Chile’s
Atacama Desert may be the driest place on Earth. Large stretches of the Atacama
have gone without moisture for as long as people have been keeping track. Yet
some precipitation does fall in the region, and that water helps shape the
landscape.
Within
this arid environment lies a salt flat, or playa, named Salar de Atacama. The
Landsat 7 satellite acquired this false-color image on March 21, 2002. Red
indicates vegetation, the most abundant of which occurs around springs that dot
the northern edge of the saltpan. Nearby soils that support some vegetation
appear tan and brown.
Although
it sits at a much higher elevation, the Salar de Atacama resembles California’s
Death Valley as a flat area in between mountain ranges. The little
precipitation that has fallen has usually drained off the mountains and flowed
into nearby valleys, creating alluvial fans.
The
salt flat is a geologically young, dynamic system. Occasional floods do reach
the saltpan, and flood waters carry gravel, sand, clay, and salt. Heavier
materials such as gravel and sand tend to drop out of the water sooner, coming
to rest outside the saltpan. Clays and salts can hitch a ride all the way to
the playa.
Floods
initially stir the sediments inside Salar de Atacama, but material eventually
settles into layers of clay and salty water. Because the playa lacks drainage,
water only leaves by evaporation. As it evaporates, salts remain behind and
form crusts. Inside the saltpan, mottled light blue indicates surface salt
crusts.
The
white color around the perimeter of the saltpan indicates a zone of clay and
carbonate-rich material that alternately forms a crust on the surface and
re-dissolves with rising and falling groundwater. Northeast of the playa, white
indicates something else: snow and ice on the volcanic peaks. Volcanic rocks
and soils range in color from burnt orange to tan.
Around
the playa, the false-color green indicates rocks that would appear red to human
eyes. Blue indicates older sedimentary rocks (deposited by wind and water) and
igneous rocks (formed from cooling lava or magma) that support no vegetation.
Not
surprisingly, Salar de Atacama is now mined for salt, and evaporation ponds
appear in the middle of the saltpan—rectangular shapes of bright turquoise and
white. The salt flat also holds the potential for lithium production from its
subsurface brine-bearing waters.
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