PREVIOUSLY: YOU SAW HOW PLUME-RIDGE SYSTEMS ARE AFFECTED BY PROPERTIES OF THE RIDGE
Mantle plumes, the hot columns of buoyant rock that result in surface volcanism in unexpected locations (Hawaii! Iceland! Japan!) are unfortunately not well understood. Humans lack the technology to drill past a couple of kilometers beneath the surface without their equipment melting, so all we know about plumes comes from less direct sources. And seismic waves and surface geology can only tell us so much. As a result, humans do not know very much about plumes! We know they are hot because they are rising through the mantle, and this ascension is driven by thermal buoyancy. But we might not know exactly how hot.
Look at what happens in the case of constant half-spreading rate and constant ridge-to-plume distance but with varying the plume temperature. In this case, the difference between 100 K is the difference of having geologic evidence of plume material at the surface and having none at all. It has such a substantial effect because temperature alters the viscosity AND because higher temperatures result in a more pronounced effect of thermal buoyancy.
Here you can see how plume temperature influences plume viscosty for three different plumes. The viscosity changes do not look like much but remember that is a log plot so we're talking orders and orders of magnitude here! I have yet to quantify the effect on the buoyant force but maybe I will.
NEXT: ALL THIS STUFF BUT NOW IN 3D