Under the US-American Yellowstone Caldera a seismic swarm is manifesting itself today. The strongest quake to date was M 2.9. EMSC indicates a total of 12 quakes with magnitudes greater than 2. The hypocenters are located at shallow depths of less than 5 km. The epicenters are concentrated in a small area southwest of Yellowstone Lake. They are located in the area of Heart-Lake and Mount Sheridan. The depression of the lake was formed by folding processes at a young fault zone. Therefore the swarm quake could be of tectonic origin. However, there is also a thermal field at the lake, so hydrothermal influences could come into play. The Heart Lake Geyser Basin is also known for its thermophilic archaebacteria, which occur here in a basic environment.