Research School of Earth Sciences
This picture illustrates the rise of a mantle plume from a hot thermal boundary layer, in a time sequence (left to right) showing temperature and several lines of tracer points. The last panel shows the variation of viscosity with depth, and the original locations of the five lines of tracers.
Heads and tails
The plume rises initially as a large spherical blob called a plume head. As this rises away from the base, it remains connected to the base by a narrow conduit called a plume tail. As the plume reaches the upper mantle, the drop in viscosity causes it to neck down, before it flattens against the base of the lithosphere at the top.
Which fluid is entrained?
The lines of tracers show how fluid from various levels becomes entrained into the plume. The fluid on the axis of the plume, which is the part that will produce the most magma near the surface, comes mainly from a very thin region at the base of the model, only about 10 km thick.
A plume movie also illustrates this process.
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