Bolivia's geography: a high plateau and the lowlands that overtook it

How the Andes divide in two across Bolivia

The National Statistics Institute, INE, places the country between the parallels of 9°38′ and 22°53′ south and the meridians of 57°26′ and 69°38′ west, an extent of more than thirteen degrees. All of it lies inside the tropics. Its dimensions are measured slightly differently: Britannica gives some 1,500 kilometres from north to south and 1,300 from east to west, the Worldmark encyclopedia 1,530 and 1,450, with land borders totalling 6,743 kilometres. INE lists the neighbours as Brazil to the north and east, Argentina to the south, Peru to the west, Paraguay to the south-east and Chile to the south-west. What overrides the latitude is the Andes, which Britannica's account of the land describes as reaching their greatest breadth and complexity here, about 640 kilometres across by the Worldmark encyclopedia's measure.

Two ranges carry the system. The Cordillera Occidental follows the border with Chile and is volcanic along its whole length: Wikipedia's geography of the country calls it a chain of dormant volcanoes and solfataras, vents that give off sulphurous gas, an extension of the volcanic region of southern Peru. Its summit is Nevado Sajama, at 6,542 metres. The south of the range receives almost no rain and is close to uninhabited.

The Cordillera Oriental enters from Peru north of Lake Titicaca. Its northern section near La Paz, the Cordillera Real, is a line of granite peaks that Britannica says keeps an average elevation above 5,500 metres for more than 320 kilometres. Illimani and Illampu, both above 6,400 metres, carry glaciers on their upper slopes, and Illimani stands over La Paz. INE divides the eastern system into further named ranges, from Apolobamba on the Peruvian border to the cordilleras of Chichas and Lípez in the far south. South of about 17° the range widens into a block of crust lifted and tilted east, which Britannica calls the Puna: steep cliffs face west onto the plateau, and gentler slopes fall east.

How much of the country the mountains occupy depends on where the line is drawn. Britannica and the Worldmark encyclopedia both say about a third; Wikipedia's climate breakdown counts the Andean zone at 28% of the territory and a separate sub-Andean belt at 13%.

What lies on the Altiplano between the ranges

Between the two cordilleras lies the Altiplano, the high plateau that runs on from southern Peru to northern Argentina. Britannica gives it a length of about 800 kilometres, a width of about 130 and elevations between 3,650 and 3,800 metres. Wikipedia explains its surface as the filling of a deep rift with sediment washed from the peaks on either side, which is why it slopes gently from north to south: more rain in the north carried more debris onto the floor.

The rain thins southwards and so does the ground cover. Around Lake Titicaca the Worldmark encyclopedia calls rainfall adequate; in the extreme south-west it records less than 13 centimetres a year. The plateau's driest end is a run of salt flats, the beds of lakes that dried out. The largest, the Salar de Uyuni in Potosí department, lies at 3,656 metres and is covered by a crust of salt that varies in elevation by less than a metre over its whole area, according to Wikipedia. Its size is given as about 10,400 square kilometres by Britannica and 10,582 square kilometres by Wikipedia's article on the flat. Under the crust is a brine rich in lithium. South of it lie the lakes Colorado and Verde, with hot springs and geysers at the foot of inactive volcanoes.

How Lake Titicaca and Lake Poopó differ

At the northern end the plateau holds Lake Titicaca, shared with Peru. The figures on record do not agree. Britannica puts its surface at 3,810 metres and its area at about 8,300 square kilometres; Wikipedia's geography of the country gives 3,811 metres and 9,064 square kilometres; the Worldmark encyclopedia gives 3,805 metres. Britannica's article on the lake records more than 25 rivers flowing in and a single outlet, the Desaguadero, which carries off only 5% of the excess water; evaporation takes the rest. The Islands of the Sun and Moon in Bolivian waters are sacred sites in Inca tradition.

The Desaguadero runs south for 436 kilometres to Lake Poopó, which is salty and shallow. Britannica records that it rarely exceeded 3 metres in depth, dried out in the mid-1990s and returned, and had disappeared altogether by the end of December 2015.

Where the rivers of a landlocked country go

Three drainage systems divide the land, and two of them reach the Atlantic. The Amazon basin covers two-thirds of the country, the La Plata basin about a fifth, and the closed basin of the Altiplano, whose water reaches no sea, the remainder. Even La Paz, Britannica notes, close as it is to Lake Titicaca, drains to the Amazon.

The northern rivers are wide and slow. The Mamoré, which Wikipedia gives a length of 2,000 kilometres, and the Beni, of 1,113 kilometres, join the Madre de Dios to form the Madeira, which flows into Brazil. Riverboats carry passengers and freight on the Beni and the Mamoré, and rapids on the Madeira close the route further downstream. The Pilcomayo rises near Sucre and Potosí, crosses the Chaco and forms part of the border with Argentina before it reaches the Paraguay River at Asunción. In the far east the lowlands adjoin Brazil's Pantanal wetland, part of which lies inside Bolivia, and the Xarayes swamps.

Why altitude decides the Bolivian climate

INE states the rule plainly: in Bolivia temperature is set by altitude as well as latitude, and air cools by 0.55°C for every additional 100 metres of height. The result is glaciers and frost on the same latitude as tropical plains. The Worldmark encyclopedia gives a mean annual temperature of about 8°C for La Paz at 3,697 metres against 26°C for Trinidad in the eastern lowlands.

On the Altiplano frosts occur every month, the days are dry under strong sun, and the nights fall to around freezing. Wikipedia's breakdown puts annual precipitation on the humid northern Altiplano at 450 to 1,300 millimetres and on the dry southern Altiplano at 50 to 400. Lonely Planet's seasonal guide gives the dry season as May to October, during the southern winter, when overnight temperatures at altitude can drop below minus 15°C; the Worldmark encyclopedia puts the core of the rains from December to February.

The lowlands are warm and wet, with up to 3,000 millimetres a year on the edge of the Amazon forest and far more in places along the Andean front. From May they dry out, though cold winds from the south, the surazos, can drop temperatures for several days at a time. The north-east floods in March and April. The Chaco, in the south-east, is close to rainless for most of the year and floods during a short wet season.

How the Yungas and Valles descend eastwards

From the Cordillera Real the land drops steeply north-east into the Yungas, an Aymara and Quechua word meaning warm valleys. Britannica describes it as rainy, heavily forested and rugged, with soils that erode wherever the forest is cleared from slopes that are not terraced. Wikipedia records an attempt in 1917 to build a railway through the Yungas from La Paz to the lowlands, abandoned after 150 kilometres.

Further south the eastern slopes descend more gradually, cut by long valleys and basins that Britannica calls the Valles. They lie mostly between 1,800 and 2,900 metres, and their deeper soils, above all around Cochabamba, respond well to irrigation. Cochabamba, Sucre and Tarija stand in these basins; the Worldmark encyclopedia describes their climate as a warmer, semi-arid Mediterranean type.

What covers the eastern lowlands

North and east of the mountains lies the Oriente. Its share is again measured differently: more than two-thirds of the country in Britannica's account and three-fifths in the Worldmark encyclopedia's. It is not one landscape. Beni and Pando in the north are rainforest and savanna on poorly drained clay that turns to swamp in heavy rain. The northern half of Santa Cruz is rolling country, drier, where forest alternates with savanna and much land has been cleared for soybeans, cotton and maize on fertile soils. The Chaco in the south is scrub.

Forest covered around 47% of the land in 2020, according to figures compiled by Wikipedia: 50,833,760 hectares, down from 57,804,720 hectares in 1990. The Worldmark encyclopedia names the clearing of land for agriculture, demand for tropical timber, overgrazing and slash-and-burn cultivation among the causes of soil erosion and forest loss, and records that in July 1987 Bolivia agreed with Conservation International to set aside 1.5 million hectares of lowland in exchange for the purchase of US$650,000 of its foreign debt.

Wikipedia's country article gives an altitude range from about 90 to 6,542 metres and counts four biomes, 32 ecological regions and 199 ecosystems inside the borders. The plateau has its own working plants: the Worldmark encyclopedia names ichu, a coarse bunch grass used for pasture, thatch and mats above 3,050 metres, and totora, the reed of Lake Titicaca from which small fishing boats are built, while the resinous yareta and the low tola bush serve as fuel. In the lowland forest grow the quina tree, source of quinine, and the Pará rubber tree, the reason Acre was worth disputing.

The one natural property on the World Heritage List is Noel Kempff Mercado National Park in north-eastern Santa Cruz, inscribed in 2000. Sajama National Park, around the summit of that name, has been on the tentative list since 2003.

How the centre of gravity moved east

For most of recorded history the weight of the country sat on the plateau. Wikipedia's geography article describes a north-south axis from La Paz through Oruro to Potosí as the economically more important one from colonial times until at least the middle of the twentieth century, because those highlands produced the silver and then the tin. Britannica notes that only a third of the territory is Andean yet most of the major cities are there.

In the late twentieth century the balance shifted. Britannica records that the eastern lowlands, the department of Santa Cruz above all, developed rapidly, and Wikipedia now describes an east-west axis from Santa Cruz de la Sierra through Cochabamba to La Paz as the corridor holding most of the population and economic activity. INE describes the trunk road network the same way, its main axis running La Paz, Oruro, Cochabamba, Santa Cruz, with a western rail network linked to Chile, Peru and Argentina and an eastern one linked to Brazil and Argentina. The far south has its own weight: Wikipedia singles out the region around Tarija for its large gas reserves.

The cultural vocabulary follows the same line. Wikipedia records the division of the country into highlanders and lowlanders, collas and cambas, with Tarija's chapacos a smaller third group.