Tufa

Tufa is a variety of limestone formed when carbonate minerals precipitate out of water in unheated rivers or lakes.

Although sometimes regarded as a distinct carbonate deposit, calcareous sinter formed from ambient temperature water can be considered a sub-type of tufa.

They lack any significant macrophyte component due to the absence of light, and for this reason they are often morphologically closer to travertine or calcareous sinter.

They are distinct from most tufa deposits in that they lack any significant macrophyte component, due to the salinity excluding mesophilic organisms.

It is generally thought that such features form from CaCO3 precipitated when carbonate rich source waters emerge into alkaline soda lakes.

On emergence, waters degas CO2 due to the lower atmospheric pCO2 (see partial pressure), resulting in an increase in pH.

Supersaturation may be enhanced by factors leading to a reduction in pCO2, for example increased air-water interactions at waterfalls may be important,[7] as may photosynthesis.

Tufa columns at Mono Lake , California
Barrage Tufa at Cwm Nash, South Wales
Rubaksa tufa plug, after drying of the river, in Ethiopia
Tufa deposits at Huanglong , Sichuan , China
Tufa at Trona Pinnacles , California
The Pyramid and Domes tufa rock structures, Pyramid Lake, Nevada
Tufa dam in Chelekwot , Ethiopia
National Park Krka
Tufa and travertine sediments visible on the Una river bed.
Tufa on Plitvice waterfalls
Hollowed out portions of these tufa cliffs once formed back walls of rooms in a large prehistoric pueblo that stood here in Bandelier National Monument. Note outlines of masonry that were the outer portions of structure, and small holes in cliff that once supported ends of floor beams.