A statistical and probabilistic study of the historic activity of Piton de la Fournaise, Reunion Island, Indian Ocean

Abstract

The Piton de la Fournaise (2635 m) is the active basaltic shield volcano of Réunion Island (55° 43′E, 21° 17′S) in the western Indian Ocean. This volcano has been built up on the western flank of an older volcano, Piton des Neiges (3069 m), whose activity dates back 22,000 y. B.P.The statistical and probabilist approach to Fournaise volcanic activity for the last 150, 50, and 15 years is based on careful investigations of archives (from 1980 to 1983). Historical periods of volcanic activity and inactivity have a statistical behaviour linked to a Poisson-law process: Fournaise's eruptions are then linked to internal phenomena due to refilling of different magma reservoirs.Three major volcanic cycles for the last 50 years have lasted between 15 and 30 years each. The main lava out-put for this last half century is 0.16 m3/s; but the lava outputs for the eruptions vary from 0.32 m3/s to 10 m3/s.While the internal processes (activity of magma chambers) essentially determine the duration and the types of activity or inactivity of Fournaise volcano, it is the external processes, such as earth tides (due to the different moon phases) which have a determinant effect on the triggering of eruptions. The earth's tides are determinant within a two-week period due to the transfer of magma to the shallow reservoir (1–2 km depth).