characterising the structures within glaciers can give unique insight into ice motion processes. On debris-covered glaciers, traditional structural glaciological mapping is challenging because the lower glacier is hidden by the supraglacial debris layer. Here, we use high-resolution optical televiewer (OPTV) image logs from four boreholes drilled into Khumbu Glacier, Nepal, to overcome this limitation and investigate englacial structural features within a Himalayan debris-covered glacier. The OPTV logs show structural features that are up to an order of magnitude thinner than those observed at the glacier surface and reveal five structural units: (I) primary stratification of ice; (II) debris-rich planes that conform with the primary stratification; (III) water-healed crevasse traces; (IV) healed crevasse traces; and (V) steeply dipping planes of basally derived fine sediment near the glacier terminus. The OPTV logs also reveal that the primary stratification both decreases in dip with depth (by up to 56° over 20 m) and rotates with depth (by up to 100° over 20 m) towards parallelism with the proximal lateral moraine. This transformation and the presence of relict layers of basally derived sediment raised into an englacial position – possibly involving thrusting – near the glacier's now stagnant terminus reveal a previously more dynamic glacier regime. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
14. Polythermal structure of a Himalayan debris-covered glacier revealed by borehole thermometry
- Author
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Miles, Katie E., Hubbard, Bryn, Quincey, Duncan J., Miles, Evan S., Sherpa, Tenzing C., Rowan, Ann V., and Doyle, Samuel H.
- Published
- 2018
- Full Text
- View/download PDF
15. An alternative interpretation of late Amazonian ice flow: Protonilus Mensae, Mars
- Author
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Souness, Colin J. and Hubbard, Bryn
- Published
- 2013
- Full Text
- View/download PDF
16. Borehole and Ice Feature Annotation Tool (BIFAT): A program for the automatic and manual annotation of glacier borehole images
- Author
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Malone, Terry, Hubbard, Bryn, Merton-Lyn, Derek, Worthington, Paul, and Zwiggelaar, Reyer
- Published
- 2013
- Full Text
- View/download PDF
17. Morphology, flow dynamics and evolution of englacial conduits in cold ice.
- Author
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Kamintzis, Jayne E., Irvine‐Fynn, Tristram D. L., Holt, Tom O., Jones, John P. P., Porter, Philip R., Jennings, Stephen J. A., Naegeli, Kathrin, and Hubbard, Bryn
- Subjects
SEA ice ,CHANNEL flow ,MELTWATER ,GLACIERS ,POINT cloud ,SPATIAL variation ,HYDROLOGY ,MORPHOLOGY ,ALPINE glaciers - Abstract
Meltwater routing through ice masses exerts a fundamental control over glacier dynamics and mass balance, and proglacial hydrology. However, despite recent advances in mapping drainage systems in cold, Arctic glaciers, direct observations of englacial channels and their flow conditions remain sparse. Here, using terrestrial laser scanning (TLS) surveys of the main englacial channel of cold‐based Austre Brøggerbreen (Svalbard), we map and compare an entrance moulin reach (122 m long) and exit portal reach (273 m long). Analysis of channel planforms, longitudinal profiles, cross‐sections and morphological features reveals evidence of spatial variations in water flow conditions and channel incision mechanisms, and the presence of vadose, epiphreatic and phreatic conditions. The entrance reach, located at the base of a perennial moulin, was characterized by vadose, uniform, channel lowering at annual timescales, evidenced by longitudinal grooves, whereas the exit portal reach showed both epiphreatic and vadose conditions, along with upstream knickpoint migration at intra‐annual timescales. Fine‐scale features, including grooves and scallops, were readily quantified from the TLS point cloud, highlighting the capacity of the technique to inform palaeoflow conditions, and reveal how pulses of meltwater from rainfall events may adjust englacial conduit behaviour. With forecasts of increasing Arctic precipitation in the coming decades, and a progressively greater proportion of glaciers comprising cold ice, augmenting the current knowledge of englacial channel morphology is essential to constrain future glacier hydrological system change. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
18. Contributors
- Author
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Ahrens, Caitlin J., Bierson, Carver J., Brough, Stephen, Butcher, Frances E.G., Castillo-Rogez, Julie, Conway, S.J., Costard, F., Dhingra, R.D., El-Maarry, Mohamed Ramy, Farnsworth, K.K., Gallagher, Colman, Galofre, Anna Grau, Garvin, James B., Godin, E., Hepburn, Adam J., Howell, Samuel M., Hubbard, Bryn, Kalousová, Klára, Keown, Lauren E. Mc, Koutnik, Michelle, Landis, Margaret E., Lasue, Jeremie, Leonard, Erin, Lisse, Carey M., Magaña, L.O., Nathan, E.M., Pathare, Asmin, Philippe, M., Rubanenko, Lior, Scanlon, Kat, Soare, Richard J., Steinbrügge, Gregor, Stillman, D., Williams, Jean-Pierre, and Wolfenbarger, Natalie
- Published
- 2024
- Full Text
- View/download PDF
19. Basal ice facies: a review and unifying approach
- Author
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Hubbard, Bryn, Cook, Simon, and Coulson, Hayley
- Published
- 2009
- Full Text
- View/download PDF
20. Basal Ice Facies and Their Formation in the Western Alps
- Author
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Hubbard, Bryn and Sharp, Martin
- Published
- 1995
- Full Text
- View/download PDF
21. Field-based research directions for investigating the interior of high-elevation debris-covered glaciers.
- Author
-
Miles, Katie E., Hubbard, Bryn, Miles, Evan S., Quincey, Duncan J., and Rowan, Ann V.
- Subjects
- *
GLACIERS - Abstract
The debris that covers the ablation areas of high-elevation debris-covered glaciers contributes to the distinctive features and processes occurring both on and within such glaciers. Despite recent advances, knowledge of the subsurface environments of high-elevation debris-covered glaciers is still extremely limited. In particular, targeted field-based data are needed to parameterise and refine the projections of these glaciers in numerical models. Here, we outline the current understanding of the internal properties of high-elevation debris-covered glaciers based on direct field-based methods and suggest future research directions for field-based studies. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
22. Characterising sediment thickness beneath a Greenlandic outlet glacier using distributed acoustic sensing: preliminary observations and progress towards an efficient machine learning approach.
- Author
-
Booth, Adam D., Christoffersen, Poul, Pretorius, Andrew, Chapman, Joseph, Hubbard, Bryn, Smith, Emma C., de Ridder, Sjoerd, Nowacki, Andy, Lipovsky, Bradley Paul, and Denolle, Marine
- Subjects
CONVOLUTIONAL neural networks ,MACHINE learning ,GLACIERS ,SEISMIC tomography ,DATA compression ,SEDIMENTS ,SEISMOLOGY - Abstract
Distributed Acoustic Sensing (DAS) is increasingly recognised as a valuable tool for glaciological seismic applications, although analysing the large data volumes generated in acquisitions poses computational challenges. We show the potential of active-source DAS to image and characterise subglacial sediment beneath a fast-flowing Greenlandic outlet glacier, estimating the thickness of sediment layers to be 20–30 m. However, the lack of subglacial velocity constraint limits the accuracy of this estimate. Constraint could be provided by analysing cryoseismic events in a counterpart 3-day record of passive seismicity through, for example, seismic tomography, but locating them within the 9 TB data volume is computationally inefficient. We describe experiments with data compression using the frequency-wavenumber (f-k) transform ahead of training a convolutional neural network, that provides a ~300-fold improvement in efficiency. In combining active and passive-source and our machine learning framework, the potential of large DAS datasets could be unlocked for a range of future applications. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
23. A synthetic study of acoustic full waveform inversion to improve seismic modelling of firn.
- Author
-
Pearce, Emma, Booth, Adam D., Rost, Sebastian, Sava, Paul, Konuk, Tuğrul, Brisbourne, Alex, Hubbard, Bryn, and Jones, Ian
- Subjects
SEISMIC wave velocity ,ICE shelves ,SURFACE waves (Seismic waves) ,SEISMIC waves ,HYDROLOGIC models ,ATMOSPHERIC models ,VELOCITY - Abstract
The density structure of firn has implications for hydrological and climate modelling and for ice shelf stability. The firn structure can be evaluated from depth models of seismic velocity, widely obtained with Herglotz-Wiechert inversion (HWI), an approach that considers the slowness of refracted seismic arrivals. However, HWI is appropriate only for steady-state firn profiles and the inversion accuracy can be compromised where firn contains ice layers. In these cases, Full Waveform Inversion (FWI) can be more successful than HWI. FWI extends HWI capabilities by considering the full seismic waveform and incorporates reflected arrivals, thus offering a more accurate estimate of a velocity profile. We show the FWI characterisation of the velocity model has an error of only 1.7% for regions (vs. 4.2% with HWI) with an ice slab (20 m thick, 40 m deep) in an otherwise steady-state firn profile. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
24. Water flow through sediments and at the ice-sediment interface beneath Sermeq Kujalleq (Store Glacier), Greenland.
- Author
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Doyle, Samuel H., Hubbard, Bryn, Christoffersen, Poul, Law, Robert, Hewitt, Duncan R., Neufeld, Jerome A., Schoonman, Charlotte M., Chudley, Thomas R., and Bougamont, Marion
- Subjects
SUBGLACIAL lakes ,GLACIERS ,SEDIMENTS ,WATER pressure ,PRESSURE drop (Fluid dynamics) ,THEORY of wave motion ,FLEXURAL vibrations (Mechanics) - Abstract
Subglacial hydrology modulates basal motion but remains poorly constrained, particularly for soft-bedded Greenlandic outlet glaciers. Here, we report detailed measurements of the response of subglacial water pressure to the connection and drainage of adjacent water-filled boreholes drilled through kilometre-thick ice on Sermeq Kujalleq (Store Glacier). These measurements provide evidence for gap opening at the ice-sediment interface, Darcian flow through the sediment layer, and the forcing of water pressure in hydraulically-isolated cavities by stress transfer. We observed a small pressure drop followed by a large pressure rise in response to the connection of an adjacent borehole, consistent with the propagation of a flexural wave within the ice and underlying deformable sediment. We interpret the delayed pressure rise as evidence of no pre-existing conduit and the progressive decrease in hydraulic transmissivity as the closure of a narrow (< 1.5 mm) gap opened at the ice-sediment interface, and a reversion to Darcian flow through the sediment layer with a hydraulic conductivity of ≤ 10
−6 m s−1 . We suggest that gap opening at the ice-sediment interface deserves further attention as it will occur naturally in response to the rapid pressurisation of water at the bed. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
25. Be‐10 Dating of Ice‐Marginal Moraines in the Khumbu Valley, Nepal, Central Himalaya, Reveals the Response of Monsoon‐Influenced Glaciers to Holocene Climate Change.
- Author
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Hornsey, Josephine, Rowan, Ann V., Kirkbride, Martin P., Livingstone, Stephen J., Fabel, Derek, Rodes, Angel, Quincey, Duncan J., Hubbard, Bryn, and Jomelli, Vincent
- Subjects
ALPINE glaciers ,GLACIERS ,GLACIAL landforms ,MORAINES ,CLIMATE change ,HOLOCENE Epoch ,GLACIAL Epoch ,GEOMORPHOLOGICAL mapping - Abstract
The dynamic response of large mountain glaciers to climatic forcing operates over timescales of several centuries and therefore understanding how these glaciers change requires observations of their behavior through the Holocene. We used Be‐10 exposure‐age dating and geomorphological mapping to constrain the evolution of glaciers in the Khumbu Valley in the Everest region of Nepal. Khumbu and Lobuche Glaciers are surrounded by high‐relief lateral and terminal moraines from which seven glacial stages were identified and dated to 7.4 ± 0.2, 5.0 ± 0.3, 3.9 ± 0.1, 2.8 ± 0.2, 1.3 ± 0.1, 0.9 ± 0.02, and 0.6 ± 0.16 ka. These stages correlate to each of the seven latest Holocene regional glacial stages identified across the monsoon‐influenced Himalaya, demonstrating that a coherent record of high elevation terrestrial palaeoclimate change can be extracted from dynamic mountain landscapes. The time‐constrained moraine complex represents a catchment‐wide denudation rate of 0.8–1.4 mm a−1 over the last 8 kyr. The geometry of the ablation area of Khumbu Glacier changed around 4 ka from a broad, shallow ice tongue to become narrower and thicker as restricted by the topographic barrier of the terminal moraine complex. Plain Language Summary: Satellite observations indicate that glaciers in the monsoon‐influenced Himalaya are changing rapidly in response to climate change. However, understanding why glaciers are changing requires observing glacier behavior over longer timescales using the glacial geological record. We mapped the geometry and measured the ages of ice‐marginal moraines built by two adjacent glaciers in the Everest region of Nepal. The moraines represent a complete record of glacier expansion during cold periods in the monsoon‐influenced Himalayan region over the last 8,000 years. Moraines formed by the large Khumbu Glacier and the smaller, steeper Lobuche Glacier also reveal differences in how these glaciers have changed since the last Ice Age. The results are useful to understand how monsoon‐influenced Himalayan glaciers respond to climate change, and to improve projections of their future behavior. Key Points: Ice‐marginal moraines in the upper Khumbu Valley represent a complete record of regional glacier change between 7.4 ka and the present dayMoraine building modified the response of Khumbu Glacier to climate change after 8 kaHolocene moraine volume indicates a catchment‐wide denudation rate of 0.8–1.4 mm per year [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
26. Rapid basal melting of the Greenland Ice Sheet from surface meltwater drainage.
- Author
-
Young, Tun Jan, Christoffersen, Poul, Bougamont, Marion, Tulaczyk, Slawek M., Hubbard, Bryn, Mankoff, Kenneth D., Nicholls, Keith W., and Stewart, Craig L.
- Subjects
ICE sheet thawing ,MELTWATER ,ICE sheets ,DRAINAGE ,POTENTIAL energy surfaces - Abstract
Subglacial hydrologic systems regulate ice sheet flow, causing acceleration or deceleration, depending on hydraulic efficiency and the rate at which surface meltwater is delivered to the bed. Because these systems are rarely observed, ice sheet basal drainage represents a poorly integrated and uncertain component of models used to predict sea level changes. Here, we report radarderived basal melt rates and unexpectedly warm subglacial conditions beneath a large Greenlandic outlet glacier. The basal melt rates averaged 14 mm · d
−1 over 4 months, peaking at 57 mm · d−1 when basal water temperature reached +0.88 ◦C in a nearby borehole. We attribute both observations to the conversion of potential energy of surface water to heat in the basal drainage system, which peaked during a period of rainfall and intense surface melting. Our findings reveal limitations in the theory of channel formation, and we show that viscous dissipation far surpasses other basal heat sources, even in a distributed, highpressure system. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
27. Water exchange between the subglacial Lake Vostok and the overlying ice sheet
- Author
-
Siegert, Martin J., Kwok, Ron, Mayer, Christoph, and Hubbard, Bryn
- Subjects
Environmental issues ,Science and technology ,Zoology and wildlife conservation - Abstract
Author(s): Martin J. Siegert (corresponding author) [1]; Ron Kwok [2]; Christoph Mayer [3]; Bryn Hubbard [4] It has now been known for several years that a 200-km-long lake, called Lake [...]
- Published
- 2000
- Full Text
- View/download PDF
28. Diurnal fluctuations in glacier ice deformation: Haut Glacier dʼArolla, Switzerland
- Author
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Mair, Douglas, Hubbard, Bryn, Nienow, Peter, Willis, Ian, and Fischer, Urs H.
- Published
- 2008
- Full Text
- View/download PDF
29. Impact of a rock avalanche on a moraine-dammed proglacial lake: Laguna Safuna Alta, Cordillera Blanca, Peru
- Author
-
Hubbard, Bryn, Heald, Andrew, Reynolds, John M., Quincey, Duncan, Richardson, Shaun D., Luyo, Marco Zapata, Portilla, Nelson Santillan, and Hambrey, Michael J.
- Published
- 2005
- Full Text
- View/download PDF
30. Regional-scale bed roughness beneath ice masses: measurement and analysis
- Author
-
Taylor, Justin, Siegert, Martin J., Payne, Antony J., and Hubbard, Bryn
- Published
- 2004
- Full Text
- View/download PDF
31. The Role of Differential Ablation and Dynamic Detachment in Driving Accelerating Mass Loss From a Debris‐Covered Himalayan Glacier.
- Author
-
Rowan, Ann V., Egholm, David L., Quincey, Duncan J., Hubbard, Bryn, King, Owen, Miles, Evan S., Miles, Katie E., and Hornsey, Josephine
- Subjects
GLACIERS ,MASS loss (Astrophysics) ,MASS budget (Geophysics) ,CLIMATE change - Abstract
Sustained mass loss from Himalayan glaciers is causing supraglacial debris to expand and thicken, with the expectation that thicker debris will suppress ablation and extend glacier longevity. However, debris‐covered glaciers are losing mass at similar rates to clean‐ice glaciers in High Mountain Asia. This rapid mass loss is attributed to the combined effects of; (a) low or reversed mass balance gradients across debris‐covered glacier tongues, (b) differential ablation processes that locally enhance ablation within the debris‐covered section of the glacier, for example, at ice cliffs and supraglacial ponds, and (c) a decrease in ice flux from the accumulation area in response to climatic warming. Adding meter‐scale spatial variations in supraglacial debris thickness to an ice‐flow model of Khumbu Glacier, Nepal, increased mass loss by 47% relative to simulations assuming a continuous debris layer over a 31‐year period (1984–2015 CE) but overestimated the reduction in ice flux. Therefore, we investigated if simulating the effects of dynamic detachment of the upper active glacier from the debris‐covered tongue would give a better representation of glacier behavior, as suggested by observations of change in glacier dynamics and structure indicating that this process occurred during the last 100 years. Observed glacier change was reproduced more reliably in simulations of the active, rather than entire, glacier extent, indicating that Khumbu Glacier has passed a dynamic tipping point by dynamically detaching from the heavily debris‐covered tongue that contains 20% of the former ice volume. Plain Language Summary: Glaciers in the Himalaya are shrinking rapidly in response to ongoing climate change. Many of these glaciers are covered with thick layers of rock debris that insulate the ice surface from atmospheric warming. Recent observations suggest that, contrary to expectations, debris‐covered glaciers are losing mass at similar rates to clean‐ice glaciers. We explore the processes driving the rapid loss of ice from a debris‐covered glacier using a glacier model with a novel representation of sub‐debris melt. Our model shows that the rapid ice loss from Khumbu Glacier, Nepal, since 1984 cannot be explained solely by accounting for variations in debris thickness and the presence of ice cliffs and ponds across the glacier surface. Instead, the glacier has passed a dynamic tipping point in the last 100 years where the upper active glacier no longer provides ice to the stagnant debris‐covered tongue. We expect that Khumbu Glacier will pass another tipping point in the next 100 years and detach completely from the debris‐covered tongue at the base of the icefall as the active glacier shrinks in response to climate change. Key Points: Debris‐covered glaciers are losing mass at a similar rate to clean‐ice glaciers in High Mountain AsiaParameterizing differential ablation in an ice‐flow model increases net mass loss from Khumbu Glacier by 29%–47%Dynamic detachment of the upper active glacier from the stagnant debris‐covered tongue after 1900 CE could have accelerated recent mass loss [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
32. Cryoegg: development and field trials of a wireless subglacial probe for deep, fast-moving ice.
- Author
-
Prior-Jones, Michael R., Bagshaw, Elizabeth A., Lees, Jonathan, Clare, Lindsay, Burrow, Stephen, Werder, Mauro A., Karlsson, Nanna B., Dahl-Jensen, Dorthe, Chudley, Thomas R., Christoffersen, Poul, Wadham, Jemma L., Doyle, Samuel H., and Hubbard, Bryn
- Subjects
ICE ,SHORTWAVE radio ,ELECTRIC conductivity ,RADIO technology - Abstract
Subglacial hydrological systems require innovative technological solutions to access and observe. Wireless sensor platforms can be used to collect and return data, but their performance in deep and fast-moving ice requires quantification. We report experimental results from Cryoegg: a spherical probe that can be deployed into a borehole or moulin and transit through the subglacial hydrological system. The probe measures temperature, pressure and electrical conductivity in situ and returns all data wirelessly via a radio link. We demonstrate Cryoegg's utility in studying englacial channels and moulins, including in situ salt dilution gauging. Cryoegg uses VHF radio to transmit data to a surface receiving array. We demonstrate transmission through up to 1.3 km of cold ice – a significant improvement on the previous design. The wireless transmission uses Wireless M-Bus on 169 MHz; we present a simple radio link budget model for its performance in cold ice and experimentally confirm its validity. Cryoegg has also been tested successfully in temperate ice. The battery capacity should allow measurements to be made every 2 h for more than a year. Future iterations of the radio system will enable Cryoegg to transmit data through up to 2.5 km of ice. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
33. Borehole‐Based Characterization of Deep Mixed‐Mode Crevasses at a Greenlandic Outlet Glacier.
- Author
-
Hubbard, Bryn, Christoffersen, Poul, Doyle, Samuel H., Chudley, Thomas R., Schoonman, Charlotte M., Law, Robert, and Bougamont, Marion
- Published
- 2021
- Full Text
- View/download PDF
34. Decline in Surface Melt Duration on Larsen C Ice Shelf Revealed by The Advanced Scatterometer (ASCAT)
- Author
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Bevan, Suzanne Louise, Luckman, Adrian John, Munneke, Peter Kuipers, Hubbard, Bryn, Kulessa, Bernd, and Ashmore, David William
- Published
- 2018
35. Observationally constrained surface mass balance of Larsen C ice shelf, Antarctica
- Author
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Munneke, Peter Kuipers, McGrath, Daniel, Medley, Brooke, Luckman, Adrian, Bevan, Suzanne, Kulessa, Bernd, Jansen, Daniela, Booth, Adam, Smeets, Paul, Hubbard, Bryn, Ashmore, David, Van den Broeke, Michiel, Sevestre, Heidi, Steffen, Konrad, Shepherd, Andrew, Gourmelen, Noel, Sub Dynamics Meteorology, Marine and Atmospheric Research, Sub Dynamics Meteorology, Marine and Atmospheric Research, and University of St Andrews. School of Geography & Sustainable Development
- Subjects
010504 meteorology & atmospheric sciences ,010502 geochemistry & geophysics ,01 natural sciences ,Ice shelf ,Glacier mass balance ,G1 ,SDG 13 - Climate Action ,lcsh:Environmental sciences ,0105 earth and related environmental sciences ,Earth-Surface Processes ,Water Science and Technology ,lcsh:GE1-350 ,geography ,GE ,geography.geographical_feature_category ,lcsh:QE1-996.5 ,Firn ,G Geography (General) ,3rd-DAS ,Snow ,lcsh:Geology ,13. Climate action ,Climatology ,Spatial ecology ,Climate model ,Spatial variability ,Ice sheet ,Geology ,GE Environmental Sciences - Abstract
This work is funded by the Netherland Polar Programme, Netherlands Earth System Science Centre (NESSC), NSF OPP research grant 0732946, NERC/GEF grants NE/L006707/1, NE/L005409/1, NE/E012914/1, GEF loans 863, 890, 1028. The surface mass balance (SMB) of the Larsen C ice shelf (LCIS), Antarctica, is poorly constrained due to a dearth of in situ observations. Combining several geophysical techniques, we reconstruct spatial and temporal patterns of SMB over the LCIS. Continuous time series of snow height (2.5–6 years) at five locations allow for multi-year estimates of seasonal and annual SMB over the LCIS. There is high interannual variability in SMB as well as spatial variability: in the north, SMB is 0.40 ± 0.06 to 0.41 ± 0.04 m w.e. year−1, while farther south, SMB is up to 0.50 ± 0.05 m w.e. year−1. This difference between north and south is corroborated by winter snow accumulation derived from an airborne radar survey from 2009, which showed an average snow thickness of 0.34 m w.e. north of 66° S, and 0.40 m w.e. south of 68° S. Analysis of ground-penetrating radar from several field campaigns allows for a longer-term perspective of spatial variations in SMB: a particularly strong and coherent reflection horizon below 25–44 m of water-equivalent ice and firn is observed in radargrams collected across the shelf. We propose that this horizon was formed synchronously across the ice shelf. Combining snow height observations, ground and airborne radar, and SMB output from a regional climate model yields a gridded estimate of SMB over the LCIS. It confirms that SMB increases from north to south, overprinted by a gradient of increasing SMB to the west, modulated in the west by föhn-induced sublimation. Previous observations show a strong decrease in firn air content toward the west, which we attribute to spatial patterns of melt, refreezing, and densification rather than SMB. Publisher PDF
- Published
- 2018
36. Decline in surface melt duration in Larsen C Ice Shelf revealed by ASCAT scatterometer
- Author
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Bevan, S., Luckman, A., Kuipers Munneke, P., Hubbard, Bryn, Kulessa, Bernd, Ashmore, David, Sub Dynamics Meteorology, and Marine and Atmospheric Research
- Abstract
Surface melting has been contributing to the surface lowering and loss of firn air content on Larsen C Ice Shelf since at least the mid-1990s. Where the amount of melting and refreezing is significant, the firn can become impermeable and begin to support ponds of surface meltwater such as have been implicated in ice shelf collapse. Although meteorological station data indicated an increase in melt on the Antarctic Peninsula over the second half of the 20th century, the existing Ku-band Quick Scatterometer (QuikSCAT) time series is too short (1999–2009) to detect any significant 21st century trends. Here we investigate a longer 21st century period by extending the time series to 2017 using the C-band Advanced Scatterometer (ASCAT). We validate our recent observations with in situ weather station data and, using a firn percolation model, explore the sensitivity of scatterometry to water at varying depths in the firn. We find that active microwave C-band (5.6-cm wavelength) instruments can detect water at depths of up to 0.75 m below a frozen firn layer. Our longer scatterometry time series reveals that Larsen C Ice Shelf has experienced a decrease in melt season length of 1–2 days per year over the past 18 years consistent with decreasing summer air temperatures. Only in western inlets, where föhn winds drive melt, has the annual melt duration increased during this period.
- Published
- 2018
37. Rapidly changing subglacial hydrological pathways at a tidewater glacier revealed through simultaneous observations of water pressure, supraglacial lakes, meltwater plumes and surface velocities
- Author
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How, Penelope, Benn, Douglas I., Hulton, Nicholas R.J., Hubbard, Bryn, Luckman, Adrian, Sevestre, Heïdi, Pelt, Ward J.J.Van, Lindbäck, Katrin, Kohler, Jack, Boot, Wim, University of St Andrews. School of Geography & Sustainable Development, and University of St Andrews. Bell-Edwards Geographic Data Institute
- Subjects
GE ,Naturgeografi ,3rd-DAS ,Svalbard ,QE Geology ,subglacial hydrology ,Physical Geography ,plumes ,QE ,SDG 14 - Life Below Water ,ice dynamics ,GE Environmental Sciences ,Water Science and Technology ,Earth-Surface Processes - Abstract
This work was funded by the Conoco Phillips-Lundin Northern Area Program through the CRIOS project (Calving Rates and Impact On Sea level, http://www.researchinsvalbard.no/project/7037). Penelope How is supported by a NERC PhD studentship. Subglacial hydrological processes at tidewater glaciers remain poorly understood due to the difficulty in obtaining direct measurements and lack of empirical verification for modelling approaches. Here, we investigate the subglacial hydrology of Kronebreen, a fast-flowing tidewater glacier in Svalbard during the 2014 melt season. We combine observations of borehole water pressure, supraglacial lake drainage, surface velocities and plume activity with modelled run-off and water routing to develop a conceptual model that thoroughly encapsulates subglacial drainage at a tidewater glacier. Simultaneous measurements suggest that an early-season episode of subglacial flushing took place during our observation period, and a stable efficient drainage system effectively transported subglacial water through the northern region of the glacier tongue. Drainage pathways through the central and southern regions of the glacier tongue were disrupted throughout the following melt season. Periodic plume activity at the terminus appears to be a signal for modulated subglacial pulsing, i.e. an internally driven storage and release of subglacial meltwater that operates independently of marine influences. This storage is a key control on ice flow in the 2014 melt season. Evidence from this work and previous studies strongly suggests that long-term changes in ice flow at Kronebreen are controlled by the location of efficient/inefficient drainage and the position of regions where water is stored and released. Publisher PDF
- Published
- 2017
38. Ice and firn heterogeneity within Larsen C Ice Shelf from borehole optical televiewing
- Author
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Ashmore, David, Hubbard, Bryn, Luckman, A., Kulessa, Bernd, Bevan, S., Booth, Adam, Kuipers Munneke, P., O'Leary, Martin, Sevestre, Heidi, Holland, Paul R., Sub Dynamics Meteorology, and Marine and Atmospheric Research
- Subjects
glaciology ,Antarctica ,ice shelves - Abstract
We use borehole optical televiewing (OPTV) to explore the internal structure of Larsen C Ice Shelf (LCIS). We report a suite of five ~90 m long OPTV logs, recording a light‐emitting diode‐illuminated, geometrically correct image of the borehole wall, from the northern and central sectors of LCIS collected during austral spring 2014 and 2015. We use a thresholding‐based technique to estimate the refrozen ice content of the ice column and exploit a recently calibrated density‐luminosity relationship to reveal its structure. All sites are dense and strongly influenced by surface melt, with frequent refrozen ice layers and mean densities, between the depths of 1.87 and 90 m, ranging from 862 to 894 kg m−3. We define four distinct units that comprise LCIS and relate these to ice provenance, dynamic history, and past melt events. These units are in situ meteoric ice with infiltration ice (U1), meteoric ice which has undergone enhanced densification (U2), thick refrozen ice (U3), and advected continental ice (U4). We show that the OPTV‐derived pattern of firn air content is consistent with previous estimates, but that a significant proportion of firn air is contained within U4, which we interpret to have been deposited inland of the grounding line. The structure of LCIS is strongly influenced by the E‐W gradient in föhn‐driven melting, with sites close to the Antarctic Peninsula being predominantly composed of refrozen ice. Melting is also substantial toward the ice shelf center with >40% of the overall imaged ice column being composed of refrozen ice.
- Published
- 2017
39. Ice and firn heterogeneity within Larsen C Ice Shelf from borehole optical televiewing
- Author
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Ashmore, David W., Hubbard, Bryn, Luckman, Adrian, Kulessa, Bernd, Bevan, Suzanne, Booth, Adam, Munneke, Peter Kuipers, O'Leary, Martin, Sevestre, Heidi, Holland, Paul R., Sub Dynamics Meteorology, Marine and Atmospheric Research, and University of St Andrews. Geography & Sustainable Development
- Subjects
G1 ,glaciology ,Antarctica ,G Geography (General) ,DAS ,ice shelves - Abstract
Research was funded by the UK Natural Environmental Research Council grants NE/L006707/1 and NE/L005409/1 and a HEFCW/Aberystwyth University Capital Equipment Grant to B.H. Data will be available via the project website (www.projectmidas.org) and the UK Polar Data Centre (https://www.bas.ac.uk/data/uk-pdc/) from mid-2017. We use borehole optical televiewing (OPTV) to explore the internal structure of Larsen C Ice Shelf (LCIS). We report a suite of five ~90 m long OPTV logs, recording a light-emitting diode-illuminated, geometrically correct image of the borehole wall, from the northern and central sectors of LCIS collected during austral spring 2014 and 2015. We use a thresholding-based technique to estimate the refrozen ice content of the ice column and exploit a recently calibrated density-luminosity relationship to reveal its structure. All sites are dense and strongly influenced by surface melt, with frequent refrozen ice layers and mean densities, between the depths of 1.87 and 90 m, ranging from 862 to 894 kg m−3. We define four distinct units that comprise LCIS and relate these to ice provenance, dynamic history, and past melt events. These units are in situ meteoric ice with infiltration ice (U1), meteoric ice which has undergone enhanced densification (U2), thick refrozen ice (U3), and advected continental ice (U4). We show that the OPTV-derived pattern of firn air content is consistent with previous estimates, but that a significant proportion of firn air is contained within U4, which we interpret to have been deposited inland of the grounding line. The structure of LCIS is strongly influenced by the E-W gradient in föhn-driven melting, with sites close to the Antarctic Peninsula being predominantly composed of refrozen ice. Melting is also substantial toward the ice shelf center with >40% of the overall imaged ice column being composed of refrozen ice. Publisher PDF
- Published
- 2017
40. Centuries of intense melt on Larsen C Ice Shelf
- Author
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Bevan, S., Luckman, A., Hubbard, Bryn, Kulessa, Bernd, Ashmore, David, Kuipers Munneke, P., O'Leary, Martin, Booth, Adam, Sevestre, Heidi, McGrath, Daniel, Sub Dynamics Meteorology, and Marine and Atmospheric Research
- Abstract
Following a southward progression of ice-shelf disintegration along the Antarctic Peninsula (AP), Larsen C Ice Shelf (LCIS) has become the focus of ongoing investigation regarding its future stability. The ice shelf experiences surface melt and commonly features surface meltwater ponds. Here, we use a flow-line model and a firn density model (FDM) to date and interpret observations of melt-affected ice layers found within five 90m boreholes distributed across the ice shelf. We find that units of ice within the boreholes, which have densities exceeding those expected under normal dry compaction metamorphism, correspond to two climatic warm periods within the last 300 years on the Antarctic Peninsula. The more recent warm period, from the 1960s onwards, has generated distinct sections of dense ice measured in two boreholes in Cabinet Inlet, which is close to the Antarctic Peninsula mountains – a region affected by föhn winds. Previous work has classified these layers as refrozen pond ice, requiring large quantities of mobile liquid water to form. Our flow-line model shows that, whilst preconditioning of the snow began in the late 1960s, it was probably not until the early 1990s that the modern period of ponding began. The earlier warm period occurred during the 18th century and resulted in two additional sections of anomalously dense ice deep within the boreholes. The first, at 61m in one of our Cabinet Inlet boreholes, consists of ice characteristic of refrozen ponds and must have formed in an area currently featuring ponding. The second, at 69m in a mid-shelf borehole, formed at the same time on the edge of the pond area. Further south, the boreholes sample ice that is of an equivalent age but which does not exhibit the same degree of melt influence. This west–east and north–south gradient in the past melt distribution resembles current spatial patterns of surface melt intensity.
- Published
- 2017
41. High-resolution distributed vertical strain and velocity from repeat borehole logging by optical televiewer: Derwael Ice Rise, Antarctica.
- Author
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Hubbard, Bryn, Philippe, Morgane, Pattyn, Frank, Drews, Reinhard, Young, Tun Jan, Bruyninx, Carine, Bergeot, Nicolas, Fjøsne, Karen, and Tison, Jean-Louis
- Subjects
AUTOMATIC tracking ,VELOCITY ,ICE ,CROSS correlation - Abstract
Direct measurements of spatially distributed vertical strain within ice masses are scientifically valuable but challenging to acquire. We use manual marker tracking and automatic cross correlation between two repeat optical televiewer (OPTV) images of an ~100 m-long borehole at Derwael Ice Rise (DIR), Antarctica, to reconstruct discretised, vertical strain rate and velocity at millimetre resolution. The resulting profiles decay with depth, from −0.07 a
−1 at the surface to ~−0.002 a−1 towards the base in strain and from −1.3 m a−1 at the surface to ~−0.5 m a−1 towards the base in velocity. Both profiles also show substantial local variability. Three coffee-can markers installed at different depths into adjacent boreholes record consistent strain rates and velocities, although averaged over longer depth ranges and subject to greater uncertainty. Measured strain-rate profiles generally compare closely with output from a 2-D ice-flow model, while the former additionally reveal substantial high-resolution variability. We conclude that repeat OPTV borehole logging represents an effective means of measuring distributed vertical strain at millimetre scale, revealing high-resolution variability along the uppermost ~100 m of DIR, Antarctica. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
42. Distributed Acoustic Sensing of Seismic Properties in a Borehole Drilled on a Fast‐Flowing Greenlandic Outlet Glacier.
- Author
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Booth, Adam D., Christoffersen, Poul, Schoonman, Charlotte, Clarke, Andy, Hubbard, Bryn, Law, Robert, Doyle, Samuel H., Chudley, Thomas R., and Chalari, Athena
- Subjects
SUBGLACIAL lakes ,GREENLAND ice ,MELTWATER ,VERTICAL seismic profiling ,GLACIERS ,ICE sheets ,SEISMIC response - Abstract
Distributed Acoustic Sensing (DAS) is a new technology in which seismic energy is detected, at high spatial and temporal resolution, using the propagation of laser pulses in a fiber‐optic cable. We show analyses from the first glaciological borehole DAS deployment to measure the englacial and subglacial seismic properties of Store Glacier, a fast‐flowing outlet of the Greenland Ice Sheet. We record compressional and shear waves in 1,043 m‐deep vertical seismic profiles, sampled at 10 m vertical resolution, and detect a transition from isotropic to anisotropic ice at 84% of ice thickness, consistent with the Holocene‐Wisconsin transition. We identify subglacial reflections originating from the base of a 20 m‐thick layer of consolidated sediment and, from attenuation measurements, interpret temperate ice in the lowermost 100 m of the glacier. Our findings highlight the promising potential of DAS technology to constrain the seismic properties of glaciers and ice sheets. Plain Language Summary: Distributed Acoustic Sensing (DAS) is a new technology for seismic surveying in which the transmission of light through fiber‐optic cables is used to record seismic energy, with unprecedented spatial resolution compared to traditional techniques. Our paper presents data from the first borehole‐glaciological deployment of DAS, in which fiber‐optic cable was installed in a 1,043 m‐deep vertical borehole on Store Glacier, a fast‐flowing outlet of the Greenland Ice Sheet. The detailed seismic anatomy of the glacier that our survey provides—an independent measurement of the seismic response every 10 m—gives new insights about its internal flow regime and temperature and even allows us to detect layers of sediment underlying it. We predict that DAS surveying will play an increasingly large role in future glaciological investigations as the recognition of its promising potential grows. Key Points: Distributed Acoustic Sensing (DAS) is a new technology for recording seismic data using laser pulses propagating in a fiber‐optic cableWe present the first borehole‐glaciological application of DAS, installing cable in a 1,043 m‐deep borehole on Greenland's Store GlacierWe evidence, at 10 m vertical resolution, anisotropic and temperate ice beyond ~880 m depth and ~20 m of consolidated subglacial sediment [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
43. An updated seabed bathymetry beneath Larsen C Ice Shelf, Antarctic Peninsula.
- Author
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Brisbourne, Alex, Kulessa, Bernd, Hudson, Thomas, Harrison, Lianne, Holland, Paul, Luckman, Adrian, Bevan, Suzanne, Ashmore, David, Hubbard, Bryn, Pearce, Emma, White, James, Booth, Adam, Nicholls, Keith, and Smith, Andrew
- Subjects
ICE shelves ,OCEAN bottom ,BATHYMETRY ,OCEAN circulation ,PENINSULAS ,THICKNESS measurement - Abstract
In recent decades, rapid ice shelf disintegration along the Antarctic Peninsula has had a global impact through enhancing outlet glacier flow and hence sea level rise and the freshening of Antarctic Bottom Water. Ice shelf thinning due to basal melting results from the circulation of relatively warm water in the underlying ocean cavity. However, the effect of sub-shelf circulation on future ice shelf stability cannot be predicted accurately with computer simulations if the geometry of the ice shelf cavity is unknown. To address this deficit for Larsen C Ice Shelf, West Antarctica, we integrate new water column thickness measurements from recent seismic campaigns with existing observations. We present these new data here along with an updated bathymetry grid of the ocean cavity. Key findings include a relatively deep seabed to the southeast of the Kenyon Peninsula, along the grounding line and around the key ice shelf pinning-point of Bawden Ice Rise. In addition, we can confirm that the cavity's southern trough stretches from Mobiloil Inlet to the open ocean. These areas of deep seabed will influence ocean circulation and tidal mixing and will therefore affect the basal-melt distribution. These results will help constrain models of ice shelf cavity circulation with the aim of improving our understanding of sub-shelf processes and their potential influence on ice shelf stability. The datasets are comprised of all the new point measurements of seabed depth. We present the new depth measurements here, as well as a compilation of previously published measurements. To demonstrate the improvements to the sub-shelf bathymetry map that these new data provide we include a gridded data product in the Supplement of this paper, derived using the additional measurements of both offshore seabed depth and the thickness of grounded ice. The underlying seismic datasets that were used to determine bed depth and ice thickness are available at 10.5285/315740B1-A7B9-4CF0-9521-86F046E33E9A (Brisbourne et al., 2019), 10.5285/5D63777D-B375-4791-918F-9A5527093298 (Booth, 2019), 10.5285/FFF8AFEE-4978-495E-9210-120872983A8D (Kulessa and Bevan, 2019) and 10.5285/147BAF64-B9AF-4A97-8091-26AEC0D3C0BB (Booth et al., 2019). [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
44. Massive subsurface ice formed by refreezing of ice-shelf melt ponds
- Author
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Hubbard, Bryn, Philippe, Morgane, and Tison, Jean-Louis
- Subjects
Glaciologie - Abstract
Surface melt ponds form intermittently on several Antarctic ice shelves. Although implicatedin ice-shelf break up, the consequences of such ponding for ice formation and ice-shelfstructure have not been evaluated. Here we report the discovery of a massive subsurface icelayer, at least 16 km across, several kilometres long and tens of metres deep, located in anarea of intense melting and intermittent ponding on Larsen C Ice Shelf, Antarctica. Wecombine borehole optical televiewer logging and radar measurements with remote sensingand firn modelling to investigate the layer, found to be ~10°C warmer and ~170 kg/m³ denser than anticipated in the absence of ponding and hitherto used in models of ice-shelffracture and flow. Surface ponding and ice layers such as the one we report are likely to formon a wider range of Antarctic ice shelves in response to climatic warming in forthcomingdecades., 0, SCOPUS: ar.j, info:eu-repo/semantics/published
- Published
- 2016
45. Debris entrainment and landform genesis during tidewater glacier surges
- Author
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Lovell, Harold, Fleming, Edward J., Benn, Douglas I., Hubbard, Bryn, Lukas, Sven, Rea, Brice R., Noormets, Riko, and Flink, Anne E.
- Subjects
WNU - Abstract
The englacial entrainment of basal debris during surges presents an opportunity to investigate processes acting at the glacier bed. The subsequent melt-out of debris-rich englacial structures during the quiescent phase produces geometrical ridge networks on glacier forelands that are diagnostic of surge activity. We investigate the link between debris entrainment and proglacial geomorphology by analyzing basal ice, englacial structures, and ridge networks exposed at the margins of Tunabreen, a tidewater surge-type glacier in Svalbard. The basal ice facies display clear evidence for brittle and ductile tectonic deformation, resulting in overall thickening of the basal ice sequence. The formation of debris-poor dispersed facies ice is the result of strain-induced metamorphism of meteoric ice near the bed. Debris-rich englacial structures display a variety of characteristics and morphologies and are interpreted to represent the incorporation and elevation of subglacial till via the squeezing of till into basal crevasses and hydrofracture exploitation of thrust faults, reoriented crevasse squeezes, and preexisting fractures. These structures are observed to melt-out and form embryonic geometrical ridge networks at the base of a terrestrially grounded ice cliff. Ridge networks are also located at the terrestrial margins of Tunabreen, neighboring Von Postbreen, and in a submarine position within Tempelfjorden. Analysis of network characteristics allows these ridges to be linked to different formational mechanisms of their parent debris-rich englacial structures. This in turn provides an insight into variations in the dominant tectonic stress regimes acting across the glacier during surges.
- Published
- 2015
46. Instruments and methods: hot-water borehole drilling at a high-elevation debris-covered glacier.
- Author
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Miles, Katie E., Miles, Evan S., Hubbard, Bryn, Quincey, Duncan J., Rowan, Ann V., and Pallett, Mark
- Subjects
GLACIERS ,ALPINE glaciers ,ATMOSPHERIC oxygen ,ATMOSPHERIC pressure ,HEAT pumps ,BOREHOLES ,WATER pumps - Abstract
While hot-water drilling is a well-established technique used to access the subsurface of ice masses, drilling into high-elevation (≳ 4000 m a.s.l.) debris-covered glaciers faces specific challenges. First, restricted transport capacity limits individual equipment items to a volume and mass that can be slung by small helicopters. Second, low atmospheric oxygen and pressure reduces the effectiveness of combustion, limiting a system's ability to pump and heat water. Third, thick supraglacial debris, which is both highly uneven and unstable, inhibits direct access to the ice surface, hinders the manoeuvring of equipment and limits secure sites for equipment placement. Fourth, englacial debris can slow the drilling rate such that continued drilling becomes impracticable and/or boreholes deviate substantially from vertical. Because of these challenges, field-based englacial and subglacial data required to calibrate numerical models of high-elevation debris-covered glaciers are scarce or absent. Here, we summarise our experiences of hot-water drilling over two field seasons (2017–2018) at the debris-covered Khumbu Glacier, Nepal, where we melted 27 boreholes up to 192 m length, at elevations between 4900 and 5200 m a.s.l. We describe the drilling equipment and operation, evaluate the effectiveness of our approach and suggest equipment and methodological adaptations for future use. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
47. Creating HiRISE digital elevation models for Mars using the open-source Ames Stereo Pipeline.
- Author
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Hepburn, Adam J., Holt, Tom, Hubbard, Bryn, and Ng, Felix
- Subjects
DIGITAL elevation models ,PIPELINES ,MARS (Planet) ,COMPUTER workstation clusters ,STEREO vision (Computer science) - Abstract
The present availability of sub-decametre digital elevation models on Mars – crucial for the study of surface processes – is scarce. In contrast to low-resolution global datasets, such models enable the study of landforms <10 km in size, which is the primary scale at which geomorphic processes have been active on Mars over the last 10–20 Myr. Stereogrammetry is a means of producing digital elevation models from stereo pairs of images. The HiRISE camera on board the Mars Reconnaissance Orbiter has captured >3000 stereo pairs at 0.25 m pixel -1 resolution, enabling the creation of high-resolution digital elevation models (1–2 m pixel -1). Hitherto, only ∼500 of these pairs have been processed and made publicly available. Existing pipelines for the production of digital elevation models from stereo pairs, however, are built upon commercial software, rely upon sparsely available intermediate data, or are reliant on proprietary algorithms. In this paper, we present and test the output of a new pipeline for producing digital elevation models from HiRISE stereo pairs that is built entirely upon the open-source NASA Ames Stereo Pipeline photogrammetric software, making use of freely available data for cartographic rectification. This pipeline is designed for simple application by researchers interested in the use of high-resolution digital elevation models. Implemented here on a research computing cluster, this pipeline can also be used on consumer-grade UNIX computers. We produce and evaluate four digital elevation models using the pipeline presented here. Each are globally well registered, with accuracy similar to those of digital elevation models produced elsewhere. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
48. An updated seabed bathymetry beneath Larsen C Ice Shelf, west Antarctic.
- Author
-
Brisbourne, Alex, Kulessa, Bernd, Hudson, Thomas, Harrison, Lianne, Holland, Paul, Luckman, Adrian, Bevan, Suzanne, Ashmore, David, Hubbard, Bryn, Pearce, Emma, White, James, Booth, Adam, Nichols, Keith, and Smith, Andrew
- Subjects
ICE shelves ,OCEAN bottom ,OCEAN circulation ,BATHYMETRY ,THICKNESS measurement ,SEA level - Abstract
In recent decades, rapid ice-shelf disintegration along the Antarctic Peninsula has had a global impact through enhancing outlet glacier flow, and hence sea level rise, and the freshening of Antarctic Bottom Water. Ice shelf thinning due to basal melting results from the circulation of relatively warm water in the underlying ocean cavity. However, the effect of sub-shelf circulation on future ice-shelf stability cannot be predicted accurately with computer simulations if the geometry of the ice-shelf cavity is unknown. To address this deficit for Larsen C Ice Shelf, west Antarctica, we integrate new water-column thickness measurements with existing observations. We present these new data here along with an updated bathymetry grid of the ocean cavity. Key findings include relatively deep seabed to the south-east of the Kenyon Peninsula, along the grounding line and around the key ice shelf pinning point of Bawden Ice Rise. In addition, we can confirm that the cavity’s southern trough stretches from Mobiloil Inlet to the open ocean. These areas of deep seabed will influence ocean circulation and tidal mixing, and will therefore affect the basal-melt distribution. These results will help constrain models of ice-shelf cavity circulation with the aim of improving our understanding of sub-shelf processes and their potential influence on ice shelf stability. The data set comprises all point measurements of seabed depth and a gridded data product, derived using additional measurements of both offshore seabed depth and the thickness of grounded ice. We present all new depth measurements here as well as a compilation of previously published measurements used in the gridding process. The gridded data product is included in the supplementary material. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
49. Surface and subsurface hydrology of debris-covered Khumbu Glacier, Nepal, revealed by dye tracing.
- Author
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Miles, Katie E., Hubbard, Bryn, Quincey, Duncan J., Miles, Evan S., Irvine-Fynn, Tristram D.L., and Rowan, Ann V.
- Subjects
- *
MELTWATER , *MARINE debris , *GLACIERS , *HYDROLOGY - Abstract
Abstract While the supraglacial hydrology of debris-covered glaciers is relatively well studied, almost nothing is known about how water is transported beneath the glacier surface. Here, we report the results of sixteen fluorescent dye tracing experiments conducted in April–May 2018 over the lowermost 7 km of the high-elevation, debris-covered Khumbu Glacier, Nepal, to characterise the glacier's surface and subsurface drainage system. Dye breakthroughs indicated a likely highly sinuous and channelised subsurface hydrological system draining water from the upper part of the ablation area. This flowpath was distinct from the linked chain of supraglacial ponds present along much of the glacier's lower ablation area, through which water flow was extremely slow (∼0.003 m s−1), likely reflecting the study's timing during the pre-monsoon period. Subsurface drainage pathways emerged at the glacier surface close to the terminus, and flowed into small near-surface englacial reservoirs that typically delayed meltwater transit by several hours. We observed rapid pathway changes resulting from surface collapse, indicating a further distinctive aspect of the drainage of debris-covered glaciers. We conclude that the surface and subsurface drainage of Khumbu Glacier is both distinctive and dynamic, and argue that further investigation is needed to refine the characterisation and test its regional applicability to better understand future Himalayan debris-covered glacier meltwater delivery to downstream areas. Highlights • Dye tracing used to investigate hydrology of debris-covered Khumbu Glacier, Nepal. • A subsurface drainage system exists, and is likely highly sinuous and channelised. • The subsurface drainage system does not link to the chain of supraglacial ponds. • Flow through the pond chain is slow and comprises a small part of total discharge. • Rapid pathway changes are observed, resulting from variable surface lowering. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
50. Thank You to Our 2018 Peer Reviewers.
- Author
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East, Amy E., Buffington, John, Coco, Giovanni, Finnegan, Noah J., Hoitink, Ton A. J. F., and Hubbard, Bryn
- Subjects
PERIODICAL editors - Abstract
The process of completing and communicating rigorous, high‐impact science depends heavily on obtaining quality peer review prior to publication. As AGU journals strive continually to publish excellent work, we recognize the demand that this places on reviewers' time, especially as most of us seem to receive ever‐increasing numbers of requests to review manuscripts. JGR‐Earth Surface typically strives to obtain three reviews per manuscript, to best ensure the quality of the science that we publish. We thank the members of the earth‐surface community who volunteered their time to complete these reviews for JGR‐Earth Surface in 2018: a total of 874 reviews provided by 650 scientists. We greatly appreciate your time, your thoughtful and constructive review comments, and especially your dedication to this all‐important part of producing high‐quality science. Key Points: The Editors thank the 2018 peer reviewers [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
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Catalog
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