USA/WY: Yellowstone NP – Mud Volcano & Sulfur Caldron
And last but not least area of volcanic geothermal activity in Yellowstone is completely out of the main area – the Mud Volcano and the Sulfur Caldron. Both are very unique and very different from everything else you see in other geyser basins. The mud volcano is full of steam vents and fumaroles and boiling lakes – all full of mud. The are was also home to several bisons who clearly enjoyed the sulfuric gases and were taking the natural steam saunas. The Sulfur Caldron was a massive boiling lake full of sulfur that you could smell and hear from far away.