H. Haflidason | University of Bergen (original) (raw)

Papers by H. Haflidason

Research paper thumbnail of Stratigraphy of fossil pigments and Cladophora and its relationship with deposition of tephra in Lake M�vatn, Iceland

Journal of Paleolimnology, 1993

Fossil plant pigments and Cladophora fragments were analyzed in a 6.53 m long sediment profile fr... more Fossil plant pigments and Cladophora fragments were analyzed in a 6.53 m long sediment profile from Lake M~vatn, Iceland, covering most of its history of about 2300 years. A decrease in myxoxanthophyll (produced by Cyanobacteria) with time and an increase in the benthic Cladophora reflects a gradual shift from planktonic to benthic primary production as water depth is reduced (to 3.15 m at the core site) because of sediment accumulation.

Research paper thumbnail of The Cenozoic western Svalbard margin: sediment geometry and sedimentary processes in an area of ultraslow oceanic spreading

Marine Geophysical Research, 2011

Research paper thumbnail of Postglacial mass movements and depositional environments in a high-latitude fjord system – Hardangerfjorden, Western Norway

Research paper thumbnail of Postglacial Mass Failures in the Inner Hardangerfjorden System, Western Norway

Advances in Natural and Technological Hazards Research, 2016

Research paper thumbnail of Slope failure dynamics and impacts from seafloor and shallow sub-seafloor geophysical data: case studies from the COSTA project

Marine Geology, 2004

Holocene and slightly pre-Holocene submarine landslide are found both in high-latitude glacial-do... more Holocene and slightly pre-Holocene submarine landslide are found both in high-latitude glacial-dominated margins and in lower latitude, river-dominated margins. This paper constitutes a major assessment on some of the best-studied submarine instabilities in the world. We review and update from original data and literature reports the current state of knowledge of Storegga, Traenadjupet and Finneidfjord slides from the mid-Norwegian margin, Afen Slide from the Faeroe-Shetland Channel,

Research paper thumbnail of The mid-Norwegian margin gas hydrate province: trace of slope stability and geo-hazard through time

Gas hydrate is stable in marine sediments on many Arctic continental slopes under present tempera... more Gas hydrate is stable in marine sediments on many Arctic continental slopes under present temperature and pressure fields. Yet, changes in the physical conditions have been shown to trigger dissolution and emanation of methane into the ocean. Access to a huge database of 2D and 3D seismic records, covering the entire mid-Norwegian margin, now provide an exceptional opportunity to test the relationship between methane release and slope stability. On the mid-Norwegian margin wedges of thick glacigenic units were deposited during past glacial intervals and covers older sequences of fine-grained hemipelagic siliceous ooze. This stratigraphic architecture combined with subsidence, large amount of biogenic methane, deep thermogenic methane reservoirs and thermal processes, provide a natural laboratory where to study the development and dynamics of methane hydrates and other digenetic processes through Cenozoic time.
Gas hydrate bearing sediments are commonly detected in our seismic profiles by the presence of cross-cutting bottom simulating reflectors (BSR’s). We also recognize the presence of a second, deeper BSR. This reflector has previously been interpreted as a fossil base of the gas hydrate stability zone caused by hydrate dissociation during postglacial sea level rise and increase bottom water temperature. Several submarine slides confine the spatial distribution of present day gas hydrates, whereas the occurrence of the second BSR is patchy and discontinuous, but appears to be detached from the mass wasting structures. This observation indicates the possible link between methane dissociation and migration from the deeper BSR to the present-day gas hydrate stability depth with ocean floor destabilization at different temporal scales. The presence of a diagenetic-related BSR deeper in the stratigraphical sequence may also suggest thermal gradient increase at depth, thus providing a complementary scenario for methane hydrates dynamics through time.

Research paper thumbnail of Gas Hydrates on the Mid-Norwegian Continental Margin: Pacemakers of Slope Stability Through Time

Research paper thumbnail of Dynamic response of gas hydrates to lithological changes: evidence from the Mid-Norwegian continental margin

Unconventional petroleum resources, including gas hydrates, offer particular challenge for future... more Unconventional petroleum resources, including gas hydrates, offer particular challenge for future production. These resources are developed and stored in ways that make many of the conventional methodologies less applicable. Development of a comparable set of theories and methodologies for commercial viability of gas hydrate as an energy source has lagged behind, despite the great importance of new alternative resources for potential future exploitation. Gas hydrate is stable in marine sediments on sub-Arctic and Arctic continental slopes under present temperature and pressure fields. The extent of these deposits can usually be inferred from seismic imaging, in which the base of the methane hydrate stability zone is frequently identifiable by a bottom simulating reflector (BSR).
New insights from extensive coverage of 2D/3D seismic data have confirmed the spatial distribution of gas hydrates on the mid-Norwegian continental margin. Supplemental shallow boring datasets provides essential information about the lithological and sedimentological constrains of gas hydrates. Off mid-Norway, wedges of thick glacigenic units were deposited during past glacial intervals and covers older sequences of fine-grained hemipelagic siliceous ooze. This stratigraphic architecture combined with subsidence, large amount of biogenic methane, deep thermogenic methane reservoirs and thermal processes, provide a natural laboratory where to study the development and dynamics of methane hydrates through time. Due to the high stratigraphical resolution and good data coverage in this site, amalgamation of seismic and core data offer an unusual opportunity to investigate the dynamic behavior of gas hydrates bearing reservoirs and their relationship with slope stability and methane release through time.

Research paper thumbnail of Gas Hydrates on the Norway-Barents Sea-Svalbard margin (GANS); an overview and preliminary results

The Norwegian national gas hydrate project, GANS (Gas Hydrates on the Norway -Barents Sea -Svalba... more The Norwegian national gas hydrate project, GANS (Gas Hydrates on the Norway -Barents Sea -Svalbard margin), has the main objective to quantify gas accumulations in the form of hydrates in sediments on the Norway-Barents Sea-Svalbard margin. This has also included an assessment of their dynamics and impacts on the seabed, to provide knowledge vital for a safe exploitation within oil and gas production. To achieve the main objective the following subgoals were also defined: a) Geophysical characterisation of gas hydrates, b) Geological and geochemical setting of gas hydrate reservoirs and seeps, c) Gas hydrate dissociation and its effects on geomechanical properties, d) Theoretical and experimental evaluation of gas hydrate dynamics. Three contrasting target areas were selected for broad geophysical, geological and geochemical studies. An overview of the results achieved within this project so far will be presented, with emphasis on the multidisciplinary studies carried out.

Research paper thumbnail of Sensitivity of the North Atlantic circulation to break-up of the marine sectors of the NW European ice sheets during the last Glacial: A synthesis of modelling and palaeoceanography

Global and Planetary Change, 2012

ABSTRACT The marine-based Atlantic periphery of the last NW European Ice Sheet experienced signif... more ABSTRACT The marine-based Atlantic periphery of the last NW European Ice Sheet experienced significant advances and retreats of its marine sector during its existence. It therefore had considerable potential to intermittently inject freshwater or ice pulses to the North Atlantic. These European inputs had poorly known consequences for ocean circulation and climate. Here we examine the history of the western margin of the European Ice Sheet, from 34 to 15 cal ka BP, and use a combination of modelling and proxy evidence to explore the impact on the North Atlantic of the fresh water and iceberg injections that accompanied phases of retreat of the marine sector of the NW European Ice Sheet. We find that the lack of geographical synchronicity in the responses of the different components of the 3000 km long sector meant that the scale of the climate consequences of ice discharge most likely remained regional, except during the final deglaciation phase, around 17–15 cal ka BP. At this time, as the later component of the recently introduced concept of an extended Heinrich event H1, both proxy and modelling evidence suggest rapid sector collapse led to partial shut-down of the Atlantic overturning and a basin-wide cooling.

Research paper thumbnail of Deglaciation history of the southwestern Fennoscandian Ice Sheet between 15 and 13 14C ka BP

Research paper thumbnail of The Storegga Slide Complex; Repeated Large Scale Sliding in Response to Climatic Cyclicity

Advances in Natural and Technological Hazards Research, 2003

... Oozes are mainly of the Oligocene to Late Pliocene Brygge and Kai Formations Property Glacial... more ... Oozes are mainly of the Oligocene to Late Pliocene Brygge and Kai Formations Property Glacialclay Marine clay Ooze Clay content 30-40% 50-60% 30-55% Water content 10-20% 25-35% 70-90% Unit weight 20-22 kN/m3 18-19 kN/m3 c. 15 kN/m3 Sensitivity Low Higher High ...

Research paper thumbnail of Paleoceanographic changes and calcium carbonate dissolution in the central Fram Strait during the last 20ka

Quaternary Research (United States), 2012

A deep-sea sediment core covering the last 20 ka and located between the Polar and the Arctic fro... more A deep-sea sediment core covering the last 20 ka and located between the Polar and the Arctic fronts in the marginal ice zone (MIZ) of the central Fram Strait has been investigated for changes in paleoceanography and calcium carbonate preservation. The reconstruction is based on the distribution patterns of planktic foraminifera, mean shell weight and the degree of fragmentation of their shells, stable isotopes and other geochemical and sedimentological data. The results show that the planktic foraminifera shells are poorly preserved throughout most of the record. Only the intervals comprising the early Holocene from 10.8 to~8 cal ka BP and the last 800 yr show improved preservation of CaCO 3 . The dissolution correlated with the extent of Arctic water and the associated marginal ice zone (MIZ) and high organic productivity. Dissolution of planktic foraminifera is generally high during the late deglaciation, mid and late Holocene prior to~800 cal yr BP. The abundance of small subpolar species increases in the surface sediments dating from the last century, which could be interpreted as a large and significant surface water warming. However, this apparent high-magnitude warming seems to be overestimated due to preservation changes in the youngest sediments.

Research paper thumbnail of Stability, mobility and failure mechanism for landslides at the upper continental slope off Vesterålen, Norway

Marine Geology, 2013

Several relatively small and spatially-isolated landslides with low mobility characterise the geo... more Several relatively small and spatially-isolated landslides with low mobility characterise the geomorphology of the upper continental slope off the Vesterålen islands. Here, we present results from a multidisciplinary study that integrates swath bathymetry data, high-resolution seismic reflection profiles and a multitude of geological and geotechnical laboratory tests from a 12 m long piston core in order to investigate the origin and hazard potential of these shallow landslides.

Research paper thumbnail of The tephrochronology of Iceland and the North Atlantic region during the Middle and Late Quaternary: a review

Journal of Quaternary Science, 2000

The tephrochronology of Iceland and the North Atlantic region is reviewed in order to construct a... more The tephrochronology of Iceland and the North Atlantic region is reviewed in order to construct a unified framework for the last 400 kyr BP. Nearly all of the tephra layers described are also characterised geochemically. A number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre-Holocene tephra layers have been given an informal denotation. The tephrostratigraphy of Ash Zone II is highlighted. Where possible the rhyolitic tephra layers found outside Iceland have been correlated to known Icelandic tephra layers or to the volcanic source area. The application of tephra fallout in various depositional environments is described and discussed.

Research paper thumbnail of Extreme sediment and ice discharge from marine-based ice streams: New evidence from the North Sea

Geology, 2007

A major problem for understanding the dynamics of ice streams has been a lack of precise data on ... more A major problem for understanding the dynamics of ice streams has been a lack of precise data on ice streaming longevity and sediment transport efficacy. Here we present the first well-constrained data on sediment flux from a paleoice stream. This has been achieved by computing the volume of sediment deposited as debris flows on the fan located at the outlet

Research paper thumbnail of Configuration, history and impact of the Norwegian Channel Ice Stream

Research paper thumbnail of Issues in the Assessment of Gravity Mass Flow Hazard in the Storegga Area Off the Western Norwegian Coast

Advances in Natural and Technological Hazards Research, 2003

Statistical analysis of the lobes of the Storegga slide reveals a power-law dependence of the run... more Statistical analysis of the lobes of the Storegga slide reveals a power-law dependence of the runout distance on the release volume. For small to moderate volumes, visco-plastic models with a (remoulded) yield strength of about 10 kPa reproduce this dependence quite well, in contrast to granular-friction models. However, either progressive wetting of the bottom shear layer or hydroplaning has to be invoked to explain the extreme runout distance and the sediment distribution of the largest slide phase. Preliminary estimates of the turbidite volume put severe constraints on the formation rate and density of the turbidity currents accompanying the slide.

Research paper thumbnail of Stratigraphy of fossil pigments and Cladophora and its relationship with deposition of tephra in Lake M�vatn, Iceland

Journal of Paleolimnology, 1993

Fossil plant pigments and Cladophora fragments were analyzed in a 6.53 m long sediment profile fr... more Fossil plant pigments and Cladophora fragments were analyzed in a 6.53 m long sediment profile from Lake M~vatn, Iceland, covering most of its history of about 2300 years. A decrease in myxoxanthophyll (produced by Cyanobacteria) with time and an increase in the benthic Cladophora reflects a gradual shift from planktonic to benthic primary production as water depth is reduced (to 3.15 m at the core site) because of sediment accumulation.

Research paper thumbnail of The Cenozoic western Svalbard margin: sediment geometry and sedimentary processes in an area of ultraslow oceanic spreading

Marine Geophysical Research, 2011

Research paper thumbnail of Postglacial mass movements and depositional environments in a high-latitude fjord system – Hardangerfjorden, Western Norway

Research paper thumbnail of Postglacial Mass Failures in the Inner Hardangerfjorden System, Western Norway

Advances in Natural and Technological Hazards Research, 2016

Research paper thumbnail of Slope failure dynamics and impacts from seafloor and shallow sub-seafloor geophysical data: case studies from the COSTA project

Marine Geology, 2004

Holocene and slightly pre-Holocene submarine landslide are found both in high-latitude glacial-do... more Holocene and slightly pre-Holocene submarine landslide are found both in high-latitude glacial-dominated margins and in lower latitude, river-dominated margins. This paper constitutes a major assessment on some of the best-studied submarine instabilities in the world. We review and update from original data and literature reports the current state of knowledge of Storegga, Traenadjupet and Finneidfjord slides from the mid-Norwegian margin, Afen Slide from the Faeroe-Shetland Channel,

Research paper thumbnail of The mid-Norwegian margin gas hydrate province: trace of slope stability and geo-hazard through time

Gas hydrate is stable in marine sediments on many Arctic continental slopes under present tempera... more Gas hydrate is stable in marine sediments on many Arctic continental slopes under present temperature and pressure fields. Yet, changes in the physical conditions have been shown to trigger dissolution and emanation of methane into the ocean. Access to a huge database of 2D and 3D seismic records, covering the entire mid-Norwegian margin, now provide an exceptional opportunity to test the relationship between methane release and slope stability. On the mid-Norwegian margin wedges of thick glacigenic units were deposited during past glacial intervals and covers older sequences of fine-grained hemipelagic siliceous ooze. This stratigraphic architecture combined with subsidence, large amount of biogenic methane, deep thermogenic methane reservoirs and thermal processes, provide a natural laboratory where to study the development and dynamics of methane hydrates and other digenetic processes through Cenozoic time.
Gas hydrate bearing sediments are commonly detected in our seismic profiles by the presence of cross-cutting bottom simulating reflectors (BSR’s). We also recognize the presence of a second, deeper BSR. This reflector has previously been interpreted as a fossil base of the gas hydrate stability zone caused by hydrate dissociation during postglacial sea level rise and increase bottom water temperature. Several submarine slides confine the spatial distribution of present day gas hydrates, whereas the occurrence of the second BSR is patchy and discontinuous, but appears to be detached from the mass wasting structures. This observation indicates the possible link between methane dissociation and migration from the deeper BSR to the present-day gas hydrate stability depth with ocean floor destabilization at different temporal scales. The presence of a diagenetic-related BSR deeper in the stratigraphical sequence may also suggest thermal gradient increase at depth, thus providing a complementary scenario for methane hydrates dynamics through time.

Research paper thumbnail of Gas Hydrates on the Mid-Norwegian Continental Margin: Pacemakers of Slope Stability Through Time

Research paper thumbnail of Dynamic response of gas hydrates to lithological changes: evidence from the Mid-Norwegian continental margin

Unconventional petroleum resources, including gas hydrates, offer particular challenge for future... more Unconventional petroleum resources, including gas hydrates, offer particular challenge for future production. These resources are developed and stored in ways that make many of the conventional methodologies less applicable. Development of a comparable set of theories and methodologies for commercial viability of gas hydrate as an energy source has lagged behind, despite the great importance of new alternative resources for potential future exploitation. Gas hydrate is stable in marine sediments on sub-Arctic and Arctic continental slopes under present temperature and pressure fields. The extent of these deposits can usually be inferred from seismic imaging, in which the base of the methane hydrate stability zone is frequently identifiable by a bottom simulating reflector (BSR).
New insights from extensive coverage of 2D/3D seismic data have confirmed the spatial distribution of gas hydrates on the mid-Norwegian continental margin. Supplemental shallow boring datasets provides essential information about the lithological and sedimentological constrains of gas hydrates. Off mid-Norway, wedges of thick glacigenic units were deposited during past glacial intervals and covers older sequences of fine-grained hemipelagic siliceous ooze. This stratigraphic architecture combined with subsidence, large amount of biogenic methane, deep thermogenic methane reservoirs and thermal processes, provide a natural laboratory where to study the development and dynamics of methane hydrates through time. Due to the high stratigraphical resolution and good data coverage in this site, amalgamation of seismic and core data offer an unusual opportunity to investigate the dynamic behavior of gas hydrates bearing reservoirs and their relationship with slope stability and methane release through time.

Research paper thumbnail of Gas Hydrates on the Norway-Barents Sea-Svalbard margin (GANS); an overview and preliminary results

The Norwegian national gas hydrate project, GANS (Gas Hydrates on the Norway -Barents Sea -Svalba... more The Norwegian national gas hydrate project, GANS (Gas Hydrates on the Norway -Barents Sea -Svalbard margin), has the main objective to quantify gas accumulations in the form of hydrates in sediments on the Norway-Barents Sea-Svalbard margin. This has also included an assessment of their dynamics and impacts on the seabed, to provide knowledge vital for a safe exploitation within oil and gas production. To achieve the main objective the following subgoals were also defined: a) Geophysical characterisation of gas hydrates, b) Geological and geochemical setting of gas hydrate reservoirs and seeps, c) Gas hydrate dissociation and its effects on geomechanical properties, d) Theoretical and experimental evaluation of gas hydrate dynamics. Three contrasting target areas were selected for broad geophysical, geological and geochemical studies. An overview of the results achieved within this project so far will be presented, with emphasis on the multidisciplinary studies carried out.

Research paper thumbnail of Sensitivity of the North Atlantic circulation to break-up of the marine sectors of the NW European ice sheets during the last Glacial: A synthesis of modelling and palaeoceanography

Global and Planetary Change, 2012

ABSTRACT The marine-based Atlantic periphery of the last NW European Ice Sheet experienced signif... more ABSTRACT The marine-based Atlantic periphery of the last NW European Ice Sheet experienced significant advances and retreats of its marine sector during its existence. It therefore had considerable potential to intermittently inject freshwater or ice pulses to the North Atlantic. These European inputs had poorly known consequences for ocean circulation and climate. Here we examine the history of the western margin of the European Ice Sheet, from 34 to 15 cal ka BP, and use a combination of modelling and proxy evidence to explore the impact on the North Atlantic of the fresh water and iceberg injections that accompanied phases of retreat of the marine sector of the NW European Ice Sheet. We find that the lack of geographical synchronicity in the responses of the different components of the 3000 km long sector meant that the scale of the climate consequences of ice discharge most likely remained regional, except during the final deglaciation phase, around 17–15 cal ka BP. At this time, as the later component of the recently introduced concept of an extended Heinrich event H1, both proxy and modelling evidence suggest rapid sector collapse led to partial shut-down of the Atlantic overturning and a basin-wide cooling.

Research paper thumbnail of Deglaciation history of the southwestern Fennoscandian Ice Sheet between 15 and 13 14C ka BP

Research paper thumbnail of The Storegga Slide Complex; Repeated Large Scale Sliding in Response to Climatic Cyclicity

Advances in Natural and Technological Hazards Research, 2003

... Oozes are mainly of the Oligocene to Late Pliocene Brygge and Kai Formations Property Glacial... more ... Oozes are mainly of the Oligocene to Late Pliocene Brygge and Kai Formations Property Glacialclay Marine clay Ooze Clay content 30-40% 50-60% 30-55% Water content 10-20% 25-35% 70-90% Unit weight 20-22 kN/m3 18-19 kN/m3 c. 15 kN/m3 Sensitivity Low Higher High ...

Research paper thumbnail of Paleoceanographic changes and calcium carbonate dissolution in the central Fram Strait during the last 20ka

Quaternary Research (United States), 2012

A deep-sea sediment core covering the last 20 ka and located between the Polar and the Arctic fro... more A deep-sea sediment core covering the last 20 ka and located between the Polar and the Arctic fronts in the marginal ice zone (MIZ) of the central Fram Strait has been investigated for changes in paleoceanography and calcium carbonate preservation. The reconstruction is based on the distribution patterns of planktic foraminifera, mean shell weight and the degree of fragmentation of their shells, stable isotopes and other geochemical and sedimentological data. The results show that the planktic foraminifera shells are poorly preserved throughout most of the record. Only the intervals comprising the early Holocene from 10.8 to~8 cal ka BP and the last 800 yr show improved preservation of CaCO 3 . The dissolution correlated with the extent of Arctic water and the associated marginal ice zone (MIZ) and high organic productivity. Dissolution of planktic foraminifera is generally high during the late deglaciation, mid and late Holocene prior to~800 cal yr BP. The abundance of small subpolar species increases in the surface sediments dating from the last century, which could be interpreted as a large and significant surface water warming. However, this apparent high-magnitude warming seems to be overestimated due to preservation changes in the youngest sediments.

Research paper thumbnail of Stability, mobility and failure mechanism for landslides at the upper continental slope off Vesterålen, Norway

Marine Geology, 2013

Several relatively small and spatially-isolated landslides with low mobility characterise the geo... more Several relatively small and spatially-isolated landslides with low mobility characterise the geomorphology of the upper continental slope off the Vesterålen islands. Here, we present results from a multidisciplinary study that integrates swath bathymetry data, high-resolution seismic reflection profiles and a multitude of geological and geotechnical laboratory tests from a 12 m long piston core in order to investigate the origin and hazard potential of these shallow landslides.

Research paper thumbnail of The tephrochronology of Iceland and the North Atlantic region during the Middle and Late Quaternary: a review

Journal of Quaternary Science, 2000

The tephrochronology of Iceland and the North Atlantic region is reviewed in order to construct a... more The tephrochronology of Iceland and the North Atlantic region is reviewed in order to construct a unified framework for the last 400 kyr BP. Nearly all of the tephra layers described are also characterised geochemically. A number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre-Holocene tephra layers have been given an informal denotation. The tephrostratigraphy of Ash Zone II is highlighted. Where possible the rhyolitic tephra layers found outside Iceland have been correlated to known Icelandic tephra layers or to the volcanic source area. The application of tephra fallout in various depositional environments is described and discussed.

Research paper thumbnail of Extreme sediment and ice discharge from marine-based ice streams: New evidence from the North Sea

Geology, 2007

A major problem for understanding the dynamics of ice streams has been a lack of precise data on ... more A major problem for understanding the dynamics of ice streams has been a lack of precise data on ice streaming longevity and sediment transport efficacy. Here we present the first well-constrained data on sediment flux from a paleoice stream. This has been achieved by computing the volume of sediment deposited as debris flows on the fan located at the outlet

Research paper thumbnail of Configuration, history and impact of the Norwegian Channel Ice Stream

Research paper thumbnail of Issues in the Assessment of Gravity Mass Flow Hazard in the Storegga Area Off the Western Norwegian Coast

Advances in Natural and Technological Hazards Research, 2003

Statistical analysis of the lobes of the Storegga slide reveals a power-law dependence of the run... more Statistical analysis of the lobes of the Storegga slide reveals a power-law dependence of the runout distance on the release volume. For small to moderate volumes, visco-plastic models with a (remoulded) yield strength of about 10 kPa reproduce this dependence quite well, in contrast to granular-friction models. However, either progressive wetting of the bottom shear layer or hydroplaning has to be invoked to explain the extreme runout distance and the sediment distribution of the largest slide phase. Preliminary estimates of the turbidite volume put severe constraints on the formation rate and density of the turbidity currents accompanying the slide.