Supervolcanoes can occur either when magma in the mantle rises into the crust from a hotspot but is unable to break through the crust , thus pressure builds in a large and growing magma pool until the crust is unable to contain the pressure ( this is the case for the Yellowstone Caldera ) , but they can also form at convergent plate boundaries ( for example , Toba ) .
Supervolcanoes can occur when magma in the Earth rises into the crust from a hotspot , but can not break through the crust .