Patagonia & Tierra del Fuego - General Information

Chapter 3 - Geology and Morphology

Geology and Morphology

In this chapter we would like to throw some light on the geological phenomena that have given rise to such a differentiated morphology in the southern regions of the South American continent: on the one side the fragmentation of the Chilean coast, starting from Isla Grande de Chiloé and continuing as far as the extreme south of the continent, into thousands of channels and islands mostly covered by a luxuriant flora; instead, on the side of the Argentine Patagonia the so-called pampa, left over from ancient lake basins, flat lands with a dry climate covered with a steppe-like vegetation.

Description of the region
The two regions are separated by the cordillera of the Andes: the real backbone of the South American continent. The Andes are geologically young mountains born about 70 million years ago that reached their present aspect about 2 million years ago.
In ancient times the coast of Chile from Puerto Montt toward the south, had a very similar physiognomy to that of the coast that at present extends further north; that is it was made up of a cordillera that ran longitudinally to the sea called Cordillera de la Costa, formed by modest relief, parallel to which there extended a valley, called Valle Central, east of which wound the high spurs of the Andes cordillera. For reasons that we will analyse later, the Valle Central starting from the zone of continental Chiloé toward the south, is now completely covered by water.
After having drawn a large bend, the Andes sink into the Estrecho de Magallanes. The chain that reappears further south in Isla Grande de Tierra del Fuego, is called Cordillera Darwin and its peaks reach 2,000 metres in height (6,560 ft).

The Isla de los Estados in itself makes up the extreme southern limit of the Andes cordillera, even though the relief continues on plunging into the waters of the Drake Passage to reappear once again in the Antarctic Peninsula.

The origins of Patagonia and the Chilean channels
Scholars believe that the origin of such a fragmented geography like that which can be seen at present along the Patagonian fjords and those of the Tierra del Fuego, can be put down to four main factors:

1. the meeting of the oceanic plate with the continental shelf;

2. complex exogenous phenomena,  especially of erosion by water  that took place  during the

pre-Tertiary periods;

3. a period of intense  glaciation,  that  started in  the  last  2 million  years and ended 14,000

years ago with the last glaciation;

4. complex  geological  phenomena,  especially  bradyseisms and earthquakes, which made the

ground  sink opening  a  breach to  the waters  of the  ocean  that  went  kilometres up  the

ancient valleys.

The enormous pressure caused by the submarine oceanic plate of Nazca, the lithosphere of which wedges itself under that of the South American continental plate, made up of lighter rocks, has created fractures at 45° angles compared to the parallel along the coast of Chile. This has given rise to the zone of continental Chiloé with fjords like the Estéro Reloncaví, the Comau or the Reñihue or even the fjord of Puyuhuapi that flows into the Canal Moraleda, not to mention the infinite number of inlets and estéros that extend to the extreme south.
This phenomenon was also the basis for the formation of the Andes cordillera.
The fact that these fractures show a slope of 45° compared to the parallel (of latitude) is simply due to the fact that in the southern hemisphere, due to the rotation of the earth, every moving body has a deviation toward the left. A typical example of this phenomenon are the trade winds.


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