Another common type of volcano forms over hotspots. We don't really know too much about hotspots, other than being able to identify (usually) the volcanic products that result from them. These volcanic products are overwhelmingly basalt, a hot, fluid type of magma. Hotspot volcanoes tend to be shield volcanoes that rarely erupt explosively, and as you can see from the map above they are almost all found on oceanic plates. This is obviously saying something about the structure of the inner Earth and how the plates tend to arrange themselves relative to this structure, but exactly what this is saying isn't clear. This particular map is only one interpretation - different authors have slightly different definitions of what constitutes hotspot volcanism and therefore slightly different hotspot maps. The Hawaiian volcanoes have been studied much more than any of the other hotspot volcanoes.

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Types of Volcanoes