Geotechnical challenges at Santorini port access road

Access to Santorini’s main port at Athinios has been temporarily suspended following a new rockfall incident along the only road connecting the port to the island’s upper settlements. The event, although described as small in scale, led to the immediate closure of the route due to the narrow geometry of the road and the location of the failure at a critical bend.

According to geotechnical experts, the broader issue is not the isolated event itself but the long-term instability of the slope system. The Athinios access road is carved into steep volcanic terrain, where slope angles, geological discontinuities, and weathering conditions contribute to ongoing rockfall susceptibility.

The area is also characterized by continuous microseismic activity, with approximately 460 small earthquakes recorded since last July. While most of these events are of low magnitude, their cumulative effect contributes to progressive weakening of the rock mass, increasing the likelihood of detachment and localized failures over time.

In addition to seismic loading, rainfall infiltration plays a critical role. Water entering fractures reduces shear strength and promotes block detachment, particularly in highly fractured volcanic formations. Combined with steep slopes and limited natural containment, these conditions create a persistent rockfall hazard along the road corridor.

Human interventions have further influenced slope stability. Excavations carried out during the construction of the road have altered the natural geometry of the slope, in some cases removing lateral support and exposing unstable sections. At the same time, protective measures along the slope are considered incomplete. While rockfall barriers have been installed at higher elevations, several lower sections remain unprotected, leaving the roadway directly exposed to falling debris.

The issue requires a comprehensive slope stability assessment rather than localized interventions. The affected slope extends over approximately 3.5 kilometres, and current mitigation measures appear inconsistent in both design and application. In some cases, materials used for protective works may not meet the required specifications to withstand future rockfall impacts.

Recommended measures include systematic installation of rockfall protection systems such as steel mesh drapery, anchored netting, and properly designed catch ditches to intercept falling debris before it reaches the roadway. These solutions must be supported by detailed geotechnical mapping and hazard assessment to identify high-risk zones and prioritize interventions.

For the immediate situation, clearance of loose material and removal of unstable blocks is expected to allow reopening of the road within a short timeframe. However, the underlying instability remains unresolved, and similar incidents are likely to recur if a coordinated stabilization strategy is not implemented.

The Santorini case highlights the challenges of maintaining infrastructure in geologically complex and seismically active environments. It also underscores the importance of integrating geotechnical design, monitoring, and long-term planning to ensure safe access to critical transport nodes such as the island’s primary port.