The Subantarctic Front (SAF), one of the three main jets of the Antarctic Circumpolar Current (ACC), flows through a narrow gap in the North Scotia Ridge and then northwestward across the continental slope of Burdwood Bank, ~150 km south of the Falkland Islands. There, the SAF flows across a fold-and-thrust belt caused by oblique convergence at the active plate boundary between the Scotia Plate and South American Plate. We here use regional 2D and 3D seismic reflection data to show the interaction of the associated bottom currents with the active margin, particularly to understand the causes and consequences of a number of large submarine landslides located in the adjacent foredeep. Kinematic indicators from the landslide deposits show that they are derived from a single point source located in an embayment on the northern slope of Burdwood Bank, where we identify a large contourite drift deposit. This drift forms the depositional sink for an alongslope sediment routing system driven by currents associated with the SAF, with sediment Journal Pre-proof J o u r n a l P r e -p r o o f being eroded from the Burdwood Terrace, transported ~200 km westward, and plastered against the middle-upper continental slope. The contourite drift is undercut by the core of the current, making the slope inherently unstable in this area. Numerical modelling of the landslides and resultant waves indicates the tsunamigenic potential of these events. Modelled peak wave elevations of up to 40 m inundate the southern coast of the Falklands for a ~100 km 3 volume landslide, with a recurrence interval of 1 Ma or less. This research highlights preconditioning mechanisms for submarine failure on continental slopes dominated by strong ocean currents, and specifically, oceanographic controls on the frequency, magnitude and location of submarine landslides associated with contourite systems.

As part of a preliminary evaluation of a deep geological repository for spent nuclear fuel, the hydraulic properties of a discrete fracture network were calibrated using published permeability data from comparable sparsely fractured crystalline rock. These permeability data exhibit two primary trends: a relatively gradual reduction with depth below c. 300 m and a marked increase above c. 300 m depth. Respectively, these are hypothesized to be caused by progressive fracture closure with increasing confining stress and periodic shear dilation of fractures proximal to stress criticality due to long-term natural fluctuations in and redistribution of stress. The links between bedrock stress, fracture geometry, and fracture hydraulic properties are widely recognized, and many numerical models describe these relationships. Several combinations of models were considered: four models for the relationship between fracture stress and hydraulic aperture, two models to identify critically stressed fractures, and two models to calculate critically stressed apertures. Appropriate calibration permitted these models to correlate well with both the major trends in the data and additional subtleties, indicating they can capture the interactions of the modelled natural processes. In contrast to empirical fitting of observed data, this suggests the models can produce predictive results.

The Olkiluoto site is a proposed spent nuclear fuel disposal facility in Finland. Surface-based drilling and logging of more than fifty drillholes has provided the basis for characterizing bedrock fracture models and associated hydraulics at the site. Alongside core and image logs, the high resolution Posiva Flow Logging (PFL) tool allowed the interpretation of fracture-specific flow statistics and their correlation with structural properties, orientation and geological domain. This permitted characterization of inter-fracture variability. However, because of the hundreds of meters between investigation holes it was not possible to conceptualize heterogeneity within single fractures. A new underground dataset has become available from the excavation of four c. 400 m deep vertical access and ventilation shafts, where dense drilling around the circumference of the shafts for several wet sections has been performed as part of pre-grouting operations. PFL testing in these holes and the subsequent grout injection data provided an opportunity to characterize both multi-meter scale in-plane heterogeneity and flow dimension, and thereby better understand flow channeling and water-rock interactions.