In the early days of the plate tectonic theory, Whitehead devised an
experiment heating fluids with different viscosities in plastic containers to simulate hot
material in Earth's mantle. Thin, worm-like streams of less dense fluid
rose buoyantly
within denser fluid toward the top and
expanded outward like balloons at the end of straws. The experiment
demonstrated how “mantle plumes” form. The plumes can cause hard ocean
crust above them to spread apart, forming a chain of volcanic mountains
between diverging tectonic plates.
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