Stock Photo - Central Andes Mountains, Salar de Arizaro, Argentina are featured in this image photographed by an Expedition 23 crew member on the International Space Station. The high plains (3,000 to greater than 5,000 meters elevation, 13,000 to 19,000 feet) of the Andes Mountains, also known as the Puna, appear in the foreground of this photograph, with a line of young volcanoes facing the much lower Atacama Desert (1,000--2,000 meters elevation). Several large dry lakes, marked by light-toned salt crusts, occupy the basins between major thrust faults in the Puna. Salar de Arizaro (foreground) is the largest of the dry lakes in this view (salar means waterless salt flat in Spanish). This panorama was taken by a station crew member looking southeast across the South American continent when the ISS was almost directly over the Atacama Desert near Chile's Pacific coast. The Atlantic Ocean coastline (River Plate where Argentina's capital city of Buenos Aires is located) is dimly visible at top left. A striking geological and landscape contrast is visible at center which separates two distinct geological zones, namely the Puna and the Sierras Pampeanas. The Sierras Pampeanas Mountains are lower in elevation and have few young volcanoes, in contrast to the Puna. Sharp-crested ranges are separated by wide, low valleys in this region. The Salinas Grandes - ephemeral shallow salt lakes at top left (salina means salt lake in Spanish) - 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, namely the deserts of the Atacama and Puna, versus the low grassy plains of central Argentina where rainfall is sufficient to promote lush prairie grass growth - known famously as the pampas in Argentina. The Salinas Grandes mark an intermediate semiarid region. What accounts for the changes in landscape? The geology of this part of the Andes is a result of the eastward subduction of the Nazca tectonic plate underneath South America. Investigations using seismic data suggest that the Puna is underlain by a steeply dipping sector of the subducting Nazca plate. The Sierras Pampeanas zone however, is underlain by a sector of the Nazca plate that is almost horizontal, possibly due to the subduction of a submarine mountain range known as the Juan Fernandez Ridge. In the simplest terms, ridges are topographic highs that are difficult to stuff down subduction zones, with profound effects on the volcanism and structures of the upper plate.