The connection of this system with that of the Rocky Mountains, which has been pointed out by many writers, has received much support from the discovery of the extensive eruptions of granite during Tertiary times, extending from the southern extremity of South America to Alaska.
The Andean range is composed of two great principal chains with a deep intermediate depression, in which, and at the sides of the great chains, arise other chains of minor importance, the chief of which is that called the Cordillera de la Costa of Chile. This starts from the southern extremity of the continent and runs in a northerly direction, parallel with the coast, being broken up at its beginning into a number of islands and afterwards forming the western boundary of the great central valley of Chile. To the north this coastal chain continues in small ridges or isolated hills along the Pacific Ocean as far as Colombia, always leaving the same valley more or less visible to the west of the western great chain.
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2 Chile-Argentina, 52°-38°S 3 Chile-Argentina from 38°S northward 4 Bolivia 5 Peru-Ecuador 6 Colombia 7 Structure |
Of the two principal chains the eastern is generally called Los Andes, and the western La Cordillera, in Colombia, Peru and Bolivia, where the eastern is likewise known as Cordillera Real de los Andes, while to the south of parallel 23°S in Chile and Argentina, the western is called Cordillera de los Andes. The eastern disappears in the centre of Argentina, and it is therefore only the Cordillera de los Andes that is prolonged as far as the south-eastern extremity of the continent.
The Cordillera de la Costa begins near
Cape Horn, which is composed principally of crystalline rocks,
and its heights are inconsiderable when compared with
those of the true Cordillera of the Andes. The latter,
as regards its main chain, is on the northern coast of the
Beagle Channel in Tierra del Fuego, bounded on the north
by the deep depression of Lake Fagnano and of Admiralty Sound. Staten Island appears to be the termination to the east. The Cordillera of the Andes in Tierra del Fuego is
formed of crystalline schists, and culminates in the snow-capped
peaks of Mount Darwin and Mount Sarmiento (7200 feet), which
contains glaciers of greater extent than those of Mont Blanc. The extent of the glaciers is considerable in this region, which, geographically, is more complex than was formerly supposed. Although in the explored portion of the Fuegian
chain the volcanoes which have been mentioned from time to
time have not been met with, there seem to have existed to the
south, on the islands, many neo-volcanic rocks, some of which
appear to be contemporaneous with the basaltic sheet that covers
a part of eastern Patagonia. The insular region between Mount
Sarmiento and the Cordillera de los Andes, properly so called,
i.e. that which extends from Magellan Strait northwards, is
not fully explored, and all that is known of it is that it is
principally composed of the same rocks as the Fuegian section,
and that the greater part of its upper valleys is occupied
by glaciers that reach down to the sea amid dense forest.
As Admiralty Sound and Lake Fagnano bound the Cordillera to
the north in Tierra del Fuego, so at the eastern side of the
Cordillera in the southernmost part of the continent there is
a longitudinal depression which separates the Andes from some
independent ridges pertaining to a secondary parallel broken
chain called the pre-Cordillera. This depression is occupied
in great part by a series of lakes, some of these filling
transversal breaches in the range, whilst others are remains
of glacial reservoirs, bordered by morainic dams, extending
as far as the eastern tableland and corresponding in these
cases with transversal depressions which reach the Atlantic Ocean. Between the larger lakes, fed by the Andine glaciers
of the eastern slope of the Southern Andes, are Lakes Maravilla, 100 square miles, and Sarmiento, 26 square miles, 51°S, which overflow into Last Hope Inlet; Argentino, 570 square miles, 50°S; and Viedma, 450 square miles, 49°30'S, which empty into the river Santa Cruz; the fjordian Lake San Martin, 49°S, and Lakes Nansen, 18 square miles; Azara, eight square miles; and Belgrano, 18 square miles, which are dependents of
Lake San Martin (380 square miles), and Lakes Pueyrredon (98 square miles)
and Buenos Aires (700 square miles), which now overflow into the
Pacific, through one of the remarkable inlets that are found
throughout the Cordillera, the Calen Inlet, which is the
largest western fjord of Patagonia. To the north of Lake Buenos Aires there is Lake Elizalde, which, while situated
on the eastern slope, sends its waters to the Pacific Ocean,
and Lakes Fontana (30 square miles) and La Plata (34 square miles), 45°S, which feed the river Senguerr, which flows to the Atlantic. Lake General Paz (66 square miles) on the eastern slope of the Andes, at 44°S, is the principal source of
the Palena River, which cuts all the Cordillera, while Lakes
Fetalauquen (20 square miles) Menendez (28 square miles), Rivadavia (10
square miles), and other smaller lakes, also situated between 43°30', and 42°30'S on the eastern slope send their waters to the Pacific by the river Fetaleufu which cuts
through the Andes by a narrow gorge. The waters of Lake
Puelo (18 square miles) likewise flow into the same ocean through
the river of that name, which also cuts the Cordillera, and
of which the principal affluent likewise drains the waters
of a system of small lakes, the largest of which, Lake
Mascardi, measures 17 square miles, which in comparatively recent
times formed part of the basin of Lake Nahuel Huapi (207 square miles), 41°S. An extensive area of glacial deposits shows that a sheet of ice formerly covered the whole eastern slope to a great distance from the mountains. To the west
another sheet reached at the same time the Pacific Ocean.
From the Strait of Magellan up to 52°S, the western
slope of the Cordillera does not, properly speaking, exist.
Abrupt walls overlook the Pacific, and great longitudinal and
transversal channels and fjords run right through the heart of the
range, cutting it generally in a direction more or less oblique
to its axis, the result of movements of Earth's crust.
The mountains forming the Cordillera between Magellan Strait
and 41°S are higher than those previously mentioned
in Tierra del Fuego. Generally composed of granite, gneiss
and Palaeozoic rocks, covered in many parts by rugged masses
of volcanic origin, their general height is not less than
6500 feet, while Mount Geikie is 7500 feet and Mount Stokes
7100 feet. To the north are Mounts Mayo (7600 feet), Agassiz
(10,600 feet), and Fitzroy, in 49°S (11,120 feet). The
section from 52°to 48°S is a continuous ice-capped
mountain range, and some of the glaciers extend from the
eastern lakes to the western channels, where they reach the
sea-level. The level of the lakes begins at 130 feet at Lake Maravilla and gradually ascends to nearly 700 feet at Lake San Martin. Passing the breach through which Lake San Martin empties itself into Calen Inlet, in 48°S, is found a wide
oblique opening in the range, through which flows the river Las
Heras, fed by Lake Pueyrredon, which is only 410 feet above the
sea-level to the east of the Andes, while Lake Buenos Aires,
immediately to the north, is 710 feet. The Andes continue to be
to the west an enormous rugged mass of ice and snow of an average
height of 9000 feet, sending glaciers to all the eastern fjords.
Mount San Lorenzo, detached from the main chain in the
Pre-Cordillera, is 11,800 feet high. Mount San Valentin
(12,700 feet) is the culminating point of the Andes in the
region extending from 49° to 46°S, a little north of
which is the river Huemules which is followed by the breach
of the river Aisen. These two rivers have emptied a large
system of lakes, which in pre-Glacial times occupied the
eastern zone, thus forming a region suitable for colonization
in the broad valleys and hollows, where the rivers, as in
the case with those in the north, cut through the Andes by
narrow gaps, forming cataracts and rapids between the snowy
peaks. Volcanic action is still going on in these latitudes,
as the glaciers are at times covered by ashes, but the
predominant rocks to the east are the Tertiary granite,
while to the west gneiss, older granite and Palaeozoic rocks
prevail. The highest peaks, however, seem to be of volcanic
origin. Farther north, up to 41°S, the water gaps are
situated at a lesser distance one from the other, owing mainly
to more continuous erosion, this section of the continent
being the region of the maximum rainfall on the western
coast to the south of the equator. Between the gaps of the
river Aisen and river Cisnes or Frias, which also pierces the
chain, is found a huge mountain mass, in which is situated
Mount la Torre (7150 feet). These form the continental
watershed, but in this region erosion is taking place so
rapidly that the day is not far distant when Lakes La Plata and
Fontana, situated to the east at a height of 3000 feet and now
tributaries of the Atlantic, may become tributaries of the
Pacific. Already filtrations from the former go to feed
western affluents through the granitic masses. To the north
of Mount la Torre flows in the river Cisnes, 44°48'S,
across another water gap, continuing the range to the north
with high peaks, as Mount Alto Nevado (7350 feet) and Mount Cacique (7000
feet). The glaciers reach almost the western channels, as is
the case at the river Quelal. The northern glaciers, descending
nearly to sea-level, are situated at 43°40'S. To the north, a well-defined western longitudinal valley, at some recent time occupied by lakes and rivers,
divides the Cordillera into two chains, the eastern being
the main chain, to which belong Mounts Alto Nevado, Cacique,
Dentista, Maldonado, Serrano, each over 7000 feet high; and
Torrecillas (7400 feet), Ventisquero (7500 feet), and Tronador
(11,180 feet); while the western chain, broken into imposing
blocks, contains several high volcanic peaks such as Mounts
Tanteles, Corcovado, Minchimahuida, Hornopiren and Yates. The
rivers Palena, with its two branches, Pico and Carrenleufu,
Fetaleufu, Puelo and Manso cut the two chains, while the rivers
Renihue, Bodadahue and Cochamo have their sources in the main
eastern ridge. Mention has been made of active volcanoes in
51°, 49°, and 47°S, but these have not been properly
located. The active volcanoes south of 41°, concerning
which no doubt exists, are the Huequen, in 43°, and the
Calbuco, both of which have been in eruption in modern times.
The surroundings of Mount Tronador, consisting of Tertiary
granite and basalt, form one of the most interesting regions
in the Pataronian Andes for the mountaineers of the future. To
the east extends the large and picturesque lake of Nahuel-Huapi,
to the west is Lake Todos Los Santos (50 square miles), to which
the access is easy and of which the scenery is of surpassing
beauty. Between 41°and 38°S, among other smaller
lakes, are Lakes Traful (45 square miles), Lacar (32 square miles),
which, properly belonging to the system of Atlantic lakes,
empties itself by the only water gap that occurs in this zone
of the Cordillera into the river Valdivia, a tributary of
the Pacific, Lake Lolog (15 square miles), Huechu-lafquen (45 square miles), and Lake Alumine (21 square miles). The volcanoes of Lanin
(12,140 feet), Quetropillan (9180 feet), Villarica (10,400 feet),
Yaimas and Tolhuaca are all more or less active; the first
is in the main chain, while the others are on the western
slope. The scenery in the neighbourhood is magnificent, the
snowy cones rising from amidst woods of araucaria, and being
surrounded by blue lakes. While the scenery of the western
slope of the Andes is exceedingly grand, with its deep fjords,
glaciers and woods, yet the severity of its climate detracts
considerably from its charm. The climate of the eastern
slope, however, is milder, the landscapes are magnificent, with
wooded valleys and beautiful lakes. The valleys are already
partly settled by colonists. Between 52°and 40°S
erosion has carried the watershed of the continent from the
summit of the Cordillera to the eastern plains of Patagonia.
From 40°S. southward the Chile-Argentine Boundary Commission
under Sir T. H. Holdich carried out important investigations in
1902; and between 38°and 33°S the Andes were somewhat
extensively explored about the close of the 19th century by
Argentine and Chilean Commissions. The highest peaks in the
latter section are volcanic and their eruptions have sensibly
modified the character of the primitive ridges. Outflows
of lava and tufa cover the mountain sides and fill up the
valleys. The Jurassic and Cretaceous formations, which in
the Southern Cordillera are situated outside of the range
to the east, form to a considerable extent the mass of the
great range, together with quartz porphyry, the Tertiary,
granite and other eruptive rocks, which have been observed
along all the chain in South America up to Alaska in the
north. Gneiss is seldom met with, but there are crystalline
rocks, belonging chiefly to the pre-Cordillera of the eastern
and to the Cordillera de la Costa on the western side.
About 38°S the Andes take a great transversal extension;
there are no wide intermediate valleys between the different
ridges but the main ridge is perfectly defined. Volcanic
cones continue to predominate, the old crystalline rocks
almost disappear, while the Mesozoic rocks are most
common. The higher peaks are in the main chain, while
the Domuyo (15,317 feet) belongs to a lateral eastern
ridge. The principal peaks between this and Mount Tupungato
at 33°S are: Mount Cochico (8255 feet), Campanario,
(13,140 feet), Peteroa (13,297 feet), Tinguiririca, Castillo
(16,535 feet), Volcano Maipu (17,576 feet), Alvarado (14,600 feet), Amarillo (15,321 feet), Volcano San Jose (19,849 feet),
Piuquenes (17,815 feet), and Volcano Bravard (19,619 feet).
North of Maipu volcano, ascended by R. P. Gussfeldt in
1883, the Cordillera is composed of two huge principal ridges
which unite and terminate in the neighbourhood of Mount
Tupungato. The valley between them is 9000 feet high; and in
that part of the Cordillera are situated the highest passes
south of 33°S, one of which, the Piuquenes Pass,
reaches 13,333 feet, whilst the easiest of transit and almost
the lowest is that of Pichachen (6505 feet), which is the most
frequented during winter. Mount Tupungato reaches 22,329
feet, according to Argentine measurement. To the north of this
mountain, situated at the watershed of the Andes, extends
a lofty region comprising peaks such as Chimbote (18,645
feet) and Mount Polleras (20,266 feet). The Pircas Pass is
situated at a height of 16,962 feet. The gaps of Bermejo and
Iglesia, in the Uspallata road, the best known of all the
passes between Argentina and Chile, are at 13,025 feet and
13,412 feet altitude respectively, while the nearest peaks,
those of Juncal and Tolorsa, are 19,358 and 20,140 feet high.
Mounts Tupungato, Aconcagua (23,393 feet) and Mercedario (21,982 feet) are the highest peaks of the central Argentine-Chilean
Andes. These three peaks are formed of eruptive rocks,
surrounded by Jurassic beds which have undergone a thorough
metamorphosis. While in the west of the Andes, from the
latitude of Aconcagua, the central valley of Chile runs
without any notable interruption to the south end of the
continent, a valley which almost disappears to the north,
leaving only some rare inflexions which are considered by
Chilean geographers and geologists to be a continuation of
the same valley; to the east in Argentina a longitudinal
valley, perfectly characterized, runs along the eastern
foot of the Cordillera, separating this from the pre-
Cordillera, which is parallel to the Cordillera de la Costa of
Chile. Between Aconcagua and Mercedario are the passes of
Espinacito (14,803 feet) and Los Patos or Valle Hermoso (11,736
feet), chosen by the Argentine General San Martin, when he
made his memorable passage across the chain during the War of
Independence. North of Valle Hermoso the Andean ridges,
while very high, are not abrupt, and the passes are more
numerous than in the south; some of them descending 10,000
feet, but most of them between 13,000 and 14,000 feet. The pass
of Quebrada Grande is 12,468 feet in altitude; Cencerro, 12,944
feet; Mercedario, 13,206 feet; Ojota, 14,304 feet; Pachon, 14,485
feet; while Gordito is 10,318 feet. Farther north the passes are
higher. Barahona Pass is 15,092 feet; Ternera, 15,912 feet;
San Lorenzo, 16,420 feet, while the peak of the volcano
reaches 18,143 feet; Mount Olivares, 20,472 feet; Porongos,
19,488 feet; Tortolas, 20,121 feet; and Potro, 19,357 feet.
As far as 28°S the Cordillera de los Andes has been
principally formed by two well-defined ridges, but to the
north, recent volcanic action has greatly modified its
orography. Only a single line of passes characterizes the
main ridge, and amongst them are the passes of Ollita (15,026
feet), Penas Negras (14,435 feet), Pircas Negras (13,615 feet),
La Gallina (16,240 feet), Tres Quebradas (15,535 feet), and
Aguita (15,485 feet). To the north of Mount Potro the peaks
in the Cordillera are not very prominent as far as the great
mass of Tres Quebradas, but here are to be met with some
that may he considered as amongst the highest of the whole
range. Mount Aguita is 20,600 feet, and the culminating
peak of those of Tres Cruces reaches 226,58 feet. To the
east of the eastern longitudinal valley, at 27°S,
begins a high volcanic plateau between the Cordillera and
the southern prolongation of the Bolivian Cordillera Real,
which contains lofty summits, such as Mount Veladero ( 20,998
feet), Mount Bonete (21,980), Mount Reclus (20,670), Mount
Pissis (22,146), Mount Ojo del Salado (21,653), and Incahuasi
(21,719). To the north of Tres Cruces is a transversal
depression in the Cordillera, which is considered to be
the southern termination of the high plateau of the Puna de
Atacama. The Cordillera of the Andes borders the Puna to the
west, while the Bolivian Cordillera Real bounds it to the
east. In that region the Cordillera of the Andes is of
comparatively recent origin, being principally constituted
by a line of high volcanoes, the chief summits being those of
Juncal, Panteon de Aliste, Azufre or Listarria (18,636 feet),
Llullaillaco (21,720), Miniques (19,357), Socompa (19,948),
Licancaur (19,685), Viscachuelas (20,605), Tapaquilcha (19,520),
Oyahua (19,242), Ancaquilcha (20,275), Olca (19,150), Mino
(20,112), Sillilica (21,100), Perinacota (20,918), Sagama
(22,339), Tacona (19,740), Misti (19,029); to the east
closes in the intermediary high plateau which begins at 28°S in Argentina. The principal peaks of the Bolivian
Andes and its prolongation from south to north, are Famatina,
in the centre of Argentina, (20,340 feet), Languna Blanca
(18,307), Diamante (18,045), (Cachi (20,000), Granadas, Lipez
(19,680), Guadalupe (18,910), Chorolque (18,480), Cuzco
(17,930), Enriaca (18,716), Junari (16,200), Michiga (17,410),
Quimza-Cruz (18,280), Illimani (21,190) and Sorata (21,490).
While the western range of the Cordillera is principally
formed by volcanic rocks, the eastern (to the east of the
range is Cerro Potosi, 15,400 feet) Andes of Bolivia are chiefly
composed of old crystalline rocks. Between the ranges in the
high plateau north to 27° are numerous isolated volcanoes
which have been in activity in recent times, such as Peinado
(18,898 feet), San Pedro (18,701), Antuco (19,029), Antofalla
(20,014), Rincon (17,881), Pastos Grandes (17,553), Zapalegui
(17,553), Suniguira (19,258), Tahue (17,458); volcanoes which
have been elevated from a lncustrine basin, which very recently
occupied the whole extension, and the remains of which are,
in the south, the Laguna Verde, at 28°, and in the north Lake
Titicaca. The discovery of great Pampean mammals in the
Pleistocene beds of that region shows that this upheaval of the
latter is very recent, for in the heart of the Cordillera, as
well as on the west coast of Bolivia and Peru, there have been
discovered, in very recent deposits, the remains of some mammals
which cannot have crossed the high range as it now exists.
The two Cordilleras that formed the Andes to the north of
28°S are continued in Peru. The western, which
reaches an altitude of about 10,000 feet, then ceases to
exist as a continuous chain, there remaining only a short,
high ridge, called by Edward Whymper the "Pacific range of
the equator," and between this ridge and the crystalline
Andean axis, the "avenue of volcanoes," to use his words,
arises amidst majestic scenery.
Chimborazo, which is not in the main chain, reaches 20,517 ft (6,272 m); since Earth bulges at the equator, its summit is further from Earth's centre than that of Mount Everest.
Cotopaxi (19,580), Antisana (19,260), Coyambo (19,200) are in the eastern range,
with many other peaks over 16,000 feet which still contain
glaciers. Sangay (17,380 feet), under the equator, according
to Wolff, appears to be the most active volcano in the
world. Pichincha (15,804 feet) and Cotocachi (16,297 feet) are
the loftiest volcanoes of the western range. In Colombia the
three principal chains are continuations of those under the
equator, and show very slight traces of volcanic action,
In the western chain, which is remarkable for its regularity,
the highest peak is 11,150 feet, and the lowest pass 6725
feet. The central chain, separated from the western chain by
the valley of the Cauca and from the eastern by the valley
of the Magdalena, is unbroken; it is the more important
owing to its greater altitudes and is of volcanic character.
To the south, near the equator, are Mounts Arapul (13,360
feet) and Chumbul (15,720 feet). The volcanoes Campainero
(12,470 feet) and Pasto (14,000 feet) are also in that zone.
Farther north is the volcano Purace, which presents a height
of 16,000 feet; then come Huila (18,000), Santa Catalina
(16,170), and Tolima (18,400), Santa Isabel (16,760), Ruiz
(17,390) and Hervas (18,340). The eastern chain begins north
of the equator at 6000 feet, gradually rises to the height
of Nevado (14,146 feet), Pan de Azucar (12,140 feet), and in
the Sierra Nevada de Cochi attains to peaks of 16,700 feet.
The snow-line of the Andes is highest in parts of Peru
where it lies at about 16,500 feet. Its general range
from the extreme north to Patagonia is 14,000 to 15,500
feet, but along the Patagonian frontier it sinks rapidly,
until in Tierra del Fuego it lies at about 4900 feet.
The structure of the Andes is least complex in the southern portion of the range. Between 33° and 36°S the chain consists broadly of a series of simple folds of
Jurassic and Cretaceous beds. It is probably separated on
the east from the recent deposits of the pampas by a great
fault, which, however, is always concealed by an enormous
mass of scree material. The Cretaceous beds lie in a broad
synclinal upon the eastern flank, but the greater part of
the chain is formed of Jurassic beds, through which, on the
western margin, rise the numerous andesitic volcanic centres.
There is no continuous band of ancient gneiss, nor indeed
of any beds older than the Jurassic. There is very little
over-folding or faulting, and the structure is that of the
Jura mountains rather than of the Alps. The inner or eastern
ridge farther north of Argentina consists of crystalline rocks
with infolded Ordovician and Cambrian beds, often overlaid
unconformably by a sandstone with plant-remains (chiefly
Rhaetic). In Bolivia this eastern ridge, separated from the
western Cordillera by the longitudinal valley in which Lake
Titicaca lies, is formed chiefly of Archaean and Palaeozoic
rocks. All the geological systems, from the Cambrian to the
Carboniferous, are represented and they are all strongly
folded, the folds leaning over towards the west. West of the
great valley the range is composed of Mesozoic beds, together
with Tertiary volcanic rocks. (The Cordillera of Argentina
and Chile is clearly the continuation of the western chain
alone.) In Ecuador there is still an inner chain of ancient
gneisses and schists and an outer chain composed of Mesozoic
beds. The longitudinal valley which separates them is
occupied mainly by volcanic deposits. North of Ecuador the
structure becomes more complex. Of the three main chains
into which the mountains are now divided, the western
branch is formed mostly of Cretaceous beds; but the inner
chains no longer consist exclusively of the older rocks, and
Cretaceous beds take a considerable share in their formation.
The great volcanoes, active and extinct, are not confined
to any one zone. Sometimes they rise from the Mesozoic
zone of the western Cordillera, sometimes from the ancient
rocks of the eastern zone. But they all he within the
range itself and do not, as in the Carpathians and the
Apennines, form a fringe upon the inner border of the chain.
The curvature of the range around the Brazilian massif,
and the position of the zone of older rocks upon the eastern
flank, led Suess to the conclusion that the Andes owe their
origin to an overthrust from east to west, and that the
Vorland lies beneath the Pacific. In the south Wehrli
and Burckhardt maintain that the thrust came from the
west, and they look upon the ancient rocks of Argentina
as the Vorland. In this part of the chain, however,
there is but little evidence of overthrusting of any kind.
Tierra del Fuego
Chile-Argentina, 52°-38°S
Chile-Argentina from 38°S northward
Bolivia
Peru-Ecuador
Colombia
Structure
Original entry came from 1911 encyclopedia
The geology in this article apparently reflects views from the first decade of the 20th Century. It is a good example of the descriptive geology of that time, but worthless when it comes to why these ranges exist and some of the structural commentary. It is a pre Plate tectonics view and no longer valid.
ANDES is an acronym for an architecture with non-sequential dynamic execution scheduling.