Fumaroles and Mudpots
          
Fumaroles
    Fumaroles, also known as steam vents, are the hottest thermal feature. Scientists believe that fumaroles result from very little water in the underground system. Fumaroles release a mixture of gases; this mixture contains- steam, carbon dioxide and hydrogen sulfide. (Hydrogen sulfide is what causes the rotten egg smell of the geyser basins.)  All of the gases are forced out when small amounts of cool water seep from above ground and hit hot rock. The water will then flash to steam. When this occurs, the steam takes up thousands of times more space than water does, and thus forces the gases up the vent. Above ground we see a continuous release of steam as it hits the air and cools.

    Fumaroles are usually static. They don't change their appearance very much and they always do the same thing.

Move Mouse Over This to see a fumarole.

Mudpots
    Mud pots start as fumaroles that have been drowned beneath surface water. This water keeps steam and other gasses from escaping directly into the atmosphere. The hydrogen sulfate, in the mixture of steam and other gasses, is oxidized in the water by chemical reactions and bacteria. This forms sulfuric acid. The solution, that can be as strong as battery acid, attacks the surrounding rock. The disintegrated rock creates the wet clay of the mud pot.

    The fumarole beneath the mud is always there, it's responsible for making the bubbles of steam causing the boiling, or plopping action of the mud pot. The amount of surface water plays a key role in how the mud pot behaves. Since the amount of water is constantly increasing and decreasing based on snowmelt and rainfall, the consistency of the mud pot changes throughout the year. The thin slurry of a "paint pot"  might become thick, cement-like mud if it dries out a bit. Occasionally a mud pot dries out completely and then it will revert back to its original form, a fumarole.

Move Mouse Over This to see a mud pot (Source: Sarah Walinga)
Move Mouse Over This to see a thick mud pot (Source: Sarah Walinga)