Control of source fertility on the eruptive activity of Piton de la Fournaise volcano, La Réunion
Résumé
The eruptive activity of basaltic hotspot volcanoes displays major fluctuations on times scales of
years to decades. Theses fluctuations are thought to reflect changes in the rate of mantle melt supply.
However, the crustal filter generally masks the mantle processes involved. Here, we show that the
cyclic and generally increasing activity of the Piton de la Fournaise volcano (La Réunion) since the mid
20th century is tightly linked to the fertility of its source, as recorded by 87Sr/86Sr and incompatible
trace elements ratios of lavas. We identify a twofold control of source fertility on eruptive activity: melt
extraction from fertile, incompatible element-enriched veins initiates decadal-scale eruptive sequences,
so that vein distribution in the plume source directly controls the cyclic activity. Indirectly, reactive
flow of enriched melts increases mantle porosity and promotes melts extraction from the peridotite
matrix. This process is thought to have caused a fourfold increase in magma supply between 1998 and
2014 at Piton de la Fournaise, and could also explain magma surges at other frequently active hotspot
volcanoes, such as Kilauea, Hawaii. The short-term eruptive activity of hotspot volcanoes appears to be
ultimately linked to the distribution and size of lithological heterogeneities in mantle plumes.
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