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Geology and geomorphology of the Cordillera Blanca

by Armin Matzl

General information

The view from the Cordillera Negra across the Río Santa Valley or Callejón de Huaylas to the Cordillera Blanca (see title image of this contribution and of the route overview) clearly reveals that the Cordillera Blanca is much higher than the Cordillera Negra. Indeed, the Cordillera Blanca - White mountain range in English - is one of the highest ranges of the entire Andes, reaching an elevation of 6768 m (Nevado Huascarán). Higher peaks only occur much farther south (Cerro Aconcagua, 6962 m) so that the Cordillera Blanca represents the highest tropical mountain range worldwide. It contains most of all tropical glaciers and, as a consequence, a large number of glacial lakes (882 of such lake have been counted). It is located approximately 300 km north of the Peruvian capital city Lima. But why are there so many high peaks? Let’s have a closer look at the geology, it’s worth it!


How the Cordillera Blanca evolved

Browse through the explanation of this WSW–ENE cross-section by clicking on the arrows. You can switch between animated and static profiles by clicking on the title symbol.

The Andes already formed a mountain range about eight million years ago. The geology of the area which we call Cordillera Blanca nowadays mainly consisted of three different units: the continental plate, some Jurassic phyllites, and Cretaceous sediments (from bottom to top). In the subduction area where the Nazca Plate dives under the continental plate the rock was melting, so that a magma chamber formed beneath the continent. The density of molten rock (or magma) is lower than the density of the surrounding rock, so it tends to rise. This process can be considered the beginning of the formation of the Cordillera Blanca.

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This model represents a simplified and distorted representation of reality, and does not claim to be complete or correct. Its purpose is to convey some idea on how the Cordillera Blanca could have developed.


The secrets of a batholith

We have already learned that the Cordillera Blanca mainly consists of a so-called batholith. The rather soft sedimentary and volcanic rocks now forming the Cordillera Negra have been sliding off this batholith slowly as a tectonic movement rather than as a landslide. But what are the characteristics of those rocks forming the batholith itself?

Consult a geological textbook in order to learn which types of rock typically form a batholith, if these rocks are arranged in a certain way, and what are the reasons for the patterns observed.

Show solution
References and links

Movie The Andes give, the Andes take with sequence on Huaraz and the Cordillera Blanca [Access movie]

This contribution was slightly revised and extended by Martin Mergili.