Pyramid Lake in western Nevada, near the California border, 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. At its peak volume during the late Pleistocene
Epoch (approximately 15,000 years ago), Lake Lahontan covered much of western Nevada and extended into California.
The deepest part of Lake Lahontan survives today as Pyramid Lake, and
it is well known to geologists because of the spectacular calcium
carbonate deposits found there. The lake takes its name from one such
pyramid-shaped deposit of tufa,
rock formed by the precipitation of calcium carbonate from spring
water, lake water, or a combination of the two. 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, the
diversion of water for human use, or both (Mono Lake in California for example).
This astronaut photograph also captures sunglint—light reflected off
of a water surface back towards the observer—on the northern (lower end
in this image) and southeastern (upper) ends of the lake. Two large
spiral whorls are visible in sunglint at the northern end, likely the
result of wind patterns that disturb the water surface and cause
localized variations in the amount of light reflected back to the
International Space Station.
Astronaut photograph ISS025-E-5259
was acquired on September 28, 2010, with a Nikon D2Xs digital camera
using a 180 mm lens, and is provided by the ISS Crew Earth Observations
experiment and Image Science & Analysis Laboratory, Johnson Space
Center. The image was taken by the Expedition 25 crew. The image in this article has been cropped and enhanced to improve contrast. Lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab
to help astronauts take pictures of Earth that will be of the greatest
value to scientists and the public, and to make those images freely
available on the Internet. Additional images taken by astronauts and
cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by William L. Stefanov, NASA-JSC.