Tuff Sheet
Posted: Tue Sep 07, 2010 9:38 pm
http://earthobservatory.nasa.gov/IOTD/view.php?id=45618 wrote: <<The landscape in the central Andes Mountains, near the border between Chile and Argentina, is dominated by volcanoes and associated landforms. Layers of older sedimentary rocks are visible to the upper middle, and many volcanic cones show grooves where water has eroded the rock 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 dark, recent lava flows (upper left). Two of these volcanoes, Cerro el Cóndor and Peinado, have likely erupted within the past 12,000 years.
Also visible is the world’s highest active volcano, Nevado Ojos del Salado, with a summit 6,887 meters above sea level. The most recent confirmed eruption has been dated to the year 700(± 300) years, but minor eruptive activity may have occurred as recently as 1993.
Stratovolcanoes such as Cerro el Cóndor, Peinado, and Nevado Ojos del Salado are formed partly by the buildup of lava flows and partly by the buildup of explosively vented material dropping back down onto the surface. One material associated with these eruptions is welded tuff, formed by molten and fragmented rock that accumulates on the ground and later solidifies. A large tuff sheet is visible at the top left. Formed very rapidly, these sheets have been termed “instant landscapes.” The Andean volcanic system has been so active that the origin of many tuffs cannot be pinpointed because the source vents have been overprinted by subsequent volcanic events.
The landscape also shows that the erosive work of rivers and glaciers in the region is slower than the upward building processes of the volcanoes. The bright blue lake -- nearly 7 km long -- near the center of the image is Laguna Verde. This and other less obvious lakes indicate that water from snowmelt or direct precipitation is unable to reach the sea, being impounded in the depressions between the volcanic edifices. >>
http://en.wikipedia.org/wiki/Ojos_del_Salado wrote:
<<Nevado Ojos del Salado ("water source of the salty river") is a massive stratovolcano in the Andes on the Argentina-Chile border and the highest volcano in the world at 6,891 metres. It is also the second highest mountain in the Western Hemisphere and the highest in Chile. It is located about 600 kilometres north of Aconcagua, the highest mountain in the Western Hemisphere at 6,962 m. Due to its location near the Atacama desert, the mountain has very dry conditions with snow only remaining on the peak during winter. Despite the generally dry conditions, there is a permanent crater lake about 100 metres in diameter at an elevation of 6,390 m on the eastern side of Ojos del Salado. This is most likely the highest lake of any kind in the world.
On Saturday, April 21, 2007, Chileans Gonzalo Bravo G. and his co-driver, Eduardo Canales Moya, claimed to have broken the New High Altitude World Record aboard a vehicle on Ojos del Salado, reaching 6,688 m in altitude, claiming a new Guinness record for Chile, surpassing the mark imposed by a German expedition during the previous March. The three previous Guinness records were achieved by German expeditions with stock vehicles in the same volcano, which, with larger budgets, had set the previous record of 6,646 m.
There are two summit peaks; one, which is slightly higher but by no more than a metre, is known as the "Chilean summit"; the other, which is more substantial, is known as the "Argentine summit". These are so named because they are usually climbed from the Chilean and Argentine sides respectively, although the international border passes over both peaks. There is a short distance but steep and dangerous drop between the two peaks, so it is unusual for climbers to reach them both.>>
