Yellowstone National Park Mammoth Hot Springs

Travertine terraces at Mammoth Hot Springs

Mammoth Hot Springs is an extensive mass of travertine terraces that have been forming over thousands of years. Travertine is a crystalline limestone that forms in mineral springs saturated with dissolved calcium carbonate (CaCO3). The deposition of travertine at Mammoth is unique as most other hot springs in the park accumulate sinter (silica or geyserite). Below Mammoth’s surface, hot water encounters limestone, which dissolves readily allowing it to become saturated with calcium carbonate. As the heated water rises to the surface, it experiences a drop in pressure and temperature allowing carbon dioxide gas to escape (much like opening a can of soda), precipitating deposits of calcium carbonate in the hot water. It then flows out as travertine forming terraces. When one flow is blocked, the water moves elsewhere, hence the ever-changing terraces.