CHAPTER XII 



THE WESTERN ANDES: THE MARITIME CORDILLERA 

 OR CORDILLERA OCCIDENTAL 



The Western or Maritime Cordillera of Peru forms part of 

 the great volcanic field of South America which extends from 

 Argentina to Ecuador. On the walls of the Cotahuasi Canyon 

 (Fig. 131), there are exposed over one hundred separate lava 

 flows piled 7,000 feet deep. They overflowed a mountainous relief, 

 completely burying a limestone range from 2,000 to 4,000 feet 

 high. Finally, upon the surface of the lava plateau new moun- 

 tains were formed, a belt of volcanoes 5,000 feet (1,520 m.) high 

 and from 15,000 to 20,000 feet (4,570 to 6,100 m.) above the sea. 

 There were vast mud flows, great showers of lapilli, dust, and 

 ashes, and with these violent disturbances also came many changes 

 in the drainage. Sixty miles northeast of Cotahuasi the outlet of 

 an unnamed deep valley was blocked, a lake was formed, and sev- 

 eral hundred feet of sediments were deposited. They are now 

 wasting rapidly, for they he in the zone of alternate freezing and 

 thawing, a thousand feet and more below the snowline. Some of 

 their bad-land forms look like the solid bastions of an ancient 

 fortress, while others have the delicate beauty of a Japanese 

 temple. 



Not all the striking effects of vulcanism belong to the remote 

 geologic past. A day's journey northeast of Huaynacotas are a 

 group of lakes only recently hemmed in by flows from the small 

 craters thereabouts. The fires in some volcanic craters of the 

 Peruvian Andes are still active, and there is no assurance that 

 devastating flows may not again inundate the valleys. In the 

 great Pacific zone or girdle of volcanoes the earth's crust is yet 

 so unstable that earthquakes occur every year, and at intervals of 

 a few years they have destructive force. Cotahuasi was greatly 

 damaged in 1912; Abancay is shaken every few years; and the 

 violent earthquakes of Cuzco and Arequipa are historic. 



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