Fig. 1: Box plots of plume buoyancy flux for different stages of plume–ridge interaction.

Box plots are calculated from 13 instances of plume–ridge interaction in the numerical model where the median is indicated by red lines and the interquartile range (Q1–Q3) is highlighted in grey. The plume buoyancy flux is calculated from the product of the mean cross-sectional area of the plume, excess mantle temperature, the upwelling velocity, the mantle reference density and reference thermal expansivity (refer to “Methods” section). The buoyancy flux of the plume in the leadup to ridge capture is calculated from timesteps where the ridge and plume are within 1000 km of each other prior to plume–ridge capture; the flux at ridge capture is calculated from 20 timesteps overlapping the point where the distance between the plume and ridge approach zero; the flux at plume–ridge anchoring is calculated at all timesteps between ridge capture and ridge de-anchoring; the flux at ridge de-anchoring is calculated from 20 timesteps overlapping the point where the distance between the plume and ridge begins to increase. The leadup to ridge capture is characterised by moderate plume buoyancy fluxes (median of 2300 kg/s) and a 1400–3400 kg/s interquartile range; plumes reach their zenith buoyancy flux during ridge capture (between 2100 and 4750 kg/s), and their widest interquartile range during plume–ridge anchoring (between 1750 and 4500 kg/s); the lowest plume buoyancy flux occurs during plume–ridge de-anchoring (median of 2000 kg/s) and narrow interquartile range of 1650–2750 kg/s.