Pyramid lake in western Nevada, USA, is a remnant of the ancient and much larger Lake Lahontan, which formed during the last ice age when the regional climate was significantly cooler and wetter. Pyramid Lake and the now-dry Lake Winnemucca are two of seven smaller lakes that collectively formed Lake Lahontan when water levels were higher. The deepest part of Lake Lahontan survives today as Pyramid Lake. The lake takes its name from one such pyramid-shaped deposit of 'tufa', rock formed by the precipitation of calcium carbonate. Over time, these deposits develop a wide variety of forms including mounds, towers, sheets, and reefs while sometimes coating other rocks. The tufa is exposed when water levels drop due to changes in regional climate or the diversion of water for human use
Photograph: ISS/Nasa
The Guardian
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