Pre-historic (< 4kyrs) explosive activity at Piton de la Fournaise volcano.

The characterization of the recent (<5 kiloyears) explosive activity and the research of violent paroxystic events over Piton de la Fournaise edifice has been performed through a drilling and excavation campaign supported by the integration of new radiocarbon ages to previous chronologic data. Fine grained "Bellecombe" phreatomagmatic ashes represent the product of the most violent explosive Piton de la Fournaise activity inside the investigated period. This activity results from a series of eruptions occurred over a time span much longer than previously thought. Anyhow, it represents the most traceable horizon (up to 13 km W-NW from the central cone) among the studied deposits and no other pyroclastic blanket exhibits a similar regional dispersion. The lack of a continuous lapilli/ash horizon from the proximal to distal areas points out that the lapilli cover on the volcano flank result of several local blankets linked to as many Hawaiian to Strombolian emission centers. As highlighted by new radiocarbon ages this kind of activity persisted along the N120 rift zone up to very recent times and ended probably just before the island's colonization, leaving no trace in historical records. Themaximumexpectedmagmatic event (Chisny-type eruption) has therefore to be related to intense Hawaiian fountaining. Its dangerousness is restricted to a relatively brief distance fromthe source and a regional deposition is strongly unlikely. The hazard represented by this type of activity resides in the possible positioning of the vent close to inhabited areas and in the possible occurrence of repeated events with short but unpredictable time interval from one to the other. Forecasting the location of the future eccentric eruptions is thus of paramount importance to minimize the potential impact of mild explosive eruptions on the inhabitants and the infrastructures.