ALBERT

Beschreibung: 〈p〉This paper presents the geohazard assessment for a proposed bridge across Bjørnafjorden in western Norway. The fjord is 〈i〉c.〈/i〉 5 km wide with a maximum depth of 550 m at the proposed bridge crossing. The main geohazards of concern are submarine slope instabilities. To identify locations of instability, their susceptibility to failure, and their potential runout distances, we performed the following analyses: (1) static and pseudo-static limit equilibrium analyses for the entire fjord crossing area; (2) 1D seismic slope stability sensitivity analyses for different slope angles and soil depths; (3) 2D static and pseudo-static finite element analyses for selected profiles; (4) back-analysis of a palaeolandslide; and (5) quasi-2D and quasi-3D landslide dynamic simulations calibrated using results from the back-analysis. The workflow progresses from simplified to more advanced analyses focusing on the most critical locations. The results show that the soils in many locations of the fjord are potentially unstable and could be the loci of landslides and debris flows. The evidence of numerous palaeosubmarine landslides identified on geophysical records reinforces this conclusion. However, the landslide triggers and timing are currently unknown. This paper demonstrates the need for comprehensive and multidisciplinary geohazard analyses for any infrastructure projects conducted in fjords.〈/p〉

Beschreibung: This paper presents the geohazard assessment for a proposed bridge across Bjørnafjorden in western Norway. The fjord is c. 5 km wide with a maximum depth of 550 m at the proposed bridge crossing. The main geohazards of concern are submarine slope instabilities. To identify locations of instability, their susceptibility to failure, and their potential runout distances, we performed the following analyses: (1) static and pseudo-static limit equilibrium analyses for the entire fjord crossing area; (2) 1D seismic slope stability sensitivity analyses for different slope angles and soil depths; (3) 2D static and pseudo-static finite element analyses for selected profiles; (4) back-analysis of a palaeolandslide; and (5) quasi-2D and quasi-3D landslide dynamic simulations calibrated using results from the back-analysis. The workflow progresses from simplified to more advanced analyses focusing on the most critical locations. The results show that the soils in many locations of the fjord are potentially unstable and could be the loci of landslides and debris flows. The evidence of numerous palaeosubmarine landslides identified on geophysical records reinforces this conclusion. However, the landslide triggers and timing are currently unknown. This paper demonstrates the need for comprehensive and multidisciplinary geohazard analyses for any infrastructure projects conducted in fjords.

Beschreibung: The history of the Late Weichselian northwestern Barents Shelf, including western Svalbard, has been investigated by provenance/sedimentologist studies of five cores from the continental shelf and slope west of Svalbard. The chronostratigraphy of the cores is based on AMS 14C dates and oxygen isotope analyses. Interpretations of the cores suggest that the ice sheets of western Svalbard and northwestern Barents Sea experienced advances and retreats in two steps. The first significant ice advance beyond the present coastline occurred ca. 22,000 14C yr B.P. and was followed by an ice advance to the shelf edge ca. 18,000 14C yr B.P. Ice recession from the outer shelf and the southwestern Barents Sea began 14,800 14C yr B.P. and was followed by a second ice recession between 13,000 and 12,000 14 C yr B.P. during which ice withdrew from the inner shelf. A minor readvance of the ice sheet on the shelf west of Svalbard occurred close to 12,400 14C yr B.P. The first deglaciation event was associated with release of icebergs containing ice-rafted detritus, while the later episode also included significant amounts of meltwater and fine-grained sediment.

Beschreibung: Highlights • Increased glacial sedimentation rates do not generate sufficient overpressure to trigger a landslide. • Simulated overpressures for different sedimentation scenarios do not significantly differ. • A glacimarine layer underneath rapidly-deposited sediments is important for overpressure build-up. • An earthquake of M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the Tampen Slide. Abstract Trough mouth fans are environments characterized by high sediment supply during glacial stages and the occurrence of large-scale instabilities. The geological record indicates that several of these environments have failed repeatedly resulting in large submarine landslides. The roles of sedimentation rate, weak layers, glacial loading and unloading as well as seismic activity on triggering megaslides in trough-mouth-fan systems is still unclear. A better understanding of the preconditioning factors, triggers and consequences of these landslides is crucial due to the hazard they pose to coastal communities and offshore industries. In this paper, we focus on the North Sea Trough Mouth Fan, which is the result of massive glacial sediment input delivered to the shelf edge through the Norwegian Channel, southeast Nordic Seas margin. The Tampen Slide, one of several large paleo-landslides that have happened within the North Sea Trough Mouth Fan, took place at c. 130 ka (end of MIS 6), and removed an estimated 1800 km3 of sediment. Here, we use boundary conditions from the Tampen Slide and 2D Finite Element Modeling (Abaqus software from Simulia) to evaluate the effects of variations in sedimentation rates as well as sediment properties on the generation of excess pore pressure, fluid flow, and slope stability along the axis of the trough-mouth-fan system. The model domain, 40 km in length and 2 km in height, is dominated by glacigenic debris flows and glacimarine sediment deposits. We use geotechnical data measured on samples of glacigenic and glacimarine sediment deposits from the nearby Ormen Lange gas field area to constrain the model. We evaluate the stability of the slope under various scenarios, including constant sediment loading, episodic changes in sedimentation rates and abrupt pulses in sediment delivery for a 61 kyr period (MIS 6). The models show that increased sedimentation rates during glacial stages do not generate sufficient excess pore pressure to set off a landslide. Furthermore, the simulated overpressures for the different sedimentation scenarios do not significantly differ at the end of the model runs. The results also highlight the importance of a basal glacimarine sediment layer underneath the rapidly-deposited sediments for the build-up of overpressure. Consequently, this glacimarine sediment layer has the inherited potential to act as a weak layer facilitating instability. However, as overpressure due to sediment deposition alone does not result in slope failure, we couple the preconditioned slope with earthquake ground shaking. Based on attenuation models, an earthquake of approximately M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the landslide. Therefore, we suggest glacial sedimentation and a glacimarine sediment layer to represent preconditioning factors, and seismic shaking as the final trigger mechanism for the Tampen Slide, i.e. similar to the situation that lead to the development of the Storegga Slide in the same area.

Beschreibung: 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 μm, 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; 217–435 mbsf) at Site 1167 on the Prydz Channel Fan.

Beschreibung: Published

Beschreibung: 184-201

Beschreibung: 2.2. Laboratorio di paleomagnetismo

Beschreibung: JCR Journal

Beschreibung: reserved

Beschreibung: 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 investigate the two sites, ODP Site 1166 on the shelf and 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, sand content, physical and magnetic properties were analysed. 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 (217 – 435 mbsf) at Site 1167 on the Prydz Channel Fan.

Beschreibung: In press

Beschreibung: 2.2. Laboratorio di paleomagnetismo

Beschreibung: JCR Journal

Beschreibung: reserved