Why are some parts of Mexico City sinking into the old lakebed?

Mexico City was built originally (ca. 1325) on an island in the middle of a lake, and eventually became the capital of the powerful Aztec Empire.

The provision of potable water is a problem that has plagued the city for centuries. Deforestation in the 19th century depleted the springs that had supplied the city with fresh water via aqueducts (some dating from precolonial times). The first fresh water well was built in the city center in 1857. By 1900 there were hundreds of wells sucking water from the underground aquifer.

As more and more water was sucked up through the wells, the city began to sink. Some parts have dropped more than seven meters (23 ft) since 1891. Parts of the city center sank more than a meter between 1948 and 1951, and another meter by 1960. The city sank two meters below what remained of Lake Texcoco, posing a serious risk of flooding during the rainy season. In response, engineers sank wells into Lake Texcoco, sucked water from the aquifer, and the lake level dropped below the height of the city center.

Rates of subsidence are very uneven. In places the weight of large buildings has caused them to sink into the dried out mud. The city’s magnificent Opera House (Palacio de Bellas Artes, see photo) sank so far that its original ground floor is now a subterranean basement. To slow down the rate of sinking in the city center, in 1950 new wells were drilled south of the city reducing central city sinking to its current rate of about 10 cm (4 in) a year. Of course, areas in the south started sinking more rapidly.

Elsewhere, buildings (including the Cathedral) have tilted and underground sewers and water pipes have cracked and broken. Furthermore, drains in the city center sank below the large drainage canals and pumps had to be added to lift storm water and sewage up to the drainage canals.

These ground movements pose major challenges for the construction and maintenance of the city’s extensive metro network.

This is a lightly edited excerpt from chapter 23 of Geo-Mexico: the geography and dynamics of modern Mexico. If you have enjoyed this post, please consider purchasing a copy of Geo-Mexico so that you have your own handy reference guide to all aspects of Mexico’s geography.