Technology

Mexico City can sink up to 65 feet


When Dario Solano Rojas He moved from his hometown of Cuernavaca to Mexico City to study at the National Autonomous University of Mexico, and was overwhelmed by city planning. Not the grid itself, but rather the way the built environment looked in turmoil, like a surreal painting. “What struck me was that everything was kind of twisted and tilted,” says Solano Rojas. At the time, I didn’t know what it was about. I just thought, ‘Oh, well, the city is so different from my hometown.’

It turned out to be different in a bad way. After completing his geology studies at university, Solano Rojas met the geophysicist Enrique Cabral Cano, who was actually looking for the surprising cause of the infrastructure chaos: The city was sinking – big time. It is the result of a geological phenomenon called subsidence, which usually occurs when a lot of water is drawn from underground, and the ground above begins to compress. According to new modeling by the researchers and their colleagues, parts of the city sank as much as 20 inches a year. According to them, in the next century and a half, areas could drop by as much as 65 feet. Spots outside of Mexico City can sink as far as 100 feet. The twisting and tilt that Solano – Rojas noticed was just the beginning of a slow-motion crisis of 9.2 million people in the fastest sinking city on Earth.

The root of the problem is Mexico City’s poor foundation. The Aztecs built their capital Tenochtitlan on an island in Lake Texcoco, which is located in a basin surrounded by mountains. When the Spanish arrived and destroyed Tenochtitlan and killed its people, they began to drain the lake and build over it. Little by little, the capital that became modern Mexico City spread, until the lake disappeared.

This brought about the material changes that began to plunge the city. When the sediments of the lake beneath Mexico City were still wet, the particles formed from the clay were arranged in an unorganized manner. Think about throwing Plates in a sink, shriekedTheir random directions allow a lot of fluid to flow between them. But remove the water – as Mexico City planners did when they drained the lake in the first place, and as the city has since done by using the ground as an aquifer – and those particles rearrange themselves to accumulate in an orderly fashion, like slabs in the place of a cupboard. With less space between the particles, sediment builds up. Or think of it like a clay face mask. When the mask dries, you can feel it tightening on your skin. “It loses water and loses volume,” says Solano j Rojas.

Mexico City officials actually realized the subsidence problem in the late 19th century, when they saw buildings sinking and began taking measurements. This gave valuable historical data for Solano-Rojas and Cabral-Cano, which were combined with satellite measurements taken over the past 25 years. By launching radar waves at the ground, these orbits measure in fine detail – a precision of 100 feet – how surface heights have changed across the city.

Using this data, the researchers estimated that it would take another 150 years for the Mexico City sediments to become fully compressed, although their new modeling shows that the rates of subsidence would in fact vary from block to block (which is why Solano – Rojas noticed the oblique architecture when it first arrived ). The thicker the clay in a certain area, the faster it sank. Other areas, especially on the outskirts of the city, may not sink much at all because they sit on rocks rather than sediments.

This sounds like a relief, but it actually is Aggravates Situation because it creates a dangerous difference. If the entire city uniformly sank, that would definitely be a problem. But since some parts are greatly degraded and others are not, the infrastructure that spans the two regions is sinking in some areas but remains at the same height in others. This threatens to cut off roads, metro and sewage networks. “The landing in itself might not be a terrible problem,” says Cabral Cano. “But that is Difference At this speed of subsidence that really puts all civilian structures under different pressures. “

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This is not just Mexico City’s problem. Wherever humans are extracting a lot of water from aquifers, the Earth is receding in response to this. Jakarta, Indonesia is sinking Up to ten inches Per year, and San Joaquin Valley, California It sank 28 feet. “It goes back centuries. The human thought was that this [water] It is an unlimited supply, “says Arizona State University geophysicist Manouchehr Sherzai, who Falling studies He was not involved in this new research. “Wherever you want, you can poke a hole in the ground and absorb it.” Historically, pumping groundwater solved immediate problems for societies – preserving lives and crops – but it caused a long-term disaster. A study earlier this year found that by 2040, it could be 1.6 billion people Affected by fall.



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