Yellowstone National Park - terraces

The terraces of Yellowstone are like self-sculpting statues formed over time by the interaction of limestone, hot water, and carbon dioxide with the slope of the ground and objects in the water’s path.

Water runs off from the surrounding mountains and seeps deep into the earth, where it is heated by partially molten rock trapped in a collapsed magma chamber from an ancient volcano. The water mingles with dissolved carbon dioxide to create a solution of weak carbonic acid. A complex web of fissures and fractures under the crust pipes the hot water to the surface.

A long gone sea once covered this area, depositing large amounts of limestone. The rising carbonic acid solution dissolves calcium carbonate, the primary compound in limestone, which is then deposited on the surface in the form of travertine, the basic building block of the Yellowstone terraces. It’s a complex set of circumstances and coincidences that brought this natural wonder into existence.


This spring flows from several vents from its top and side. The striking colours come from the thermophiles living in the hot water. It’s already huge, and growing larger every day.


The greyish steps on the left have stopped growing without the regular flow of water. The orange thermophile bloom in the middle, and the vivid white travertine slope on the right are “alive,” washed by the stream of calcium carbonate loaded water.


This is Angel Terrace. It was dry and crumbling for decades until it suddenly resumed activity in 1985. The combination of steam and vivid colours lends the landscape an otherworldly quality that has inspired any number of Science Fiction sets. If not for the threat of imminent death by scalding and the risk of damaging this fragile environment, I would have loved to don protective clothing and venture out onto the terrace. In my fantasy of exploration I felt a bit like an astronaut, and a bit like a movie star, despite mentally costuming myself in a most unflattering hooded hazmat onesie.


This is my favourite formation. Water flowed up from a fissure to build this ridge, which an early tour guide thought resembled the back of an elephant. The guide had a point, and the name stuck.


This unusual formation is the 11m (37 foot) high Liberty Cap. It was created by a high pressure hot spring that burst forth from the same hole in the crust over a long period of time. Although dormant now, the Liberty Cap is estimated to be 2,500 years old, with mineral deposits building this spire over the course of centuries. The name, Liberty Cap, might not be what you think. The name dates from a survey in 1871 and was given because the formation resembles the peaked knit caps that symbolised freedom and liberty (but were associated with terror and instability) during the French Revolution. Modern semantic acrobatics around these ideas are sufficiently similar that the Liberty Cap remains thoroughly contemporary and firmly erect despite its extreme old age.