Mounded Terrace
Yellowstone National Park
Inactive until recently, Mounded Terrace has begun recently to flow again at Mammoth Hot Springs. Hot water with dissolved carbon dioxide makes a solution of weak carbonic acid. As the solution rises through rock, it dissolves calcium carbonate, the primary compound in limestone. At the surface, the calcium carbonate is deposited in the form of travertine, the rock that forms the terraces of Mammoth Hot Springs. Photo © copyright by Ed Fuhr.