The full range of Survey publications is available from the BGS Sales Desks at Nottingham and Edi... more The full range of Survey publications is available from the BGS Sales Desks at Nottingham and Edinburgh; see contact details below or shop online at www.thebgs.co.uk The London Information Office maintains a reference collection of BGS publications including maps for consultation. The Survey publishes an annual catalogue of its maps and other publications; this catalogue is available from any of the BGS Sales Desks. The British Geological Survey carries out the geological survey of Great Britain and Northern Ireland (the latter as an agency service for the government of Northern Ireland), and of the surrounding continental shelf, as well as its basic research projects. It also undertakes programmes of British technical aid in geology in developing countries as arranged by the Department for International Development and other agencies. The British Geological Survey is a component body of the Natural Environment Research Council.
A new apparatus for the determination of shrinkage limit is described. Two versions have been pro... more A new apparatus for the determination of shrinkage limit is described. Two versions have been produced: a manually operated prototype ‘version1' followed by an automated version named SHRINKiT. Test results using the former for British and overseas clay soils are described and comparisons made with the British Standards preferred method. A further set of test results is described for SHRINKiT. However, it was not possible to compare these with the BS 1377 method owing to the introduction of a ban on the use of mercury in the British Geological Survey's geotechnical laboratories. The new method is set in the context of the huge cost of shrink/swell-related subsidence damage in Britain and the relative disuse of both BS 1377 methods for shrinkage limit, for reasons of safety. The shrinkage behaviour of different soils types and sample states is discussed, in addition to the advantages and disadvantages of the new method.
The effective porosity, saturated sonic velocity and saturated uniaxial compressive strength were... more The effective porosity, saturated sonic velocity and saturated uniaxial compressive strength were determined on a large number of Borrowdale Volcanic Group volcaniclastic core samples from three boreholes at Sellafield, Cumbria. The worked formed part of the UK Nirex Limited site investigation into whether the Sellafield area could be suitable as a repository for intermediate and low level radioactive waste. Most of the intact samples were of low to very low effective porosity, had a high sonic velocity and were very strong to extremely strong. However, a proportion of values deviated significantly from this. Bivariate analysis showed a negative relationship exists between sonic velocity and effective porosity. The cross plots of these two parameters with uniaxial compressive strength showed a wide range of strength values for samples of low effective porosity and high sonic velocity. Six failure types were identified during the uniaxial compressive strength tests. The strongest samples tended to fail through the matrix and the weakest rock samples tended to fail through haematized material or along haematized veins. Effective porosity and sonic velocity measurements could not distinguish between those samples that failed through the matrix and those that failed along discrete narrow veins. The presence of narrow haematized veins has a major effect on the intact rock strength.
Geological Society, London, Special Publications, 2010
The paper describes recent applications by the British Geological Survey (BGS) of the technique o... more The paper describes recent applications by the British Geological Survey (BGS) of the technique of mobile terrestrial LiDAR surveying to monitor various geomorphological changes on English coasts and estuaries. These include cliff recession, landslides and flood defences, and are usually sited at remote locations undergoing dynamic processes with no fixed reference points. Advantages, disadvantages and some practical problems are discussed. The role of GPS in laser scanning is described.
Ground Penetrating Radar (GPR) offers a relatively rapid and non-intrusive method for detecting b... more Ground Penetrating Radar (GPR) offers a relatively rapid and non-intrusive method for detecting buried utilities. In congested urban environments, where most buried utilities are to be found, this translates into significantly reduced disruption to highway users and reduced risk for developers and contractors. However, GPR performance varies significantly over large geographical areas due to variations in soil type and water content. Therefore, GPR utility location can be perceived by clients as largely hit-and-miss in terms of its planning, as full information may not be known in advance for determination of expected penetration depths and the most appropriate signal frequency ranges. This paper details the current state of predictive soil electromagnetic property mapping, from which it will be concluded that existing geotechnical databases and techniques can provide useful data on which to base such maps. In so doing, it also extends knowledge on the efficacy of predictive mapping for potential use internationally.
This report is the published product of a study by the British Geological Survey (BGS) and detail... more This report is the published product of a study by the British Geological Survey (BGS) and details the methodology, results and conclusions of an annual and biannual monitoring programme of coastal landslides at three test sites on the North Norfolk coast from 2000 to 2006. The three sites are coastal sections at Happisburgh, Sidestrand and Weybourne.
Expansive soils present significant geotechnical and structural engineering challenges the world ... more Expansive soils present significant geotechnical and structural engineering challenges the world over, with costs associated with expansive behaviour estimated to run into several billion annually. Expansive soils are soils that experience significant volume change associated with changes in water contents. These volume changes can either in the form of swell or in the form shrinkage and this is why they are sometime known as swell/shrink soils. Key aspects that need identification when dealing with expansive soils include: soil properties, suction/water conditions, water content variations temporal and spatial, e.g. generated by trees, and the geometry/stiffness of foundations and associated structures. Expansive soils can be found in humid environments where expansive problems occur with soils of high Plasticity Index (Ip) or in arid/semi arid soils where soils of even moderate expansiveness can cause significant damage. In the UK damage often occurs as a direct result of interact...
Proceedings Of The 16th Multidisciplinary Conference On Sinkholes And The Engineering And Environmental Impacts Of Karst, 2020
Ripon is a historic city and market town in North Yorkshire. It is unique in being the only city ... more Ripon is a historic city and market town in North Yorkshire. It is unique in being the only city in the UK to define planning zones based on the potential for bedrock dissolution. The underlying geology comprises marls, limestone and gypsum of the Permian Edlington, Brotherton and Roxby formations, capped by glacial deposits (till). It is the rapid rate of dissolution of the gypsum (hydrated calcium sulphate) that enables the karst to evolve on human time scales. Following the collapse that formed a sinkhole in the rear garden of a property in Magdalens Road, Ripon, UK in November 2016 the British Geological Survey, funded by a Natural Environment Research Council grant, initiated a programme of monitoring of a nearby depression. This feature is forming in a recreation area and is one that local residents reported to have grown in dimensions. The density of development precludes the use of satellite-based monitoring systems. Instead, we have integrated ground-based LiDAR imaging with geophysical techniques (micro-gravity and passive seismic). Monitoring has revealed that this depression lies over a palaeosinkhole that is in the order of 10 m in diameter and extends to a depth of a similar order of magnitude. The monitoring has been continued in the context of PhD research (University of Sheffield) that is more broadly focused on understanding sinkhole triggering processes. The developing sinkhole is on the eastern side of Ripon close to the southerly flowing River Ure, where upwelling confined groundwater contributes to the river base flow. In this context the hypotheses that growth can be correlated with rainfall or river discharge can be tested.
The current UK concept for the disposal of low-and intermediate-level radioactive wastes involves... more The current UK concept for the disposal of low-and intermediate-level radioactive wastes involves a mined geological disposal facility (GDF) located several hundreds of metres below the surface. The waste material will be encapsulated in a cementitious matrix within steel or concrete containers, and will be placed in disposal vaults backfilled with a cement-based material. After closure, the vaults will saturate with groundwater and become part of a modified regional groundwater flow system. Groundwater will equilibrate with the cement and produce an alkaline leachate. This will migrate from the repository into the surrounding rock and produce a 'chemically disturbed zone' (CDZ) with an elevated pH. Reactions will occur between the alkaline waters and the rock, potentially causing mineral dissolution and precipitation, which will modify the local geosphere prior to possible eventual radionuclide release. These changes in the CDZ will be critical controls on radionuclide behaviour and transport, and thus on the safety and environmental impact of a GDF. Consequently, it is desirable to understand these reactions and their impacts in terms of predicting localised changes to the transport properties of the host rock (porosity, permeability) and changes in groundwater flow, together with alteration of minerals and mineral surfaces that may have an effect on radionuclide migration and retardation. This work focuses on experiments designed to simulate the evolution of the alkaline plume from the GDF, to evaluate the spatial and temporal distribution of mineral alteration within the CDZ, and to quantify its impact on porosity and permeability. The results presented here represent a summary of the mineralogical observations from Stage 1 of the column experiments, which investigate the interaction of a K-Ca-rich Young Cement Leachate (pH 13.1) with a "model" host rock. Significant interaction is observed within the reacted columns, with physical movement of fines, dissolution of silicate minerals, and the precipitation of secondary K-Al-bearing calcium silicate hydrate phases, all of which will impact on the transport properties of the host rock.
The London Information Office also maintains a reference collection of BGS publications including... more The London Information Office also maintains a reference collection of BGS publications including maps for consultation. The Survey publishes an annual catalogue of its maps and other publications; this catalogue is available from any of the BGS Sales Desks. The British Geological Survey carries out the geological survey of Great Britain and Northern Ireland (the latter as an agency service for the government of Northern Ireland), and of the surrounding continental shelf, as well as its basic research projects. It also undertakes programmes of British technical aid in geology in developing countries as arranged by the Department for International Development and other agencies. The British Geological Survey is a component body of the Natural Environment Research Council.
This report is a published product of a study by the British Geological Survey (BGS) into the shr... more This report is a published product of a study by the British Geological Survey (BGS) into the shrinking and swelling of London Clay. This is a factual laboratory report showing the results of a suite of tests carried out on samples collected from the London Clay Formation of southeast UK. The study of the London Clay Formation is the fifth phase of the BGS project entitled "The shrinkage and swelling behaviour of UK clay soils", the others having dealt with the clays of the Gault Formation, the mudstones of the Mercia Mudstone Group, the clays of the Lambeth Group, and the Lias Group. Contents
The surveying setup , weighing more than 50kg, deployed on the glacial foreland, Virkisjökull, Ic... more The surveying setup , weighing more than 50kg, deployed on the glacial foreland, Virkisjökull, Iceland. *This is a rocky promontory where in 1788 James Hutton made one of the fundamental breakthroughs in the history of geology. He realised that rock formations created at different times and by different forces came together here, providing compelling evidence for his theories on the Earth's age and on the forces that shape it.
Journal of Geophysical Research: Earth Surface, 2013
Since 2007, Falljökull in southeast Iceland has been undergoing passive downwasting, providing an... more Since 2007, Falljökull in southeast Iceland has been undergoing passive downwasting, providing an ideal opportunity to study a range deformation structures developed in response to ice-marginal collapse and retreat. An integrated terrestrial lidar, Ground Penetrating Radar, and glaciological structural study of the clean, debris-free ice at the margin of Falljökull has allowed a detailed model of the surface and subsurface 3D structure to be developed. Collapse of the glacier margin takes the form of a multiple rotational failure controlled by large-scale, down-ice dipping normal faults. As the fault-bound blocks of ice are displaced downslope, they rotate leading to localized compression and the formation of down-faulted graben-like structures. Moulins present within the marginal zone of Falljökull are closely associated with the zones of relatively more intense brittle deformation which crosscut the glacier. A model is proposed where the moulins have formed in response to the progressive collapse of englacial drainage channels located along down-ice dipping normal faults. The preferential development of the moulins and englacial drainage channels along the normal faults weakens the ice along these structures, promoting or even accelerating further collapse of the ice margin. The complex pattern of surface lowering within the marginal zone of Falljökull has also been shown to be directly related to movement on the main faults controlling the collapse of the ice margin. This evidence suggests that structurally controlled collapse may, in some instances, have a profound effect on glacier surface lowering and geodetic mass balance measurements.
The Soufrière Hills volcano on the British dependant Caribbean island of Montserrat began to erup... more The Soufrière Hills volcano on the British dependant Caribbean island of Montserrat began to erupt in July 1995, after about 400 years of remaining dormant. Phreatomagmatic explosions were followed by the extrusion of an andesitic lava dome within English crater. Its periodic collapse resulted in the generation of pyroclastic and explosive events, from 1996 onwards. Engineering geologists and geotechnical engineers have been involved in the various stages of the volcanic crises. These have included hazard identification, evaluation and zonation, risk assessments, monitoring, evacuation, exploration, redevelopment and construction. Various ground deformation features were observed, monitored and investigated on the crater walls and expanding lava dome. These included rock falls, pyroclastic flows, explosions, lahars, landslides and distinct, steep-sided subsidence depressions. Secondary geological hazards were also investigated on the island, beyond the area of primary volcanic activ...
Journal of Geophysical Research: Earth Surface, 2014
Over the past two decades Iceland's glaciers have been undergoing a phase of accelerated retreat ... more Over the past two decades Iceland's glaciers have been undergoing a phase of accelerated retreat set against a backdrop of warmer summers and milder winters. This paper demonstrates how the dynamics of a steep outlet glacier in maritime SE Iceland have changed as it adjusts to recent significant changes in mass balance. Geomorphological evidence from Falljökull, a high-mass turnover temperate glacier, clearly shows that between 1990 and 2004 the ice front was undergoing active retreat resulting in seasonal oscillations of its margin. However, in 2004-2006 this glacier crossed an important dynamic threshold and effectively reduced its active length by abandoning its lower reaches to passive retreat processes. A combination of ice surface structural measurements with radar, lidar, and differential Global Navigation Satellite Systems data are used to show that the upper active section of Falljökull is still flowing forward but has become detached from and is being thrust over its stagnant lower section. The reduction in the active length of Falljökull over the last several years has allowed it to rapidly reequilibrate to regional snowline rise in SE Iceland over the past two decades. It is possible that other steep, mountain glaciers around the world may respond in a similar way to significant changes in their mass balance, rapidly adjusting their active length in response to recent atmospheric warming. This paper presents the results of a multidisciplinary study at Falljökull, SE Iceland, (Figure 1a) and shows that this glacier does not fit the simple two-end-member model of retreat. Continuous differential Global Navigation Satellite Systems (GNSS) monitoring of glacier surface velocity over a 12 month period, Ground Penetrating Radar (GPR) and terrestrial light detection and ranging (lidar) surveys, coupled with detailed structural glaciological studies and geomorphological analysis of recent glacial landforms are used to show that Falljökull has undergone an evolving, structurally complex history of retreat which reflect changes in its dynamics. The study, which builds upon the previous work of Bradwell et al. [2013] and Phillips et al. [2013] allows this retreat history to be divided into three stages, each corresponding to changes in glaciological response as it retreated from a well-constrained position at the end of a significant ice front advance between 1970 and 1990 [Sigurðsson et al., 2007; Bradwell et al., 2013]. A structural glaciological model is proposed by which Falljökull and potentially other Alpine-type glaciers with steep gradients can rapidly adapt to negative changes in their mass balance by reducing their active length.
The full range of Survey publications is available from the BGS Sales Desks at Nottingham and Edi... more The full range of Survey publications is available from the BGS Sales Desks at Nottingham and Edinburgh; see contact details below or shop online at www.thebgs.co.uk The London Information Office maintains a reference collection of BGS publications including maps for consultation. The Survey publishes an annual catalogue of its maps and other publications; this catalogue is available from any of the BGS Sales Desks. The British Geological Survey carries out the geological survey of Great Britain and Northern Ireland (the latter as an agency service for the government of Northern Ireland), and of the surrounding continental shelf, as well as its basic research projects. It also undertakes programmes of British technical aid in geology in developing countries as arranged by the Department for International Development and other agencies. The British Geological Survey is a component body of the Natural Environment Research Council.
A new apparatus for the determination of shrinkage limit is described. Two versions have been pro... more A new apparatus for the determination of shrinkage limit is described. Two versions have been produced: a manually operated prototype ‘version1' followed by an automated version named SHRINKiT. Test results using the former for British and overseas clay soils are described and comparisons made with the British Standards preferred method. A further set of test results is described for SHRINKiT. However, it was not possible to compare these with the BS 1377 method owing to the introduction of a ban on the use of mercury in the British Geological Survey's geotechnical laboratories. The new method is set in the context of the huge cost of shrink/swell-related subsidence damage in Britain and the relative disuse of both BS 1377 methods for shrinkage limit, for reasons of safety. The shrinkage behaviour of different soils types and sample states is discussed, in addition to the advantages and disadvantages of the new method.
The effective porosity, saturated sonic velocity and saturated uniaxial compressive strength were... more The effective porosity, saturated sonic velocity and saturated uniaxial compressive strength were determined on a large number of Borrowdale Volcanic Group volcaniclastic core samples from three boreholes at Sellafield, Cumbria. The worked formed part of the UK Nirex Limited site investigation into whether the Sellafield area could be suitable as a repository for intermediate and low level radioactive waste. Most of the intact samples were of low to very low effective porosity, had a high sonic velocity and were very strong to extremely strong. However, a proportion of values deviated significantly from this. Bivariate analysis showed a negative relationship exists between sonic velocity and effective porosity. The cross plots of these two parameters with uniaxial compressive strength showed a wide range of strength values for samples of low effective porosity and high sonic velocity. Six failure types were identified during the uniaxial compressive strength tests. The strongest samples tended to fail through the matrix and the weakest rock samples tended to fail through haematized material or along haematized veins. Effective porosity and sonic velocity measurements could not distinguish between those samples that failed through the matrix and those that failed along discrete narrow veins. The presence of narrow haematized veins has a major effect on the intact rock strength.
Geological Society, London, Special Publications, 2010
The paper describes recent applications by the British Geological Survey (BGS) of the technique o... more The paper describes recent applications by the British Geological Survey (BGS) of the technique of mobile terrestrial LiDAR surveying to monitor various geomorphological changes on English coasts and estuaries. These include cliff recession, landslides and flood defences, and are usually sited at remote locations undergoing dynamic processes with no fixed reference points. Advantages, disadvantages and some practical problems are discussed. The role of GPS in laser scanning is described.
Ground Penetrating Radar (GPR) offers a relatively rapid and non-intrusive method for detecting b... more Ground Penetrating Radar (GPR) offers a relatively rapid and non-intrusive method for detecting buried utilities. In congested urban environments, where most buried utilities are to be found, this translates into significantly reduced disruption to highway users and reduced risk for developers and contractors. However, GPR performance varies significantly over large geographical areas due to variations in soil type and water content. Therefore, GPR utility location can be perceived by clients as largely hit-and-miss in terms of its planning, as full information may not be known in advance for determination of expected penetration depths and the most appropriate signal frequency ranges. This paper details the current state of predictive soil electromagnetic property mapping, from which it will be concluded that existing geotechnical databases and techniques can provide useful data on which to base such maps. In so doing, it also extends knowledge on the efficacy of predictive mapping for potential use internationally.
This report is the published product of a study by the British Geological Survey (BGS) and detail... more This report is the published product of a study by the British Geological Survey (BGS) and details the methodology, results and conclusions of an annual and biannual monitoring programme of coastal landslides at three test sites on the North Norfolk coast from 2000 to 2006. The three sites are coastal sections at Happisburgh, Sidestrand and Weybourne.
Expansive soils present significant geotechnical and structural engineering challenges the world ... more Expansive soils present significant geotechnical and structural engineering challenges the world over, with costs associated with expansive behaviour estimated to run into several billion annually. Expansive soils are soils that experience significant volume change associated with changes in water contents. These volume changes can either in the form of swell or in the form shrinkage and this is why they are sometime known as swell/shrink soils. Key aspects that need identification when dealing with expansive soils include: soil properties, suction/water conditions, water content variations temporal and spatial, e.g. generated by trees, and the geometry/stiffness of foundations and associated structures. Expansive soils can be found in humid environments where expansive problems occur with soils of high Plasticity Index (Ip) or in arid/semi arid soils where soils of even moderate expansiveness can cause significant damage. In the UK damage often occurs as a direct result of interact...
Proceedings Of The 16th Multidisciplinary Conference On Sinkholes And The Engineering And Environmental Impacts Of Karst, 2020
Ripon is a historic city and market town in North Yorkshire. It is unique in being the only city ... more Ripon is a historic city and market town in North Yorkshire. It is unique in being the only city in the UK to define planning zones based on the potential for bedrock dissolution. The underlying geology comprises marls, limestone and gypsum of the Permian Edlington, Brotherton and Roxby formations, capped by glacial deposits (till). It is the rapid rate of dissolution of the gypsum (hydrated calcium sulphate) that enables the karst to evolve on human time scales. Following the collapse that formed a sinkhole in the rear garden of a property in Magdalens Road, Ripon, UK in November 2016 the British Geological Survey, funded by a Natural Environment Research Council grant, initiated a programme of monitoring of a nearby depression. This feature is forming in a recreation area and is one that local residents reported to have grown in dimensions. The density of development precludes the use of satellite-based monitoring systems. Instead, we have integrated ground-based LiDAR imaging with geophysical techniques (micro-gravity and passive seismic). Monitoring has revealed that this depression lies over a palaeosinkhole that is in the order of 10 m in diameter and extends to a depth of a similar order of magnitude. The monitoring has been continued in the context of PhD research (University of Sheffield) that is more broadly focused on understanding sinkhole triggering processes. The developing sinkhole is on the eastern side of Ripon close to the southerly flowing River Ure, where upwelling confined groundwater contributes to the river base flow. In this context the hypotheses that growth can be correlated with rainfall or river discharge can be tested.
The current UK concept for the disposal of low-and intermediate-level radioactive wastes involves... more The current UK concept for the disposal of low-and intermediate-level radioactive wastes involves a mined geological disposal facility (GDF) located several hundreds of metres below the surface. The waste material will be encapsulated in a cementitious matrix within steel or concrete containers, and will be placed in disposal vaults backfilled with a cement-based material. After closure, the vaults will saturate with groundwater and become part of a modified regional groundwater flow system. Groundwater will equilibrate with the cement and produce an alkaline leachate. This will migrate from the repository into the surrounding rock and produce a 'chemically disturbed zone' (CDZ) with an elevated pH. Reactions will occur between the alkaline waters and the rock, potentially causing mineral dissolution and precipitation, which will modify the local geosphere prior to possible eventual radionuclide release. These changes in the CDZ will be critical controls on radionuclide behaviour and transport, and thus on the safety and environmental impact of a GDF. Consequently, it is desirable to understand these reactions and their impacts in terms of predicting localised changes to the transport properties of the host rock (porosity, permeability) and changes in groundwater flow, together with alteration of minerals and mineral surfaces that may have an effect on radionuclide migration and retardation. This work focuses on experiments designed to simulate the evolution of the alkaline plume from the GDF, to evaluate the spatial and temporal distribution of mineral alteration within the CDZ, and to quantify its impact on porosity and permeability. The results presented here represent a summary of the mineralogical observations from Stage 1 of the column experiments, which investigate the interaction of a K-Ca-rich Young Cement Leachate (pH 13.1) with a "model" host rock. Significant interaction is observed within the reacted columns, with physical movement of fines, dissolution of silicate minerals, and the precipitation of secondary K-Al-bearing calcium silicate hydrate phases, all of which will impact on the transport properties of the host rock.
The London Information Office also maintains a reference collection of BGS publications including... more The London Information Office also maintains a reference collection of BGS publications including maps for consultation. The Survey publishes an annual catalogue of its maps and other publications; this catalogue is available from any of the BGS Sales Desks. The British Geological Survey carries out the geological survey of Great Britain and Northern Ireland (the latter as an agency service for the government of Northern Ireland), and of the surrounding continental shelf, as well as its basic research projects. It also undertakes programmes of British technical aid in geology in developing countries as arranged by the Department for International Development and other agencies. The British Geological Survey is a component body of the Natural Environment Research Council.
This report is a published product of a study by the British Geological Survey (BGS) into the shr... more This report is a published product of a study by the British Geological Survey (BGS) into the shrinking and swelling of London Clay. This is a factual laboratory report showing the results of a suite of tests carried out on samples collected from the London Clay Formation of southeast UK. The study of the London Clay Formation is the fifth phase of the BGS project entitled "The shrinkage and swelling behaviour of UK clay soils", the others having dealt with the clays of the Gault Formation, the mudstones of the Mercia Mudstone Group, the clays of the Lambeth Group, and the Lias Group. Contents
The surveying setup , weighing more than 50kg, deployed on the glacial foreland, Virkisjökull, Ic... more The surveying setup , weighing more than 50kg, deployed on the glacial foreland, Virkisjökull, Iceland. *This is a rocky promontory where in 1788 James Hutton made one of the fundamental breakthroughs in the history of geology. He realised that rock formations created at different times and by different forces came together here, providing compelling evidence for his theories on the Earth's age and on the forces that shape it.
Journal of Geophysical Research: Earth Surface, 2013
Since 2007, Falljökull in southeast Iceland has been undergoing passive downwasting, providing an... more Since 2007, Falljökull in southeast Iceland has been undergoing passive downwasting, providing an ideal opportunity to study a range deformation structures developed in response to ice-marginal collapse and retreat. An integrated terrestrial lidar, Ground Penetrating Radar, and glaciological structural study of the clean, debris-free ice at the margin of Falljökull has allowed a detailed model of the surface and subsurface 3D structure to be developed. Collapse of the glacier margin takes the form of a multiple rotational failure controlled by large-scale, down-ice dipping normal faults. As the fault-bound blocks of ice are displaced downslope, they rotate leading to localized compression and the formation of down-faulted graben-like structures. Moulins present within the marginal zone of Falljökull are closely associated with the zones of relatively more intense brittle deformation which crosscut the glacier. A model is proposed where the moulins have formed in response to the progressive collapse of englacial drainage channels located along down-ice dipping normal faults. The preferential development of the moulins and englacial drainage channels along the normal faults weakens the ice along these structures, promoting or even accelerating further collapse of the ice margin. The complex pattern of surface lowering within the marginal zone of Falljökull has also been shown to be directly related to movement on the main faults controlling the collapse of the ice margin. This evidence suggests that structurally controlled collapse may, in some instances, have a profound effect on glacier surface lowering and geodetic mass balance measurements.
The Soufrière Hills volcano on the British dependant Caribbean island of Montserrat began to erup... more The Soufrière Hills volcano on the British dependant Caribbean island of Montserrat began to erupt in July 1995, after about 400 years of remaining dormant. Phreatomagmatic explosions were followed by the extrusion of an andesitic lava dome within English crater. Its periodic collapse resulted in the generation of pyroclastic and explosive events, from 1996 onwards. Engineering geologists and geotechnical engineers have been involved in the various stages of the volcanic crises. These have included hazard identification, evaluation and zonation, risk assessments, monitoring, evacuation, exploration, redevelopment and construction. Various ground deformation features were observed, monitored and investigated on the crater walls and expanding lava dome. These included rock falls, pyroclastic flows, explosions, lahars, landslides and distinct, steep-sided subsidence depressions. Secondary geological hazards were also investigated on the island, beyond the area of primary volcanic activ...
Journal of Geophysical Research: Earth Surface, 2014
Over the past two decades Iceland's glaciers have been undergoing a phase of accelerated retreat ... more Over the past two decades Iceland's glaciers have been undergoing a phase of accelerated retreat set against a backdrop of warmer summers and milder winters. This paper demonstrates how the dynamics of a steep outlet glacier in maritime SE Iceland have changed as it adjusts to recent significant changes in mass balance. Geomorphological evidence from Falljökull, a high-mass turnover temperate glacier, clearly shows that between 1990 and 2004 the ice front was undergoing active retreat resulting in seasonal oscillations of its margin. However, in 2004-2006 this glacier crossed an important dynamic threshold and effectively reduced its active length by abandoning its lower reaches to passive retreat processes. A combination of ice surface structural measurements with radar, lidar, and differential Global Navigation Satellite Systems data are used to show that the upper active section of Falljökull is still flowing forward but has become detached from and is being thrust over its stagnant lower section. The reduction in the active length of Falljökull over the last several years has allowed it to rapidly reequilibrate to regional snowline rise in SE Iceland over the past two decades. It is possible that other steep, mountain glaciers around the world may respond in a similar way to significant changes in their mass balance, rapidly adjusting their active length in response to recent atmospheric warming. This paper presents the results of a multidisciplinary study at Falljökull, SE Iceland, (Figure 1a) and shows that this glacier does not fit the simple two-end-member model of retreat. Continuous differential Global Navigation Satellite Systems (GNSS) monitoring of glacier surface velocity over a 12 month period, Ground Penetrating Radar (GPR) and terrestrial light detection and ranging (lidar) surveys, coupled with detailed structural glaciological studies and geomorphological analysis of recent glacial landforms are used to show that Falljökull has undergone an evolving, structurally complex history of retreat which reflect changes in its dynamics. The study, which builds upon the previous work of Bradwell et al. [2013] and Phillips et al. [2013] allows this retreat history to be divided into three stages, each corresponding to changes in glaciological response as it retreated from a well-constrained position at the end of a significant ice front advance between 1970 and 1990 [Sigurðsson et al., 2007; Bradwell et al., 2013]. A structural glaciological model is proposed by which Falljökull and potentially other Alpine-type glaciers with steep gradients can rapidly adapt to negative changes in their mass balance by reducing their active length.
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