Travel Reference
In-Depth Information
A Mountain Turning Itself Inside Out
In more than 140 years of recorded history, Mammoth's terraces have grown tremendously
in height and width. In fact, the average yearly buildup of travertine in active areas is about
8 inches (20 cm) and can be as much as 2 feet (60 cm).
What Makes the Terraces?
The Mammoth area is underlain at depth by limestones, sediments consisting mostly of
calcium carbonate
[GEO.24]
. Hot water dissolves the limestone from deep below Mam-
moth and carries it through cracks to the surface. As the water rises, the pressure confining
it decreases, the water cools, and hot gas, mostly carbon dioxide, escapes. The water be-
comes supersaturated with calcium carbonate, which precipitates out on the surface as
travertine.
The water in Mammoth's springs remains at about 163°F (73°C) year round. Where
does all this hot water comes from? The heat comes from magma deep below the earth's
surface, perhaps from the very large magma chamber under the Yellowstone Caldera or
possibly from a separate magma source near Mammoth. The water all originated as rain
or snow in different locations and travels to Mammoth along faults. Most comes from the
Gallatin Range to the northwest, traveling deep underground and taking at least 60 but
maybe even 10,000 years to arrive. A smaller amount travels north from Norris as shallow
groundwater, and some is recycled local precipitation.
Why Are here No Geysers at Mammoth?
Two factors essential to create geysers are missing here: geysers require superheated water,
and they need rock that can provide the required plumbing and buildup of pressure.
Geyser-rich areas, such as Upper Geyser Basin, are underlain by rhyolite rocks of the Yel-
lowstone Caldera that are rich in silica and provide the right conditions.
Colors and Patterns in the Terraces
Some of the bright colors in the runoff come from mineral deposits, but most come from
microorganisms that thrive in hot water. These microorganisms begin to appear just a few
days after a new spring is born.
The resident bacteria and algae help extract some of the carbon dioxide from the hot-
spring water. Calcium carbonate is precipitated on top of the organisms, which in turn
seek sunlight and begin to build up above the mineral deposits. Looking closely, you can
find filamentous patterns in the formations, showing the results of this precipitation and
growth.
