Understanding coastal evolution through multi-temporal LiDAR analysis of deep-seated landslides: Stonebarrow Hill and The Landslip, UK

Coastal cliffs are dynamically changing and understanding their evolution is crucial for managing hazards and protecting communities and ecosystems. The UK’s 17,381 km coastline is one of Europe’s fastest-eroding, with both new failures and reactivation of ancient landslides. Coastal instability is influenced by site-specific geology, hydrogeology, and external forcing factors; however, the role of climate-driven changes-such as sea-level rise, increased precipitation, and more frequent storm events-and the contribution of environmental preconditioning to landslide reactivation remain poorly understood. Along the southwest coast of the UK, many large, active landslide complexes occur where low-permeability mudstones, including Gault Clay, are overlain by more permeable sandstones, creating hydrologically sensitive and mechanically unstable slopes.

This study analyses the recent evolution of two such deep-seated landslide complexes in southern England-Stonebarrow Hill (Dorset) and The Landslip (Isle of Wight). The two systems exhibit notably different landslide behaviour and activity patterns despite comparable geological conditions that may have evolved in time with stress building up on the slope to cause failure. We used high-resolution LiDAR digital elevation models (DEM) between 2004 and 2025 alongside optical imagery and field-based geomorphological mapping. This enabled us to estimate mobile erosional and depositional volume, quantify erosional rate along with the assessment of cliff-top and toe evolution, characterise morphological changes and identify areas of instability. Through multi-temporal DEM differencing, we quantified both horizontal and vertical ground displacement and examined how failure mechanisms vary between the two sites.

The results indicate a clear divergence in recent activity. At The Landslip, deformation is extensive, affecting several parts of the complex and including marked upslope retreat, suggesting that the system has undergone a significant phase of renewed movement/reactivation. Stonebarrow Hill, in contrast, is dominated by smaller-scale failures focused along the sea-cliff frontage, accompanied by persistent toe erosion but limited evidence of deeper or inland progression. The spatial configuration of change mapped at The Landslip suggests that earlier movement lower on the slope weakened support and contributed to subsequent instability higher up the slope.

Understanding these patterns helps predict how similar cliffs might respond to changing conditions. The study also provides a foundation for developing predictive models that combine displacement data with climate and environmental factors. Such models can guide targeted management strategies, reduce hazard risks, and support the protection of vulnerable coastal landscapes across the UK. More broadly, the work emphasises the importance of long-term, high-resolution geospatial monitoring for recognising when deep-seated landslide systems are transitioning from background activity to more substantial reactivation, offering insights relevant to other clay-rich coastal settings.