|Landlocked Bolivia sits astride the Andes in the west-central part of
the South American continent. With an area of 1,098,581 square kilometers,
the country is about the size of Texas and California combined, or twice
the size of Spain. Bolivia has 6,083 kilometers of land boundaries, which
adjoin five countries. The country is bounded by Brazil to the north and
east, Paraguay to the southeast, Argentina to the south, Chile to the
southwest, and Peru to the northwest.
Stretching in a broad arc across western Bolivia, the Andes define the country's three geographic zones: the mountains and Altiplano in the west, the semitropical Yungas and temperate valleys of the eastern mountain slopes, and the tropical lowlands or plains (llanos) of the eastern lowlands, or Oriente. The Andes run in two great parallel ranges or cordilleras. The western range (Cordillera Occidental) runs along the Peruvian and Chilean borders. The eastern range (Cordillera Oriental) is a broad and towering system of mountains stretching from Peru to Argentina. Between the two ranges lies the Altiplano, a lofty plateau 805 kilometers long and 129 kilometers wide.
Mountains and Altiplano
The Cordillera Occidental is a chain of dormant volcanoes and solfataras, volcanic vents emitting sulfurous gases. Bolivia's highest peak, the snowcapped Sajama (6,542 meters), is located here. The entire cordillera is of volcanic origin and an extension of the volcanic region found in southern Peru. Most of the northern part of this range has an elevation of about 4,000 meters; the southern part is somewhat lower. Rainfall, although scanty everywhere, is greater in the northern half, where the land is covered with scrub vegetation. The southern area receives almost no precipitation, and the landscape consists mostly of barren rocks. All of the Cordillera Occidental region is sparsely populated, and the south is virtually uninhabited.
The Altiplano, the high plateau between the two cordilleras, comprises four major basins formed by mountainous spurs that jut eastward from the Cordillera Occidental about halfway to the Cordillera Oriental. Along the Altiplano's eastern side is a continuous flat area, which has served as Bolivia's principal north-south transportation corridor since colonial times. The entire Altiplano was originally a deep rift between the cordilleras that gradually filled with highly porous sedimentary debris washed down from the peaks. This sedimentary origin explains its gradual slope from north to south; greater rainfall in the north has washed a larger quantity of debris onto the platform floor.
The most prominent feature of the Altiplano is the large lake at its northern end, Lake Titicaca. At 3,810 meters above sea level, it is the highest navigable body of water in the world. With a surface area of 9,064 square kilometers, it is larger than Puerto Rico and is South America's largest lake. Lake Titicaca is also deep, about 370 meters at its maximum, but with an average depth of 215 meters; its volume of water is large enough to maintain a constant temperature of 10° C. The lake actually moderates the climate for a considerable distance around it, making crops of corn and wheat possible in sheltered areas.
Lake Titicaca drains southward through the slow-moving, reedfilled Desaguadero River to Lake Poopó. In contrast to the freshwater Lake Titicaca, Lake Poopó is salty and shallow, with depths seldom more than four meters. Because it is totally dependent on seasonal rainfall and the overflow from Lake Titicaca, Lake Poopó's size varies considerably. Several times in the twentieth century, it nearly dried up when rainfall was low or the Desaguadero River silted. In years of heavy rainfall, however, Lake Poopó has overflowed to the west, filling the Coipasa Saltpan with shallow water.
Rainfall in the Altiplano decreases toward the south, and the scrub vegetation grows more sparse, eventually giving way to barren rocks and dry red clay. The land contains several salt flats, the dried remnants of ancient lakes. The largest of these is the Uyuni Saltpan, which covers over 9,000 square kilometers. The salt is more than five meters deep in the center of this flat. In the dry season, the lake bed can be traversed by heavy trucks. Near the Argentine border, the floor of the Altiplano rises again, creating hills and volcanoes that span the gap between the eastern and western cordilleras of the Andes.
The much older Cordillera Oriental enters Bolivia on the north side of Lake Titicaca, extends southeastward to approximately 17 south latitude, then broadens and stretches south to the Argentine border. The northernmost part of the Cordillera Oriental, the Cordillera Real, is an impressive snow-capped series of granite mountains. Many of these peaks exceed 6,000 meters, and two--Illimani (6,322 meters), which overlooks the city of La Paz, and Illampu (6,424 meters)--have large glaciers on their upper slopes. South of 17 south latitude, the range changes character. Called the Cordillera Central here, the land is actually a large block of the earth's crust that has been lifted and tilted eastward. The western edge of this block rises in a series of steep cliffs from the Altiplano. The backbone of the cordillera is a high, rolling plain, with elevations from 4,200 to 4,400 meters, interspersed with irregularly spaced high peaks. Too high to be exploited for large-scale commercial grazing, this area takes its name from the predominant vegetation type, the puna.
Yungas and Other Valleys
The northeastern flank of the Cordillera Real is known as the Yungas, from the Aymara word meaning "warm valleys." The steep, almost inaccessible slopes and peaks of this mainly semitropical valley area northeast of La Paz offer some of the most spectacular scenery in Bolivia. Rainfall is heavy, and lush vegetation clings to the sides of narrow river valleys. The land is among the most fertile in Bolivia, but poor transportation has hindered its agricultural development. The government attempted to build a railroad through the Yungas in 1917 to connect La Paz with the eastern lowlands. The railroad was abandoned, however, after completion of only 150 kilometers.
The eastern slopes of the Cordillera Central descend gradually in a series of complex north-south ranges and hills. Rivers, draining to the east, have cut long narrow valleys; these valleys and the basins between the ranges are favorable areas for crops and settlement. Rich alluvial soils fill the low areas, but erosion has followed the removal of vegetation in some places. The valley floors range from 2,000 to 3,000 meters above sea level, and this lower elevation means milder temperatures than those of the Altiplano. Two of Bolivia's most important cities, Sucre and Cochabamba, are located in basins in this region.
The eastern lowlands include all of Bolivia north and east of the Andes. Although comprising over two-thirds of the national territory, the region is sparsely populated and, until recently, has played a minor role in the economy.
Differences in topography and climate separate the lowlands into three areas. The flat northern area, made up of Beni and Pando departments and the northern part of Cochabamba Department, consists of tropical rain forest. Because much of the topsoil is underlain by clay hardpan, drainage is poor, and heavy rainfall periodically converts vast parts of the region to swamp. The central area, comprising the northern half of Santa Cruz Department, has gently rolling hills and a drier climate than the north. Forests alternate with savanna, and much of the land has been cleared for cultivation. Santa Cruz, the largest city in the lowlands, is located here, as are most of Bolivia's petroleum and natural gas reserves. The southeastern part of the lowlands is a continuation of the Chaco of Paraguay. Virtually rainless for nine months of the year, this area becomes a swamp for the three months of heavy rains. The extreme variation in rainfall supports only thorny scrub vegetation and cattle grazing, although recent discoveries of natural gas and petroleum near the foothills of the Andes have attracted some settlers to the region.
Most of Bolivia's important rivers are found in the water-rich northern parts of the lowlands, particularly in the Alto Beni (Upper Beni), where the land is suitable for crops such as coffee and cacao. The northern lowlands are drained by wide, slow-moving rivers, the three largest of which--the Mamoré, Beni, and Madre de Dios--all flow northward into the Madeira River in Brazil and eventually into the Amazon. Riverboats along the Beni and the Mamoré carry both passenger and freight traffic; rapids on the Madeira prevent river traffic farther into Brazil. Near the Paraguayan border, shallow sandy streams carry the seasonal runoff into the Pilcomayo or Paraguay rivers.
Although Bolivia lies entirely within tropical latitudes, climatic conditions vary widely from tropical in the lowlands to polar in the highest parts of the Andes. Temperatures depend primarily on elevation and show little seasonal variation. In most locations, rainfall is heaviest during the Southern Hemisphere summer, and yearly amounts tend to decrease from north to south.
Northern lowland areas have a tropical wet climate with yearround high temperatures, high humidity, and heavy rainfall. Daytime highs average more than 30° C all year in most locations. The rain-bearing northeast trade winds, blowing across the Amazon Basin, bring significant rainfall amounts. Rain often falls in brief thunderstorms, sometimes accompanied by strong winds and hail.
Central lowland areas have a tropical wet and dry climate. From October through April, northeast trade winds predominate, and the weather is hot, humid, and rainy. From May through September, however, dry southeast trade winds take control, and precipitation is minimal. During this season, clear days and cloudless nights allow for higher daily maximums and lower nightly minimums than occur during the rainy season. Occasional incursions of strong winds from the south, called surazos, can reach this region during winter and bring cool temperatures for several days.
The Chaco has a semitropical, semiarid climate. The northeast trade winds bring rain and hot humid conditions only from January through March; the other months are dry with hot days and cool nights. Bolivia's highest maximum temperature, 47° C, was recorded here. Surazos also affect the Chaco; their approach is usually signaled by a squall line.
Temperatures and rainfall amounts in mountain areas vary considerably. The Yungas, where the moist northeast trade winds are pushed up by the mountains, is the cloudiest, most humid, and rainiest area, receiving up to 152 centimeters annually. Sheltered valleys and basins throughout the Cordillera Oriental have mild temperatures and moderate rainfall amounts, averaging from 64 to 76 centimeters annually. Temperatures drop with increasing elevation, however. Snowfall is possible at elevations above 2,000 meters, and the permanent snow line is at 4,600 meters. Areas over 5,500 meters have a polar climate, with glaciated zones. The Cordillera Occidental is a high desert with cold, windswept peaks.
The Altiplano, which also is swept by strong, cold winds, has an arid, chilly climate, with sharp differences in daily temperature and decreasing amounts of rainfall from north to south. Average highs during the day range from 15° C to 20° C, but in the summer tropical sun, temperatures may exceed 27° C. After nightfall, however, the thin air retains little heat, and temperatures rapidly drop to just above freezing. Lake Titicaca exerts a moderating influence, but even on its shores, frosts occur in almost every month, and snow is not uncommon.
SOURCE: Library of Congress Country Studies/Area Handbook
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