Tufa towers at Mono Lake, California

Tufa is the name for an unusual geological formation.

Tufa is a rough, thick, rock-like calcium carbonate deposit that forms by precipitation from bodies of water with a high dissolved calcium content. Tufa deposition occurs in six known ways:

1. Mechanical precipitation by wave action against the shore. This form of tufa can be useful for identifying the shoreline of extinct lakes (for example in the Lake Lahontan region).
2. Precipitation from supersaturated hot spring water entering cooler lake water.
3. Precipitation in lake bottom sediments which are fed by hot springs from below.
4. Precipitation from calcium-bearing spring water in an alkaline lake rich in carbonates.
5. Precipitation throughout the lake as the lake dries out.
6. Through the agency of algae.

There are some prominent towers of Tufa at Mono Lake in California, USA, formed by method 4, above. Tufa is also common in Armenia.