The axis of symmetry runs along the center of the plot.
Contours are temperature.
Colors indicate radial velocity. More intense colors denote higher velocity. In 1971, W. J. Morgan suggested that intraplate volcanism such as the hotspot at Hawaii derives from hot upwelling plumes in the mantle. Our current understanding of the mantle suggests that convection takes the form of subducting plates and upwelling, approximately axisymmetric plumes. According to this model, hotspots are the surface manifestation of mantle plumes.