407 results on '"Hubbard, Bryn"'
Search Results
202. Alpine subglacial hydrology
- Author
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Hubbard, Bryn, primary and Nienow, Peter, additional
- Published
- 1997
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203. On the sedimentological character of Alpine basal ice facies
- Author
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Hubbard, Bryn, primary, Sharp, Martin, additional, and Lawson, Wendy J., additional
- Published
- 1996
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204. Comments on the use of chemically based mixing models in glacier hydrology
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Sharp, Martin, primary, Brown, Giles H., additional, Tranter, Martyn, additional, Willis, Ian C., additional, and Hubbard, Bryn, additional
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- 1995
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205. The character, structure and origin of the basal ice layer of a surge-type glacier
- Author
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Sharp, Martin, primary, Jouzel, Jean, additional, Hubbard, Bryn, additional, and Lawson, Wendy, additional
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- 1994
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206. Optical-televiewer-based logging of the uppermost 630m of the NEEM deep ice borehole, Greenland.
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HUBBARD, Bryn and MALONE, Terry
- Subjects
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ICE sheets , *BOREHOLES , *LIGHT scattering , *LUMINOSITY - Abstract
We report on the application of optical televiewing (OPTV) to the uppermost 630m of the North Greenland Eemian Ice Drilling (NEEM) deep ice borehole, Greenland. The resulting log reveals numerous natural and drilling-related properties, including the integrity of the borehole casing and its joints, the presence of drill-tooth scoring on the ice wall of the borehole and the presence of regularly repeated layering, interpreted to be annual, to a depth approaching 200 m. A second OPTV log was acquired from a nearby shallow borehole. With the exception of the uppermost ~10 m, this log shows a gradual decrease in luminosity with depth, interpreted as a decrease in light scattering with firnification. This shallow log also clearly images annual layers, allowing the construction of an age-depth scale. Comparing this with an independent core-based scale reveals that the OPTV record yields an age of 1724 at the deepest common point of both scales (80 m), 13 years older than the core-based record at 1737. However, all of this deviation accrues in the uppermost ~30m of the OPTV record where highly reflective snow saturates the luminosity of the borehole image, an artefact that can be reduced by further adaptation of the OPTV system. [ABSTRACT FROM AUTHOR]
- Published
- 2013
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207. Weertman regelation, multiple refreezing events and the isotopic evolution of the basal ice layer
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Hubbard, Bryn, primary and Sharp, Martin, additional
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- 1993
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208. Modelling ice-bed coupling during a glacier speed-up event: Haut Glacier d'Arolla, Switzerland.
- Author
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Fischer, Urs H., Mair, Doug, Kavanaugh, Jeffrey L., Willis, Ian, Nienow, Peter, and Hubbard, Bryn
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GLACIER speed ,SEDIMENT analysis ,ICE sheets ,SENSITIVITY analysis - Abstract
Copyright of Hydrological Processes is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2011
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209. Possible interactions between bacterial diversity, microbial activity and supraglacial hydrology of cryoconite holes in Svalbard.
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Edwards, Arwyn, Anesio, Alexandre M, Rassner, Sara M, Sattler, Birgit, Hubbard, Bryn, Perkins, William T, Young, Michael, and Griffith, Gareth W
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BACTERIAL diversity ,GLACIOLOGY ,CRYOCONITE ,BIOTIC communities ,RESTRICTION fragment length polymorphisms ,LOCUS (Genetics) - Abstract
The diversity of highly active bacterial communities in cryoconite holes on three Arctic glaciers in Svalbard was investigated using terminal restriction fragment length polymorphism (T-RFLP) of the 16S rRNA locus. Construction and sequencing of clone libraries allowed several members of these communities to be identified, with Proteobacteria being the dominant one, followed by Cyanobacteria and Bacteroidetes. T-RFLP data revealed significantly different communities in holes on the (cold) valley glacier Austre Brøggerbreen relative to two adjacent (polythermal) valley glaciers, Midtre Lovénbreen and Vestre Brøggerbreen. These population compositions correlate with differences in organic matter content, temperature and the metabolic activity of microbial communities concerned. No within-glacier spatial patterns were observed in the communities identified over the 2-year period and with the 1 km-spaced sampling. We infer that surface hydrology is an important factor in the development of cryoconite bacterial communities. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
210. Freezing-rate effects on the physical characteristics of basal ice formed by net adfreezing
- Author
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Hubbard, Bryn, primary
- Published
- 1991
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211. Cross-coupled flow modeling of coincident streaming and electrochemical potentials and application to subglacial self-potential data.
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Kulessa, Bernd, Hubbard, Bryn, and Brown, Giles H.
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- 2003
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212. Basal ice formation and deformation: a review.
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Hubbard, Bryn and Sharp, Martin
- Published
- 1989
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213. Physical Conditions of Fast Glacier Flow: 2. Variable Extent of Anisotropic Ice and Soft Basal Sediment From Seismic Reflection Data Acquired on Store Glacier, West Greenland
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Hofstede, Coen, Christoffersen, P, Hubbard, Bryn, Doyle, Samuel, Young, Tun Jan, Diez, Anja, Eisen, Olaf, Hubbard, Alun, Christoffersen, Poul [0000-0003-2643-8724], Young, Tun [0000-0001-5865-3459], and Apollo - University of Cambridge Repository
- Subjects
subglacial ,sliding ,deformation ,seismic ,anisotropy ,VDP::Mathematics and natural science: 400::Geosciences: 450::Quaternary geology, glaciology: 465 ,VDP::Matematikk og Naturvitenskap: 400::Geofag: 450::Kvartærgeologi, glasiologi: 465 ,patches - Abstract
Source at https://doi.org/10.1002/2017JF004297. Outlet glaciers of the Greenland Ice Sheet transport ice from the interior to the ocean and contribute directly to sea level rise because discharge and ablation often exceed the accumulation. To develop a better understanding of these fast‐flowing glaciers, we investigate the basal conditions of Store Glacier, a large outlet glacier flowing into Uummannaq Fjord in west Greenland. We use two crossing seismic profiles acquired near the centerline, 30 km upstream of the calving front, to interpret the physical nature of the ice and bed. We identify one notably englacial and two notably subglacial seismic reflections on both profiles. The englacial reflection represents a change in crystal orientation fabric, interpreted to be the Holocene‐Wisconsin transition. From Amplitude‐Versus‐Angle (AVA) analysis we infer that the deepest ∼80 m of ice of the parallel‐flow profile below this reflection is anisotropic with an enhancement of simple shear of ∼2. The ice is underlain by ∼45 m of unconsolidated sediments, below which there is a strong reflection caused by the transition to consolidated sediments. In the across‐flow profile subglacial properties vary over small scale and the polarity of the ice‐bed reflection switches from positive to negative. We interpret these as patches of different basal slipperiness associated with variable amounts of water. Our results illustrate variability in basal properties, and hence ice‐bed coupling, at a spatial scale of ∼100 m, highlighting the need for direct observations of the bed to improve the basal boundary conditions in ice‐dynamic models.
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214. Deep ice-filled crevasses at Store Glacier, Greenland, revealed by borehole optical televiewing.
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Hubbard, Bryn, Christoffersen, Poul, Doyle, Samuel, Chudley, Tom, Law, Robert, Bougamont, Marion, and Schoonman, Charlotte
- Subjects
- *
MELTWATER , *GLACIERS , *ICE mechanics , *SURFACE strains , *POLYNYAS , *DEFORMATIONS (Mechanics) , *REINFORCING bars - Abstract
Surface crevassing is common on most of Earth's glaciers and particularly prevalent on fast-moving outlet glaciers characterised by high surface strain rates. As well as having implications for the mechanics of ice deformation and net strength, crevasses represent a means of transferring surface-generated meltwater and associated heat into the interior, and ultimately possibly to the base, of ice masses. Theoretically, surface crevasses are restricted to the uppermost tens of metres of an ice mass, but this can be extended by hydrofracturing where crevasses are water-filled. However, details - such as the locations of hydrofracturing both within a crevasse field and more locally within individual crevasses - are poorly understood such that vertical crevasse extent remains largely unconstrained. This knowledge gap mainly reflects the challenges associated with obtaining measurements of crevasse depth at glaciers, in terms of both obtaining direct access and geophysical imaging, especially of water-filled crevasses.Borehole optical televiewing (OPTV) records a high-resolution, geometrically-accurate image of the complete wall of any logged borehole, revealing the visible ice types and structures intercepted by that borehole. The technique therefore represents one means of investigating deep crevasses at ice masses, noting that such crevasses need to be inclined sufficiently to intersect an approximately vertical borehole. Here, we report evidence from a 325 m-long OPTV log of a borehole drilled ~30 km upglacier of the terminus of Store Glacier, a fast-moving tidewater glacier in west Greenland. While most structural features in the OPTV log are low-angle alternating decimetre-scale layers of clear ice and bubble-rich ice, interpreted as stratification, several high-angle features were also imaged. These were present to a depth of ~275 m and were typically centimetres to decimetres thick and composed of predominantly bubble-free ice. In one case, parallel crystal edges indicative of a directional freezing front were evident. Close inspection of the OPTV log also reveals that most of the high-angle layers enclosed one or more (and exceptionally, 11) structurally concordant millimetre-thick bubbly layers. We interpret the steeply-dipping layers as crevasses containing refrozen meltwater, and the fine bubbly layers as individual episodes of crevasse re-opening, refilling and refreezing – each expelling a new layer of gas as freezing completes. Implications for the transfer of mass and heat from the glacier's surface to its interior are explored by (i) comparing measured borehole temperatures with modelled englacial temperatures, and (ii) a spatial analysis of local surface crevassing. [ABSTRACT FROM AUTHOR]
- Published
- 2019
215. 3D structure of Khumbu Glacier, Nepal, from borehole experiments.
- Author
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Hubbard, Bryn, Quincey, Duncan, Miles, Evan, Miles, Katie, Pallett, Mark, and Rowan, Ann
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GLACIERS , *BOREHOLES , *CLIMATE change research , *ICE cores , *MELTING points , *INFORMATION modeling , *KNOWLEDGE gap theory , *COMPUTER simulation - Abstract
Predicting the response of Earth's high-elevation debris-covered glaciers (HEDCGs) to anticipated climate change represents an important current research challenge. While 2D and 3D computer models of glacier motion and geometrical change are now highly sophisticated, their application to HEDCGs is hampered by a dearth of empirical information for model calibration and validation. This knowledge gap principally reflects logistical difficulties associated with carrying out research at such glaciers, particularly in terms of obtaining information relating to subsurface conditions and processes. Thus, key information that could be used to guide models such as englacial temperature fields, the occurrence and nature of glacier drainage, sediment incorporation and transfer, and 3D dynamic characteristics remain largely unknown.Here, we report on 27 boreholes drilled and instrumented at five sites across the debris-covered tongue of Khumbu Glacier, Nepal, for the EverDrill research project. We report on our drilling experiences, including challenges that were anticipated and encountered and the adaptations made to overcome them, and on the results of experiments undertaken in the boreholes. The latter includes measurements of ice temperature, ice deformation, and the glacier's englacial debris load. Temperatures were measured to be approaching melting point. Ice deformation was found to be low but variable. While the englacial ice contained surprisingly little distributed debris – allowing two boreholes to be drilled to greater than ~150 m - discrete shallow layers of impenetrable debris, interpreted to originate from valley-side avalanches, were encountered during drilling. [ABSTRACT FROM AUTHOR]
- Published
- 2019
216. Investigating hydrological forcing of fast glacier flow in Greenland using passive seismology.
- Author
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Schoonman, Charlotte, Christoffersen, Poul, Hofstede, Coen, Young, Tun Jan, Pettersson, Rickard, McCallum, Adrian, Doyle, Sam, and Hubbard, Bryn
- Published
- 2019
217. Thermodynamics of a fast-moving Greenlandic outlet glacier revealed by fiber-optic distributed temperature sensing
- Author
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Law, Robert, Christoffersen, Poul, Hubbard, Bryn, Doyle, Samuel H, Chudley, Thomas R, Schoonman, Charlotte M, Bougamont, Marion, Des Tombe, Bas, Schilperoort, Bart, Kechavarzi, Cedric, Booth, Adam, and Young, Tun Jan
- Subjects
13. Climate action - Abstract
Measurements of ice temperature provide crucial constraints on ice viscosity and the thermodynamic processes occurring within a glacier. However, such measurements are presently limited by a small number of relatively coarse-spatial-resolution borehole records, especially for ice sheets. Here, we advance our understanding of glacier thermodynamics with an exceptionally high-vertical-resolution (~0.65 m), distributed-fiber-optic temperature-sensing profile from a 1043-m borehole drilled to the base of Sermeq Kujalleq (Store Glacier), Greenland. We report substantial but isolated strain heating within interglacial-phase ice at 208 to 242 m depth together with strongly heterogeneous ice deformation in glacial-phase ice below 889 m. We also observe a high-strain interface between glacial- and interglacial-phase ice and a 73-m-thick temperate basal layer, interpreted as locally formed and important for the glacier's fast motion. These findings demonstrate notable spatial heterogeneity, both vertically and at the catchment scale, in the conditions facilitating the fast motion of marine-terminating glaciers in Greenland.
218. Cryoegg: development and field trials of a wireless subglacial probe for deep, fast-moving ice
- Author
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Prior-Jones, Michael R., Bagshaw, Elizabeth A., Lees, Jonathan, Clare, Lindsay, Burrow, Stephen, Werder, Mauro, Karlsson, Nanna B., Dahl-Jensen, Dorthe, Chudley, Thomas R., Christoffersen, Poul, Wadham, Jemma L., Doyle, Samuel H., and Hubbard, Bryn
- Subjects
Glacier hydrology ,glaciological instruments and methods ,subglacial processes ,7. Clean energy - 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., Journal of Glaciology, 67 (264), ISSN:0022-1430, ISSN:1727-5652
219. Supraglacial lake drainage at a fast-flowing Greenlandic outlet glacier
- Author
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Chudley, Thomas R, Christoffersen, Poul, Doyle, Samuel H, Bougamont, Marion, Schoonman, Charlotte M, Hubbard, Bryn, and James, Mike R
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13. Climate action ,ice sheets ,Greenland ,glaciology ,lakes ,hydrology - Abstract
Supraglacial lake drainage events influence Greenland Ice Sheet dynamics on hourly to interannual timescales. However, direct observations are rare, and, to date, no in situ studies exist from fast-flowing sectors of the ice sheet. Here, we present observations of a rapid lake drainage event at Store Glacier, west Greenland, in 2018. The drainage event transported 4.8 × 106 m3 of meltwater to the glacier bed in ∼5 h, reducing the lake to a third of its original volume. During drainage, the local ice surface rose by 0.55 m, and surface velocity increased from 2.0 m⋅d-1 to 5.3 m⋅d-1 Dynamic responses were greatest ∼4 km downstream from the lake, which we interpret as an area of transient water storage constrained by basal topography. Drainage initiated, without any precursory trigger, when the lake expanded and reactivated a preexisting fracture that had been responsible for a drainage event 1 y earlier. Since formation, this fracture had advected ∼500 m from the lake's deepest point, meaning the lake did not fully drain. Partial drainage events have previously been assumed to occur slowly via lake overtopping, with a comparatively small dynamic influence. In contrast, our findings show that partial drainage events can be caused by hydrofracture, producing new hydrological connections that continue to concentrate the supply of surface meltwater to the bed of the ice sheet throughout the melt season. Our findings therefore indicate that the quantity and resultant dynamic influence of rapid lake drainages are likely being underestimated.
220. Physical Conditions of Fast Glacier Flow: 2. Variable Extent of Anisotropic Ice and Soft Basal Sediment From Seismic Reflection Data Acquired on Store Glacier, West Greenland
- Author
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Hofstede, Coen, Christoffersen, P, Hubbard, Bryn, Doyle, Samuel, Young, Tun Jan, Diez, Anja, Eisen, Olaf, and Hubbard, Alun
- Subjects
subglacial ,13. Climate action ,sliding ,deformation ,seismic ,anisotropy ,patches - Abstract
Outlet glaciers of the Greenland Ice Sheet transport ice from the interior to the ocean and contribute directly to sea level rise because because discharge and ablation often exceed the accumulation. To develop a better understanding of these fast flowing glaciers, we investigate the basal conditions of Store Glacier, a large outlet glacier flowing into Uummannaq Fjord in West Greenland. We use two crossing seismic profiles acquired near the centreline, 30 km upstream of the calving front, to interpret the physical nature of the ice and bed. We identify one notably englacial and two notably subglacial seismic reflections on both profiles. The englacial reflection represents a change in crystal orientation fabric, interpreted to be the Holocene–Wisconsin transition. From Amplitude Versus Angle (AVA) analysis we infer that the deepest 80 m of ice of the parallel-flow profile below this reflection is anisotropic with an enhancement of simple shear of 2. The ice is underlain by 45 m of unconsolidated sediments, below which there is a strong reflection caused by the transition to consolidated sediments. In the across-flow profile subglacial properties vary over small scale and the polarity of the ice–bed reflection switches from positive to negative. We interpret these as patches of different basal slipperiness associated with variable amounts of water. Our results illustrate variability in basal properties, and hence ice-bed coupling, at a spatial scale of 100 m, highlighting the need for direct observations of the bed to improve the basal boundary conditions in ice-dynamic models.
221. Thermodynamics of a fast-moving Greenlandic outlet glacier revealed by fiber-optic distributed temperature sensing
- Author
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Law, Robert, Christoffersen, Poul, Hubbard, Bryn, Doyle, Samuel H, Chudley, Thomas R, Schoonman, Charlotte M, Bougamont, Marion, Des Tombe, Bas, Schilperoort, Bart, Kechavarzi, Cedric, Booth, Adam, and Young, Tun Jan
- Subjects
13. Climate action ,37 Earth Sciences ,3705 Geology ,3709 Physical Geography and Environmental Geoscience - Abstract
Measurements of ice temperature provide crucial constraints on ice viscosity and the thermodynamic processes occurring within a glacier. However, such measurements are presently limited by a small number of relatively coarse-spatial-resolution borehole records, especially for ice sheets. Here, we advance our understanding of glacier thermodynamics with an exceptionally high-vertical-resolution (~0.65 m), distributed-fiber-optic temperature-sensing profile from a 1043-m borehole drilled to the base of Sermeq Kujalleq (Store Glacier), Greenland. We report substantial but isolated strain heating within interglacial-phase ice at 208 to 242 m depth together with strongly heterogeneous ice deformation in glacial-phase ice below 889 m. We also observe a high-strain interface between glacial- and interglacial-phase ice and a 73-m-thick temperate basal layer, interpreted as locally formed and important for the glacier's fast motion. These findings demonstrate notable spatial heterogeneity, both vertically and at the catchment scale, in the conditions facilitating the fast motion of marine-terminating glaciers in Greenland.
222. Thermodynamics of a fast-moving Greenlandic outlet glacier revealed by fiber-optic distributed temperature sensing.
- Author
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Law, Robert, Christoffersen, Poul, Hubbard, Bryn, Doyle, Samuel H., Chudley, Thomas R., Schoonman, Charlotte M., Bougamont, Marion, des Tombe, Bas, Schilperoort, Bart, Kechavarzi, Cedric, Booth, Adam, and Tun Jan Young
- Subjects
- *
GLACIERS , *MELTWATER , *BOREHOLES , *THERMODYNAMICS , *GREENLAND ice - Published
- 2021
- Full Text
- View/download PDF
223. Estimating the volume of mid-latitude glacier-like forms on Mars.
- Author
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Brough, Stephen, Hubbard, Bryn, and Hubbard, Alun
- Subjects
- *
MARS (Planet) , *ALBEDO - Published
- 2018
224. Ground penetrating radar evidence of refrozen meltwater in the firn column of Larsen C Ice Shelf.
- Author
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Booth, Adam, Sevestre, Heidi, Kulessa, Bernd, Bevan, Suzanne, Hubbard, Bryn, Luckman, Adrian, Munneke, Peter Kuipers, Buzzard, Sammie, Ashmore, David, and O'Leary, Martin
- Published
- 2018
225. Mechanical response of Larsen C Ice Shelf following the A68 calving event: observations from field-based geophysical measurements.
- Author
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Booth, Adam, Luckman, Adrian, White, Jim, Pearce, Emma, Cornford, Stephen, Kulessa, Bernd, Brisbourne, Alex, and Hubbard, Bryn
- Published
- 2018
226. Polyphase mid-latitude glaciation on Mars evidenced by dating of superimposed lobate debris aprons.
- Author
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Hepburn, Adam, Ng, Felix, Livingstone, Stephen J., and Hubbard, Bryn
- Published
- 2018
227. 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
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- View/download PDF
228. Part Introduction.
- Author
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Montanez, Isabel, Hambrey, Michael J., Christoffersen, Poul, Glasser, Neil F., and Hubbard, Bryn
- Published
- 2007
- Full Text
- View/download PDF
229. 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
230. 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
231. Massive subsurface ice formed by refreezing of ice-shelf melt ponds.
- Author
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Hubbard, Bryn, Luckman, Adrian, Ashmore, David W., Bevan, Suzanne, Kulessa, Bernd, Kuipers Munneke, Peter, Philippe, Morgane, Jansen, Daniela, Booth, Adam, Sevestre, Heidi, Tison, Jean-Louis, O'Leary, Martin, and Rutt, Ian
- Published
- 2016
- Full Text
- View/download PDF
232. Full Waveform Inversion to determine the seismic structure of firn
- Author
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Pearce, Emma Valerie Eve, Booth, Adam, Rost, Sebastian, Hubbard, Bryn, Brisbourne, Alex, and Jones, Ian
- Abstract
The compaction of firn (the transition of snow to ice) is a process in glaciology that is difficult to constrain without the use of intrusive geophysical techniques. Full Waveform Inversion (FWI) is a seismic imaging technique used to obtain high-resolution images of the subsurface. This research introduces FWI to glaciological modelling and shows that FWI can improve upon the Herglotz-Wiechert travel time tomography method that's use is currently widespread. Using synthetic firn velocity models, acoustic FWI was shown to recover the compressional (P) wave velocity gradient of the firn column and could correct a velocity model that was a poor representation of the subsurface structure (up to a 5% velocity error). Additionally, FWI was able to detect ice layers of a minimum thickness of 10 m (half the minimum wavelength) within the firn column and provide constraints on their depth providing the ice slab did not occur in the shallow surface (20 m or less), where the steepest velocity gradient occurs. FWI is applied to two datasets. Firstly, legacy data acquired by the British Antarctic Survey on Pine Island Glacier were problematic, owing to an inconsistent, high-frequency source waveform that made FWI vulnerable to cycle skipping. Consequently, no improvement was observed to the seismic structure. Secondly, a dataset acquired specifically for this research was collected on Norway's Hardangerjøkulen Ice Cap. With this dataset a combination of Travel Time and Least-Squares FWI can be successful due to the use of a repeatable seismic source with lower frequency content (10 Hz), A VSP survey used to provide near-surface velocity constraints and near offset small receiver spacing (1 m). FWI provided a 6% change to the starting velocity model and improved the data match by 47%. The results showed that acoustic FWI must be considered from the seismic acquisition stage for the technique to be successful in characterising firn velocity structure. In this case, FWI can improve the model of the subsurface velocity structure from the HW technique and increase the match of the modelled seismic data.
- Published
- 2021
233. 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
234. 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
- 2023
- Full Text
- View/download PDF
235. Book reviews.
- Author
-
Goudie, A.S., Finlayson, Brian, Sutherland, Ross A., Drake, Frances, Migon, Piotr, Denholm-Price, James, Hubbard, Bryn, Viles, Heather A., Pain, Colin, New, Mark, Duck, R.W., and Shakesby, Rick
- Subjects
PHYSICAL geography - Abstract
Aberg, A.and Lewis, C., editors, 2000: The rising tide: archaeology and coastal landscapes. Oxford: Oxbow. iv + 122 pp. £25.00 paper. ISBN: 1 84217 028 7. Acreman, M., (editor in association with the British Hydrological Society), 2000: The hydrology of the UK: a study of change. London: Routledge. 303 pp. £24.99 paper. ISBN 0 451 1876 1. Foster, I.D.L., editor, 2000: Tracers in geomorphology. Chichester: John Wiley. xv + 560 pp. £85.00 (US$150.00) cloth. ISBN: 0 471 89602 0 Grove, A.T.and Rackham, O.2001: The nature of Mediterranean Europe: an ecological history. London and New Haven, Yale University Press. 384 pp. £45.00/$75.00 cloth. ISBN: 0 300 08443 9. Porembski, S.and Barthlott, W., editors, 2000: Inselbergs: biotic diversity of isolated rock outcrops in tropical and temperate regions. Ecological Studies, vol. 746. Berlin: Springer Verlag. 524 pp. DM 298. ISBN: 3 540 67269 9. Rayner, J.N.2000: Dynamic climatology. Basis in mathematics and physics. Oxford: Blackwell. xix + 280 pp. £50.00 cloth, £16.99 paper. ISBN: 1 577 18015 1 cloth, 1 577 18016 X paper. Sharp, M., Richards, K.S.and Tranter, M., editors, 1998: Glacier hydrology and hydrochemistry. Chichester: Wiley. 342 pp. £40.00 paper. ISBN 0 471 98168 0. Short, A.D., editor, Handbook of beach and shoreface morphodynamics. Chichester: Wiley. xii and 380 pp. ISBN: 0 471 96570 7. Summerfield, M.A., editor, 2000: Geo-morphology and global tectonics. Chichester: Wiley. xvii + 368 pp. £100.00 cloth. ISBN: 0 471 97193 6. Tyson, P.D.and Preston-Whyte, R.A.2000: The weather and climate of Southern Africa(2nd edn.). Oxford: Oxford University Press. xii + 396 pp. £32.50 paper. ISBN: 0 19 571806 2. van der Lee, W.T.B.2000: The settling of mud flocs in the Dollard estuary, The Netherlands. Nederlandse Geografische Studies 274. Utrecht: The Royal Dutch Geographical Society/Faculty of Geographical Sciences, Utrecht University. 148 pp. Dfl 34.50 paper. ISBN: 90 6809 29... [ABSTRACT FROM AUTHOR]
- Published
- 2001
- Full Text
- View/download PDF
236. Field-based investigations of the subsurface environment of a high-elevation debris-covered glacier
- Author
-
Miles, Katharine, Hubbard, Bryn, Irvine-Fynn, Tristram, and Quincey, Duncan Joseph
- Subjects
551.31 - Abstract
Debris-covered glaciers comprise around a third of all glaciers in High Mountain Asia, and thus represent a critical source of meltwater for those living in the foothills of the region. Many of these debris-covered glaciers are situated at elevations exceeding 4,500 m above sea level and display a number of unique supraglacial features and mass balance characteristics arising from the spatially variable thickness of their supraglacial debris layers. Given their remoteness, these glaciers are difficult to access; field-based data are severely lacking, particularly for the subsurface environment, meaning both the parameterisation and validation of numerical modelling experiments are frequently based on assumptions and calculations. To address this gap, this research investigates the subsurface environment of a high-elevation debris-covered glacier, Khumbu Glacier, Nepal Himalaya, through a series of field-based experiments. In particular, the thermal regime, subsurface hydrology, and englacial debris content of Khumbu Glacier are targeted. The results reveal that Khumbu Glacier has a polythermal regime, with a notable proportion of temperate, and potentially warming, ice towards the terminus, which may support the presence of a persistent subsurface hydrology. The glacier's drainage system transports meltwater inefficiently during the early melt season, but has the capacity for more efficient transport with greater inputs. Meltwater transit through a large chain of linked supraglacial ponds is slow, which may promote enhanced surface ablation and, together with a warming thermal regime, may increase the glacier's sensitivity to future climatic warming through time. However, in contrast, the continued melt-out of a relatively high englacial debris content may act to suppress melt rates within only a few decades. Combined, the data presented in this thesis provide a suite of empirical observations that can reduce the current uncertainties inherent in contemporary numerical predictions of debris-covered glacier evolution and water resource availability within the region.
- Published
- 2020
237. Centuries of intense surface melt on Larsen C Ice Shelf.
- Author
-
Bevan, Suzanne L., Luckman, Adrian, Hubbard, Bryn, Kulessa, Bernd, Ashmore, David, Munneke, Peter Kuipers, O'Leary, Martin, Booth, Adam, Sevestre, Heidi, and McGrath, Daniel
- Subjects
- *
METAMORPHISM (Geology) , *BOREHOLES , *SOIL sampling , *ICE streams ,ANTARCTIC environmental conditions - 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 meltaffected 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. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
238. Basal ice facies and their formation in the western Alps
- Author
-
Hubbard, Bryn Pugh
- Subjects
- 551.31, Glaciers
- Published
- 1992
239. 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
240. 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
241. Debris-covered glaciers in the European Alps : from the glacier to the mountain range scale
- Author
-
Lardeux, Pierre, Glasser, Neil, Holt, Tom, and Hubbard, Bryn
- Subjects
551.31 - Abstract
Like in other mountain ranges around the world (the Southern Alps, the Himalayas and the Rockies), glaciers in the European Alps are a major source of fresh water for human usage and actively contribute to sea-level rise. Among European Alpine glaciers, this study shows that 12% are debris-covered, representing 54% in ice volume. Debris-covered glaciers are those presenting a layer of rock debris on their surface. This debris layer has an insulation effect on the glacier, which influences the response to climate change of this type of glacier. However, little is known about their long-term historical evolution and their future behaviour in the face of climate change. By directly comparing debris-covered glaciers and clean-ice glaciers at several different spatial and temporal scales, this study shows the large impact that debriscovered glaciers have on the Alpine cryosphere. On a glacier-wide scale, this study shows that, over 200 years, a debris-covered glacier (Glacier Noir in the French Alps) has retreated 21% less than an adjacent clean-ice glacier (Glacier Blanc) under the same climatic conditions (a temperature rise of minimum 2°C since the 1960s). On the scale of the European Alps, this study shows that debris-covered glaciers will extend the water supply of 145 million inhabitants. By the middle of the 21st century, debris-covered glaciers will contribute more than 22% of the total glacier runoff from the Alps, with a slower release than clean-ice glaciers. The importance of debris-covered glaciers in terms of behaviour and quantity could change the way they are represented in numerical models and could also change forecasts of the fate of glaciers in the European Alps under future climate scenarios.
- Published
- 2017
242. Origins of foliations and related phenomena in valley glaciers and ice sheets
- Author
-
Jennings, Stephen James Arthur, Glasser, Neil, Hubbard, Bryn, and Hambrey, Michael
- Subjects
551.31 - Abstract
This study examines how longitudinal foliation develops in glaciers and ice sheets in a wide range of topographic, climatic, and dynamic settings, at a variety of spatial scales. Study locations include four valley glaciers in Svalbard (Austre Brøggerbreen, Midtre Lovénbreen, Austre Lovénbreen, and Pedersenbreen), a valley glacier in Canada (Sermilik Glacier), and seven outlet glaciers in Antarctica (Hatherton Glacier, Taylor Glacier, Ferrar Glacier, Lambert Glacier, Recovery Glacier, Byrd Glacier, and Pine Island Glacier). Detailed structural mapping of the valley glaciers from satellite imagery and field-based measurements were used to document the formation of longitudinal foliation in small-scale ice masses. These findings were ‘up-scaled’ and applied to much larger glaciers and ice streams. Longitudinal foliation develops in concentrated bands at flow unit boundaries as a result of enhanced simple shear. However, longitudinal foliation is not directly observable from satellite imagery at the surface of larger-scale valley glaciers. The longitudinal structures visible at the surface of larger-scale glaciers form at flow unit boundaries and are composed of bands of steeply dipping longitudinal foliation; however, they appear as individual linear features on satellite imagery as a result of the comparatively low spatial resolution of the imagery. The persistence of flowlines in the Antarctic Ice Sheet through areas of crevassing and net ablation (blue-ice areas) suggests that they are the surface representation of a threedimensional structure. Flowlines are therefore inferred to be the surface expression of flow unit boundaries composed of bands of steeply dipping longitudinal foliation. The survival and deformation of flowlines in areas of ice flow stagnation indicates that flowlines form in their initiation zones and not along their entire length. Furthermore, these ice stagnation areas indicate that flowlines record past ice dynamics and switches in ice flow.
- Published
- 2017
243. Current and former volume and dynamics of mid-latitude glacier-like forms on Mars
- Author
-
Brough, Stephen, Hubbard, Bryn, and Hubbard, Alun
- Subjects
551.31 - Abstract
The mid-latitudes of Mars host numerous ice-related landforms that bear many similarities to terrestrial ice masses. One particular landform has a strong resemblance to valley or debris-covered glaciers found on Earth and have subsequently become known as ‘glacier-like forms’ (GLFs). GLFs have detailed surface morphologies consistent with recent deposition and viscous deformation of ice, but there is still uncertainty regarding their formation, current and former volume, and dynamic evolution. Specifically, this thesis presents new observations and results that assess the current and former volume and dynamics of Mars’ mid-latitude GLFs. The findings presented in this thesis suggest that at the broadest level Mars’ midlatitudes appear to preserve a complex and spatially heterogeneous record of glaciation and that GLFs appear to be the manifestation of a more localised period of alpine glaciation. GLFs represent an active component of the near-surface water budget of Mars, locking away an estimated global equivalent water layer of between 3 ± 1 and 10 ± 3 mm. Evidence of recession and mass loss was identified in approximately one-third (n = 436) of the GLF population, suggesting that these landforms once contributed a larger volume of water to the near-surface water budget of Mars. Assessment of environmental and topographical controls over current ice volume and ice-mass loss revealed that their distribution and size is unlikely to be purely controlled by insolation forcing. Instead it is suggested that regional to local meteorological and topographical conditions also play an important role in GLF ice accumulation and/or preservation, with variation in physical environments providing microclimates favourable for accumulation and/or preservation of ice. The emerging picture shows that Mars’ GLFs appear to have been dynamically active, and that they have played an important role in altering the surface landscape of Mars through erosion, transport and deposition of material.
- Published
- 2017
244. Basal ice facies and their formation in the Western Alps
- Author
-
Sharp, Martin and Hubbard, Bryn
- Published
- 1995
245. 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
246. 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
247. GPS-based investigations of Greenland Ice Sheet dynamics
- Author
-
Doyle, Samuel Huckerby, Hubbard, Alun, and Hubbard, Bryn
- Subjects
551.31 - Abstract
Accurate forecasting of the Greenland Ice Sheet's contribution to global sea level change requires detailed knowledge of how ice ow responds to surface water inputs. Both ice velocities and surface melt have increased significantly over the last decade but recent research suggests that ice ow acceleration over the summer is regulated by the seasonal evolution of the subglacial drainage system. To investigate these and associated processes, a network of continuously-operating, dual-frequency global positioning system (GPS) receivers was deployed on a 140-km-long land-terminating transect in West Greenland, providing centimetre-precise, high-frequency records of ice motion. These data reveal that the enhanced summer ow regime is comprised of discrete, transient accelerations driven by the diurnal melt cycle, rapid in situ supraglacial lake drainage and rainfall/melt events. In 2010, a comprehensive array of instruments captured the rapid ( ~ 2 hour) drainage of a large supraglacial lake via a 3-km-long fracture, hydraulically-driven through km-thick ice. A further pronounced, widespread and sustained acceleration driven by rainfall and melt, observed in late August 2011, suggests that the predicted increase in cyclonic activity over Greenland may drive widespread off-season melt, rainfall and ow acceleration across the ice sheet. Together these events provide new insights into the basal hydrodynamic controls on ice sheet motion. Furthermore, observations of a persistent year-on-year acceleration in ice ow between 2009 and 2012 at a high elevation site located ~ 50 km inland of the equilibrium line support the hypothesis that the observed inland expansion of supraglacial lakes is driving faster ice ow at high elevations. These observations contrast with the prevailing self-regulation model and reveal that despite surface melt increasing water inputs to the bed are still insuffcient to develop effective subglacial drainage in the ice sheet's interior.
- Published
- 2014
248. Distribution and character of mid-latitude glacier-like forms on Mars
- Author
-
Souness, Colin James, Hubbard, Bryn, and Quincey, Duncan Joseph
- Subjects
550 - Abstract
Mars‟ mid-latitudes host a range of apparently flow-related landforms that strongly resemble terrestrial glaciers. Such „glacier-like forms‟ (GLFs) are strikingly similar to alpine valley glaciers found on Earth. These martian GLFs are believed to be composed of massive water ice but little is known about how they formed, how they evolve, and how they interact with the martian surface. This thesis presents various studies of Mars‟ mid-latitude GLFs that were designed to address some of these issues. New observations and new results were obtained using survey and mapping techniques. The findings presented in this thesis suggest that GLFs, observed ubiquitously in Mars‟ mid-latitudes, are all composed of a similar material and were formed in a similar way, most likely under Earth-like „mass-balance‟ conditions whereby ice accumulated at altitude and subsequently flowed, under its own weight, downhill and into an ablation zone where GLFs experienced net mass loss. It is likely these conditions existed on Mars during a past martian ice age. From their geographical distribution (relative to latitude, elevation and relief) it would appear that those GLFs that remain on Mars today are relict deposits that have survived where local conditions impair ablation, and that these residual GLFs appear currently to flow under the influence of local relief and gravity. From the examination of crevasse patterns it appears that this flow occurs under an englacial strain regime similar to that which commonly defines spatial flow patterns in terrestrial glaciers. This thesis also observes and identifies various small-scale features and textures that suggest that the evolution and subsequent flow of GLFs has been (or may currently be) sensitive to many environmental factors common on Earth, such as the agency of liquid water. This suggests that GLFs (and possibly other associated ice masses) may have been significant movers and shapers of Mars‟ surface sediments and structures, contributing widely to the evolution of Mars‟ present-day surface.
- Published
- 2013
249. Modern & Past Glacial Environments. Revised Student Edition (Book).
- Author
-
Hubbard, Bryn
- Subjects
- *
GLACIERS , *NONFICTION - Abstract
Reviews the book "Modern & Past Glacial Environments," edited by J. Menzies.
- Published
- 2004
- Full Text
- View/download PDF
250. BOOK REVIEWS.
- Author
-
Hubbard, Bryn
- Subjects
- GLACIERS (Book : Knight)
- Abstract
Reviews the book `Glaciers,' by P.G. Knight.
- Published
- 2000
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