GEOGRAPHY OF COLOMBIA

GEOGRAPHY OF Colombia

The Land

• Relief

Few countries boast such striking physical variety as does Colombia. Its broken, rugged topography, together with its location near the Equator, creates an extraordinary diversity of climates, vegetation, soils, and crops. The Andean cordillera, one of the world’s great mountain ranges, dominates the landscape of the western part of the country, where most of the people live. North of the border with Ecuador the cordillera flares out into three distinct parallel ranges. Two great river valleys, those of the Magdalena and the Cauca, separate them and provide avenues of penetration from the Atlantic coastal lowlands into the heart of the country. Volcanic activity in the geologic past blocked the middle course of the Cauca River to form a great lake that once filled the western inter-Andean trough for some 120 miles (190 km) south of Cartago. The river eventually broke through the dam to leave the level floor of the Cauca valley at some 3,000 feet (900 metres) above sea level; today it is one of the nation’s most productive agricultural areas.

The Colombian cordilleras belong to the northern portion of the great Andean mountain system, which extends along the Pacific coast of South America. The Andes are among the world’s most youthful mountain ranges and among the highest. The geologic history of this northern sector is less well understood than that of the central and southern parts. It is clear, however, that the entire cordillera has been thrust up through the subduction of the crumpled eastern margin of the Nazca Plate and, to the north, the Caribbean Plate under the more rigid but lighter South American Plate, which has been forced westward by the spreading Atlantic seafloor. These tectonic forces, similar to those found elsewhere around the Pacific Rim, continue to operate, as is evidenced by the high frequency of often destructive earthquakes. At the Pasto Massif, near the Ecuadoran border, the mountains divide into the Cordillera Occidental (“Western Range”), which runs parallel to the Pacific coast, and the Cordillera Central (“Central Range”), which, with its numerous volcanoes, forms the backbone of the system in Colombia and runs generally southwest to northeast. At the Great Colombian Massif of the Cordillera Central, near the San Agustín Archeological Park, the Cordillera Oriental (“Eastern Range”) branches off in a more decidedly northeasterly direction.

Of the three ranges, the nonvolcanic Cordillera Occidental, which forms the barrier between the Cauca valley and the rain-drenched Pacific coast, is the lowest and least populated. Two passes at elevations less than 5,000 feet (1,500 metres) between Cali and Buenaventura on the Pacific coast mark the lowest depressions in the range. Elsewhere the crest is much higher, reaching 12,992 feet (3,960 metres) at Mount Paramillo in the department of Antioquia. From there the Cordillera Occidental fingers north into the three distinct serranías of Abibe, San Jerónimo, and Ayapel, forested ranges that drop gradually toward the piedmont plains of the Caribbean littoral. A lesser topographic feature on the Pacific coast is the Baudó Mountains, separated from the Cordillera Occidental by the valley of the Atrato River, which empties into the Caribbean Gulf of Urabá; the Baudó Mountains represent a southward extension of the Isthmus of Panama.

The Cordillera Central is the highest of the Andean ranges of Colombia, rising to an average height of 10,000 feet (3,000 metres). It is a continuation of the Ecuadoran volcanic structure. Crystalline rocks are exposed at several places on its flanks and are the foci of localized gold and silver deposits. Sandstones and shales of the Paleogene and Neogene periods (about 65 to 2.6 million years ago) are also a part of the older basement that has been capped by ash and lava derived from some 20 volcanoes of the Quaternary Period (the past 2.6 million years). Several of the latter reach well into the zone of permanent snow, above 15,000 feet (4,600 metres). The highest are Mount Huila (18,865 feet [5,750 metres]), southeast of Cali, and the Ruiz-Tolima complex (some 17,700 feet [5,400 metres]) between Manizales and Ibagué. The fertile ash from their eruptions has produced the high, cool plateaus of Nariño department and the often steep slopes to the north that support much of Colombia’s coffee production. In November 1985 Mount Ruíz erupted, melting the snow and ice that covered it and sending great mudflows downslope, destroying the city of Armero and killing more than 25,000 in one of the country’s greatest catastrophes.

North of Mount Ruíz, near Sonsón in the department of Antioquia, the volcanic Cordillera Central gives way to the deeply weathered, granitic Antioquia batholith (an exposed granitic intrusion), a tableland averaging some 8,000 feet (2,500 metres) above sea level. It is divided into two parts by the deep transverse cleft of the Porce River, which occupies the U-shaped valley in which is situated the expanding metropolis of Medellín, Colombia’s second city. The batholith contains gold-bearing quartz veins, which were the source of the placer gravels that gave rise to an active colonial mining economy. Beyond Antioquia the lower, remote San Lucas Mountains extend northward toward the confluence of the Magdalena and Cauca rivers.

The massive Cordillera Oriental, separating the Magdalena valley from the Llanos, is composed chiefly of folded and faulted marine sediments and older schists and gneisses. Narrow to the south, it broadens out in the high, unsettled massif of Sumapaz, with elevations up to 13,000 feet (4,000 metres). High plateaus were formed in the Quaternary Period by the deposition of sediments in depressions that had been occupied by lakes. The most important of these is the savanna area called the Sabana de Bogotá. Farther northeast beyond the deep canyons cut by the Chicamocha River and its tributaries, the Cordillera Oriental culminates in the towering Mount Cocuy (Sierra Nevada del Cocuy), which rises to 18,022 feet (5,493 metres). Beyond this point, near Pamplona, the cordillera splits into two much narrower ranges, one extending into Venezuela, the other, the Perijá Mountains, forming the northern boundary range between Colombia and Venezuela. The Perijás then descend northward toward the Caribbean to the arid La Guajira Peninsula, the northernmost extension of the Colombian mainland.

The isolated Santa Marta Mountains are an imposing fault-bounded granitic massif rising to 18,947 feet (5,775 metres) at the “twin peaks” of Cristóbal Colón and Simón Bolívar, the highest point in the country (for a discussion of the height of the Santa Marta Mountains, see Researcher’s Note: Heights of the “twin peaks” of the Santa Marta Mountains); the massif ascends abruptly from the Caribbean littoral to snow- and ice-covered summits. The Atlantic lowlands spread out southward behind it. Although it is a distinct geomorphic unit and not a part of the Andes, some geologists have suggested that it might be considered an extension of the Cordillera Central, from which it is separated by the Mompós depression in the lower Magdalena valley.

The steep and rugged Andean mountain masses and the high intermontane basins descend into plains that extend along the Caribbean and Pacific coasts and across the eastern interior toward the Orinoco and Amazon river systems. From the shores of the Caribbean Sea inland to the lower spurs of the three major cordilleras extends a slightly undulating savanna surface of varying width, generally known as the Atlantic lowlands (also called the Caribbean coastal lowlands). Dotted with hills and with extensive tracts of seasonally flooded land along the lower Magdalena and the Sinú rivers, it surrounds the inland portion of the Santa Marta Mountains. A much narrower lowland apron extends along the Pacific shoreline from the point of Cape Corrientes southward to the Ecuadoran border.

A wide range of features characterize the country’s two coastlines. Steep and articulated bays, inlets, capes, and promontories accentuate the shoreline on the Pacific side toward the Panama border and on the Caribbean side where the sea beats against the base of the Santa Marta Mountains. These features are interspersed with sandy beaches, along with barrier islands and brackish lagoons.

The eastern two-thirds of the country, lying beyond the Andes, differs from cordilleran Colombia in practically all aspects of physical and human geography. The eastern lowland extends from the Venezuelan boundary along the Arauca and Meta rivers in the north to the Peruvian-Ecuadoran border stream, the Putumayo, some 600 miles (1,000 km) to the south and from the base of the Cordillera Oriental eastward to the Orinoco-Negro river line, a distance of more than 400 miles (650 km). A region of great topographic uniformity, it is divided into two contrasting natural landscapes by a major vegetation boundary. In southern Colombia the Amazonian rainforest, or selva, reaches its northern limit. From the Guaviare River northward the plains between the Andes and the Orinoco River are mostly grass-covered, forming the largest savanna complex in tropical America. This part of the lowland is called the Llanos Orientales (“Eastern Plains”) or simply the Llanos.

In the central part of the plain, between the Guaviare and Caquetá rivers, the eroded rocks of the ancient Guiana Shield are exposed, producing a broken topography of low, isolated mountains, tablelands, and buttes with rapids in the streams. This slightly higher ground forms the watershed between the Amazon and Orinoco systems. Some 60 miles (100 km) south of Villavicencio the elongated, forested La Macarena Mountains rise 8,000 feet (2,500 metres) from the surrounding lowlands, an isolated tropical ecosystem.

• Drainage and soils

In Colombia’s rugged terrain the rivers have been historically important as routes of transportation and settlement. By far the most important river system is the Magdalena. Its drainage basin, including that of its major tributary, the Cauca, covers some 100,000 square miles (260,000 square km), or nearly one-fourth of the surface of the country. Within it are found most of the nation’s socioeconomic activity and more than three-fourths of its population. Originating in the Andean Páramo de Las Papas, the Magdalena flows northward in the structural depression between the Cordilleras Central and Oriental for almost 1,000 miles (1,600 km) to empty into the Caribbean near Barranquilla. The Dique Canal, begun during the colonial period, links its lower course with the coastal city of Cartagena. The Cauca River, which contributes a substantial part of its total flow, rises in the mountains south of Popayán and, after passing through the floor of the Cauca valley near Cali, occupies deep canyons in most of its passage through the departments of Caldas and Antioquia before emerging onto the floodplain of the lower Magdalena.

The Magdalena, a shallow, braiding stream in its upper and middle course, served as a major transport artery for most of the country’s history, but deforestation and soil erosion have led to silting and increased flow variation so that its role has become less significant. Because of its rapids, the Cauca has never been of much importance for the moving of goods. Among the major affluents of the Magdalena, besides the Cauca, are the Sogamoso, Cesar, San Jorge, Saldaña, Lebrija, and Carare rivers. The Sinú and the Atrato are other major streams that flow directly into the Caribbean.

The great eastern watershed is subdivided into two sections, the waters flowing into the Orinoco and the Amazon rivers, which carry them to the Atlantic Ocean. The Arauca and Meta, the lower reaches of which cross into Venezuela, and the Vichada, Inírida, and Guaviare are among the main rivers that flow into the Orinoco. Among the streams that flow into the Amazon are the Vaupés, Caquetá, and Putumayo. The rivers that flow into the Pacific are relatively short, descending rapidly from the Cordillera Occidental to the sea. They carry large volumes of water, however, because they drain areas of extremely heavy rainfall. Among the rivers belonging to the Pacific watershed are the Baudó, San Juan, Dagua, Naya, San Juan de Micay, Patía, and Mira, which rises in Ecuador.

The wide variety of soils encountered in the country reflects climatic, topographic, and geologic conditions. Those best suited for modern, mechanized agriculture are the alluvial soils found in the principal river valleys, such as the Magdalena, Cauca, Sinú, Cesar, and Ariguaní. The former lake beds of some of the inter-Andean basins, notably the Sabana de Bogotá and the Ubaté and Chiquinquirá valleys, also fall into this category. Elsewhere, soils of volcanic origin, especially in the coffee-growing districts of the Cordillera Central, can be exceptionally productive if protected from erosion. The Quindío department, west of Bogotá, is especially renowned for its rich soils.

• Climate

Because of the country’s close proximity to the Equator, its climate is generally tropical and isothermal (without any real change of seasons). Temperatures vary little throughout the year. The only genuinely variable climatic element is the amount of annual precipitation. Climatic differences are related to elevation and the displacement of the intertropical convergence zone between the two major air masses from which the northeast and southeast trade winds originate. Human settlement is more oriented to vertical zoning in Colombia than anywhere else in Latin America.

The climate of the tropical rainforest in the Amazon region, the northern Pacific coast, and the central Magdalena valley is marked by an annual rainfall of more than 100 inches (2,500 mm) and annual average temperatures above 74 °F (23 °C). A tropical monsoon climate, marked by one or more dry months but still supporting rainforest vegetation, occurs along the southern Pacific coast, on the Caribbean coast, and at places in the interior—the Quindío department and near Villavicencio.

The tropical savanna conditions of alternately wet and dry seasons constitute the predominant climate of the Atlantic lowlands; the dry season occurs from November to April, and the wet season (broken by dry periods) from May to October. This climate is found also in the Llanos region and in part of the upper Magdalena valley. It is characterized by an annual rainfall of 40 to 70 inches (1,000 to 1,800 mm) and annual average temperatures usually above 74 °F (23 °C). The dry season, accompanied by dust and wind, coincides with the true winter of the Northern Hemisphere.

A drier savanna climate prevails on the Caribbean littoral from the Gulf of Morrosquillo to the La Guajira Peninsula in the northeast. The rains normally occur in two brief periods (in April and in October–November, respectively) but rarely exceed 30 inches (760 mm) annually. The average temperature is hot—more than 81 °F (27 °C)—with the daily range greatest where the humidity is low. This type of climate also occurs in the rain shadows of the deep gorges of such rivers as the Patía, Cauca, Chicamocha, and Zulia and in parts of the upper Magdalena valley. The climate reaches near-desert conditions in the far northern department of La Guajira.

In the mountain regions temperature is directly related to elevation. Average temperatures decrease uniformly about 3 °F per 1,000 feet of ascent (0.6 °C per 100 metres). Popular terminology recognizes distinct temperature zones (pisos térmicos), which are sometimes referred to as tierra caliente (up to about 3,000 feet [900 metres]), tierra templada or tierra del café (3,000 to 6,500 feet [900 to 2,000 metres]), and tierra fría (6,500 to 10,000 feet [2,000 to 3,000 metres]). The majority of Colombians live in the interior cordilleras in the tierra templada and the tierra fría zones. The tierra templada has moderate rainfall and temperatures between 65 and 75 °F (18 and 24 °C). In the tierra fría is Bogotá, which lies 8,660 feet (2,640 metres) above sea level and has an average of 223 days of precipitation, although the average rainfall is scarcely 40 inches (1,000 mm). The city’s average temperature is 57 °F (14 °C). The climate of the high mountain regions—the páramos, ranging from about 10,000 to 15,000 feet (3,000 to 4,600 metres)—is characterized by average temperatures below 50 °F (10 °C), fog, overcast skies, frequent winds, and light rain or drizzle. At elevations above 15,000 feet (4,600 metres) there is perpetual snow and ice.

• Plant and animal life

The diversity of life-forms and habitats in Colombia has impressed observers since the days of the German explorer Alexander von Humboldt. The complex pattern of climate, soil, and topography has produced an extraordinary range of plants and plant communities that vary through both vertical and horizontal zones. They range from the mangrove swamps of the coasts, the desert scrub of La Guajira, the savanna grasslands and gallery ecosystems of the Atlantic lowlands and the Llanos, and the rainforest of Amazonia and the Chocó region to the widely diverse and complex montane ecosystems of the Andean slopes.

Human intervention has vastly altered what must have been the original vegetation of the Atlantic lowlands and the Andean region. Forests probably covered all but the highest and driest areas, where the soils were unsuited to support them. Today they are restricted to the steepest, most inaccessible slopes and to areas of especially high rainfall in the inner Andes. Elsewhere pasture, crops, or degraded scrub and grass have replaced the original cover of broad-leaved evergreen trees. The first chroniclers often described the Andes as sparsely wooded, a condition they usually attributed to Indian agriculture and burning. In more recent times, with the increasing number of European cattle, the area in grassland has been vastly extended, both in the mountains and on the Atlantic lowlands. Introduced grass species of African origin are particularly conspicuous.

Even in the most lush forest tracts that remain, such as those that flank the outer sides of the eastern and western ranges, there is much evidence of earlier human occupation. These wet montane forests are characterized by lianas, mosses, orchids, and bromeliads and by such economically valued plants as cinchona, the latex-bearing balata, ivory nut (tagua), and the giant American bamboo. Lumbering has had a minor role because of the singular difficulty of access as well as the absence of forests of any one commercial species. In modern times technological advances have made possible the exploitation of forest species in accessible parts of the Atrato River basin and on the Pacific coast near Buenaventura.

The distinctive páramo biome of the equatorial high mountains reaches its greatest development in Colombia. This alpine vegetation is characterized by tussock grasses, cushion plants, and the treelike frailejón (Espeletia), a curious-looking hairy-leafed genus of some 50 different species. Fire-resistant and adapted to low temperatures and high humidity, it gives special character to the páramo landscape. The lower páramo, below 12,000 feet (3,650 metres), is a transitional belt in which scattered clumps of trees occur. Despite its bleak and forbidding climate, much of the páramo has been significantly altered by human activity, especially wood cutting and burning to promote better grazing. Agriculture has also impinged on its lower reaches, but extensive tracts remain relatively untouched by humans.

The animal life of the forests of the Amazon and Pacific coastal Chocó regions is particularly rich and has supported a considerable export trade to North American and European zoos. It includes anteaters, sloths, several monkey species, tapirs, peccaries, spectacled bears, deer, and such large tropical rodents as agoutis, pacas, and capybaras. Carnivores include pumas and jaguars, which were considered endangered species by the 1980s, and raccoons.

Bird habitats are influenced by elevation, and many species are specific to narrow altitudinal bands, ranging upward and downward only very short distances. The extremely lush birdlife encompasses more than 1,500 species, including toucans, hummingbirds, and those that migrate annually from North America. Among the reptiles, turtles, lizards, snakes, caimans, and crocodiles abound. Some quite unusual species inhabit the land, including earthworms that grow up to six feet in length. Freshwater fish include catfish, bocachica (“smallmouth”), and characins (small, brightly coloured tropical fishes). Electric eels also inhabit the inland waters. The Magdalena and Cauca once supported rich river fisheries, but pollution and unrestrained commercial exploitation have taken a heavy toll.

• Settlement patterns

Colombia can be divided into five traditional geographic regions: the Atlantic lowlands, the Pacific coastal region, the Andean region, the Llanos, and the Amazonian rainforest.

Of early colonial importance, the Atlantic lowlands are now second to the Andean region in population and economic significance. The area is home to one-fifth of Colombia’s population, partly concentrated in Barranquilla, Cartagena, and Santa Marta, the country’s principal Caribbean ports. Cattle raising and mixed agriculture are the traditional economic activities, but large-scale commercial farming, especially of rice, cotton, and bananas, has been successful. Irrigation has expanded since the mid-20th century, especially in the valleys of the Sinú and Cesar rivers. Bananas are grown for export in the Urabá region.

The Pacific coast, including the department of Chocó, with its lush rainforest and infertile soils, is sparsely inhabited. Most of its people are descendants of liberated African slaves who settled in agricultural clearings along the rivers. It has little commercial activity. The coastal city of Buenaventura is the only port of note and the main population centre.

The Andean region is the centre of national political and economic power, with most of the country’s population and large cities, including Bogotá, Medellín, and Cali, the three most populous. The Cauca valley, with its vast tract of alluvial soil, the Sabana de Bogotá, and the Antioquia highlands are perhaps the most dynamic centres of economic activity and growth.

Although the Llanos and the Amazonian rainforest together make up nearly two-thirds of the country’s land area, they contain only a tiny fraction of the population. About one-third of this number are in the department of Meta in the Llanos, where cattle raising has long been the traditional way of life. New penetration roads extending down from the Andes have encouraged colonization along the margins of both of these areas, as have discoveries of petroleum. The remoter areas of the Amazon region were sparsely inhabited only by small groups of Indians until the 1990s, when coca growers and guerrilla groups joined them.