Why Is the Ground Under Mexico City Sinking?

According to a recent study published in the Journal of Geophysical Research: Solid Earth, Mexico City is sinking at an alarming rate, with little hope of halting the process. The ground is caving in at a rate of up to 50 centimeters (19.7 inches) per year, potentially setting the stage for the widespread destruction of homes and public infrastructure, as well as a possible water crisis.

Despite a water extraction limit enforced since the 1950s, the sinking persists. Subsidence commonly occurs when water is extracted from the ground. Groundwater drilling has certainly played a part in causing Mexico City to sink, but the city’s initial construction also contributed significantly.

The sinking of Mexico City can be partly attributed to its construction on unstable foundations. The Aztec capital, Tenochtitlan, was built on an island within Lake Texcoco. The subsequent Spanish conquest led to the destruction of Tenochtitlan and the draining of Lake Texcoco, allowing for construction to take place on the remaining land. The draining of the lake caused the ground’s clay particles to change from a disorganized formation that allowed for efficient water flow to a more compact arrangement. With less space between particles, the sediment becomes compacted, and the reduction in volume results in subsidence.

The sinking of the ground was recognized in the late 1800s, when officials began recording the subsidence. Researchers have used historical records and satellite measurements spanning 25 years to track these changes. They predict that it will take 150 years for Mexico City’s sediment to compact completely.

However, the Mexican capital is not sinking uniformly. Some regions are at higher elevations, while others have already sunk below the level of the former lake bed. This disparity can lead to more problems, as fractures in the ground surface can cause extensive damage to roads, gas pipelines, buildings, and sewers and potentially contaminate water supplies. With 1.1 million homes in Mexico City already lacking access to clean and safe water, ongoing subsidence and contamination of the water supply could lead to a water pollution crisis.

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