Travel Reference
In-Depth Information
Clepsydra Geyser erupts from two major jets and several minor ones. Spasm Geyser's two vents are in
the foreground.
Several more geysers, as well as many hot springs, cover the flats between here and the
river. You may catch sight of them erupting from the boardwalk, but there's no public access
to the area.
Geyserite
As you tour the geyser basins of Yellowstone, you'll notice that a white or pale gray brittle
rock surrounds the geysers and hot springs and forms gravelly areas. With a few excep-
tions (such as Terrace Springs and the Firehole Drive area) this rock is made of
hydrous
silicon dioxide.
Other names for it are
siliceous sinter,
geyserite, or sometimes simply
sinter
or silica.
The volcanic rhyolite that underlies most of the park's thermal areas contains a lot of
silica. When hot water percolates through the rhyolite, silica dissolves and is brought to the
surface. There, the water cools and precipitates the silica as geyserite. In some places this
process creates vast, nearly flat rocky areas, such as here at Fountain Flats.
Microorganisms that thrive in these hot waters can form microbial mats that some-
times act as templates, controlling the shapes that the geyserite takes. Sometimes the silica
