RHH's photos with the keyword: calcium carbonate

This is a steam vent where the steam and hot water have made these biscuit-like formations.

This area of thermal activity covers the side of a mountain, thus the name. The description from the National Park website describes it thus: "Roaring Mountain, located 4.5 miles north of Norris Geyser Basin, is a barren, furrowed, white ridge, rising 400 feet from the base. The mountain side is spotted with steam vents or fumaroles, and the fumaroles' vents are rimed with bright yellow, crystalline sulfur deposits. The leaching of sulfuric acid has produced the stark, barren environment."

This is a scan of an old slide taken in 1979 on an autumn visit to Yellowstone. At that time Opal Terrace was very active, as were the terraces across the road. All that has changed more recently with Opal Terraces completely inactive and very much less activity in the larger terraces across the road.