The Stenungsund (Sweden) Quick-Clay Landslide of 2023: Anthropogenic Influence and Infrastructure Consequences

On 23 September 2023, a major quick-clay landslide occurred at the Stenungsund interchange on the E6 highway in southwestern Sweden. It caused extensive damage to critical transport infrastructure, resulting in long-term regional disruption and underscoring the societal vulnerability of development in sensitive clay terrains. This study presents an integrated geological, geomorphological, hydrological, and anthropogenic analysis of the Stenungsund landslide, aiming to clarify the mechanisms that led to failure and to extract lessons relevant for hazard assessment and land-use planning.

The landslide affected approximately 15 hectares, with a runout distance of about 620 m and an estimated displaced volume of ~1.85 million m³. We combine field mapping, stratigraphic logging, geotechnical data, historical documentation, and LiDAR-derived terrain models with aerial and satellite imagery and hydrological modelling to reconstruct pre-failure conditions, failure kinematics, and post-event morphology. The geological setting consists of thick sequences of late- to postglacial marine clay in a fracture-valley landscape, interbedded with permeable silt, sand, shell-rich horizons, and glaciofluvial sediments. These conditions promote groundwater flow, clay pore-water salt leaching, and the development of quick clay.

Our results indicate that failure initiated at depth within weak clay layers beneath recently placed fill and evolved into a translational progressive landslide. Anthropogenic loading from construction activities acted as the primary trigger, while altered drainage and groundwater pathways raised pore-water pressures. Hydrological modelling shows that excavation, blasting, and filling redirected runoff toward the site and increased infiltration along fractured bedrock and permeable sediment layers. Heavy rainfall in the days before the event likely added to the pressure build-up and influenced the timing of failure. Once downslope resistance was lost, rapid mobilization of quick clay produced large horizontal displacements and complex deformation patterns, including subsidence, heave, and circular-cylindrical failures.

The Stenungsund case highlights the tight coupling between geological predisposition and human modification in quick-clay terrain. It shows how short-term construction activity can destabilize systems that may appear stable under conventional assessments. Integrated evaluations that consider hydrogeological connectivity, stratigraphic variability, and cumulative anthropogenic effects are needed to improve risk mapping and guide controls on loading and drainage changes. Enhanced monitoring of groundwater conditions is likewise essential. As extreme rainfall events become more frequent, reassessing design methodologies and land-use practices in sensitive clay landscapes become increasingly important.