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Mexico City, Mexico

Mexico City, Mexico

Founded in the fourteenth century, Mexico City has been a center for three great civilizations: the Aztecs, the Spanish, and the modern-day Mexicans. But in addition to an imposing political background, its geographical location has assured the city a fascinating ecological and environmental history . Mexico City lies in a basin 7,350 feet (2,240 m) high. It is surrounded by mountain ranges on all sides, and the presence of the extinct volcanoes Ixtacihuatl and Popocatepetl to the east are a reminder that the city lies on an active earthquake fault.

Most of Mexico City's environmental problems are caused by a combination of its geographical location and growing population. In 1900, the population was estimated at 350,000; the rest of the century has seen nothing but rapid growth. Population has leapt from 1,029,000 in 1930 to 4,871,000 by 1960, and then to 12,000,000 in the mid-1970s, and then 15,000,000 by 1981. According to some estimates, Mexico City will have more than 32 million inhabitants by the year 2000, making it the most populous urban area in the world.

The amount of pollution produced by a city of this size would be difficult to control in even the most favorable geographic circumstances. But the basin in which Mexico City is built traps the ozone , nitrogen oxides , sulfur, and particulates that are released each day. Soft coal , wood, and low-grade gasoline and oil are burned widely throughout the city, contributing greatly to this problem. In addition, prevailing winds from the northeast carry dust particles into the city from rural areas, further degrading air quality . The city has gone from having one of the most perfect natural settings and ideal climates in the world to being the most heavily polluted. Pollution levels can rise so high that schools are occasionally forced to close so students can remain indoors and not breathe the polluted air. Entrepreneurs have even set up booths on city streets where people can pay to breath oxygen from tanks.

Lying near the boundary of the Pacific and North American geological plates, Mexico City has long been at risk for major earthquakes, a risk which has been greatly increased by the city's history. When the Aztecs first settled the area, it was largely covered by an enormous lake, Lake Tenochititlán, which either was filled in or dried out as the city began to grow. Today, Mexico City sits on a soft subsoil that is highly unstable. Some parts it are actually sinking into the old lake bed, while the whole area rides out each earthquake like a boat on an unsettled ocean.

The geographical instability of the area has been worsened by the fact that residents traditionally obtain their water from wells . As the population grows, more water is removed and subsidence increases. In some parts of the old city, buildings have actually sunk more than 6 ft (2 m) below street level. Since measurements were first made in 1891, subsidence in some areas has exceeded 26 ft (8 m), and it measures at least 13 ft (4 m) in nearly all parts of the city.

See also Air pollution control; Air quality criteria; Los Angeles Basin; Nitrogen cycle; Population growth; Sulfur cycle; Sulfur dioxide

[David E. Newton ]



Poland, J. F., and G. H. Davis, "Land Subsidence Due to Withdrawal of Fluids." In Man's Impact on the Environment, edited by T. R. Detwyler. New York: McGraw-Hill, 1971.


"Line Up to Breathe." BioScience (September 1991): 591. "School Days and Lethal Haze." Environment 30 (March 1988): 23.

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