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Prosjekt: “Slope Stability on Europe’s Passive Continental Margins” Prosjektnr: 158733/V30 Prosjektleder: Professor Juergen Mienert, Institute of Geology, University of Tromsø 2nd year Report: 2005 (with contributions by UiT, UiB, NGI, UiBA, UiCa, AWI) Tromsø 03.10.2005 Abstract During the 2nd year of the project (2005) we have achieved detailed mapping and geotechnical studies of a giant Arctic slide in a seasonally sea- ice covered region north of Svalbard. The two giant and retrogressive slope failures, Storegga slide of the mid-Norwegian margin and Hinlopen slide of the Arctic margin, are now object of a detailed investigation of their glide planes including age dating of the Hinlopen slide. Both submarine slides show clear evidence for multiphase events involving immense volumes of sediments. The headwall heights of the Arctic slide phases are unprecedented, ranging from a few hundred metres to an enormous height of 1400 m. The Arctic Slide is extreme not in terms of the area affected but in terms of the volume of sediments removed from the headwall area due to a very deep cut of the slides into Plio-Pleistocene sediments. Laboratory studies to calculate the effect of gas hydrate melting on pore pressure build up are ongoing. The giant slides and their triggering events on glacially influenced margins appear to concentrate during sea level rise while slides of river influenced margins of the W-Mediterranean concentrate during a lower sea level. Another major achievement was the 2nd International conference on “Submarine mass movements and their consequences” (5-7 Sept. 2005, Oslo ), where we presented our results of the project to an international audience. Moreover, we received (proposed by Locat, Mienert and Urgeles) the UNESCO IGCP-511 for pursuing an international effort in “understanding submarine mass movements and their consequences, including tsunamis”. The secretarial office will be placed at the International Centre of Geohazard (ICG) in Oslo. Our major goals of the 2nd year period (2005) have been reached, and we do report in the following about our results for the five individual projects (IP) of the collaborative research project. Because this is a report to NFR, we concentrate on the Norwegian partners but include briefly all partners in order to provide an overview about our interactions and milestones attained.

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Integrated project IP1: Slide headwall development in upper continental slopes

Professor Julian Dowdeswell

Scott Polar Research Institute, University of Cambridge, UK

Aims and Synthesis Our work is based around three areas of study. (1) The collection, analysis and interpretation of marine geophysical data from the Yermak Plateau, north of Spitsbergen. This work, in collaboration with Norwegian colleagues, will focus on evidence for slope failures and past glacial activity. (2) The interpretation of industrial 3-dimensional seismic evidence for the changing direction of fast-glacier flow on the Norwegian margin, and its implications for the changing focus of deposition and major depocentre buildup on that margin. (3) Relating geophysical and geological evidence on the development of modern and Late Cenozoic ice-sheet influenced continental margins to the understanding of the large-scale sedimentary record of an ancient ice sheet, specifically the northern margin of the huge pan-African ice sheet of the Late Ordovician. Main scientific achievements and progress

(1) Marine geophysical work on the Yermak Plateau and Svalbard We are at present at the stage of planning a cruise of the UK RRS James Clark Ross to this area. The cruise will take place in late summer 2006. Tasks include liaison with Prof. J. Mienert to maximise the scientific yield of this cruise in the context of bathymetry data already collected from this area during the project. We have also analysed and interpreted existing swath bathymetric data from several Svalbard fjords and have produced a model of the suite of superimposed submarine landforms that are characteristic of surging tidewater glaciers. This work has been submitted as a paper to the Journal of Geophysical Research.

(2) Ice stream switching on the Norwegian margin Today, fast- flowing ice streams and outlet glaciers drain over half of the mass from the Antarctic and Greenland ice sheets. Some temporal and spatial variability has been observed in the flow of modern West Antarctic ice streams, but major shifts in the location of ice streams flowing in deep channels has not been observed. We use an extensive three-dimensional seismic dataset from the Norwegian margin to demonstrate and explain how an ice stream, over 400 km long and draining an interior basin of over 100,000 km2, has undergone major switching in flow direction. We show that the ice stream flowed south-westward down a major depression during repeated glacial episodes, depositing a large accumulation of sediment eroded from beneath the parent ice sheet on the continental margin of mid-Norway. The direction and fast flow of ice is inferred from the pattern of build-up of glacier-derived debris and the observation of streamlined landforms on former subglacial beds. However, a change in orientation of these streamlined landforms indicates that the flow direction of this ice stream switched dramatically by 90º between the penultimate (Saalian) and most recent (Weichselian) glacial periods, as the accumulation of sediments deposited during previous glacials progressively obstructed southwestward flow. The ice stream eroded a new, 150 m-deep trough in underlying sediments, built a new depositional center some 100

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km north of its previous terminus region, and became about 120 km shorter. This demonstrates that ice streams can undergo major changes in flow direction as a result of long-term modification of their large-scale topographic setting over the course of an Ice Age, with considerable implications for the sedimentary architecture of the continental margin involved. Switching is linked to the long-term pattern of glacial erosion, transport and deposition of tens of thousands of cubic kilometers of debris over several cycles of ice-sheet growth and decay since the first build-up of ice on Scandinavia about 2.5 million years ago. A paper on this work has been submitted to Geology.

(3) The Late Ordovician Glaciation of Northern Africa We are working together with ENI-AGIP on 3-dimensional seismic datasets from Libya, at the tidewater northern margin of the Late Ordovician ice sheet. We are using our extensive knowledge of Late Cenozoic glacier- influenced margin architecture in both the Arctic and Antarctic seas, to interpret the ancient record. A research student began working on this sub-project in October 2004 and has gained a thorough grasp of the stratigraphy and sedimentary architecture of the North African margin over the period since then. The student is at present preparing an overview paper on the area, and will shortly begin to examine the industrial 3-dimensional seismic data in detail.

Dissemination of Results

Dowdeswell, J.A., Ottesen, D. and Rise, L. Flow-switching and large-scale deposition by ice streams draining former ice sheets. Submitted to Geology.

Ottesen, D. and Dowdeswell, J.A. Assemblages of submarine landforms produced by tidewater glaciers in Svalbard. Submitted to the Journal of Geophysical Research.

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Integrated project IP2: Slope stability of river-fed and carbonate margins

Professor Miquel Canals

University of Barcelona, Spain

Aims and Synthesis Causes that may bring a portion of a submarine slope to fail on river- fed and carbonate margins, and whether this slope may fail again or not are issues not always easy to answer because of the inaccessibility of the deep sub-seabed marine environment. The fluvial sediments delivered by the Ebro river to the Ebro margin are distributed under the influence of regional southward geostrophic currents and by its vortices penetrating the continental shelf. Recurrent slope instability events catastrophically disrupt the development of the channelized systems, reshaping their upper parts by destruction and their lower parts by infilling. This study tackles those questions for a relatively large (2200 km2, 26 km3), 11 kyr old landslide off the Ebro Margin, NW Mediterranean by means of geophysical (multibeam

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bathymetry, seismic reflection profiles and side-scan sonar data), sedimentological and geotechnical data (Figure 1). Main scientific achievements and progress Backanalysis of the slide and interpretation of the geophysical data sets determine that undrained failure occurred in the form of small rotational retrogressive slides. Pre-conditioning factors promoting instability of the slope included oversteepening, reduction of shear strength along a failure plane and overloading due to differential compaction and faulting associated to a deep-rooted inactive volcanic dome, and recent avulsion and deposition of sediments from a channel- levee complex. Seismic activity associated with these faults is considered as the most likely triggering mechanism since regional earthquakes do not appear to induce accelerations large enough.

Fig. 1: Swath bathymetry of the BIG’95 debris flow area with location of the landslide boundaries. Debris flow deposit is shown as solid line, main scar as white, thick solid hatched line, secondary scars are shown as white solid hatched lines.

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Dissemination of Results

Urgeles, R., Leynaud, D., Lastras, G., Canals, M., Mienert, J. (in press) Back-analysis and failure mechanisms of a large submarine slide on the Ebro slope, NW Mediterranean. Marine Geology.

Canals, M., Lastras, G., Amblas, D. Urgeles, R., Acosta, J., Casamor, J.L. 2005. Slope

instabilities on the northern Iberian and Balearic continental margin: an overview. International Symposium on Submarine Mass Movement and Their Consequences, 4-8 September 2005, Oslo, Norway. Oral presentation. Abstract published in: NGF Abstracts and Proceedings of the Geological Society of Norway, 2005, issue 2, 23-24.

Urgeles, R., Lynaud, D., Lastras, G., Canals, M., Mienert, J., 2005. Back-analysis and failure

mechanisms of a large submarine slide on the Ebro slope, NW Mediterranean. International Symposium on Submarine Mass Movement and Their Consequences, 4-8 September 2005, Oslo, Norway. Oral presentation. Abstract published in: NGF Abstracts and Proceedings of the Geological Society of Norway, 2005, issue 2, 88.

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Integrated Project IP3: Slope stability of glacier-fed siliciclastic margins Professor Juergen Mienert

Postdoktorstipendiat: Dr. Maarten Vanneste University of Tromsø

Aims and Synthesis Our research activities within IP3 of the EUROMARGINS project focuses on submarine mass wasting processes and their development on the glacially- influenced high- latitude Norwegian-Svalbard continental margins. The analysis is based on the interpretation and integration of EM300 swath-bathymetry, high-resolution 2D and 3D seismic reflection data, echo-sounding data, and gravity cores, all collected during two EUROMARGINS surveys onboard R/V Jan Mayen (fig. 1). The aim of the first expedition (July 2004) was to study and understand submarine slide development and history in a shallow water, glacier-dominated dynamic setting, between two major cross-shelf troughs (Isfjorden and Kongsfjorden), west of Svalbard. During the second expedition (October 2004), we investigated the nature,

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development, extent and timing of a giant submarine slope failure located at the shelf edge in front of the Hinlopen Trough of N-Svalbard. As such, the first months of the project were entirely devoted to the preparation, planning, acquisition and processing of these multi-disciplinary geophys ical data sets. The use of new acquisition systems (e.g. EM300 swath bathymetry, 3D high-resolution PCable system) implied that some time was spent to learn and improve data processing and visualization techniques. During the last 12 months, we completed a first analysis and integration of the data and understanding of the geological processes involved in both target areas. Results, of which a summary is given below, have already been presented on several international conferences, and manuscripts are being prepared for submission to peer-reviewed international scientific journals. Main scientific achievements and progress

(1) Rotational slope failures west of Svalbard The geophysical data acquired at the southern tip of the Kongsfjorden Trough reveal a sedimentation history dominated by glacial activity and incipient slumping (fig. 2). The target area runs along the axis of a shelf embayment where water depth increases from 120 to 475 m. The data reveal four sharp and arcuate escarpments, of which the lowermost three are sub-parallel and occur in close succession. These escarpments correspond to faulted slide blocks, and therefore suggest structural deformation of the sediments. The presence of small-scale sedimentary ridges (few m high), and some downslope elongated depressions (about 1 km long, 100 m wide and 10 m deep) are probably related to glacio-tectonic processes. The subsurface imaged by 3D seismic sections show a prograding wedge of glacial-derived deposits overlying glacigenic or glacimarine layers that are partly deformed. From the fault configuration (listric faults, detachment, and toe-thrusts), we infer that gravitation slope mobilization of glacial sediments, accommodated by rotation is currently taking place. Since part of the sediments involved in the mass movement consists of morainic deposits dated at Late Weichselian (Landvik et al., 2005), the mass movement is a relatively recent and still ongoing process. The seismic data also reveal a small catchment area in which well-stratified sediments have been accumulating adjacent to the lowermost fault. These sediments are probably derived from contour currents of the warm, northward flowing West-Spitsbergen Current. At present, these results are being written up in a scientific paper.

(2) Complex, giant slope failure north of Svalbard New swath-bathymetry data unveil a giant, complex submarine landslide on the passive northern Svalbard margin (fig. 3), bordering the Arctic Ocean. The sediment cover in this area has been influenced by both glacigenic debris lobes resulting from ice sheet and glacier dynamics as well as contouritic sediments caused by the a branch of the W-Spitsbergen current. The Arctic Slide has a well-defined slide scar with prominent bottleneck downslope. The inner slide area reveals a composite set of steep and irregular scarps. The headwall heights are unprecedented, ranging from a few hundreds of metres to an enormous height of 1400 m, i.e. up to 4 times higher than the headwalls of the giant Storegga Slide on the mid-

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Norwegian margin. The Arctic Slide is a remarkable feature, not in terms of the area affected by mass movement but rather in terms of the volume of sediments removed: from the relatively small 2,200 km2 slide scar area, an estimated large volume of 1,350 km3 of sediments has been transported to the deep Arctic Nansen Basin. This volume is based on a reconstruction of the pre-slide bathymetry, by interpolating the bathymetry data from the undisturbed part surrounding the well-defined scarp. On average, this implies that a slab of c. 610 m has been removed. The rafted blocks present in the intermediate part of the slide downslope the bottleneck are huge, measuring up to 450 m high, 5.4 km long and 2.1 km wide, and as such an order of magnitude bigger than blocks released by other well documented submarine landslides (e.g. Storegga). These numbers make the Arctic Slide a unique feature, clearly one of the biggest landslides observed on the seabed worldwide. Other morphological features observed within the slide area are detached sediment ridges, arcuate pressure ridges, isolated sediment blocks and some blocky debris lobes. Note however that most of the sediments have been transported to the distal Arctic basins located well beyond our survey area. From the geomorpho logy, we infer that the slide was a translational, multi-phase slope failure that developed retrogressively. The slide has not been dated yet, however, the available geophysical data suggest a relatively recent age, around the time of disintegration of the northern Svalbard ice sheet. Such a slide should clearly be considered a hazard with tsunamigenic potential. Similarities with the Holocene Storegga Slide and its setting suggest that changes in sedimentation related to glacial- interglacial cycles are the most likely processes contributing to slope failure. From the sediment cores, several sections have been selected for detailed geotechnical analyses by NGI, Oslo. From the analysis, it appears that the sediment cores did not penetrate the slip planes. A first paper describing the morphology observed will be submitted for publication in early October 2005. Upcoming activities for the next 12 months

Ø Merging, Integration and Interpretation of swath-bathymetry data sets and seismic reflection data collected by the University of Tromsø (headwall and intermediate area) and AWI (distal ice-covered slide area) north of Svalbard, in order to obtain a better understand ing of and constraints on the slide dimensions, volumes and mass wasting processes involved.

Ø Core analysis, description and sub-sampling in order to investigate sedimentary processes and the timing of slope failure.

Ø Collaboration with project partner NGI (Oslo) in order to model the tsunamigenic potential of the Arctic Slide and its consequences as well as the implications of sea ice cover, based on the estimated slide volume and geometry.

Ø Cruise plan jointly with the colleagues from Spain on the research vessel RV Hesperides

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Ø Organisation of a SPACOMA progress workshop with all partners in autumn 2005/ spring 2006.

Ø Reporting research activities and results to the scientific committee, during International Conferences and Workshops (e.g. EGU 2006, Vienna; AAPG Annual meeting, Houston; and others) as well as publishing in peer-reviewed international journals.

Dissemination of Results Mienert, J., Vanneste, M., Bünz, S. (invited) 2005. What did we learn from giant submarine

slides and their gas hydrate systems offshore the Mid-Norwegian margin and the Arctic? GEOITALIA 2005, Spoleto, Sept. 21-23. Abstract published in: GeoItalia 2005 Vol. 1, Federazioen Italiana di Scienze della Terra, Epitom2 2005, p. 153.

Mienert, J. Slope instability and their consequences, EGU General Assembly, 24-29 April 2005, Vienna, Austria. Oral presentation. Abstract published in: Geophysical Research Abstracts, Vol. 7, EGU 05-A-05147.

Mienert, J., Vanneste, M., Bünz, S. Arctic continental margins north of Svalbard show evidence for submarine megasliding and possible gas hydrates. 19th Winter Conference, 9-12 January 2005, Røros, Norway. Oral presentation. Abstract published in: NGF Abstracts and Proceedings of the Geological Society of Norway, 2005, issue 1, p.76.

Mienert, J., and Caanls, M., (invited) 2004. Continental slope stability – Europe and future mass movement studies in Europe. 57th Canadian Geotechnical Conference Proceedings, Quebec, Canada.

Planke, S., Berndt, C., Eriksen, F.N., Eidem, T.R., Mienert, J., Åsheim, S. The PCable: Intelligent and versatile acquisition of low-fold, high-resolution 3D seismic data. Norway. International Symposium on Submarine Mass Movement and Their Consequences, 4-8 September 2005, Oslo, Norway. Abstract published in: NGF Abstracts and Proceedings of the Geological Society of Norway, 2005, issue 1, p.70.

Planke, S., Eriksen, F.N., Eidem, T.R., Berndt, C., Mienert, J., Åsheim, S. The PCable: Intelligent and versatile acquisition of low-fold, high-resolution 3D seismic data. 19th Winter Conference, 9-12 January 2005, Røros, Norway. Abstract published in: NGF Abstracts and Proceedings of the Geological Society of Norway, 2005, issue 1, p.94.

Vanneste, M., Berndt, C., Mienert, J. 3D seismic imaging of submarine slide development on the Western Svalbard margin. Edvard Suess session - EUROMARGINS, EGU General Assembly, 24-29 April 2005, Vienna, Austria. Poster presentation. Abstract published in: Geophysical Research Abstracts, Vol. 7, EGU 05-A-06727.

Vanneste, M., Bünz, S., Mienert, J. Multi-phase submarine mega-slide development on the Arctic continental margin off North Svalbard. EUROMARGINS conference, 11-13 November 2004, Barcelona, Spain. Poster presentation. Abstract published in: 2nd EUROMARGINS Conference - Book of Abstracts.

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Vanneste, M., Bünz, S., Mienert, J. Multi-phase submarine mega-slide development on the Arctic continental margin north of Svalbard. Edvard Suess session - EUROMARGINS, EGU General Assembly, 24-29 April 2005, Vienna, Austria. Oral presentation. Abstract published in: Geophysical Research Abstracts, Vol. 7, EGU 05-A-06387.

Vanneste, M., Bünz, S., Mienert, J. Multi-phase submarine mega-sliding on the Arctic continental margin north of Svalbard: Characteristics, Morphology and Volume Estimates. International Symposium on Submarine Mass Movement and Their Consequences, 4-8 September 2005, Oslo, Norway. Oral presentation. Abstract published in: NGF Abstracts and Proceedings of the Geological Society of Norway, 2005, issue 2, 91-92.

Vanneste, M., Mienert, J. Gas hydrates and slope stability: Examples from the Norwegian-Svalbard margin. 2nd EUROMARGINS conference, 11-13 November 2004, Barcelona, Spain. Oral presentation. Abstract published in: 2nd EUROMARGINS Conference - Book of Abstracts.

Vanneste, M., Mienert, J. Sub-marine slope failures along the continental margins of Svalbard: Results from swath-bathymetry and high-resolution seismic surveying. Lecture on EURODOM Training Course Processes related to slope stability and fluids in continental margins. 30 May 2005, University of Tromsø, Norway.

Vanneste, M., Mienert, J., Berndt, C. 3D seismic imaging of submarine slide development on the Western Svalbard margin. 2nd EUROMARGINS conference, 11-13 November 2004, Barcelona, Spain. Poster presentation. Abstract published in: 2nd EUROMARGINS Conference - Book of Abstracts.

Peer-reviewed scientific papers In light of the results obtained within the EUROMARGINS project, we currently work on several papers, to be submitted to international peer-reviewed journals. Dependent on the outcome of further research activities and upcoming results, this list will be expanded. Mienert, J. Weaver, PPE., Berné, S., Dullo, W-Chr., Evans, D., Freiwald, A., Henriet, J.-P.,

Joergensen, B.B., Lericolais, G., Lykousis, V., Parkes, J., Trincardi, F., Westbrook, G., 2004. Overview of recent, ongoing, and future investigations on the dynamics and evolution of European margins. Oceanography, Vol.17, No.4, p.16-33.

Landvik, J., Ingólfsson, Ó., Mienert, J., Lehman, Sc. J., Solheim, A., 2005. Rethinking Late Wechselian ice-sheet dynamics in coastal NW-Svalbard. Boreas, 7-24.

Vanneste, M., Bünz, S., Mienert, J. (in prep.). A giant, tsunamigenic submarine slope failure on the Arctic continental margin of North-Svalbard.

Vanneste, M., Berndt, C., Mienert, J. (in prep.). Swath-bathymetry and high-resolution 3D seismic data reveal incipient slope failure on the western Svalbard margin.

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Mienert, J., Canals, M., Vanneste, M. (in prep.) Retrogressive submarine slides on Antarctic and Arctic margins.

Mienert, J. Haflidason, H., Vanneste, M. (in prep). Processes leading to giant submarine slope failures on the passive Norwegian and Arctic N-Svalbard continental margins.

Leynaud, D., Mienert, J., Vanneste, M., (in prep.). Submarine sliding on glaciated and non-glaciated European continental margins: Triggering mechanisms and precond itions to failure. subm Marine Geology

Networking and training

During the last year, we organised a EURODOM training course “Processes related to slope stability and fluids in continental margins” at the University of Tromsø. This included a 3-day course in 3D seismic interpretation followed by a series of lectures related to this topic. A total of 10 PhD students from different nations attended this training course.

Additionally, M. Vanneste has spent three weeks at the National Oceanographic Centre (NOC, UK), to process the newly acquired 3D seismic data west of Svalbard in collaboration with C. Berndt (NOC).

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Figure 1: Overview map of the Svalbard margins, indicating the EUROMARGINS target areas (white boxes) within IP3. (Abbreviations used: AS = Arctic Slide; KFj = Kongsfjord; IFj = Isfjord; HS = Hinlopen Strait; HT = Hinlopen Trough; PKF = Prins Karls Foreland; KR = Knipovich Ridge)

Figure 2: Swath-bathymetry (left) data acquired simultaneously with high-resolution 3D data (right) across the shelf edge west of Svalbard.

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Figure 3: c. 4000 km2 swath bathymetry data unveiling a complex slope failure north of Svalbard.

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D. Winkelmann Bremerhaven, 28.09.2005

Alfred Wegener Institute for Polar and Marine Research D-27568 Bremerhaven Germany phone: +49 471 4831 1571 e-mail: dwinkelmann@awi-bremerhaven.de Aims and Synthesis The synthesis of already existing AWI data (bathymetry, PARASOUND, seismic) reached a comprehensive level and has been the basis for the expedition ARK-XX/3 (31.08. - 03.10. 2004) with research icebreaker “Polarstern” to the target area north of Spitsbergen. During ARK-XX/3 additional detailed bathymetric and shallow acoustic (PARASOUND) data have been acquired on key profiles as well as 36 sediment cores – 18 gravity cores recovered on key locations and key transects of the Yermak Slide area (Figure 1). Core- logging as well as opening of cores and first sampling has directly been performed after recovery aboard RV “Polarstern”. Accomplished sedimentological investigation of selected cores includes geochemical bulk parameter, physical properties, magnetic susceptibility and x-ray radiography. Ongoing sedimentological investigation includes stable isotopes of Neogloboquadrina. pachyderma sin. and XRF scanning of selected cores. Analysis of geochemical bulk parameter of further cores will depend upon their priority level. Dating of microfossils from key cores with highest priority has been accomplished. Dating of further core material will depend upon their amount of available microfossils as well as on their priority level. Main scientific achievements and progress The slide extend of the Yermak Slide has been revised. It extends further west within Sophia Basin than has previously been reported by Cherkis et al. (1999). The Yermak Slide funnelled out into Nansen Basin between Polarstern Seamount and the adjacent shelf north of Nordaustlandet. The overall extent is not known yet since extensive information of its distal part do not exist (Figure 2). Thus the total area affected by the slide might well exceed 10.000 km2. The slide consists of one major event dated back into MIS 3 repeatedly followed by minor events visible as debris flows in topographic lows on the main debris body. The sedimentological characterisation of the submarine landslide includes development of debris flows, turbidites and a debris avalanche with a number of mega blocks reaching extensions of more than 4 km and a relief of more than 300 m above the surrounding debris. Upcoming activities for the next 12 months First volume calculation based on seismic data will be refined fro the distal part. Further GIS-based integration of geophysical data into a comprehensive slide model as baseline for a Tsunami model will go on. Submission and publishing of research progress in reviewed journals started. A webpage to enhance the project's visibility is in progress.

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Figure 1: position of slide related cores and recovery of gravity cores recovered during ARK-XX/ 3 (Stein 2005). Right: Nordaustlandet

Figure 2: Position and minimum extent of the Yermak Slide north of Spitsbergen. ___________________________________________________________________________

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Integrated project IP4: Geo-mechanical controls on the formation and trigger mechanisms of submarine slides. Drs. Carl-Fredrik Forsberg and Tore-Jan Kvalstad Postdoktorstipendiat Dr. Shaoli Yang (NGI) Norwegian Geotechnical Institute and International Centre for Geohazards (ICG) Aims and Synthesis To obtain an improved understanding of the geo-mechanical control on the triggering and development of submarine slides under various physiographic conditions including the headwall development. The results of laboratory experiments, partly designed to study the effects of gas hydrates, as well as parameter values from data compilations will also form important input to the numerical modelling to be performed under IP5. Main scientific achievements and progress Work has continued on the understanding the variability of the properties of natural sediments. Down-hole log data from selected geotechnical boreholes in the Ormen Lange area have been statistically analyzed (e.g. Figure 1 below) and compared to the results of geotechnical measurements on samples. The results are promising and two papers have been submitted dealing with sample and log statistics. The next phase of this work needs to take the effect of gravitational compaction into account.

Figure 1: Cluster analysis of down-hole logs from Site 31 in the Ormen Lange area. Results for 3 (left) and 4 (right) groups. The results fit stratigraphic data from samples quite well.

In cooperation with the International Centre for Geohazards (ICG) a study has been performed to evaluate the potential for using seismic attributes to predict potential slip planes and geotechnical properties in an area. An ICG report is being written and will be finished during November 2005. Post stack analyses of attributes help to delineate potential failure

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surfaces, but more advanced pre stack analyses (e.g. amplitude versus offset) are required for the prediction of property changes. Oedometer testing of samples from the Hinlopen/Yermak Slide were performed to obtain the maximum past load on the samples from the overburden. The results indicate that samples of sediments from below slide masses had not been obtained. Advanced geotechnical analyses were therefore not performed. Two year position filled by Post Doc. Shaoli Yang financed in cooperation ICG. Planned financing for 2005 by Euromargins project but maternity leave September 2005 to August 2006 means postponement of last four months until 2006.

Networking activity

Participation by C.F. Forsberg and S. Yang in “workshop” in Tromsø for opening cores from the Hinlopen /Yermak Slide. Shaoli Yang visited Barcelona for discussions concerning geotechnical properties of the sediments associated with the BIG95 slide. Upcoming activities 1. Continue the work on the use of statistical analyses of logs for the evaluation of the

significance of variability of sediment properties for glide plane development. Submission of 1 or 2 papers.

2. Finalise program on effect of gas hydrate melting on clay behaviour using laponite (clear artificial clay) and very soft natural clay.

Produce R11-hydrate and mix with Laponite and natural clay in an amount giving gas volume after melting similar 10% methane gas hydrate in 1000 m water depth

Document hydrates dissociation process in Laponite with photos and video. (Transparent Laponite samples allows visualisation of hydrate dissociation and gas bubble formation process)

Compare volume expansion of Laponite and natural clay

X-ray samples of Laponite and natural clay with and without hydrate before and after heating/dissociation

CT-scanning of Laponite and natural clay before and after dissociation, and if possible, also during dissociation process.

3. Conclude on:

How representative Laponite is as a replacement for natural clay

Sample disturbance effects to be expected (Xray and CT scan)

Expected reduction in strength of clays subjected to gas hydrate melting

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One publication on the effect of gas hydrate dissociation on clayey sediments in relation to gas bubble formation, fracturing, reduction of shear strength and triggering of submarine mass flows.

4. Carry out planned investigation on ooze clays

Deepwater samples with ooze material will be tested to compare with experience from marine and glacial marine clays regarding index/classification parameters, mineralogy, shear strength, compressibility and permeability in order to evaluate if oozes represent an increased hazard with respect to mass wasting processes. UiB will provide intact samples. NGI will perform test program as planned, starting mid October, 2005.

One publication on comparison of ooze rich clays and normal marine clays regarding geotechnical sediment properties relevant for assessment of submarine mass flow potential

Dissemination of Results

Schnellmann, M., Solheim, A., Forsberg, C.F., Lecomte, I., Kvalstad, T., Yang, S. Identifying weak layers and potential slip planes by integrating Amplitude versus O.set (AVO) analyses and post-stack seismic attributes. Submarine Mass Movements and Their Consequences. 2nd International Symposium. 5-7 September, 2005, Oslo, Norway

Yang, S, Lacasse, S. and Forsberg, C.F. Application of packing models on geophysical

property of sediments. 16 ICSMGE, 16th International Conference on Soil mechanics and Geotechnical Engineering. September 12-16, 2005, Osaka, Japan.

Yang, S.L. and Sandven, R. Evaluation of the properties of silty soils with high fines

content. Proceedings Fifteenth (2005) International Offshore and Polar Engineering Conference, 19-24 June, 2005, Seoul, Korea. 696-702.

Yang, S.L., Solheim, A., Kvalstad, T, Forsberg, C.F., Schnellmann, M. Behaviour of the

sediments in Storegga Slide interpreted by steady state concept. Submarine Mass Movements and Their Consequences. 2nd International Symposium. 5-7 September, 2005, Oslo, Norway

Yang, S. L., Kvalstad, T. J., Solheim, A. and Forsberg, C.F. Parameter studies of

sediments in the Storegga Slide area. European Geosciences Union General Assembly 2005, 24-29th April 2005, Vienna, Austria (EGU05-A-04515)

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Numerical modelling of sediment break up, mobility and run out Aims and Synthesis The existing and new experiments together with the assessment of transport mechanisms and the correlations between geological and geotechnical parameters provide a basis for developing more complete flow models. This requires: (1) developing criteria based on material properties (rheology) and topography to predict whether a potential subaqueous gravity mass flow will evolve into a turbidity current (suspension flow), a granular flow, a hydroplaning or a non-hydroplaning (visco-plastic) debris flow, or a glide block; (2) linking the typical geotechnical parameters quantified in the laboratory analysis to the rheology and "flow parameters" used in the numerical flow simulations (yield strength, viscosity, etc.): and (3) considering more sophisticated rheological models including e.g. strain-softening, shear-thinning, and/or dry friction. The geotechnical parameters are hard to quantify for three reasons: (i) the areas of interest are not easily accessible, (ii) the material properties of the sediments prior to release may differ significantly from the properties of the flow deposits, and (iii) the properties of the deposits may have changed over the normally long period of time since the event took place. The model development is also linked to the project of the International Centre for Geohazards (ICG) “Slide dynamics and mechanics of disintegration”. A loose link exists to the EU project “SATSIE Avalanche Studies and Model Validation in Europe”. For the application of the slide model to a slide scenario, the Yermak slide is a candidate. The output of the slide model will be used as input to an existing tsunami model. In this part there is also a connection to the project of the International Centre for Geohazards (ICG) “Tsunami modeling and prediction”. Upcoming activities

• At the moment, the model BING, which is based on the Bingham rheology, is often used for numerical simulations of clay-rich debris flows for several years. However, the BING model does not treat so-called extensional flow correctly. This defect is all the more important as it influences the study of stretching and neck formation observed in the laboratory and most probably of importance in many slides and in the formation of outrunner blocks. Here, it is planed in a new implementation to put the Bingham rheology on a firm basis including stretching. Simultaneously, the program should be more user-friendly so that it can be used by wider group. • In a next step, the recoded BING model shall be extended for hydroplaning and shear-wetting. • Developments towards a rheological model for sand-rich flows. • Study of Yermak-slide - coupling to existing tsunami model.

Abstracts and Presentations on Conferences, Workshops, Courses Publications are planned for special volume of the Norwegian Journal of Geology.

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Gauer, P., A. Elverhøi, D. Issler, and F. V. De Blasio On numerical simulations of subaqueous slides: Back-calculations of laboratory experiments

Elverhøi, A., De Blasio, F.V., Engvik, L., Issler, D., Nystuen, J.P., Ilstad, T., Harbitz, C. & Gauer, P. Understanding the high mobility of subaqueous debris flows

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Integrated project IP5: Slide frequencies in regions of long-term instability in relation to sea-level change Profs. Halflidi Haflidason, Hans-Petter Sejrup Doktorstipendiat Kristin Johanne Grasmo Postdoktorstipendiat Dr. Atle Nygård University of Bergen Aims and Synthesis The aims are twofold: firstly individual slide morphologies and sediment of underlying sediments are to be determined, and secondly the identified slides are to be dated. The research cruises addressed the first issue and the dating of individual slides is underway. Two cruises addressing these research issues have been carried out by the University of Bergen during the last year. A coring cruise conducted to the distal North Sea Fan/Storegga Slide area for retrieving cores for dating the number of paleo slides identified in this margin area (27. Sept – 16. Oct. 2004). A cruise conducted to the Svalbard margin for marine geological analyses (multidisciplinary); (4.-14. Sept. 2004). NB. The scheduled cruise to the northern margin of Svalbard (Sept. 2004) was cancelled due to weather and ice conditions. A coring cruise to the Storegga Slide headwall for studying the last glacial maximum and deglaciation glacimarine and plumite deposits deposited inside the Storegga Slide depression area (28. Jun – 14.Jul. 2005). Main scientific achievements and progress An important focus in the last 12 months has been on detailed mapping of the northern Storegga Slide escarpment. The main objectives of this part of the study have been to: (1) Review the morphological interpretation along the northern Storegga Slide flank, and identify age relationship between evolutions of channels/blocks/slumps. (2) Reconstruct post-Storegga Slide geometry/geomorphology (before last slide event). The cruises have allowed to collect shallow seismic data, bathymetry and cores. The bathymetry shows that an erosional remnant from the slide defines a “headland” along the backwall of the slide (Fig. 2 and 3). The seabed shows a series of cracks, with one particularly large (Fig. 3), indicating that the sediments in the “headland” have been translated slightly downslope during the Storegga Slide. Further investigation of the “headlands” resistance relies on interpretation of the TOPAS sub-bottom profiles and analysis of the collected core material. The TOPAS profile in Figure 3 show an acoustically transparent diamicton thinning basinward above a laminated package. The genesis of the diamicton is uncertain, potential explanations might be a) glacigenic debris flows from the shelf edge b) ice berg turbate c) winnowing from the significant current which flow along the margin segment. A combination of these factors is favored as an explanation; however this issue might be resolved by future sampling in the area. Preliminary analysis of

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the distribution of the diamicton shows that the Storegga Slide headwall seems to follow the distal edge of the diamicton, possibly suggesting that the diamicton has had a stabilizing effect on the underlying laminated sediments. This hypothesis will be investigated further during the next year of the project. The core GS138-07GC was collected from in situ sediments just behind the headwall, penetrating the laminated sediments prone to failure (Fig. 3). The core sampled the uppermost part of a widespread laminated sequence, which is representative for the failed sediments in this area of the Storegga Slide. The laminations, which could be recognized visually in the core, are probably deposited rapidly in an ice-proximal environment during the deglaciation (a single date show an age of ca. 16000 14C yrs BP). One cruise (GS138-04) has been carried out to the distal part of the North Sea Fan and the Storegga Slide in the Norway Basin. The aim of this cruise was to collect cores to date older slides originating from the “Storegga Slide Complex”. The Storegga Slide Complex has seen repeated sliding activity in the last 0.5 Ma, and the working hypothesis is that at least two older slides subcrop relatively thin packages of hemipelagic sediments in different places. However, due to bad weather conditions it was impossible to core the optimal sites. One core was retrieved and is currently under investigation. This core has unfortunately only a limited potential to yield information on the older (>100 ka BP) slides. Upcoming research activities and cruises: A new cruise is planned to the Norway Basin area summer 2006 to retrieve cores suitable for dating the older slides in the Storegga Slide complex. Improving the dating of the large Slide R buried at the northern Storegga Slide escarpment area. A 34 m long IMAGES core (MD992288) is located at the undisturbed Storegga Slide escarpment penetrating down to the Slide R debris. The present core is taken at the same location as previously studied IMAGES core MD992289 but is 10 m longer and is possibly penetrating through MIS6. Investigate the relation between the rapidly deposited laminated sediments and the headwall morphology of the Storegga Slide main headwall and possible influences on slide development by overlying diamicton.

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Figure 1: Overview map from the survey GS140-05 to the Storegga Slide and the North Sea. The location of Figure 2 is from the Storegga Slide headwall at Storneset.

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Figure 2: Colour shaded multibeam map (EM1002) of the Storegga Slide headwall at Storneset based on data from surveys GS138-04 and GS140-05. Location in Figure 1.

Crack

Fig. 3 and core location

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Figure 3: TOPAS parametric echo sounder profile across the headwall of the Storegga Slide. The core sampled in situ laminated sediments representative for the failed sediments in the area. Dissemination of Results Haflidason, H., Lien, R., Sejrup, H.P., Forsberg, C.F. and Bryn, P., 2005. The dating and

morphometry of the Storegga Slide. Marine and Petroleum Geology 22, 123-136. Parsons, B. S., Vogt, P.R., Haflidason, H. and Jung, W.-Y., 2005. Sidescan and video

exploration of the Storegga slide headwall region by submarine NR-1. Marine Geology 219, 195-205.

Lekens, W., Sejrup, H.P., Haflidason, H., Petersen, G.Ø., Hjelstuen, B. and Knorr, G., 2004. Laminated sediments in the Northern North Sea and Southern Norwegian Sea. Marine Geology 216, 27-50.

Nygård, A., Sejrup, H.P., Haflidason, H. and Bryn, P., 2005. The glacial North Sea Fan, southern Norwegian Margin: architecture and evolution from the upper continental slope to the deep-sea basin. Marine and Petroleum Geology 22, 71-84.

Presentations and Reports Haflidason, H., Sejrup, H. P., Nygård, A. and Lekens, W., 2005. The age of the Storegga-

North Sea Fan mega slides and their timing in relation to sea- level stand. EGU Meeting Vienna, April 2005. Geophysical Research Abstracts, Vol. 7 (Abstract).

Iversen, H., Nygård, A., Haflidason, H, Sejrup, H.P. 2004. 3D seismic data from the mid-Norwegian Margin provide evidence for marine based ice sheet dynamics. Poster. EOS Transactions, AGU 85(47), Fall Meeting Suppl. 13-17 Dec. San Francisco, USA

Nygård, A.; Sejrup, H.P.; Lekens, W.; Haflidason, H.; Iversen, H. 2005. High output rates of subglacial till at the outlet of a paleo- ice stream draining the southwestern Fennoscandian

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Ice Sheet. EGU General Assembly, Vienna, April 2005. Geophysical Research, Vol. 7 (Abstract).

Nygård, A., Sejrup, H.P., Lekens, W., Haflidason, H., 2004. Extreme Weichselian output rates of subglacial till at the front of the Norwegian Channel Ice Stream. Poster. EOS Transactions, AGU 85(47), Fall Meeting Suppl. 13-17 Dec. San Francisco, USA

Gram, I. H., Haflidason, H., Sejrup, H. P., Nygård, A. and Bryn, P., 2004. The Storegga Slide: Morphological provinces and slide phases. 32nd IGC - Florence, 2004 (Abstract).

Haflidason, H., Sejrup, H. P., Nygård, A. and Bryn, P., 2004. The Storegga Slide rheology: analyses of the geometrical parameters. 32nd IGC - Florence, 2004 (Abstract).

Haflidason, H., Sejrup, H. P., Nygaard, A., Gram, I. H. and Bryn, P., 2004. The Holocene (7.250 14C yrs BP) Storegga Slide, Mid-Norwegian Margin: The Modern Analogue To Paleo High-Latitude Mega Slides. AGU Fall Meeting, San Francisco, USA, 11-17.12.2004.

Brendryen, J. and Haflidason, H., 2004. Refining Of The MIS 5 Tephrostratigraphic Record In Marine Cores From The S-Norwegian Margin; A Tool For High-Resolution Dating And Correlation Of Climatic Archives. AGU Fall Meeting, San Francisco, USA, 11-17.12.2004.

Lekens, W. A., Sejrup, H. P., Haflidason, H., Ostvik Petersen, G. and Knorr, G., 2004. Meltwater Outflow and Laminated Plume Deposition in the Southern Norwegian Sea Preceding Heinrich Event 1. AGU Fall Meeting, San Francisco, USA, 11-17.12.2004.

Haflidason, H., Sejrup, H.P., Nygård, A., Hjelstuen, B.O., Grasmo, K.J., Vikebø, J., Monsen, S., Hughes, A., Pask, E., Germond, F. and Rabbe, N.P., 2005. Marine Geological Cruise Report to Nordfjord, Måløy Plateau, South Storegga Slide, North Sea Fan, North Sea Plateau and Hardangerfjord. Report No. 100-05/01, Department of Earth Science, University of Bergen, Bergen, 85 pp.

Dokken, T., Nygård, A., Blindheim, D. I., Monsen, S., Senneset, L., Nyland, B. F., Euler, C., Moe, S. T., Birkeland, R. and Granberg, R., 2004. Cruise report R/V G.O. Sars to the North Atlantic UoB Cruise No. GS138-04. Report No. 100-04/02, Department of Earth Science, University of Bergen, Bergen, 39 pp.