The
Washburn Expedition and the Hayden Survey discovered Mud Volcano during
the early 1870s. Both groups heard the sound "resembling the reports
of distant artillery" for several miles before arriving at Mud
Volcano. Mud Volcano at that time exploded with mud from its hillside
alcove. Since then Mud Volcano has quieted but still remains a bubbling,
seething spring.
Mud Volcano Area, also known for Black
Dragon's Caldron, Sour Lake, Mud Caldron, Dragon's Mouth Spring, and
Sulfur Caldron, is very acidic. Iron sulfide is responsible for the
dark-gray, blacker brown-colored water, while hydrogen sulfide produces
the "rotten egg" smell common to the Mud Volcano area.
Sulfur Caldron is an unusual spring.
It has a high acidity of nearly pH 1.2, similar to citric acid, and
the growth of a specific bacterium has produced a yellow-colored spring
which contrasts to the other dark-gray or black, iron sulfide springs.
DRAGON'S MOUTH 
Temperature 170.2°F Dimensions 18x30 feet. Depth 16 feet. Dragon's
Mouth is a turbulent hot spring with a cavernous mouth. Water sloshes
rhythmically in and out of the cavern giving the impression of a large
overflow; however, the actual discharge is quite small. Much of the
activity and energy is located within the cavern. As hot water rises
to the surface, hydrogen sulfide, carbon dioxide, and water vapor gases
expand creating a pressure explosion in the cavern. The resulting activity
is sloshing, belching, and steaming.
"The Essenstials for
Planning your
Trip to Yellowstone Park" |
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MUD VOLCANO 
Temperature 184°F Dimensions 27x36 feet. Depth 17 feet. The 1871
Hayden Expedition named this thermal feature. At that time Mud Volcano
was a very active mud spring with bellowing and exploding mud. In later
years since its discovery it has not shown the same forcefulness. However,
minor earthquake tremors during 1979 increased heat and water activity
and Mud Volcano began bursting from the crater, spilling mud across
the boardwalks. This activity decreased shortly thereafter and it has
since been a quiet caldron with occasional churning caused by rising
gases.
BLACK DRAGON'S CALDRON 
Temperature 191 °F Dimensions 80x200 feet. Depth 36 feet. This
thermal feature did not exist before the winter of 1947-1948, and it
was first discovered on June 10,1948. Thermal activity may have shifted
from Sour Lake to form Black Dragon's Caldron. When it was discovered,
a crater about 43x68 feet existed at the northern end of the present
pool. Since then, eruptive activity has slowly moved south 200 feet
along a natural crack. Hydrogen sulfide rising within the spring has
combined with oxygen to form sulfuric acid, creating a hostile environment
for plant life. Iron sulfides are responsible for the black color of
the caldron.
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