Whether volcanic intraplate hot spots are underlain by deep mantle plumes continues to be debated 40 years after the hypothesis was proposed by Morgan [1972]. Arrivals of buoyant plume heads may have been among the most disruptive agents in Earth's history, initiating continental breakup, altering global climate , and triggering mass extinctions. Further, with the temporary shutdown of European air traffi c in 2010 caused by the eruption of Eyjafjallajökull, a geologically routine eruption in the tail end of the presumed Iceland plume, the world witnessed an intrusion of hot spot activity into modern-day life. The larger interest in intraplate hot spots stems from the suspicion that their volcanism is fueled by mantle plumes, which are deep-seated, columnar upwellings of hot rock, possibly originating from the core-mantle boundary. Depending on their numbers and typical heat fl uxes, mantle plumes could be major factors in Earth's heat budget, providing direct cooling to the core. Seismology could settle the controversy regarding their existence and signifi cance by imaging plume conduits—or lack thereof—in situ, but the most promising hot spots are located well into the oceans, and large-scale instrumentation of the seafl oor has been coming into reach only recently. In an effort to learn more about plume origins and dynamics through seismology, scientists from France and Germany are focusing on the Indian Ocean's La Réunion Island. Its close proximity to major landmasses (Madagascar and mainland Africa) allows for excellent seismic illumination, reducing the need for expensive ocean bottom sensors to record earthquakes around the globe. The Réunion Hotspot and Upper Mantle– Réunions Unterer Mantel (RHUM-RUM) project aims to seismologically image the crust and mantle under the island at all depths. Through what is thus far the most expansive attempt to work out the deep plumbing of hot spots, RHUM-RUM scientists may be able to clarify the feeding mechanism for hot spot volcanism, estimate ascending material and heat fl uxes, and document interaction with the overlying African plate and with neighboring mid-ocean ridges. RHUM-RUM: The Biggest Seismological Plume Hunt So Far La Réunion Island in the western Indian Ocean (Figure 1) is among the most active volcanoes in the world and a very strong candidate for a hot spot underlain by a deep, " classical " mantle plume [e.g., Courtillot et al., 2003]. Its location has been the site of geochemically characteristic intraplate volcanism for 65 million years, and its 5500-kilometer-long, time-progressive volcanic track leads northward to the Deccan Traps of India, one of the most voluminous fl ood basalt provinces on Earth and the presumed manifestation of plume head arrival. The hot spot sits atop one of two " superswells " in the lowermost mantle, the suspected origin regions for most deep plumes. RHUM-RUM relies on island and ocean bottom seismometers deployed on and around La Réunion to piece together fi nely scaled plume structures directly below the hot spot. Existing land instrumentation on Africa and Madagascar extends the effective array aperture to several thousand kilometers. The wide view gained by stations far afi eld is needed to image into the lowermost mantle and sets RHUM-RUM apart from previous oceanic plume imaging efforts [Barruol et al., 2002; Suetsugu et al., 2009; Wolfe et al., 2009]. To illuminate the mantle structures under the island down to about a 1000-kilometer depth, RHUM-RUM researchers deployed 57