Earth Observations taken by the Expedition 25 crew

ISS025-E-005259 (28 Sept. 2010) --- Pyramid Lake in Nevada is featured in this image photographed by an Expedition 25 crew member on the International Space Station (ISS). Pyramid Lake, located in western Nevada near the California border, is a remnant of the ancient and much larger Lake Lahontan. According to scientists, Lake Lahontan formed during the last Ice Age when the regional climate of Nevada was significantly cooler and wetter than today—abundant precipitation and low rates of evaporation led to the formation of numerous lakes that began to coalesce as they overfilled their original basins. Pyramid Lake and the nearby now-dry Lake Winnemucca are two of seven lakes that formed Lake Lahontan. At its highest water level, during the late Pleistocene Epoch (approximately 15,000 years ago), Lake Lahontan covered much of western Nevada and extended into California, according to scientists. The deepest part of Lake Lahontan survives today as the perennial Pyramid Lake. Pyramid Lake is well known to geologists because of the spectacular tufa—calcium carbonate—deposits found here; the lake takes its name from one such pyramid-shaped deposit. Tufa is a rock formed by precipitation of calcium carbonate from spring water, lake water, or a combination of the two. Over time, these deposits can develop a wide variety of forms including mounds, towers, sheets, reefs and coatings on other rocks. These may then be exposed when the water level drops due to changes in regional climate, diversion of water for human use, or both (Mono Lake in California for example). This photograph also captures sunglint—light reflected off of a water surface back towards the observer on the space station—on the northern and southeastern ends of the lake. Two large spiral whorls are visible in sunglint at the northern end of the lake; these likely trace surface wind patterns disturbing the water surface that cause localized variations in the amount of light reflected back to the ISS.