Travel Reference
In-Depth Information
thermal action suddenly appeared in the parking lot. Features here are roiling, not boiling.
here are no geysers.
Rangers sometimes lead hikes to visit fascinating off-trail features in this area; inquire at
Fishing Bridge Visitor Center.
Mud Volcano Loop Walk
This trail loops around all the features in less than one mile (1.5 km). The climb is a little more
gradual going clockwise (starting to your left).
NOTE: Only the north length of boardwalk, which includes Dragon's Mouth Spring, is
wheelchair-accessible, since there are steps above Mud Volcano.
The first feature encountered,
Mud Geyser,
viewed from above, was a spectacular geyser when
the park was first explored. It erupted to 40 or 50 feet (12-15 m) from its large pool and then
drained dramatically. It's now usually a bubbling muddy lake with rare eruptions.
You can see evidence here that the soil is now too hot for any trees to grow. In 1978-79 a
surge of local earthquake activity caused changes, including an increase in soil temperature
that killed lodgepole pines, which were then blown down all around. The increased heat
also created the
Cooking Hillside,
where the trail goes uphill.
Sizzling Basin
and
Churning
Caldron
(up the hill) were affected, too. Sizzling Basin used to sizzle more than it does now,
while Churning Caldron is now too hot for bacteria to form.
The newest large feature, south of the main walkway, is a seething mud pot,
Black
Dragon's Caldron,
which formed in the winter of 1947-48. It must have begun with a terrific
explosion, because trees were blown out by their roots, but no one happened to be here to see
it. The pool has since grown much larger: it's about 200 feet (60 m) long. Hydrogen sulfide
bubbles to the surface. The black color (or sometimes a deep gray when there's lots of water)
is due to iron
sulfides.
Huge and very acid
Sour Lake
beyond Black Dragon's Caldron is less hot than some of
its neighbors, allowing bacteria and algae to thrive and color the water green. As you can see
from the steam rising beyond Sour Lake, there are more thermal features where the board-
walk doesn't go. Please don't leave the boardwalk unless you're with a ranger.
The walkway crosses quiet meadow and forest, where you may see wildlife before reaching
Grizzly Fumarole.
This feature changes seasonally from a large, spattering mud pot to some
quiet, steaming holes, depending on its water supply.
