Rio Negro is recognizable by astronaut crews from orbit as one of the
most meandering rivers in South America. In this astronaut photograph,
the entire floodplain (mostly ~10 kilometers wide) is covered with
curved relicts of channels known as meander scars.
Meander scars show the past positions of river bends. The Rio Negro is
a dramatic example of how mobile a river can be; these meanders were
produced as the river snaked across the plain in the very recent
geological past, probably during the last few hundred years.
The main channel of the river, flowing south at this point—sixty
kilometers south of the city of Choele Choel (not shown)—appears in
partial sun glint at image right. Sun glint occurs when light is
reflected off a water surface directly back towards the viewer, like a
mirror, imparting a silvery sheen to those areas. When meander scars
contain water they are known as oxbow lakes, some of which are also highlighted by sun glint in the image.
The orange tint to the water in one of the oxbow lakes (image
center) could result from orange salt-loving algae. Their appearance
here would be unusual since floodplain lakes are usually too fresh for
algae blooms. But an explanation may lie in the location of the Rio
Negro on the margin of Argentina’s arid Patagonian region, where annual
rainfall is less than 300 millimeters (12 inches). Evaporation in this
cloudless region could be high enough for some lakes to become salty.
The Rio Negro flows generally southeast from the Andes Mountains to
the Atlantic Ocean. Its floodplain supports the biggest pear- and
apple-growing region of Argentina. Rectangular farm boundaries can be
seen at bottom center in the image. The river also hosts the world’s
longest kayak regatta, which lasts six days. During the 1800s, the
river was also the demarcation line between farmlands of European
settlers and territory controlled by indigenous people.
Astronaut photograph ISS022-E-19513
was acquired on January 4, 2010, with a Nikon D2Xs digital camera
fitted with an 800 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 22 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 M. Justin Wilkinson, NASA-JSC.