The two waves struck a 96-kilometer stretch of coastline with surprising force. Near Nice, the water reached 3 meters high. At La Salis, near Antibes, the waves crested at 3.5 meters before diminishing in amplitude along the coast. The water surged up to 150 meters inland in some areas. Eleven people were swept away in Nice and one more in Antibes, bringing the total death toll to 18 when combined with the seven workers killed in the initial collapse. For a coastline accustomed to gentle Mediterranean swells, the event was shocking -- tsunamis of this scale are extremely rare in the western Mediterranean, and most residents had no frame of reference for what was happening.

The origin of the two waves became a subject of intense academic and judicial debate. One hypothesis held that the airport landfill collapse directly caused the first tsunami, and that material from that slide triggered a secondary submarine landslide on the steep continental shelf, which generated the second wave. An alternative theory proposed that a preexisting submarine landslide, unrelated to the construction, was the primary cause. The distinction mattered enormously -- if construction activity caused the disaster, liability would fall on the builders and planners who had chosen to extend the airport platform over an inherently unstable submarine slope. The underwater terrain off Nice drops away steeply, and the continental shelf is narrow, making the area geologically predisposed to submarine slides. Whether human activity merely accelerated a natural process or created an entirely new hazard remained contested for years.

The disaster's most lasting consequence was strategic rather than physical. The airport extension was completed despite the catastrophe -- Nice Cote d'Azur is today the third-busiest airport in France -- but plans for a new port facility for Nice were permanently shelved. The event demonstrated that the narrow continental shelf off the Riviera coast, long considered merely a geographic footnote, posed genuine hazards for large-scale coastal construction. The 1979 collapse and its tsunamis entered the scientific literature as a case study in construction-triggered submarine landslides, informing coastal engineering decisions across the Mediterranean. For the families of the 18 people who died -- construction workers, beachgoers, and residents caught by waves that arrived without warning -- the academic debates over causation offered cold comfort. The Riviera's glamorous image absorbed the shock with characteristic speed, but the event left a permanent mark on how engineers assess the risks of building on the edge of the Mediterranean's deepest coastal waters.