Origin of shallow submarine mass movements and their glide planes—Sedimentological and geotechnical analyses from the continental slope off northern Norway

Abstract

Submarine landslides are often characterized by a basal surface of rupture parallel to the stratigraphy, in which downslope movement is initiated. However, little is known about the sedimentology and physical properties of the sediments within these surfaces. In this study, we present a multiproxy analysis of the sediments collected from a giant piston core penetrating a shallow submarine mass transport deposit, in combination with high-resolution seismoacoustic data to identify and characterize the basal glide plane and the weaker sediments in which movement was initiated. The initial phase of instability consists of a single fracture that formed due to the downslope movement of a mostly intact slab of sediments. The 16 m long core, comprising mostly undisturbed massive and laminated ice-rafted debris-rich clay penetrated this slab. The base of the slab is characterized by a high-amplitude semicontinuous reflection visible on the subbottom profiler data at about 12.5 m depth, interpreted to originate from the glide plane on top of a plumite deposit. This plumite has dilative behavior with pore pressure decrease with increasing shear strain and high undrained shear strength. Movement probably started within contouritic sediments immediately above the glide plane, characterized by higher sensitivities and higher water contents. The occurrence of the mass movements documented in this study are likely affected by the presence of a submarine landslide complex directly downslope. The slide scar of this landslide complex promoted retrogressive movement farther upslope and progressive spreading of strain softening along the slide base and in the slide mass. Numerical models (infinite slope, BING, and retrogressive slope models) illustrate that the present-day continental slope is essentially stable and allow reconstruction of the failure processes when initiated by an external trigger.

Chronology and extent of the Lofoten–Vesterålen sector of the Scandinavian Ice Sheet from 26 to 16 cal. ka BP

“…1). Column 1 = calibrated radiocarbon ages; 2 = chronology of the stratigraphical units in lake Endletvatn; 3 = July mean temperature on Andøya, interpreted from pollen and plant macrofossils in lake cores; 4 = glacial events as described in this paper; FS = Flesen inter-event period; EF = Endleten -Flesen inter-event period; 5 = lithostratigraphy and chronology of core GS10-163-3-PC from the Lofoten Contourite Drift based on data from Baeten et al (2014); 6 = IRD curve from the same core displaying a five-point running average based on the original data in Rørvik et al (2010); 7 = shoreline displacement on northern Andøya. Columns 1, 2, 3 and 7 are from Vorren et al (2013).…”

“…Dahlgren & Vorren (2003), based on seismic data and cores (JM98-625/1) (Fig. 1) Baeten et al (2014) analysed a giant piston-core (GS10-163-3PC) retrieved from the Lofoten Contourite Drift (location in Fig. 1).…”

“…9). Baeten et al (2014) inferred that two plumite beds dated to around 25.5 (Egga I) and 22.2 (Egga II) cal. ka BP were derived from meltwater outbursts, as also interpreted from other locations on the Norwegian continental slope (Haflidason et al 2004;Lekens et al 2005;Lucchi et al 2012).…”

“…The younger plumite was deposited contemporaneously with the deglaciation of the northern tip of Andøya, indicating parallel melting/deglaciation in the two areas. About 200 years later, a 0.9-m-thick debrisflow that could have been released by the ice sheet reaching the shelf break was deposited (Baeten et al 2014). The debrisflow deposits cannot be correlated to the nearby core MD99-2294 (location in Fig.…”

Submarine Mass Movements and their Consequences

“…Haflidason et al 2004;Baeten et al , 2014Elger et al 2015). Haflidason et al 2004;Baeten et al , 2014Elger et al 2015).…”