An international team of researchers in 2014 concluded that super-volcanos could erupt at any time without outside triggers, making predicting such an event more challenging.
This is due to a phenomenon called the “buoyancy effect,” which occurs when the molten magma inside the super-volcano reaches critically high pressures due to the much denser rock around it, forcing it to the surface.
Tests conducted at the European Synchrotron Radiation Facility in Grenoble, France, suggest that the transition from solid to liquid magma alone can create pressures strong enough to crack more than six meters of the Earth’s crust above the caldera.
Using synchrotron X-rays, the scientists established that a super-volcano eruption might occur spontaneously, driven only by magma pressure without the need for an external trigger.
Super-volcano triggers recreated in X-ray laboratory
http://www.esrf.eu/home/news/general/content-news/general/supervolcano-triggers-recreated-in-x-ray-laboratory.html
Timothy French 