- Post Two on My Favorite Hot Springs
Yellowstone Park is blessed with gems you can see but not purchase. Yet they are priceless. The ones I’m thinking of are Emerald Spring and Emerald Pool.
Most deep hot pools are blue, because their water absorbs all colors of sunlight except blue, which is reflected back to our eyes. Emerald Spring at Norris Geyser Basin, however, is lined with yellow sulfur, so when combined with the blue of the water, that gives us green.
This spring has a somewhat acidic pH, and its temperature has varied from around 181ºF to 196ºF over the years. Its frequent turbulence comes from gases like carbon dioxide, but on occasion it has heated up enough to erupt as a geyser. In fact, in 1931 its nearly constant eruptions could reach 60 to 75 feet, according to geyser expert T. Scott Bryan.
Much larger and even more beautiful is Emerald Pool at Black Sand Basin, near Old Faithful village. Its color comes not from a sulfur lining but—being too cool to act as a geyser (about 144ºF to 156ºF) and not acidic—yellow bacteria can grow happily here. This accounts for its gorgeous green color and yellow surrounding bacterial mats.
Park Historian Lee Whittlesey tells us in his Yellowstone Place Names that Emerald Pool was named by members of the Hayden Expedition during summer 1872, just after Yellowstone became the world’s first national park. An 1894 writer called it “the most beautiful thing in the way of wonderland water I have ever seen” and pointed out that its rim looks like “rough-grained gold,” making it “an emerald set in gold.”
Black Sand Basin has got to be my favorite easy walk. In less than a mile of walking you can enjoy a welcoming geyser (Cliff Geyser), which may be erupting as you get out of your car, then Rainbow Pool and Sunset Lake to the north. Save the crown jewel, Emerald Pool, on its own short boardwalk, for the last.