Mexico City may sink up to 65 feet


Darío Solano-Rojas (Darío Solano-Rojas) He moved from his hometown of Cuernavaca to Mexico City and studied at the National Autonomous University of Mexico. The layout of this metropolis puzzled him. Please note that it is not the grid itself, but the architectural environment that seems to be in a state of chaos, like a surrealist painting. “To my surprise, everything is twisting and tilting,” Solano-Rojas said. “At that time, I didn’t know what it was. I just thought, “Oh, well, this city is very different from my hometown. “”

It turns out that the situation is different. Solano-Rojas met Enrique Cabral-Cano, a geophysicist doing geological research at the university, who was actually studying the surprising cause of infrastructure chaos: the city sank for a long time. This is the result of a geological phenomenon known as sinking, which usually occurs when too much water is drawn from the ground and the land above begins to become dense. According to the new model of the two researchers and their colleagues, parts of the city sink as much as 20 inches per year. They estimate that the area may drop as much as 65 feet in the next century and a half. Attractions near Mexico City may sink 100 feet. The distortion and tilt that Solano-Rojas noticed was only 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 the bad roots of Mexico City. Tenochtitlan, the capital of the Aztecs, built an island on an island in Lake Texcoco, located in a basin surrounded by mountains. After the Spanish arrived, they destroyed Tenochtitlan and massacred its people. They began to drain the lake and build houses on the lake. Little by little, the metropolis that became modern Mexico City spread until there were no more lakes.

The ensuing physical changes started the sinking of the city. When the lake sediments under Mexico City are still wet, the clay particles that make up it are arranged in an irregular manner.Consider throwing Turn into a sink, willy-nilly-Their random orientation allows many liquids to flow between them. But to get rid of the water (as the planners of Mexico City did when the lake was drained first, and then the city did it by tapping the ground with aquifers), and then the particles rearranged neatly, like a pile The plates are arranged neatly on the plate. A cupboard. The space between the particles is smaller and the sediment becomes tighter. Or imagine it as applying a clay mask. After the mask dries, you will feel it close to your skin. Solano-Rojas said: “It is losing water and it is losing volume.”

Officials in Mexico City were actually aware of the settlement problem in the late 1800s, when they saw the building sinking and began to measure it. This provides Solano-Rojas and Cabral-Cano with valuable historical data and combines them with satellite measurements obtained over the past 25 years. By launching radar waves on the ground, these orbiters can accurately measure details (with a resolution of 100 feet) and how the ground height of the entire city changes.

Using these data, the researchers calculated that it would take 150 years for the sediments in Mexico City to be fully compacted, although their new model shows that the rate of settlement actually varies from block to block. (This is why Solano-Rojas noticed sloping buildings when he first arrived.) The thicker the clay in a given area, the faster it will sink. Other areas, especially in the suburbs of cities, may not sink at all because they sit on rocks instead of sediments.

It sounds like a relief, but in fact Intensify This situation, because it will make a dangerous difference. If the entire city sinks evenly, it must be a problem. However, because some parts have fallen sharply and others have not, the infrastructure that spans the two areas is sinking in some areas while remaining at the same height in other areas. This can damage roads, subway networks and sewer systems. Cabral-Cano said: “The livelihood itself is not a terrible problem.” “But it is the difference At this speed of survival, virtually all civil structures are under different pressures. “

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This is not just a problem in Mexico City. As long as someone extracts too much water from the aquifer, the land will recede with it.Sinking in Jakarta, Indonesia Up to ten inches One year, California’s San Joaquin Valley (San Joaquin Valley) Sink 28 feet. “It goes back centuries. The human mind is [water] It’s an unlimited supply,” said Manoochehr Shirzaei, a geophysicist at Arizona State University. Research settlement But did not participate in this new study. “Whatever you want, you can poke a hole in the ground and suck it out.” Historically, pumping water has solved the immediate problem of the community-keeping people and crops alive-but has caused long-term disaster.A study earlier this year found that by 2040, there will be 1.6 billion people Affected by settlement.


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