Rising plume phenomena at Yellowstone - Monday 3.1 R @ 6 mi.; Tuesday 3.1 R @ 5.8 mi.; Wednesday 3.4 R @ 5.4 mi. - all on same exact location. That means a subsurface plume is hammering its way up.
http://earthquake.usgs.gov/earthquakes/recenteqsus/Maps/US2/44.46.-112.-110.php