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A new, massive reactivation of landslides along the Molise coast has cut Italy in two. The Petacciato landslide (among the largest in Europe) caused structural damage which forced the precautionary closure of strategic sections of the A14 motorway and state road 16 (where a bridge had already fallen), and limitations on the Adriatic railway, effectively isolating Puglia from the main communication arteries with the north of the peninsula.
An emergency that turns the spotlight back on one of the most impressive and complex hydrogeological threats of the entire European continent. And which underlines the urgency of mitigation interventions that have been postponed for too long.
A record landslide
The Petacciato landslide is not a simple superficial landslide: it extends from the town centre, located at around 225 meters above sea level, until it reaches below the level of the Adriatic Sea. The main landslide body covers an area of over 4.5 square kilometers and involves hundreds of millions of cubic meters of earth. In terms of extension and depth – the lowest sliding surfaces were identified over 100 meters below ground level – it is considered among the largest active landslides in Europe.
Not just Niscemi: the towns sitting on a landslide
It is not a single homogeneous body, but a complex system of connected landslides, ready to reactivate in periods of heavy rainfall: the first confirmed movements date back to 1916, and were repeated at least 12 more times in the following century. To understand why the Petacciato terrain moves with such unstoppable regularity, it is necessary to analyze its lithological nature, that is, the type of rocks that make up this stretch of coast. The entire slope is in fact composed of the so-called “Plio-Pleistocene grey-blue clays”, materials which were formed by sedimentation on the bottom of ancient marine basins and possess extremely unfavorable mechanical characteristics.
Clays are sedimentary rocks composed of very fine particles which, due to their chemical and physical nature, absorb water, increasing in volume and losing cohesion. In technical terms, the shear resistance of the soil collapses, creating “slip planes” along which the entire slope, weighted and lubricated, begins to move downstream under the effect of gravity.
The role of water
Precipitation is therefore what fuels the Petacciato landslide. “The Petacciato area has a natural predisposition to landslide, but it is the presence of water underground that favors and triggers the slide,” Domenico Angelone, president of the Order of Geologists of Molise, explains to Dossier The Vermilion. “When there is intense rainfall for a prolonged period, as we have seen in recent days, the ground becomes overloaded and the landslide can be reactivated. These are phenomena that have always occurred, but which are becoming more common with climate change and to which we should therefore pay even more attention than in the past”.
Furthermore, Petacciato is not an isolated case, but the most striking example of a fragility that unites the entire Adriatic coast, from Ancona to Termoli. The morphology of the Molise and Abruzzo side is dotted with similar, albeit less impressive, phenomena, such as that of Vasto, where the landslide of 1956 destroyed part of the historic district, or that of Ancona, with the famous Barducci landslide of 1982 which destroyed hundreds of buildings and the oncology hospital.
The entire coastal strip is a precarious balance between the soft clays and the erosive action of the sea, which, by undermining the base of the slopes, contributes to destabilizing the slopes.
Infrastructures “to be moved”
The danger of the Petacciato landslide is linked to its geographical position. In fact, the landslide does not only put the neighboring municipality at risk, but crosses perpendicularly all the infrastructures that connect central-northern Italy with the south-east of the peninsula. State road 16, the A14 motorway and the Adriatic railway line (Bologna-Lecce) all run at the base of the unstable slope. And they were damaged, in various ways, during the reactivations of the landslide. In 1916 and 1932, the railway was literally washed away, with the tracks buckled and moved tens of meters towards the beach. In 1991, one of the most serious events in recent history, the land emerged violently on the current beach, raising the shoreline and destroying the coastal defense works, while the railway underwent horizontal translations such as to interrupt national traffic for weeks.
Today, the current reactivation is reproducing the same scenario. The closure or slowdown of these arteries means blocking the transit of goods and passengers towards Puglia, forcing logistical flows to make kilometre-long diversions across the Apennines, with enormous economic costs for the country system.
“They tell me that the instrumental measurements indicate that the landslide is slowing down, and based on the behavior it has had in the past it is likely that the emergency will end soon, awaiting new reactivations in the years to come – explains Angelone – Unfortunately the issue of hydrogeological instability is a problem that concerns the entire peninsula, and which should be addressed in a structural way, both in terms of prevention and adaptation and mitigation. Here in Petacciato there are ancient responsibilities, probably construction should have been avoided the motorway and the railway in an area where it was already known that there was a large landslide that reactivates periodically. Today one could also imagine moving these infrastructures, but they would be complex and expensive projects, especially for the railway, and are choices made by the managers and the regional and national government”.
Consolidation projects: 40 million euros
Since these are hydrogeological phenomena fed by water present in depth, to contain the risks it is necessary to act on the aquifer. This is what involves a consolidation project that the Region has been working on for many years now, and which after long bureaucratic delays (almost five years) was recently put out to tender and entrusted to the Technital company of Verona. The intervention aims to cure the main cause of the landslide – excess water – using twelve large diameter drainage wells tens of meters deep, which should intercept the aquifers under pressure in the depths of the slope and collect the excess water.
The collected water will then be removed from the landslide body and discharged into the sea in a controlled manner, preventing it from stagnating and lubricating the sliding surfaces. The cost of the operation – which also involves the installation of sensors to measure every slight movement of the ground in real time, and consolidation works in the upper part of the slope – is over 40 million euros, and construction times are estimated at approximately three years from the opening of the construction sites. With the reactivation of the landslide, however, the times are destined to extend further.
Because the Petacciato landslide cannot be stopped
“The tender was in the tender procedure phase, but now it will be necessary to evaluate whether the project is still valid, or whether changes or new measures are needed instead, and it is something that cannot be done on the spot,” concludes Angelone. “However, a state of natural disaster should be declared shortly, as requested by the Molise Region, and this could speed up the implementation process of the consolidation and mitigation projects, and possibly also bring new funds to strengthen the interventions already planned. Such a large landslide is impossible to block completely, but if we managed to reduce the intensity of the reactivations and lengthen the latency periods – perhaps facing a reactivation every 30 years, instead of one every 10 – it would already be an achievement important.”
Dossier is the exclusive subscription investigative section of The Vermilion. If you want to support our journalistic work and subscribe, visit our showcase by clicking here.