A gigantic bulge in the north rim of the Yellowstone caldera is the latest sign of volcanic activity in the national park. Geologists call this type of bulge “volcanic uplift.” It’s often caused by the movement of magma or gas underground. What does this mean for the Yellowstone supervolcano? Yes, like most areas with a lot of volcanic activity, it can be hazardous. But not because of any immediate danger of a supereruption of the Yellowstone caldera.