The Mud Volcano Area of Yellowstone National Park is filled with hot springs and boiling pools of acid and mud, as well as the unmistakable rotten-egg odor of sulfur that bombards you as soon as you exit the car. The sulfur smell is abundant throughout the geyser basins and hot spring/caldron areas of the park. Nearly all of the pools of liquid in these photos would dissolve you instantly were you unfortunate enough to stumble into them.
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Butterfly (center). Also a bee to the upper left.
Thick, boiling mud of the Grizzly Fumarole.
Sulphur Caldron Overlook
Mud Volcano
Dragon’s Mouth Spring. It actually does look like a dragon’s mouth from this angle.
Dragon’s Mouth Spring
Mud Caldron
Mud Caldron
Michael Rappa 