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Earth's Mantle and Crust - John Seach
The mantle is the solid region of the earth between the crust and core. The mantle is 2850 km thick.
The overlying crust varies from 7 km in oceanic regions to 70 km in the Himalayas. Magma is generated by melting of the mantle.
Hot spot volcanoes are generated by plumes originating at the core - mantle boundary. The few dozen hot spot locations represent a different form of volcanism.