Any single volcano releases more energy. Hawaii alone should destroy the world or the Philippines or Iceland or the thousand and one volcanoes under the ocean.
True (about the energy released.) Mt. St. Helens is estimated to have released about 24 megatons, total, IIRC. I would guess you have to get up into at least Pinatubo territory to discern a significant global effect — granted that nukes might have a bit of an advantage per kt when it comes to the follow-up fires. Plus it seems to me I read somewhere that smaller explosions have an “efficiency” advantage, at least in terms of destruction per kt. OTOH, really big volcanoes probably have an advantage over multiple “smallish” nukes, in injecting (projecting!!) material well into the stratosphere.
IMO, where the radioactive fallout of a 100 warhead nuclear war would go is a more valid concern.