When Darío Solano-Rojas he moved from his hometown of Cuernavaca to Mexico City to study at the National Autonomous University of Mexico, confused by the organization of the metropolis. Not the grid itself, remember, but the way the built environment seemed to be in a storm, like a surreal painting. “What surprised me was that everything was a little twisted and tilted,” says Solano-Rojas. “I didn’t know what it was at the time.” I just thought, ‘Well, the city is so different from my hometown. ”
It turned out otherwise, in the wrong sense. When Solano-Rojas began studying geology at university, he met geophysicist Enrique Cabral-Can, who was actually investigating the surprising reason for this infrastructural chaos: The city was sinking – a great time. It is the result of a geological phenomenon called subsidence, which usually happens when too much water is pumped from the underground and the land above begins to compact. According to new modeling by two scientists and their colleagues, parts of the city dive up to 20 inches a year. They estimate that in the next century and a half, the areas could fall by as much as 65 feet. The spots just in front of Mexico City itself could sink 100 feet. The fact that Solano-Rojas noticed that it turned and tilted was just the beginning of a slowing crisis for 9.2 million people in the fastest sinking city on Earth.
The problem is based on the poor foundation of Mexico City. The Aztecs built their capital Tenochtitlán on an island in Lake Texcoco, which is set in a basin surrounded by mountains. When the Spaniards arrived, they destroyed Tenochtitlán and massacred its inhabitants, began draining the lake and building on it. Little by little, the metropolis, which became present-day Mexico City, spread out until the lake was gone.
And that set in motion the physical changes that began the sinking of the city. When the lake sediment below Mexico City was still wet, its clay particles were arranged in a messy manner. Think about throwing washbasin plates, will-want—The random orientations allow a lot of liquid to flow between them. But remove the water — as Mexico City’s planners did when they drained the lake, and as the city has since done by tapping the ground like an aquifer — and these particles rearranged to stack neatly, like discarded plates of a cupboard. With less space between the particles, the sediment compacts. Or think of it as a clay face mask. As the mask dries, you can feel it tighten on the skin. “It loses water and loses volume,” says Solano-Rojas.
Indeed, Mexico City officials acknowledged the decline problem in the late 19th century when they saw buildings sink and began measuring. This has provided Solano-Rojas and Cabral-Cano with valuable historical data, which they have combined with satellite measurements made over the past 25 years. By orbiting radar waves to the ground, these orbits measure in fine detail – a resolution of 100 feet – how altitudes change across the city.
Based on these data, the researchers calculated that it would take another 150 years for the sediment in Mexico City to completely condense, although their new modeling shows that the rate of decline will vary from block to block. (That’s why Solano-Rojas noticed the sloping architecture when it first came.) The thicker the clay in the area, the faster it sinks. Other areas, especially on the outskirts of the city, may not sink at all, because instead of sediment it sits on a rock.
That sounds like a relief, but in reality worsens situation because it makes a dangerous difference. If the whole city sank in unison, it would be a problem for sure. But because some parts are declining dramatically and others are not, the infrastructure that spans the two zones sinks in some areas, but remains at the same height in others. And that threatens to break roads, subway networks and sewers. “Existence alone doesn’t have to be a terrible problem,” says Cabral-Cano. “But it is.” difference in this existential speed, which in fact exposes all civilian structures to various pressures. “
This is not just a problem in Mexico City. Wherever people extract too much water from aquifers, the earth’s reaction decreases. Jakarta, Indonesia is sinking up to ten inches year and the California valley of San Joaquin has sunk 28 feet. “It’s coming back centuries ago.” The human thought was that this [water] is an unlimited supply, ”says Manoochehr Shirzaei, a geophysicist at Arizona State University declines in studies but was not involved in this new research. “Wherever you want, you can punch a hole in the ground and suck it.” Historically, groundwater abstraction has solved the immediate problems of communities – keeping people and crops alive – but has created a much longer-term catastrophe. A study earlier this year found that by 2040, that could be 1.6 billion people affected by the decline.