Hotspot chains, such as Louisville or Hawaii, are created by the interaction between an upwelling mantle plume and the lithosphere drifting over the plume (Wilson, 1963). The interaction creates a volcanic chain composed of tens of volcanoes and a topographic swell. The ages of the volcanoes increase from the youngest extremity of the chain, often associated with active volcanism, to the oldest extremity, which would have been above the plume millions to tens of millions of years ago. The swell is a positive depth anomaly, hundreds of kilometers wide, and with an amplitude of several hundred meters (Crough, 1983;Sleep, 1990). It is created by the buoyant upwelling of a mantle plume (Sleep, 1990). Therefore, swells are commonly used to quantify plume strength (Adam