Geothermal activity, from the Greek geo meaning earth and therme meaning heat, seethes from cracks in the streets, steams from backyard hot pools, bursts from geysers throughout the area, and bubbles from cauldron-like mud pools.
In this video by SightsForSeeing, watch as the sulfurous steam belches up through the thick liquid, sending drops of volcanic ash and clay splattering and plopping everywhere. It smells of H2S (Hydrogen Sulphide) there; imagine the smell of rotten eggs. To hear the boiling, listen to these mudpots in Yellowstone.
Related watching: geysers.