This paper discusses the influence of sedimentary environment and geological setting on geotechnical and physical properties of resulting sedimentary deposits. For this study, two different geological settings were considered, one is a river-fed and the other is a glacier-fed sedimentary environment. For both sedimentary environments, various geotechnical properties were considered and compared. These include plasticity, activity, compressibility, undrained shear strength and sensitivity. Results indicate that physical and geotechnical properties of sediments deposited in these two settings are significantly different. These differences are then interpreted in terms of the various mechanisms involved in submarine slope failure initiation in river-fed versus glacier-fed sedimentary environments.

Trough mouth fans are formed by aggradation of glacial debris flows from sediment deposited by fast flowing ice streams extending to the shelf edge. We here present investigations at two sites, ODP Site 1166 on the shelf and ODP Site 1167 drilled on the Prydz Channel Fan in order to contribute to the understanding of Neogene ice flow patterns in Prydz Bay. The mineralogy, wt.% >63 mu m, physical and magnetic properties were analyzed. The mineralogy of Neogene strata at Site 1166 can be correlated to nearby ODP Site 742 drilled during Leg 119. Moreover an increase in the shear strength of the sediments (Leg 119 load event 3) is found both at Site 1166 and Site 742. This load event probably indicates that the oldest glacial configuration involved thicker glaciers than the later ones. The results from Site 1167 show that there has been a significant change in the provenance of the sediments during the past 2 million years. The greatest change occurred at about 1. 13 Ma and implies a shift in the glacial configuration in Prydz Bay with a greater contribution of material from western parts of the drainage basin during the deposition of Unit II (> 1. 13 Ma; 217-43 5 mbsf) at Site 1167 on the Prydz Channel Fan. (C) 2008 Elsevier B.V. All rights reserved.

The Hinlopen-Yermak Slide (HS) is one of the largest exposed submarine landslides on the world's continental margins, and is comparable in dimensions as well as slope failure processes to the Storegga Slide (SS). Index properties of the sediments from gravity cores retrieved from the upper slidescar area of the Hinlopen -Yermak Slide are analysed in this study. Sediment type, plasticity, activity, compressibility, undrained shear strength and remoulded undrained shear strength from fall cone tests are presented and compared with results from Storegga slide when possible. The available data illustrate that the sediments in the Hinlopen-Yenmak Slide area are inorganic and inactive with low to medium plasticity. The compressibility is lower than that in the Storegga Slide, whereas the sensitivity is generally higher than those from similar locations in the Storegga Slide.

Various types of slope processes, mainly landslides and avalanches (snow, rock, clay and debris) pose together with floods the main geohazards in Norway. Landslides and avalanches have caused more than 2000 casualties and considerable damage to infrastructure over the last 150 years. The interdisciplinary research project "GeoExtreme" focuses on investigating the coupling between meteorological factors and landslides and avalanches, extrapolating this into the near future with a changing climate and estimating the socioeconomic implications. The main objective of the project is to predict future geohazard changes in a changing climate. A database consisting of more than 20 000 recorded historical events have been coupled with a meteorological database to assess the predictability of landslides and avalanches caused by meteorological conditions. Present day climate and near future climate scenarios are modelled with a global climate model on a stretched grid, focusing on extreme weather events in Norway. The effects of climate change on landslides and avalanche activity are studied in four selected areas covering the most important climatic regions in Norway. The statistical analysis of historical landslide and avalanche events versus weather observations shows strong regional differences in the country. Avalanches show the best correlation with weather events while landslides and rockfalls are less correlated. The new climate modelling approach applying spectral nudging to achieve a regional downscaling for Norway proves to reproduce extreme events of precipitation much better than conventional modelling approaches. Detailed studies of slope stabilities in one of the selected study area show a high sensitivity of slope stability in a changed precipitation regime. The value of elements at risk was estimated in one study area using a GIS based approach that includes an estimation of the values within given present state hazard zones. The ongoing project will apply the future climate scenarios to predict the changes in geohazard levels, as well as an evaluation of the resulting socioeconomic effects on the Norwegian society in the coming 50 years.

The 33rd IGC was hosted jointly by the five Nordic countries, Norway, Sweden, Denmark, Finland and Iceland, and held in Oslo in the period 6–14 August 2008. This was the third IGC ever held in one of the Nordic countries after Stockholm in 1910 and Copenhagen in 1960. Over 6,000 delegates enjoyed the nine days of congress activities and social events. The patron of 33rd IGC, His Majesty, King Harald V of Norway, opened the Congress in the late afternoon of the first day. After His Majesty’s speech, the full plenary hall was exposed to a lively and colourful opening ceremony, quite different from previous conference ceremonies. It consisted of a mix of music and dance performances and spectacular video postcards from each of the five Nordic countries. The Grand Finale of the ceremony was a rock version of Edward Grieg’s “In the hall of the mountain king” accompanied by live fireworks. The ceremony set the stage for the following Congress days, with intense science sessions and lots of fun, despite the unfortunately quite miserable weather. A total of 6,259 participants registered for the 33rd IGC. Of these 24 were Youth Congress participants (see below) and 310 were accompanying persons. Of the remaining 5,925 who participated in the 33rd IGC science and exhibition, participation was greatest from Norway (960), Russia (505), USA (394), China (376), and Italy (367). 1,428 came from the Nordic countries, while 4,497 were from outside of Norden. The IGCs are truly international congresses, and the 33rd IGC comprised participants from 113 different countries, thus fulfilling the informal name “Geoscience World Congress 2008”. In line with previous congresses, 33rd IGC had a significant Geohost programme, enabling 577 Geohost stipendiaries to participate. The Congress venue was the Norway Convention Centre, located 20 km north of Oslo’s city centre. A favourable arrangement with the Norwegian Railway System (NSB) made transportation easy between the city (where most hotels are located), the venue, and the Gardermoen International airport. The train from the city centre to the venue takes only 12 minutes, and the registration fee included transportation, with the name badge as travel pass. The venue itself is primarily set up for large trade fairs, and whereas the available area was more than big enough, the main challenge was to build enough lecture theatres to serve the up to 33 parallel oral sessions. This was done by building extra auditoriums in two of the main halls of the centre. A “speaker ready room” was set up, from where all PowerPoint presentations were distributed electronically to the various auditoriums. 100 Conference Reports 433

The Krishna and Godavari rivers have formed the Krishna-Godavari delta where they enter the ocean. Both the rivers, which drain a significant part of the Indian peninsula, and the delta are influenced by a seasonal sediment supply controlled by the monsoon rains. The delta system receives nearly all its sediment during this annual flushing of the river system. The slope instabilities on the delta are most likely driven by excess pore pressure induced by rapid sedimentation and therefore reflect sedimentation history and distribution. The overall geometry of delta shows that the Pleistocene subsidence on the inner part of the sub-aqueous delta is associated with toe-thrusts in more distal regions and that the morphology of the delta front is comprised of channel-levee systems with overbank and mass transport deposits. The climatically induced fluctuations in sea level have probably shifted the main depocentre through time with the more distal sedimentation occurring during sea-level lowstands. This study is based on 2D and 3D-seismic data that has been combined with geotechnical information from boreholes. This investigation demonstrates the role regional geology has for the distribution and timing of mass movements.

In this study, the slope stability at Northern Flank of Storegga slide was analyzed by Plaxis. Six slopes were selected and geological, geotechnical and geophysical data were combined for obtaining parameters. The safety factors for all the six slopes were higher than 1, the slip surfaces were located at the marine clay layers. More data are needed for an accurate slope stability analysis at the lower part of the Northern Flank.

Abstract Submarine slides pose the most critical offshore geohazard. Seafloor mass movements occur in continental margins worldwide, and at all scales, from the smallest ones, barely detectable by acoustic methods, to the gigantic Storegga Slide off Mid-Norway. As most deepwater petroleum resources are located in continental slope settings, seafloor instability is a major concern, not forgetting that other geohazards, such as shallow gas, gas hydrates, and mud volcanism also must be assessed. The slope angles in general are small, so the most important factors controlling stability are sediment types and the presence of excess pore pressure. Both are functions of geological setting and depositional regime and history. Two important causes of excess pore pressure in the uppermost sediment layers are high sedimentation rates combined with unfavourable layering, and the trapping and accumulation of gas seeping from deeper levels. Along the high latitude, formerly glaciated NW European margin, the climatically induced variability between glacial and interglacial situations seems to have been the main controlling factor for instability. Excess pore pressures were created in stacked interglacial and glacial units during rapid burial by glacial debris during peak glacial periods. The water source may have been underlying biogenic oozes. Mineralogical factors, such as smectite content, appear to have limited influence here. The major, large scale sliding has also formed seafloor topography with numerous steep local escarpments from which smaller slides may threaten seafloor installations. In lower latitude, river-fed settings the mechanisms are different. In the Krishna-Godavari River delta off East India, the sedimentation rate varies greatly laterally and temporally, often at short time scales. The temporal variations are caused by the long term climatic variations as well as by the seasonal monsoons. In the lower latitude continental margins significant sea level low-stands, such as during the Last Glacial Maximum (LGM), may have caused exposure of the shelf, with erosion and delivery of river sediments directly to the upper slope. Small mass movements (but still large enough to be a significant threat to installations) seems to occur frequently in this setting, partly supported by locally extreme sedimentation rates. Introduction Offshore geohazards comprise a number of geological phenomena, such as submarine slides, shallow gas and dissociation of gas hydrates, shallow water flow, mud volcanism, and seismicity. Of these, the most serious is probably submarine sliding, which not only has an immediate effect on any seafloor installation in and downstream of the slide scar, but also may have serious third-party consequences if the slide has tsunamigenic potential. Hydrocarbon exploration and exploitation have, over the last decade moved into increasingly deeper waters of the world's continental margins. This also means it has moved into increasingly more slide-prone areas. At the same time, the tools for detailed seafloor investigations have developed immensely, and new areas are mapped at great detail. This again has led to the discovery of submarine slides of various sizes in all margin areas of the world.

Based on classification tests, oedometer tests, fall-cone tests and triaxial tests, physical and mechanical properties of sediments in the Storegga Slide region were analysed to assess parameter interrelationships. The data show good relationships between a number of physical and mechanical parameters. Goodness of fit between compression index and various physical parameters can be improved by multiple regression analysis. The interclay void ratio and liquidity index correlate well with the undrained shear strength of clay. Sediments with higher water content, liquid limit, activity, interclay void ratio, plasticity index and liquidity index showed higher compression index and/or lower undrained shear strength. Some relationships between parameters were tested by using data from two other sites south of the Storegga Slide. A better understanding of properties of sediments in regions such as that of the Storegga Slide can be obtained through this approach.

The Sklinnadjupet Slide Scar is a large buried feature on the continental slope southeast of the Vøring Plateau. The mass-flow occurred ca. 250,000 years ago on a slope angle of ca. 0.5°, and removed glacial debris from the up to 350-m-thick Naust S sequence on the upper slope. This part of the mid-Norwegian margin appears to have been fairly stable throughout the last 2.8 million years. Naust S represents the third last glacial unit in the Skjoldryggen region, and was deposited during the Elsterian (ca. 400–200 ka BP). During this glaciation, a wide depression was formed on the continental shelf between Haltenbanken and Trænabanken, with the strongest glacial erosion in the west-trending Sklinnadjupet palaeo-trough. This trough leads directly towards the deep, 90-km-wide slide scar, indicating that a local depocentre was formed here before the mass-flow occurred. The shallowest crest of the Helland-Hansen Arch is located below the southern part of the slide scar, and two large craters were formed on the surface of this anticlinal structure. Our model suggests that the deposition of glacial sediments above the Helland-Hansen Arch caused high excess pore pressures along the shallowest crest of this structure and formed a high pore-pressure gradient towards the sea floor on its western flank. An earthquake possibly triggered the initial slide where the slope was steepest west of the crest. Most of the slide scar was already formed when the slide finally eroded into the anticline. High excess fluid pressure subsequently mobilised the diatomaceous oozes in the Helland-Hansen Arch and formed the craters. Much of this material flowed down-slope without being totally disintegrated, and was deposited as levee ridges and mounds above slide deposits from the first phase of the mass-flow. They have previously been wrongly interpreted as diapirs.

Storegga Silide has been studied intensively due to the development of the big Ormen Lange gas field. Both marine and glacial deposits were involved in this slide, and marine layers were the sliding planes. Data from different wireline logs in the Storegga Slide area are analyzed using principal components and cluster statistical methods to characterize the two different kinds of sediments. The results show that the marine layer with high water content, high clay content and low strength can be differentiated from the glacial deposits. Moreover, the analysis from log response are compared with the physical parameters from the geotechnical boreholes, a good correlation exists in the dataset.

Seven large pre-Holocene slides on the mid-Norwegian continental margin between 62 and 67°N have been investigated. Most of the slides are located in the area of the Holocene Storegga Slide and in the North Sea Fan. The largest of the pre-Holocene slides are comparable in size to the Storegga Slide. With the exception of one slide, the sliding took place after the onset of continental shelf glaciations at 0.5Ma. Despite limited chronostratigraphic resolution, at least one large slide apparently occurs during every 100ky, following glacial–interglacial cyclicity. The slides have several common characteristic features, and they detach in fine-grained, seismically stratified hemipelagic deposits, commonly developed as contourite drifts. The instability is most likely created by pore overpressure built up in the hemipelagic deposits by rapid loading from glacial deposits. In some cases fluid flow from underlying oozes, may be a cause of overpressure. Earthquakes are the most likely trigger. The slide morphologies and other characteristic features favour a retrogressive slide development, as also suggested for the Storegga Slide. The area of the Storegga Slide Complex is particularly slide prone because of its structural setting and the preference for fine grained drift deposition in this region.

New marine geological evidence provides a better understanding of ice-sheet dynamics along the western margin of the last Svalbard/Barents Sea Ice Sheet. A suite of glacial sediments in the Kongsfjordrenna cross-shelf trough can be traced southwards to the shelf west of Prins Karls Forland. A prominent moraine system on the shelf shows minimum Late Weichselian ice extent, indicating that glacial ice also covered the coastal lowlands of northwest Svalbard. Our results suggest that the cross-shelf trough was filled by a fast-flowing ice stream, with sharp boundaries to dynamically less active ice on the adjacent shelves and strandflats. The latter glacial mode favoured the preservation of older geological records adjacent to the main pathway of the Kongstforden glacial system. We suggest that the same model may apply to the Late Weichselian glacier drainage along other fjords of northwest Svalbard, as well as the western margin of the Barents Ice Sheet. Such differences in glacier regime may explain the apparent contradictions between the marine and land geological record, and may also serve as a model for glaciation dynamics in other fjord regions.

Between about 12 and 4–3 Ma, slope-parallel bottom currents dominated the Neogene sedimentation on the slope of the Mid-Norwegian margin, and large-scale sediment bodies accumulated to thicknesses up to 1000 m. These bedforms are morphologically classified as sheeted and elongated mounded contourite drifts. An increase in sediment supply from about 4 to 3 Ma, due to onshore uplift and glaciation, resulted in a massive influx of downslope-derived material onto the continental margin. Only on the Vøring Plateau was contourite sedimentation little affected by this change in sedimentary style. During the last 0.5 My contouritic deposits occurred also in the Storegga area as 100–150 m thick infill drifts inside the scars of two palaeo-slides (R and S). Holocene post-slide deposits in the scar of the Storegga Slide (8.2 ka) have the typical morphological features and distribution of contourite drifts with the upslope limit at the lower base of the warm northward flowing North Atlantic Current at 500–700 m depth and the downslope limit at depths of approximately 1200 m. Detailed chronostratigraphy of the post-slide sediments show relatively constant high sedimentation rates in the order of 1–2 m/ky during the last 8000 years. This is equivalent to the estimated rates for the older infill drifts. The infill drifts consist mainly of clays with silty and sandy lamina and represents marine and glaciomarine conditions. The main influence of contourite drifts on slope stability relates to their physical properties forming a more sensitive and brittle deposit than the glacial deposits and their exposure to downslope sedimentation. In addition, the potential for build-up of excess pore pressure due to rapid loading from subsequent glacial depositions, their seabed smoothing effect, and great lateral extent, make the contourite drift deposits particularly important for slope instability in this region.

A large volume of geological, geophysical and geotechnical data have been acquired over the last decade in order to perform a safe development of the Ormen Lange gas field, which is located in the scar of the Holocene Storegga Slide, the last in a series of large slides in this region over the last 500ky. Based on high resolution seismic data and a series of geotechnical borings, a unified Pleistocene stratigraphy has been established for the area. Two main modes of deposition prevailed in the Pleistocene. During periods of peak glaciation, when glaciers extended to the shelf break, basal tills were deposited on the shelf, and glacial debris flows on the continental slope. During the much longer periods of reduced ice cover, including interglacial periods, normal marine and distal glacial marine deposition prevailed, partly developed as contourites on the slope. The resulting two sediment types are unsorted glacial diamictons, and fine grained, partly laminated sediments, respectively. These display distinctly different sedimentological and geotechnical properties, and the failure planes for all the major slides are found in the fine grained marine deposits.

A great effort has been undertaken to investigate potential geohazards in relation to the development of the Ormen Lange gas field offshore Mid-Norway. The field is located in the scar left after the giant, tsunami-generating Storegga Slide, which occurred roughly 8150 years ago, and the slide risk has consequently received particular focus. The studies have been multi-disciplinary in character, and have involved a number of companies, universities, and research institutions. The results of the project have lead to a significant advance in our understanding of the Storegga Slide in particular, and submarine slope instability in general, and played an important role in the approval of field development by Norwegian authorities. This special issue comprises 26 individual contributions in addition to this representing the wide span of topics addressed in the project, and this introductory paper gives a brief summary of their contents.

Two large submarine slides, The Storegga and the Traenadjupet Slides, occurred on the Mid-Norwegian margin during the Holocene. The Ormen Lange gas field is located within the scar of the Storegga Slide. This gigantic submarine slide occurred about 8200 years ago, and caused large waves (tsunamis) that reached the coasts of Norway, Scotland, Shetland and the Faroe Islands. The objectives of this chapter are to present the challenges and the slide risk assessment related to the development the Ormen Lange gas field. The risk evaluation is based on a qualitative approach for large natural slides, and a quantitative approach for new small slides in the vicinity of the development area.The work programme includes extensive, regional multi-disciplinary studies, carried out jointly by academia, industry and research institutions. The database includes an extensive grid of seismic data, detailed sea-floor morphology and sediment properties from a number of 'geoborings' (combined geological and geotechnical borings to sub-bottom depths of 200-400 m). Stability of the steepest slopes in the vicinity of the development area is calculated. Effects of excess pore pressures, earthquakes, reservoir compaction during depletion and underground gas blowouts into possible permeable layers have all been included in the stability calculations. To understand the recent slide history in the area and to find the frequency of the sliding, extensive sea-floor mapping and coring to date slide events are also included.A geological model for the Plio-Pleistocene of the area explains the large-scale sliding as a response to climatic variability. Over long periods, marine deposition prevailed with focused deposition due to current effects in the locations of the Storegga and the Traenadjupet Slides. During short intervals of peak glacial conditions, till and glacial debris flow sediments were deposited at high rates directly on the continental slope. This created excess pore pressures in the thick marine deposits. The most likely triggering mechanism of the slides is a strong earthquake following the onshore uplift after the glaciation. This explains why the slides take place after a glacial period. Since all the soft unstable clays were removed from the Storegga Margin during the last slide, it is concluded that a new cycle with sedimentation of soft clays and deposition of glacial sediments in the upper slopes are needed, to create a new unstable situation in the Storegga area. At present, the slopes in the Ormen Lange area have high safety factors, and the likelihood of new slides, both local and regional, is considered very low.

There is an urgent need to Improve the basic understanding of geohazards and our ability to deal with the risks associated with them. The International Centre for Geohazards (ICG) does research on the assessment, prevention and mitigation of geohazards, offshore as well as on land. The main focus is placed on landslides and their effects, such as tsunamis. Activities include hazard and risk assessment for slides and earthquakes, evaluation of soil and rock slopes, instrument design and monitoring, geophysical methods, field studies, application of SAR technology for monitoring of slopes, further development of GIS as a tool in geohazard assessment, tsunami research, and numerical modelling. Education is given high priority, and graduate programmes in geohazards have been established at both the University of Oslo and at NTNU in Trondheim. Over the next few years, emphasis will also be placed on monitoring, early warning systems, and mitigation measures.

A 12.5 m long core was retrieved from the continental margin off Dronning Maud Land, Antarctica. Magnetostratigraphy, stable isotopes, 14C accelerator mass spectrometer and amino acid analyses indicate a continuous sediment record going back 1.3 Myr. Comparison of CaCO3 results with those from ODP Site 1089 and an index of North Atlantic Deep Water (NADW) influence in surface waters indicate that NADW upwelled along the Antarctic continental margin during the whole of this period. The mid-Pleistocene transition (1.0–0.6 Ma) was accompanied by an apparent decline in the NADW influence, and was followed by extended carbonate dissolution during the interglacials of marine isotope stages (MIS) 13 and 11. Less extensive periods of dissolution occur at the end of the interglacials younger than MIS 11. While interglacial dissolution is characteristic of the Pacific and Indian oceans, the carbon isotopes return to pre-transition values indicative of renewed NADW upwelling. The concentration of ice-rafted debris may reflect changes in the relative rate of interglacial sedimentation. It is speculated that the high ice rafted debris (IRD) concentrations during interglacials younger than 400 kyr may be due to a reduced relative sedimentation rate of other interglacial components whereas the low concentrations during interglacials before the mid-Pleistocene transition may be due to a higher relative sedimentation rate of these.