If this thing went off global warming would cease to be an issue as about 25 cubic miles of debris would be shot into the air. Farming in the mid west and Canada would take a bit of a vacation, and the damage would be, what is that word? Catastrophic.
Happens ever few then thousand years or so.
Probably would not have much of an impact on the plates moving. Kind of like a zit or boil bursting. Discomfort, but really not life threatening to the earth. Would not want to be standing near it though.