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June 2, 2014
(22 Aug. 2010) --- This photograph, featuring a landscape in the central Andes mountains near the Chile/Argentina border dominated by numerous volcanoes and associated landforms, was photographed by an Expedition 24 crew member on the International Space Station. Layers of older sedimentary rocks are visible to the southeast (upper right). Many of the volcanic cones show grooves eroded by water to form gullies. Such erosion has occurred since the host volcano was built up, indicating that most volcanoes in this view have been inactive for centuries or millennia. A few volcanoes exhibit much less erosion, and even show tongues of recent, dark lava flows (top left). According to scientists, two of these volcanoes, Cerro el Condor and Peinado have likely erupted within approximately the last 12,000 years (the Holocene Epoch). Also visible in the image is the world's highest active volcano, Nevado Ojos del Salado, with a summit at 6,887 meters above sea level. The most recent confirmed eruption of this volcano has been dated to 700 (approximately 300 years), but minor eruptive activity may have occurred as recently as 1993. Stratovolcanoes such as Cerro el Condor, Peinado, and Nevado Ojos del Salado are formed partly by buildup of lava flows and partly by buildup of explosively vented material dropping back down onto the surface. One type of material associated with explosive eruptions is welded tuff, which is formed by molten and fragmented rock that accumulates on the ground and later solidifies. A large tuff sheet is visible at top left. Formed very rapidly, these sheets have been termed "instant landscapes." So active has the Andean volcanic system been that the origin of many of the tuffs in the Andes cannot be pinpointed since source vents have been overprinted by subsequent volcanic events. The volcanic landscape also shows that the erosive work of rivers—and glaciers repeatedly in the recent past—is slower than the opposite processes of the upward building of the volcanoes. The bright blue, nearly 7-kilometer-long lake near the center of the image is known as Laguna Verde. This and other less obvious lakes indicate that water (snowmelt or direct precipitation) is unable to reach the sea, but is rather impounded in the depressions between the volcanic edifices.

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