ABSTRACT The rifted Precambrian margin of western Laurentia is hypothesized to have consisted of a series of ~330°-oriented rift segments and ~060°-oriented transform segments. One difficulty with this idea is that the 87 Sr/ 86 Sr i = 0.706 isopleth, which is inferred to coincide with the trace of this rifted margin, is oriented approximately N-S along the western edge of the Idaho batholith and E-W in northern Idaho; the transition between the N-S– and E-W–oriented segments occurs near Orofino, Idaho. We present new paleomagnetic and geochronologic evidence that indicates that the area around Orofino, Idaho, has rotated ~30° clockwise since ca. 85 Ma. Consequently, we interpret the current N-S–oriented margin as originally oriented ~330°, consistent with a Precambrian rift segment, and the E-W margin as originally oriented ~060°, consistent with a transform segment. Independent geochemical and seismic evidence corroborates this interpretation of rotation of Blue Mountains terranes and adjacent Laurentian block. Left-lateral motion along the Lewis and Clark zone during Late Cretaceous–Paleogene time likely accommodated this rotation. The clockwise rotation partially explains the presence of the Columbia embayment, as Laurentian lithosphere was located further west. Restoration of the rotation results in a reconstructed Neoproterozoic margin with a distinct promontory and embayment, and it constrains the rifting direction as SW oriented. The rigid Precambrian rift-transform corner created a transpressional syntaxis during middle Cretaceous deformation associated with the western Idaho and Ahsahka shear zones. During the late Miocene to present, the Precambrian rift-transform corner has acted as a fulcrum, with the Blue Mountains terranes as the lever arm. This motion also explains the paired fan-shaped contractional deformation of the Yakima fold-and-thrust belt and fan-shaped extensional deformation in the Hells Canyon extensional province.

Abstract Characterized by an active margin to the west, passive margins to the east and north, and numerous fjords and estuaries, the seafloor of Canada is prone to subaqueous landslides. The Geological Survey of Canada (GSC) facilitates government response in times of crisis by providing timely and concise information to Canadians, and informs the strategies to address natural hazards. Thus, the GSC is conducting a national assessment of the subaqueous landslide hazard. This paper reviews dozens of major subaqueous mass movement deposits with an emphasis on recent publications and summarizes the attempt to produce a national database. The types range from ephemeral turbidity current deposits to very large deposits (>100 km 3 ). To date, 1266 deposits are identified with many more expected as mapping progresses. This work is important as it will feed into the larger national tsunami strategy, and is a step forward for the national government to manage the risk. Canada is among the first countries to enter its entire database using the consistent morphometric characterization recommended by members of the UNESCO IGCP-640 (S4SLIDE) Community.

Abstract Turbidity currents transport globally significant volumes of sediment and organic carbon into the deep-sea and pose a hazard to critical infrastructure. Despite advances in technology, their powerful nature often damages expensive instruments placed in their path. These challenges mean that turbidity currents have only been measured in a few locations worldwide, in relatively shallow water depths (<<2 km). Here, we share lessons from recent field deployments about how to design the platforms on which instruments are deployed. First, we show how monitoring platforms have been affected by turbidity currents including instability, displacement, tumbling and damage. Second, we relate these issues to specifics of the platform design, such as exposure of large surface area instruments within a flow and inadequate anchoring or seafloor support. Third, we provide recommended modifications to improve design by simplifying mooring configurations, minimizing surface area and enhancing seafloor stability. Finally, we highlight novel multi-point moorings that avoid interaction between the instruments and the flow, and flow-resilient seafloor platforms with innovative engineering design features, such as feet and ballast that can be ejected. Our experience will provide guidance for future deployments, so that more detailed insights can be provided into turbidity current behaviour, in a wider range of settings.

Abstract Central America is a small and culturally homogeneous region that, since the 1990s, has experienced economic and political integration of its six countries, which share the same threats of volcanic eruptions, disastrous earthquakes and tsunamis. The Pacific coastline of 1700 km is common for Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica and Panama, and the Pacific subduction zone has the potential for creating huge tsunamis that threaten this coast. In addition to the natural hazard, the growing tourist industry is expanding its infrastructure along the Pacific beaches, which again enhances the exposure and tsunami risk. Even though the 1992 tsunami disaster in Nicaragua did not severely hit the tourist beaches, it raised the risk awareness, and special attention is now given to ‘slow’ earthquakes that may be modest in shaking while still having a large tsunami potential. The tsunami hazard mapping is well advanced in Nicaragua, Costa Rica and El Salvador, and initiatives are ongoing to improve the mapping in all countries. National systems for early warning were established in Nicaragua and El Salvador, while the other four countries rely on rapid information from the Pacific Tsunami Warning Center. Mitigation measures and information campaigns are presently conducted on a national basis in all countries, but a regional centre for early tsunami warning and coordinated information campaigns (CATAC) is expected to become operational in the near future.