The coasts of Greece, southern Italy, Algeria, and the Eastern Mediterranean basin are known for the occurrence of boulder accumulations interpreted as tsunami deposits, but to a lesser extent com-pared with storm events. The effect of storms on the accumulation of boulders in Provence is unknown. Therefore, the question of the origin of these boulder accumulations is important for understanding the geomorphological processes and assessing the local risk to the population and economic activities. The boulder accumulations are situated very close to the largest industrial port of France, in the Gulf of Fos.

In this paper, we report evidence of cataclysmic waves events affecting the rocky coast of Provence and present the first dating results on these boulder accumulations.

Although we cannot rule out the combined effects of tsunamis and storms to explain boulder accumulations along the rocky coast of the Gulf of Fos, these accumulations are most probably associated with exceptional south-westerly storms. The prevailing winds in this area are from the N and NW, especially in winter during the stormy season. The Gulf of Lion is notorious for bad weather and sudden changes of conditions.
While strong NW winds, known as the Mistral, can be frequent, the wind rose shows another dominant direction from the S-SE creating a very-high-energy hydrodynamic regime with sea surges during onshore winds. The peculiar submarine morphology and orientation of the shoreline protect the study area from SE winds. On the contrary, being sheltered from south-easterly winds, the study area is very exposed to south-westerly to westerly winds and swells. The large fetch of the Gulf of Lion and the occurrence of rare but rather strong south-westerly winds could explain the displacement of megablocks by storms of exceptional force and unusual direction. In the case of this coast, the South-Westerly winds will create the strongest waves and swells (Ullmann et al., 2008).

The occurrence of numerous tsunamis in this region is not favoured because of the strong dispersal of radiocarbon ages, the presence of very fresh marks of movement and the very young ages (in the modern period) obtained from some blocks, which suggest a significant number of episodes of movement. In addition, historical data and information about tsunamis in France from 2000 BC to 1991AD indicate only 35 events during this period (Soloviev et al., 1997).

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