Tufa shelves, clear water
Mono County, California
Tufa formation can be rapid, with up to an inch added in one day. The visible formations at Mono Lake are within a few centuries old.
Underwater springs bring one component for tufa formation; the high-carbonate lake water brings the rest. The calcium comes from water in springs under the lake. It is dissolved as Ca2+. The lake water provides carbonate as CO32– and the lake’s alkaline environment allows the oppositely charged ions to precipitate into nearly insoluble CaCO3. This accumulates as tufa. Because the less dense spring water rises, the tufa accumulates near the top of the tube.
In the past decade or so, as Los Angeles has slowed its water withdrawl from streams feeding the lake, water levels are rising, hiding some of the tufa visible in my pictures, but improving the health of the lake's ecosystems.