An astronaut flying over central South America was following the Sun’s reflection point (also known as sunglint) as it flashed across the water surfaces of the Iberá Wetlands. Sunglint makes for startling images that appear more like black-and-white photos. The many bright, irregular, elongated patches (especially on the lower right) are bigger lakes, while the smaller, more circular features are hundreds of tiny ponds (upper left). Interestingly, the name Iberá comes from ý berá, the local Guaraní words meaning “bright water.”

South America’s second-largest river, the Paraná, used to flow through this area from top right to lower left. The river built up a great inland delta, leaving the larger lakes in the slightly lower areas of the floodplain. The tiny lakes are situated on older river terraces, which stand 3 to 9 meters higher than the average local elevation. The region is so waterlogged that farming is difficult and is restricted to the higher, drier ground. (See the farm fields near the top right.)

It is unclear why the higher areas have the lakelets, or why they are so round in shape. But one idea is that during very dry times in the last Ice Age, dry winds scoured out numerous hollows, as we see in many deserts today. When the climate grew wetter, these depressions filled with water and marshy vegetation colonized the shorelines. As sediment slowly washed into the lakelets, all angular shoreline shapes became smoothed and rounded. The smallest ponds are almost completely filled with vegetation, except for a halo along the shorelines where open water reflects the Sun. It is unclear why the ponds have developed this interesting vegetation pattern.

Astronaut photograph ISS049-E-1090 was acquired on September 10, 2016, with a Nikon D4 digital camera using a 800 millimeter lens, and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by a member of the Expedition 49 crew. The image has been cropped and enhanced to improve contrast, and 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 M. Justin Wilkinson, Texas State University, Jacobs Contract at NASA-JSC.