Asthenosphere:
About 100 kilometres below Earth’s surface lies the asthenosphere, a zone of relatively free-flowing rock held between two horizontal layers of stiffer rock. Iceland’s plume, they say, injects hot, runny rock into this layer that then spreads out horizontally into fingers. Other plumes don’t form such tendrils, says White, because the rock within them is not sufficiently hot and runny, or injected with enough force (Earth and Planetary Science Letters, doi.org/b6h9). [“Strange mantle plume under Iceland helps keep Scotland afloat,” Colin Barras, NewScientist (6 May 2017)]
