Mexico City can catch 65 feet

When Darío Solano-Rojas He moved from his hometown of Cuernavaca to Mexico City to study at the National Autonomous University of Mexico, where he was confused by the design of the metropolis. Not the grid itself, attentive, but the built environment seemed to be in turmoil, much like surreal painting. “What surprised me was that everything was twisted and twisted,” says Solano-Rojas. “At the time, I didn’t know what he was talking about. I just thought, ‘Oh, well, the city is much different than my hometown.’

Different, it happened in a bad way. When Solano-Rojas received his study of university geology, he met the geophysicist Enrique Cabral-Cano, and he was really investigating the amazing reason for this infrastructure chaos: the city was sinking, at a great time. It is the result of a geological phenomenon called the bottom, which usually occurs when too much water comes out from under the ground and the topsoil begins to compact. According to new models made by the two researchers and their colleagues, parts of the city are sinking 20 inches a year. It is estimated that in the next century and a half the surfaces could drop to 65 meters. Places on the outskirts of Mexico City could sink 100 meters. Solano-Rojas noticed that the bend and bend was just the beginning of the slow-moving crisis of 9.2 million people on Earth.

The basis of the problem is the bad foundation of Mexico City. The Aztec people built the capital Tenochtitlan on an island in Lake Texcoco, located in a mountainous basin. When the Spaniards arrived, when Tenochtitlan was destroyed and the local people were massacred, they began to drain the lake and build on it. Gradually, the metropolis that became present-day Mexico City expanded until the lake disappeared.

And this set in motion the physical changes that began to sink the city. When the sediment of the lake below Mexico City was still wet, the clay particles of its components were arranged in a disorganized manner. Think about throwing it away plates in a sink, as desired—His random orientation spills a lot of liquid between them. But remove the water — as Mexico City organizers did when they drained the lake, and the city has since hit the ground as an aquifer — and reorganize these particles to accumulate neatly, like stored plates. a closet. With a smaller gap between the particles, the sediments are compacted. Or think of it as applying a clay face mask. As the mask dries, you feel your skin tighten. “It’s losing water and it’s losing volume,” says Solano-Rojas.

Mexico City officials recognized the sinking problem in the late 1800s when they saw the buildings collapse and began taking action. This provided Solano-Rojas and Cabral-Cano with valuable historical data that they combined with satellite measurements over the past 25 years. By throwing radar waves to the ground, these orbits accurately measure — at a resolution of 100 meters — how surface elevations are changing across the city.

Using these data, the researchers estimated that it would take another 150 years for sedimentation in Mexico City to fully compact, although their new models show that crustal rates will change block by block. (That’s why Solano-Rojas noticed the crooked architecture when he first arrived). The thicker the clay in a given area, the faster it sinks. Other sites, especially on the outskirts of the city, may not sink much at all because they are sitting on the rock instead of sediment.

It seems relief, but really increases because it creates a dangerous differential situation. If the whole city sank evenly, it would be a problem, for sure. But because some parts are being badly damaged and others are not, the infrastructure that fills the two areas is sinking in some areas, but in others it remains at the same elevation. And that threatens to break down roads, subway networks and sewer systems. “Living may not be a huge problem in itself,” Cabral-Cano says. “It simply came to our notice then difference at that rate of survival that puts all civilian structures under different stresses. “

This is not just a problem for Mexico City. Everywhere humans get too much water out of aquifers, the earth is calming down in response. Jakarta, Indonesia is sinking up to ten inches and the San Joaquin Valley of California 28 meters sunk. “It’s been around for centuries. This was human thought [water] supply is unlimited, ”says Arizona State University geophysicist Manoochehr Shirzaei examines the sinking but was not involved in this new research. “Wherever you want, you can throw a hole in the ground and absorb it.” Historically, pumping groundwater has solved the immediate problems of communities — keeping people and crops alive — but it has caused a catastrophe in the much longer term. A study earlier this year found that by 2040 there could be 1.6 billion people caused by sinking.