How can the Yellow Stone super volcano be a composite volcano if it is on a hotspot?
I think it would be more correct to say that hot spots have been identified in oceans by shield volcanoes such as the Hawaiian Islands. But the reasons that they are shield volcanoes is related to the source of the magma. In a simple-minded way, a hot-spot is a Bunsen burner at depth heating the overlying material. In the middle of the Pacific Ocean, that is asthenosphere mantle beneath a low-temperature relatively refractory lithosphere. The magma that is produced and ultimately feeds the volcano is a low-viscosity relatively dry basalt. A Bunsen burner under Yellowstone initially also melts asthenospheric mantle but on top of that is a thick continental mantle and crust. The material that came out of the Yellowstone collapse had very little relation to the initial mantle melt. Much of it was remelted continental crust — sedimentary material with lots of water and silica so the magma was high viscosity and wet. The solubility of water in magma decreases rapidly as you lower pressure
