May 1, 2004 | David F. Coppedge

Tufa Mounds Formed “Instantaneously,” Geologically Speaking

Tufa towers have been found forming in Big Soda Lake, Nevada, at the rate of 30mm/year.  Now more than 3 meters tall, that means they could have reached their current height in only 100 years.  Rosen et al., who reported this in the May issue of Geology,1 warn that “care should be taken when trying to determine the significance of variations in isotopic or chemical compositions of tufas that may have been caused by mixing with groundwater,” because “The exceptionally fast growth of the tufa mounds indicates that large tufa deposits may form almost instantaneously in geologic time.”  They point out that similar structures “have been used as proxy for paleoclimate throughout the world” such as in Spain.  They conclude,

The presence of large, fast-growing tufa mounds in a modern closed-basin lake indicates that care must be taken when evaluating the growth rate of ancient tufa mounds for paleoclimate or signatures and paleohydrologic information.  In particular, if overgrowth and/or recrystallization such as described here occur, there is ample possibility of obtaining a mixed signature from tufa that may not be representative of either groundwater recharge sources or local surface water.  In such cases, caution must be exercised in elucidating the paleoclimate or paleohydrologic signature.

1Rosen, Arehart and Lico, “Exceptionally fast growth rate of 100-yr-old tufa, Big Soda Lake, Nevada: Implications for using tufa as a paleoclimate proxy,” Geology Vol. 32, No. 5 (May 2004), pp. 409�412, doi: 10.1130/G20386.1.

Large tufa mounds are found around the world.  Some notable examples are at Mono Lake and Searles Dry Lake in California.  Before assuming these structures took long ages to form, or can tell us about past climates, we should take note of these geologists’ surprising findings.

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