Siġġiewi’s Lunzjata Chapel near Laferla Cross threatened by ground movement

The historic Lunzjata Chapel perched on a rocky promontory in Siġġiewi, serves as a stark reminder of the fragile relationship between Malta’s cultural heritage and its volatile geology. 

Long plagued by instability, the 15th century chapel has undergone repeated cycles of damage and reconstruction following major earthquakes in 1693, 1856, and 1923. However, the most pressing threat today is not a sudden seismic event but a slow, relentless process of ground displacement that is gradually deforming the structure. 

This information emerges from a new study entitled Active Spreading At Maltese Heritage Sites: Unravelling Instability Mechanisms Via Integrated InSAR, Photogrammetry, And Geotechnical Analysis. The research published in the journal Catena (Volume 268, 2026) was led by Giona Bucci Monica of the University of Malta, alongside Alfredo Rocca, Adrian Mifsud, Christian Schembri, Colica Emanuele, Veronica Mercuri, Daniel Fenech, Christopher Gauci and Aaron Micallef. 

The multidisciplinary team combined satellite-based Interferometric Synthetic Aperture Radar (InSAR) with drone-based Structure-from-Motion photogrammetry and geotechnical analysis to investigate instability at key heritage locations. 

Scientists involved in the study documented that the Lunzjata Chapel displays transversal cracks across its structure, extending from ground to roof level. These fractures indicate that the building’s foundation is undergoing longitudinal extension and outward rotation toward the valley. The damage is consistent with gradual slope movement rather than abrupt structural failure. 

Advanced satellite monitoring quantified this instability. The research shows that the chapel exhibits displacement velocities between 7.6mm and 17.6mm per year, with cumulative movements reaching as much as 72mm during the observed period. These shifts are not constant. Geotechnical sensors identified a consistent correlation between total displacement and rain, suggesting a seasonal cycle. 

The ground tends to move toward the slope during hot, dry periods and retract slightly during wetter months. Despite these minor retractions, the process is cumulative, gradually undermining the structural integrity of the masonry vaults. 

Ongoing restoration works currently underway at the chapel confirm the structural concerns noted in the study. The restoration of the Lunzjata Chapel next to the Laferla Cross in Siġġiewi began in October 2023 under an agreement between the government and the Archdiocese of Malta. Initially expected to finish within a year, the project missed its October 2024 deadline after structural problems emerged once works started.  

The science behind the threat  

The underlying mechanism is a geological phenomenon known as lateral spreading. Malta’s landscape is characterised by a “layer cake” stratigraphy, where a heavy layer of Upper Coralline Limestone sits atop a thick, impermeable layer of Blue Clay. Rainwater infiltrates the porous limestone until it reaches the clay interface, where it accumulates. This causes the clay to swell and lose strength. Under the weight of the limestone plateau, the softened clay is squeezed outward, creating a self-sustaining cycle of plateau instability that is difficult to arrest. Over time, this process forms deep fissures parallel to cliff edges, eventually leading to the detachment of large rock blocks. 

While the Lunzjata Chapel faces one of the most complex challenges due to its position on an active landslide, the study also points at the significant risks at the Madonna tal-Aħrax monument in Mellieħa. Situated near a precarious cliff edge, the site is threatened by erosion of the underlying Blue Clay. Using high-resolution 3D modelling, the researchers identified approximately 173,000 cubic metres of rock currently at risk of mobilisation. 

Popeye Village and Ġnejna Tower 

Other historically and culturally significant locations mentioned as susceptible to these spreading processes include Popeye Village, the Ġnejna Tower, and various sites along the northwest coast of Malta and Gozo. 

The study identifies Popeye Village at Anchor Bay as particularly vulnerable because the coastal fringe shares the same limestone-over-clay geology. In this setting, lateral spreading continues to exert pressure on the landscape, gradually increasing the risk to structures located near cliff edges. 

Popeye Village is also vulnerable to geological movement

To safeguard these landmarks, the authors propose several recommendations. For monuments such as the Madonna tal-Aħrax statue, researchers propose relocating the structure further inland—considered the most practical long-term safeguard against cliff collapse. In contrast, permanent structures like the Lunzjata Chapel require ongoing geotechnical reinforcement, including stabilisation and underpinning to counteract sliding ground. 

In 2023, the Planning Authority approved relocating the Tal-Aħrax statue a few metres inland to address geological risks identified near its original site. However, further instability identified through satellite imagery studies conducted by the University of Malta’s InSAR.SPREAD project revealed the need for a safer location. 

Supported by IPAS+ grants, this project tracked geological movement between 2011 and 2015 and identified displacement velocities of up to 10.2mm per year in some areas. During dismantling works, the original masonry pedestal was discovered beneath the concrete casing. 

The authors of the latest study advocate a multi-disciplinary approach that integrates continuous satellite monitoring with ground-truth validation from geotechnical sensors. Such a framework, they argue, provides public authorities with actionable knowledge to proactively monitor and protect Malta’s historic landscape before the slow march of lateral spreading results in irreparable loss.