An Exploratory Modelling Study on Late Pleistocene Mega-Tsunamis Triggered By Giant Submarine Landslides in the Mediterranean

Abstract

Gigantic submarine landslides are among the most energetic events on the Earth surface. During the Late Pleistocene the Mediterranean Sea was the scenario of a 9 number of such events, some of whose geological fi ngerprints are the 500 km 3 mass transport deposit SL2 at the Nile delta fan (dated at ca. 110 ka BP) and the Herodotus Basing Megaturbidite (HBM, a 400 km 3 deposit dated at ca. 27.1 ka BP). This paper presents an exploratory study on the tsunamigenic potential of these slides by using a numerical model based on the 2D depth-averaged non-linear barotropic shallow water equations. The sliding mass is modelled both as a rigid block with a prescribed motion and as a viscous fl ow layer. The 26 km 3 debris fl ow BIG'95 scenario (at the Ebro continental slope, 11.5 ka BP) served for model com-parison against independent modelling works. Based upon the available geologicalstudies, several source scenarios have been modelled. Our results show that the generated tsunamis would have had up to hundred fold the peak energy of some extreme historical ones, such as the 1755 Lisbon tsunami. Thus, the HBM tsunami could have reached peak energies over one hundred Megatons, producing runups over 50 m height along some 1300 km 2 of shoreline in the eastern Mediterranean.The study also comprises their propagation pattern, their impacts along the former shoreline and their energy partitioning. The highest tsunami energies were associated to thick landslides at shallow depths, with high slope angles and within a gulf geometry.

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“…As a practical approach, the former slide at its initial position will be superposed onto the present-day bathymetry of the source area. The greatest part of the energy transfer to the water column takes place during the first stage of the slide displacement (approximately until the time of its maximum velocity) [38]. Details of the subsequent history (including deformation and breaking up of the slide, and the accurate update of the seafloor bathymetry) will contribute only as second order corrections.…”

“…The "two slope angle" kinematics is a model choice, being more general than the single sinus function used by Harbitz (1992) [36], but containing it as a particular case, and it allows generating asymmetric velocities profiles (as the ones used by Lastras et al, 2005, [39]). Applications of this model can be found in Periáñez and Abril (2014a) [25] and in Abril and Periáñez (2015) [38]. Friction stresses over the moving slide are formulated in terms of relative speed, as in Harbitz (1992) [36], in such a way that a slice moving faster than the water column can transfer energy to it.…”

“…A further validation for the performance of the numerical model with its flood-drying algorithm can be found in Periáñez and Abril (2015) [44]. The submarine landslide submodel has been tested against independent modelling works and subject to extensive sensitivity tests [38,44]. The effects of model resolution and sensitivity to the friction coefficient have been studied in Periáñez and Abril (2014b) [31].…”