Yellowstone National Park - Mammoth Hot Springs Terraces

At Mammoth Hot Springs, a rarer kind of spring is born when the hot water ascends through the ancient limestone deposits of the area instead of the silica-rich lava flows of the hot springs common elsewhere in the park. The results are strikingly different and unique. They invoke a landscape that resembles a cave turned inside out, with its delicate features exposed for all to see. The flowing waters spill across the surface to sculpt magnificent travertine limestone terraces. As one early visitor described them, "No human architect ever designed such intricate fountains as these. The water trickles over the edges from one to another, blending them together with the effect of a frozen waterfall."

As ground water seeps slowly downward and laterally, it comes in contact with hot gases charged with carbon dioxide rising from the magma chamber. Some carbon dioxide is readily dissolved in the hot water to form a weak carbonic acid solution. This hot, acidic solution dissolves great quantities of limestone as it works up through the rock layers to the surface hot springs. Once exposed to the open air, some of the carbon dioxide escapes from solution. As this happens, limestone can no longer remain in solution. A solid mineral reforms and is deposited as the travertine that forms the terraces.