Limestone is a sedimentary rock composed of calcium carbonate that was deposited on the bed of an ancient inland sea, underlying an area in Yellowstone National Park known as Mammoth Hot Springs.

Heated by Yellowstone’s volcano, water travels through the buried limestone, dissolving it as it goes. The water becomes saturated with calcium carbonate and as it nears the surface, pressure and temperature decrease, allowing carbon dioxide gas to escape from the solution. The resulting deposits of calcium carbonate that form in and near the hot springs are called travertine terraces.

Some studies show that travertine builds up at an average rate of eight inches a day. For this reason, change is the only constant at Mammoth Hot Springs. Terraces that were active one year might be dry the next, and new areas become active and build terraces at the geologically stunning rate.

Fresh travertine is bright white, but it turns grey as it weathers. Travertine is a soft rock, it both breaks down and builds up rapidly. Where there are holes in the travertine, birds are building nests and raising families!

Mineral-laden hot water from deep beneath the Earth’s crust finds its way to the surface and builds tier upon tier of cascading, terraced stone.

Areas that appear orange or yellow in colour contain thermophiles, heat-loving organisms such as bacteria and algae that thrive in the warm waters of hot springs.