tufa

One of the two main types of stone used in ancient Roman buildings. It was cheap and easily worked, but too soft to use in load-bearing structures or places subject to heavy wear (Travertine was used in those areas).

Roman buildings were made of concrete, so a soft stone such as tufa could be safely used for cladding, giving the appearance of stone building at lower cost.

Augustus Caesar was fond of boasting "I found Rome built of brick, and left it built of marble." It would be more accurate to say that he left it built of tufa cladding.

First off, picture those pillars in the deep ocean... the mid-oceanic ridge and deep sea vents. Superheated water filled with nutrients and minerals comes out of the sea floor and slowly builds up towers of minerals. A similar system is at work just over a mile above sea level in Mono Lake.

At Mono Lake, a formation known as the tufa towers can be seen. They are very well photographed, including the album cover for Wish You Were Here by Pink Floyd (the one of the man with his legs sticking out of the water). Tufa is formed when freshwater rich in calcium bubbles up into Mono Lake itself. The lake water is very rich in carbonates and combines to form calcium carbonate (limestone) which is deposited around the spring. Over the years (tufa grows at the rate of millimeters a year - a one meter tall tufa tower takes on the order of 500 years to grow) the towers form. Tufa only forms under water - the calcium and carbonate reaction needs to happen in water.

Another form of tufa known as sand tufa occurs under the lake bed when the calcium rich fresh water bubbles up through sand. This type of tufa is thought to form in hours rather than years (though it is much more rare) as the calcium carbonate reaction takes place around the sand grains. The sand forms a skeleton of a sort allowing for more rapid growth. However, this type of tufa is much more fragile than the lithoid tufa described above.

Much of the tufa has been exposed since 1941 when the Los Angeles Department of Water and Power used the streams that feed Mono Lake as a source of water. Between 1941 and 1962, the lake had dropped 25 feet and between 1962 and 1994 the lake level had dropped another 15 feet. Since the Water Board Decision in 1994, Mono Lake has risen 8 feet.

Along with Mono Lake, tufa can also be found at:

• Pyramid Lake
• Winnemucca Lake (dry)
• Walker Lake (Nevada)
• Death Valley
• Panamint Valley
• Searles Dry Lake (size of small hills)

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http://www.pinkfloyd-co.com/hy/hyb.html
http://www.monolake.org/

Tu"fa (?), [It. fufo soft, sandy stone, L. tofus, tophus. Cf. Tofus, Toph, and Tophin.] Min. (a)

A soft or porous stone formed by depositions from water, usually calcareous; -- called also calcareous tufa.

(b)

A friable volcanic rock or conglomerate, formed of consolidated cinders, or scoria.

 

© Webster 1913.