Mexico City sinking at 20 cm per year

Walk into any of the buildings in Mexico's capital, Mexico City, and you feel immediately that something isn't right. The buildings tilt. Resting on a lake bed in the Valley of Mexico, Mexico City has been slowly going under for hundreds of years. According to geologists, there are parts of the metropolis that are sinking by as much as 20 centimeters per year. That's 8 inches. It is estimated that during the 20th century, the city as a whole has sunk approximately 9 to 11 meters.

The problem dates back centuries. The Aztecs built their capital city, Tenochtitlan, on an island in the middle of lake Texcoco. After the Spanish defeated the Aztecs, Spanish colonizers began building drainage canals in an attempt to control the floods Tenochtitlan regularly faced. As the water disappeared, the city settled into the mud of the lake bed, creating a hump in the drainage canals. The city built additional drainage tunnels to get through the higher ground, but as the city sank, they, too, have begun tilting backward. Approximately 25% of the population doesn't have fresh water plumbing due to dislocated, broken pipes and tunnels.