Judith Elger

Submarine slope failures due to pipe structure formation

There is a strong spatial correlation between submarine slope failures and the occurrence of gas hydrates. This has been attributed to the dynamic nature of gas hydrate systems and the potential reduction of slope stability due to bottom water warming or sea level drop. However, 30 years of research into this process found no solid supporting evidence. Here we present new reflection seismic data from the Arctic Ocean and numerical modelling results supporting a different link between hydrates and slope stability. Hydrates reduce sediment permeability and cause build-up of overpressure at the base of the gas hydrate stability zone. Resulting hydro-fracturing forms pipe structures as pathways for overpressured fluids to migrate upward. Where these pipe structures reach shallow permeable beds, this overpressure transfers laterally and destabilises the slope. This process reconciles the spatial correlation of submarine landslides and gas hydrate, and it is independent of environmental change and water depth.There is a strong correlation between submarine slope failures and the occurrence of gas hydrates. Here, the authors use a combination of seismic data and numerical modelling to show that overpressure at the gas hydrate stability zone leads to potential destabilization of the slope and submarine landslides.

The Fram Slide off Svalbard: a submarine landslide on a low-sedimentation-rate glacial continental margin

Submarine slope failures are a widespread, hazardous phenomenon on continental margins. The prevailing opinion links large submarine landslides along the glaciated NW European continental margins to overpressure generated by the alternation of rapidly deposited glacigenic and hemipelagic material. Here, we report a newly discovered large landslide complex off NW Svalbard. It differs from all known large slides off NW Europe, as the available data rule out that this slope failure resulted from rapid glacigenic deposition. This suggests that processes such as contour currents, tectonic faulting, and overpressure build-up related to the gas hydrate system must be considered for hazard assessment. Supplementary material: Supplementary data are available at http://www.geolsoc.org.uk/SUP18803.

Arctic megaslide at presumed rest

Slope failure like in the Hinlopen/Yermak Megaslide is one of the major geohazards in a changing Arctic environment. We analysed hydroacoustic and 2D high-resolution seismic data from the apparently intact continental slope immediately north of the Hinlopen/Yermak Megaslide for signs of past and future instabilities. Our new bathymetry and seismic data show clear evidence for incipient slope instability. Minor slide deposits and an internally-deformed sedimentary layer near the base of the gas hydrate stability zone imply an incomplete failure event, most probably about 30000 years ago, contemporaneous to or shortly after the Hinlopen/Yermak Megaslide. An active gas reservoir at the base of the gas hydrate stability zone demonstrate that over-pressured fluids might have played a key role in the initiation of slope failure at the studied slope, but more importantly also for the giant HYM slope failure. To date, it is not clear, if the studied slope is fully preconditioned to fail completely in future or if it might be slowly deforming and creeping at present. We detected widespread methane seepage on the adjacent shallow shelf areas not sealed by gas hydrates.

Corrigendum: Arctic megaslide at presumed rest

Scientific Reports 6: Article number: 38529; published online: 06 December 2016; updated: 17 May 2017 In Figure 1, the latitudes ‘80.5 N’ and ‘81.0 N’ were incorrectly given as ‘81.0 N’ and ‘81.5 N’ respectively. In addition, the scale between 0 km and 40 km was incorrectly given as between 0 km and80 km.

RV SONNE 252 Cruise Report / Fahrtbericht,Yokohama: 05.11.2016 - Nouméa: 18.12.2016.SO252: RITTER ISLAND Tsunami potential of volcanic flank collapses

Large volcanic debris flows associated with volcanic island flank collapses may cause devastating tsunamis as they enter the ocean. Computer simulations show that the largest of these volcanic debris flows on oceanic islands such as Hawaii or the Canaries can cause ocean-wide tsunamis (Lovholt et al., 2008; Waythomas et al., 2009). However, the magnitude of these tsunamis is subject to on-going debate as it depends particularly on landslide transport and emplacement processes (Harbitz et al. 2013). A robust understanding of these factors is thus essential in order to assess the hazard of volcanic flank collapses. Recent studies have shown that emplacement processes are far more complex than assumed previously. With a collapsed volume of about 5 km3 the 1888 Ritter Island flank collapse is the largest in historic times and represents an ideal natural laboratory for several reasons: (I) The collapse is comparatively young and the marine deposits are clearly visible, (II) the pre-collapse shape of the island is historically documented and (III) eyewitness reports documenting tsunami arrival times, run-up heights and inundation levels on neighboring islands are available. We propose to collect bathymetric, high resolution 2D and 3D seismic data as well as seafloor samples from the submarine deposits off Ritter Island to learn about the mobility and emplacement dynamics of the 1888 flank collapse landslide. A comparison to similar studies from other volcanic islands will provide an improved understanding of emplacement processes of volcanic island landslides and their overall tsunamigenic potential. In addition, a detailed knowledge of the 1888 landslide processes in combination with tsunami constraints from eyewitness reports provides a unique possibility to determine the landslide velocity, which can then be used in subsequent hazard analyses for ocean islands.