A multidisciplinary approach to study slope instability in the Alboran Sea shoreline: Study of the Tamegaret deep-seated slow-moving landslide in Northern Morocco

Coastal landslides cause great economic damage to human installations along the Mediterranean shoreline. In the Alboran Sea, this phenomenon is very common and causes many problems for residential resorts and road infrastructures in coastal areas. In the last two decades, such slope instability processes were the subject of many studies, which employed multidisciplinary approaches to understand their underlying mechanisms and surficial kinematics in Southern Spain and elsewhere in the Mediterranean. However, advanced and new investigation methods and techniques used in these studies have never been performed in Northern Morocco despite the geomorphological, geological and climatic resemblance between the two regions. In this paper we analyze the mechanisms and processes controlling the Tamegaret slow-moving deep-seated landslide (Northern Morocco) in order to bridge this knowledge gap and to understand landslide slope dynamics on their regional context. To do so, Electrical resistivity Tomography, field investigations and multi-temporal Synthetic Aperture Radar Interferometry (InSAR) were performed to characterize slope instability processes at the study area. The interpretation of Historic aerial photographs and UAV surveys was also conducted to study the major redistribution of mass caused by recent road widening work at the landslide headscarp. Results show that the Tamegaret landslide owes its existence to deep creep processes controlled by a rock flow type gravitational deformation. Extensional tectonic structures and marine erosion processes that eliminate landslide deposits from the foot area constitute the most relevant control factors of this dynamic. InSAR results show that this deep-seated landslide is currently (2017-2019) characterized by very slow displacement rates (2-3 cm/year maximum). Yet, the substantial deformation observed both in the field and on aerial/satellite photographs suggests that the acceleration occurred during the road-widening work which caused major changes to the natural topography in the period (2009-2012). This deformation phase was manifested by local shoreline advancement at the landslide foot area. Such results show that studying historic shoreline variations can be an effective low-cost time-saving tool allowing the reconstruction of active landslide kinematics in coastal areas. On a regional scale, findings of this study highlight the resemblance between the coasts of Southern Spain and Northern Morocco in terms of (i) the geomorphological processes controlling the coastal slope dynamics at the region; (ii) the displacement rates measured in Tamegaret compared to other unstable slopes in the Northern shore of the Alboran Sea and (iii) the bad-engineering on old dormant landslides which compromises their stability. Therefore, we suggest limiting construction work on coastal hillslopes of Northern Morocco in order to prevent bad construction practices from causing economic losses in the Southern shoreline of the Alboran Sea as well.

Automated summary

This study investigates the mechanisms and processes controlling the Tamegaret slow-moving deep-seated landslide in Northern Morocco, highlighting the importance of understanding slope dynamics to prevent economic losses. The study suggests limiting construction work on coastal hillslopes of Northern Morocco in order to prevent bad construction practices from causing damage to human installations along the Mediterranean shoreline. The research employs multidisciplinary approaches and advanced investigation methods to analyze slope instability processes and bridge the knowledge gap between Southern Spain and Northern Morocco.