Mexico City is experiencing ongoing land subsidence, meaning parts of the city are steadily sinking. This phenomenon has been occurring for at least 150 years. The city’s unique geographical setting within a mountain basin makes it particularly susceptible to this process.
Mexico City’s Unique Foundation
Mexico City was originally founded by the Aztecs as Tenochtitlan, an island city in Lake Texcoco. The Spanish conquest led to the extensive draining of these lakes, transforming the landscape. The city now sits predominantly on the dried bed of Lake Texcoco, which consists of soft, highly compressible lacustrine clay layers. This underlying soil resembles a wet sponge, inherently prone to compaction when water is removed.
The Role of Water Extraction
The primary driver of Mexico City’s ongoing subsidence is the extensive extraction of groundwater from deep aquifers. As water is pumped out, pressure supporting the overlying clay layers decreases, causing these saturated soils to compact and consolidate. This process is irreversible; once water is removed, the clay does not rebound. Approximately 60-70% of Mexico City’s water supply comes from these aquifers.
The rate of sinking has been substantial, with some areas descending by 40 to 50 centimeters (15 to 20 inches) annually in recent decades. Parts of the city have dropped by 10 meters (33 feet) or more over the last century. Increasing demand for water due to urbanization and population growth intensifies the compaction of the soft clay.
Impacts on Infrastructure and Daily Life
The sinking ground has widespread consequences for Mexico City’s infrastructure and the daily lives of its residents. Buildings, roads, and utilities experience significant damage as the land beneath them settles unevenly. This differential sinking leads to structural stress, visible tilting of historic structures like the Metropolitan Cathedral, and cracks in foundations and pavement. Subsurface infrastructure, including water and drainage pipes, is particularly vulnerable, resulting in frequent ruptures and leaks that contribute to water loss and contamination.
The city’s extensive metro system is also severely impacted by the uneven subsidence. Changes in ground elevation can deform railway lines, leading to safety hazards, service interruptions, and costly repairs. The altered topography caused by sinking exacerbates the risk of flooding, especially during the rainy season, as natural drainage patterns are disrupted. This combination of infrastructure damage and increased flood risk poses ongoing challenges for the city.
Strategies to Address Subsidence
Addressing Mexico City’s subsidence requires a multi-faceted approach focused on sustainable water management and adaptive engineering. Efforts include reducing reliance on deep aquifers by seeking alternative water sources and implementing strategies for artificial aquifer recharge. Technologies such as rainwater harvesting and the treatment and reuse of wastewater are being explored to augment the city’s water supply and lessen the strain on underground reserves. These measures aim to balance water demand with the aquifer’s replenishment rate.
In terms of infrastructure, engineers have developed specialized foundation designs for new constructions, such as compensated or “floating” foundations that reduce the load on the soil. For existing structures, particularly historic monuments, techniques like deep pile foundations that extend to more stable ground or targeted leveling efforts are employed to mitigate damage from differential settlement. Urban planning initiatives also consider the varying rates of subsidence across the city to guide development and implement proactive measures to safeguard essential services.