Mono's Magnificent Monuments
These things are weird!
--Anonymous Mono Lake Visitor
WE'RE NOT TALKING ABOUT BEAN CURD
Call them weird, call them bizarre, call them what you will, but the unusual rock formations that grace Mono Lake's shores are known to geologists as tufa (too'-fah). Tufa forms in a variety of ways at Mono Lake, but the most visible and remarkable formations are the towers that grace Mono's shoreline. The greatest concentration of these towers is located at the South Tufa grove just off of Hwy 120 East, at the south end of Mono Lake. Many first-time visitors to Mono Lake, unfamiliar with the geologic term "tufa" have been known to ask directions to the "tofu." Your nearest grocery store or the Mono Market is the best bet.
A COMMON ROCK IN RARE FORM
Tufa is essentially common limestone. What is uncommon about this limestone is the way it forms. Typically, underwater springs rich in calcium (the stuff in your bones) mix with lakewater rich in carbonates (the stuff in baking soda). As the calcium comes in contact with carbonates in the lake, a chemical reaction occurs resulting in calcium carbonate--limestone. The calcium carbonate precipitates (settles out of solution as a solid) around the spring, and over the course of decades to centuries, a tufa tower will grow. Tufa towers grow exclusively underwater, and some grow to heights of over 30 feet. The reason visitors see so much tufa around Mono Lake today is because the lake level fell dramatically after water diversions began in 1941.
Tufa towers are not the only form of tufa at Mono Lake. Calcium carbonate crystals will also precipitate out of lakewater far from springs and coat lakebottom surfaces like pumice boulders, beer cans, dead vegetation, dead birds, and anything else that might end up in the lake (instant fossils!). Another way tufa is formed is through biogenesis, the biological activity of organisms like the alkali fly. When an adult alkali fly emerges from an underwater pupae case it leaves behind a minute deposit of calcium carbonate, a waste product from its earlier life stage beneath the salty, alkaline lake. Alkali flies, on a small scale, actually contribute to the growth of underwater tufa towers!
Where else does tufa exist? The answer lies around the world and back in time, and possibly even on Mars. Tufa grows in many places where the right chemical environment exists. Some tufa even grows in the ocean off the coast of Greenland! Tufa is common at other Great Basin desert lakes, but Mono Lake has the most active formations around. Some Great Basin dry lakes in California and Nevada reveal old tufa formations that once were active when these lakes were full during the last ice age. Mono Lake has its own ice age tufa hundreds of feet above the historical level of the lake. If you think Mono Lake looks impressive now, you should have seen at the end of the last ice age when it was five times bigger than it is today!
To protect these fragile formations, at the urging of the Mono Lake Committee the California legislature established the Mono Lake Tufa State Reserve in 1981.
If you would like to make tufa at home, see the chemistry page for how to make Mono Lake water. Then, just add calcium chloride dissolved in fresh water to make tufa (although the reaction won't be as vigorous as it is in real Mono Lake water).