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  Image: Geographic Location Direction Photo #: ISS023-E-5251 Date: Mar. 2010
Geographic Region: CHILE

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  View Low-Resolution Image  
  Image Caption: Laguna del Negro Francisco

An astronaut aboard the International Space Station used a long lens to photograph an unusual lake in the high Andes Mountains of central Chile. Its two contrasting colors are separated by a narrow bank of sand. Dry desert washes lead down from adjacent highlands, spreading out as alluvial fans on all sides of the lake.

The contrasting colors of Laguna del Negro Francisco are controlled by the salt content of the water on either side of the sand bank. The 5 kilometer-long north basin is orange because it is shallow: evaporation results in salt accumulation that allows salt-loving algae to thrive. These organisms display different colors depending on the temperature and salinity of the water. Previous photos suggest that orange is an uncommon color for this lake, which is usually a light yellow-green.

By contrast, the south basin is fed by a larger watershed and is fresher, deeper, and more permanent. It is rich with wetland vegetation, and the depth of the water helps maintain a dark green color.

Strong westerly winds (from top left) blow most of the year and affect many landforms in the high Andean deserts. The winds promote wave action in the north basin, which is probably responsible for building the curved central sand bank. Wind has had a different effect on the south basin. Here the wind drives several slowly rotating water circulations in the deeper water. Over time, these currents sweep sand from the bank into the lake, forming short capes or spits. Sand spits are typical in shallow lakes, and have been observed by astronauts in other South American lakes.

Old shorelines ring Laguna del Negro Francisco, showing that water levels have been sometimes high enough in the past to drown the sand bank and make a single continuous body of water.

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Images: All Available Images Low-Resolution 238k
Mission: ISS023  
Roll - Frame: E - 5251
Geographical Name: CHILE  
Center Lat x Lon: 27.5S x 69.2W
Film Exposure:   N=Normal exposure, U=Under exposed, O=Over exposed, F=out of Focus
Percentage of Cloud Cover-CLDP: 10
Camera: N2
Camera Tilt: 21   LO=Low Oblique, HO=High Oblique, NV=Near Vertical
Camera Focal Length: 800  
Nadir to Photo Center Direction: SW   The direction from the nadir to the center point, N=North, S=South, E=East, W=West
Stereo?:   Y=Yes there is an adjacent picture of the same area, N=No there isn't
Orbit Number: 919  
Date: 20100318   YYYYMMDD
Time: 134038   GMT HHMMSS
Nadir Lat: 26.5S  
Latitude of suborbital point of spacecraft
Nadir Lon: 68.5W  
Longitude of suborbital point of spacecraft
Sun Azimuth: 67   Clockwise angle in degrees from north to the sun measured at the nadir point
Space Craft Altitude: 189   nautical miles
Sun Elevation: 40   Angle in degrees between the horizon and the sun, measured at the nadir point
Land Views: BASIN, DESERT  
Water Views: LAKE, WAVE  
Atmosphere Views:  
Man Made Views:  
City Views:  
Photo is not associated with any sequences

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