There are several ways, exactly 1 of the mutual ones happens when the magma inwards a magma sleeping room has fourth dimension to split (called “differentiation” ). Just similar lighter grease volition bubble to the orbit of a pan of spaghetti sauce, thus volition felsic magma bubble upwards inwards a magma chamber. So what you lot tin larn is a vehement felsic explosion, followed past times an intermediate or mafic eruption afterwards the pressure level is released together with magma from deeper inwards the magma sleeping room tin live on released. For example: Crater Lake inwards Oregon. The initial eruption blew off the orbit of Mt. Mazama together with made the hole for Crater Lake, exactly thus a mafic cinder cone erupted within the caldera together with formed Wizard Island.