Eivissa slides, western Mediterranean Sea: morphology and processes

Abstract

After obtaining full-coverage swath bathymetry data in 1995 and very high-resolution acoustic profiles in 2002, four slides at the Balearic Margin of the Eivissa Channel in the western Mediterranean Sea were revisited in 2004 when side-scan sonar data were collected using a MAK-1M deep-towed acoustic system. These new findings, higher in resolution than those for the swath bathymetry, show two main features previously undetected within these submarine landslides: (1) a series of step-forming inclined and detached slabs oriented perpendicular to the slide movement and located in the uppermost part of the slides, and (2) arcuate regular positive ridges oriented also normal to the slide movement and located in the depositional lobes of some of the slides. The former are interpreted as extensional ridges, suggesting a retrogressive post-failure evolution of the slides. The latter are interpreted as compression ridges, related to plastic deformation of the sediment before movement freezing. Moreover, the new data show that fluid escape features are even more widespread in the Eivissa Channel than previously thought, dozens of new pockmarks less than 20 m in diameter having been identified

Morphology and mechanics of submarine spreading: A case study from the Storegga Slide

“…Spreading primarily involves extensional deformation. In some places, however, the spread may have undergone compression, as suggested by the presence of groups of high convex‐downslope ridges and troughs (Figure 4a), and as previously described in other mass movements [e.g., Lastras et al , 2006]. This compression is attributed to the slowing down of the leading edge because of, for example, increased fragmentation and the associated reduction in pore pressure, or a decrease in the gradient of the slip surface.…”

“…(b) TOBI side‐scan sonographs of the Nyk Slide headwall, modified from Lindberg et al [2004], reprinted with permission from Elsevier, copyright 2004. (c) MAK‐1M sidescan sonar system sonograph across the Nuna Slide headwall scar, modified from Lastras et al [2006, Figure 4], reprinted with kind permission of Springer Science and Business Media. (d) TOBI side‐scan sonographs of the headwall of the BIG'95 debris flow, modified from Lastras et al [2003, Figure 2], reprinted with kind permission of Springer Science and Business Media.…”

Submarine Mass Movements and their Consequences

“…In the upper part of the scar area, we observe the presence of a series of stepforming inclined and detached slabs, that can be interpreted as extensional ridges (Lastras et al 2006). Lastras et al 2006;Moscardelli et al 2006). A possible rafted block identified in the eastern slide (profile C-D in Fig.…”

“…The channels on the slope are erosional features that are probably related to density flows from a process analogous to dense shelf water cascading (DSWC) seen in the marine environment (Canals et al 2006;Puig et al 2008). The density of the flows is unlikely to be due to suspended sediments as the basin accumulation rate is low.…”

“…In this paper we address the hypothesis that, by influencing pore pressure in sub-seafloor sediment, shallow gas can promote the development of a weak layer above which submarine spreading can occur. Nevertheless, the characteristic submarine spreading morphology, in the form of a recurring pattern of ridges and troughs, can be observed in numerous submarine landslides around the world (Lastras et al 2003(Lastras et al , 2006Micallef et al 2013;Piper et al 1999;. 42.1).…”