Lluta River (Chile, July 2012), from the Earth Observing-1 satellite.The Lluta River runs through th

Lluta River (Chile, July 2012), from the Earth Observing-1 satellite.The Lluta River runs through the Atacama Desert, which is the driestplace on earth, with less than a millimetre of rain per year.  About24km west of this photo is the town of Arica, which has the lowestprecipitation of any city in the world – 0.8mm per year, about 75less than California’s Death Valley.A few types of cacti can survive in the Atacama, and some otherdrought-tolerant species.  In the canyons, however, there is far morevegetation.  The canyons were carved by the Lluta and San JoséRivers, both of which have their headwaters in the east (at thefoothills of the Andes) and flow into the Pacific Ocean.  To thenorth-east is the stratovolcano Tacora, and glaciers on this volcanoprovide enough water for the Lluta to flow year-round.  Few rivers inthe area can do this.Along the bottom of the Lluta and Apaza Valleys there are blocks ofgreen colour from irrigation, carried out by residents of the smallfarming villages in the canyon bottoms.  However, despite theseemingly-lush fields, the Lluta Valley has major problems with waterquality.  This is because the Lluta River is quite saline and acidic,and also has dangerously high levels of arsenic, boron, sulphate, andother unwanted substances that flow into the river from naturalgeothermal springs and upstream mining operations.Because of this, the Lluta can only be used to irrigate pasturelandand a few tolerant crops (such as onions and potatoes).  Those livingin the area struggle economically, and rely on bottled water from theChilean government.The scarps (steep slopes) forming the Lluta Valley’s wallsmake it difficult to reach the valley floor from the plateau.  One ofthe few access points is Route 11 near the village of Churina.  Theslope on the southern wall was lessened because of the complicatednetwork of drainage channels that join the river from the east, andthe lower gradient made it easier to build the road.A few kilometres to the east is a massive amphitheatre-shaped scarpcaused by the Lluta Collapse, and the water running off it createdthe distinct drainage pattern.  The Lluta Collapse happened about 2.5million years ago, making it one of the oldest-known landslides inthe world, and it displaced 25 cubic kilometres of material.The San José River, a few kilometres south of the Lluta, carved theApaza Valley.  Its clean waters can support a wide variety ofhigh-quality crops, particularly olives. -- source link

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