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Abstract

Swath bathymetry data from the glacier-fed northern Svalbard margin reveal geomorphological details of a large submarine landslide, the Hinlope-Yermak Landslide. Multiple planar escarpments have several hundreds of meters of relief, with a maximum headwall height exceeding 1400 m at the mouth of the Hinlopen cross-shelf Trough. Within the slide-scar area, this landslide created a rugose seabed geomorphology, with little mass-transport deposition in the immediate vicinity of major escarpments. Beyond a pronounced constriction, occurrence of semitransparent acoustic units on seismic profiles indicates that mass-transport deposits are likely the accumulation of remolded and/or fluidized debris flows that are in places hundreds of meters thick. The surface expression of the masstransport deposits is hummocky with flow structures, arcuate pressure ridges, and rafted blocks. Smaller debris lobes close to landslide sidewalls are the result of secondary, marginal failures. At the outer rim of extensive mass-transport deposits, numerous rafted blocks rise from the semitransparent sediment unit, and tower hundreds of meters above the surrounding debris. Maximum remobilized volume from the slide-scar area, estimated from pre-landslide bathymetric reconstruction, is approximately 1350 km3. Headwall heights, the ratio of excavated volume and slide scar area, and the height of rafted blocks are large, compared to other landslides documented on siliciclastic margins.

The position, thickness, and shape of the mass-transport deposits illustrate high mobility of sediments involved in submarine landsliding. Their dimensions require numerical modeling to understand landslide dynamics and potential to generate tsunamis. In simulations of sediment dynamics, large blocks are rafted by a loose debris flow, derived from disintegrating landslide material in the headwall area. The main failure process finishes after approximately 1 hour. The upper slide scar is probably not the source area for large rafted blocks.

The Hinlopen-Yermak landslide most likely created a significant tsunami, considering that remobilized sediment volume, initial acceleration, maximum velocity, and possible retrogressive development govern landslide-generated tsunamis. Steep waves, implying dispersive and nonlinear effects, probably were more pronounced than for most other tsunamis induced by submarine landslides. These features exist because of the combination of high speed and substantial thickness of mass transport. Propagation and coastal impact of the tsunami is simulated by a weakly nonlinear and dispersive Boussinesq model. Close to the landslide area, simulations return sea-surface elevations exceeding 130 m, whereas sea-surface elevations along coasts of Svalbard and Greenland are on the order of tens of meters.

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