This panorama was taken by an astronaut looking southeast across the
South American continent when the International Space Station (ISS) was
almost directly over the Atacama Desert near Chile’s Pacific coast. The
high plains (3000–5000 meters, or 13,000–19,000 feet) of the Andes
Mountains, also known as the Puna, appear in the foreground, with a line
of young volcanoes (dashed line) facing the much lower Atacama Desert
(1000–2000 m elevation). Several salt-crusted dry lakes (known as salars in Spanish) occupy the basins between
major thrust faults in the Puna. Salar de Arizaro (foreground) is the
largest of the dry lakes in this view. The Atlantic Ocean coastline,
where Argentina’s capital city of Buenos Aires sits along the Río de la
Plata, is dimly visible at image top left.
Near image center, the transition (solid line) between two distinct
geological zones, the Puna and the Sierras Pampeanas, creates a striking
landscape contrast. Compared to the Puna, the Sierras Pampeanas
mountains are lower in elevation and have fewer young volcanoes.
Sharp-crested ridges are separated by wide, low valleys in this region.
The Salinas Grandes—ephemeral shallow salt lakes—occupies one of these
valleys. The general color change from reds and browns in the foreground
to blues and greens in the upper part of the image reflects the major
climatic regions: the deserts of the Atacama and Puna versus the grassy
plains of central Argentina, where rainfall is sufficient to promote
lush prairie grass, known locally as the pampas.
The Salinas Grandes mark an intermediate, semiarid region.
What accounts for the changes in topography between the Puna and the
Sierras Pameanas? The geology of this part of the Andes is a result of
the eastward subduction of the Nazca tectonic plate underneath South
America. Seismic data suggest that beneath the Puna, the Nazca Plate is
dipping down steeply. Beneath the Sierras Pampeanas zone, however, the
underlying Nazca plate is almost horizontal. The levelness may be due to
the subduction of a submarine mountain range known as the Juan
Fernández Ridge. In the simplest terms, ridges are topographic highs
that are difficult to stuff down into the subduction zone, and that has
profound effects on the volcanism and structures of the overlying South
Astronaut photograph ISS023-E-28353
was acquired on April 26, 2010, with a Nikon D3S digital camera fitted
with an 80 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
23 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.