Eruptive patterns for the volcano piton de la fournaise, Reunion Island

A study of the historic record of activity of Piton de la Fournaise has revealed a cyclic pattern of eruption involving effusion of oceanite lava from major-flank centers every 20-40 years. Calculated volumes of the recent lava flows and pyroclastic ejecta have established an effusion rate of 3.9 m³ s^-1 since 1931 and 6.2 m³ s^-1 since 1951. Flank eruptions outside the present caldera define a distribution maximum which is expected to correlate with the depth range of a high-level magma reservoir. A model has been constructed which requires replenishment of a high-level magma chamber at a constant rate and regular eruption from summit and minor-flank centers, acting as "safety valves" to the magma chamber; when the magma chamber reaches its maximum expansion, a major-flank outburst of oceanitic lava occurs. The fact that calculated effusion rates are not consistent with radiometric dates implies an increase in effusion volume with time for the volcano.