Mono Lake Tufa

Lake Mono’s Tufas. Photo Credit: Tim Malabuyo

The unusual rock formations that grace Mono Lake’s shores are known as tufa.

Mono Lake is a large, shallow saline lake located in Mono County, California, United States. It is located in the eastern Sierra Nevada Mountains, east of Yosemite National Park and south of Lake Tahoe.

Many columns of limestone rise above the surface of Mono Lake. These limestone towers consist primarily of calcium carbonate minerals such as calcite (CaCO₃). This type of limestone rock is referred to as tufa, which is a term used for limestone that forms in low to moderate temperatures.

 

Lake Mono is one of North America’s oldest lakes−over 1 million years old in fact, with a salinity of about 2.5 times than the ocean. Rivers and streams that flow down from the Sierra Nevada give the lake its unusually high salt and mineral content. The lake is also well known for being very alkaline with a pH of about 9.8, due to its high concentrations of carbonates.

Seemingly out of a science fiction film, these formations, called tufas, rise up from the depths of the lake. Tufas are formed when calcium rich fresh water from springs interacts with the high alkaline lake water that is rich in carbonates. The ending results are these tufas which is actually your common limestone. The limestone builds from the ground up, creating these odd looking structures in the lake that have formed over millions of years.

Mono Lake's "South Tufa" area. Photo: By Nandaro CC

How does tufa form?

All tufa at Mono Lake forms underwater. Beneath Mono Lake, calcium-rich freshwater springs seep up from the lake bottom and mix with lake water rich in carbonates (think baking soda). As the calcium comes in contact with the carbonates in the lake, a chemical reaction occurs, resulting in calcium carbonate, or 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 can grow to heights of over 30 feet underwater.