The volcano island of La Réunion is one of the strongest candidates worldwide for a hotspot underlain by a deep, "classical" mantle plume.

RHUM-RUM (Réunion Hotspot and Upper Mantle - Réunions Unterer Mantel) is a French-German passive seismic experiment designed to image an oceanic mantle plume – or lack of plume – from crust to core beneath La Réunion Island, and to understand these results in terms of material, heat flow and plume dynamics. La Réunion hotspot is one of the most active volcanoes in the world, and its hotspot track leads unambiguously to the Deccan Traps of India, one of the largest flood basalt provinces on Earth, which erupted 65 Ma ago. The genesis and the origin at depth of the mantle upwelling and of the hotspot are still very controversial. 

In the RHUM-RUM project, 57 German and French ocean-bottom seismometers (OBS) have been  deployed in 2012 over an area of 2000 km x 2000 km2 centered on La Réunion Island, using the “Marion Dufresne” and they will be recovered in 2013 by the “Meteor” vessel. The one-year OBS deployment (Oct. 2012 – Oct. 2013) is augmented by terrestrial deployments in the Iles Eparses in the Mozambique Channel, in Madagascar, Seychelles, Mauritius, Rodrigues and La Réunion islands. A significant number of OBS will be also distributed along the Central and South West Indian Ridges to image the lower-mantle beneath the hotspot, but also to provide independent opportunity for the study of these slow to ultra-slow ridges and of possible plume-ridge interactions.