The ceilings of the Metropolitan Cathedral of Mexico City harbor some significant cracks.
The cracks in the historical monument are not the only ones observed in the capital, many other buildings have fractures in their facades and structures, including some of the floors in areas such as the Iztapalapa mayor's office.
These fissures are one of the ways in which the sinking of the city manifests itself before the eyes of the citizens.
In some areas where Lake Texcoco was once located, home to the Aztec capital of Tenochtitlán, on which the capital is built, the ground sinks as much as 40 centimeters a year.
Inside the cathedral, a man looks at the damage to the ceiling.
"With the last earthquake there were hardly any landslides," he says, while in the background the first words of the midday mass begin.
It refers to the 7.7 magnitude earthquake that shook Mexico on the 19th.
A worker repairing the monument, who prefers not to reveal his name, says that some of the cracks could be seen even before the 2017 earthquake, a tremor that left extensive damage in the capital.
The man says that the cathedral, like the city, is sinking.
And the causes are not only the frequent earthquakes.
The drought and the construction boom in the city are altering the watery foundations of the Mexican capital.
In 10 years, the population has grown by almost half a million people,
Panoramic view of the Zócalo of Mexico showing the Metropolitan Cathedral and the collapse towards the left side of its frontal face.Hector Guerrero
“If you look at the cathedral from the Zócalo square, you will see how it is a little sunken on the left side,” says the man at the moment in which he tilts his arm to gesture the way in which the monument sinks into the ground.
The researcher from the Institute of Engineering of the National Autonomous University of Mexico (UNAM), Javier Lermo, indicates that, indeed, the cathedral is sinking at an angle.
"It is not the most illustrative example of the way the city does it, such as the Palace of Fine Arts or the Angel of Independence, which do sink in a more balanced way," says Lermo.
The researcher asserts that the "interesting" process that Mexico City is undergoing is mainly due to the extraction of groundwater.
Lermo assures that in the city "more water is extracted than can be introduced after the rains", a fact that is due to the daily consumption of the nine million people in the city.
The researcher adds that the increase in constructions does not help, since they seal the soil and prevent water from seeping in.
In data, the Inegi realizes that in 2020 Mexico City had 2.7 million homes, 300,000 more than 10 years ago.
The sinking phenomenon is not new.
Entities such as the Mexican Society of Geotechnical Engineering (SMIG) put a date and precursor to the discovery of this event.
Engineer Roberto Gayol reported in 1925 to the Association of Engineers and Architects that the city was being buried.
A few years later, the civil engineer and former UNAM rector, Nabor Carrillo, analyzed the influence of water extraction on the sinking of the city.
Carrillo explained that the origin of the lowering of the land was due to the pressure in the subsoil aquifers as a result of the pumping of water.
Currently, there is even a mechanism for evaluating the phenomenon.
Data from the so-called Piezometry and Subsidence Monitoring System of the Valley of Mexico due to Groundwater Extraction indicates that, in some parts of the valley, 40 centimeters of settlement per year are exceeded, which has caused that, since 1982, some areas of the city have dropped more than 13 meters.
People walk in front of a slightly tilted building in the Historic Center of Mexico City.Rebecca Blackwell (AP)
The volcanoes behind the cracks
Javier Lermo finds a clear problem in this process: the capital is not sinking evenly in all areas.
Mexico City is surrounded by mountains, such as Santa Catarina, Las Cruces or Tepeyac, produced by volcanoes.
"The volcanoes near the valley caused basalt spills in the closest areas," says Lermo.
The presence of this type of rock in the subsoil is the origin of the second major problem of subsidence: cracks.
The engineer points out that the settlement causes fractures in the ground because the basalt "soil" (harder) remains, while the land located in what was Lake Texcoco (a softer ground) sinks.
Lermo says that, at this point, it is difficult to predict the appearance of cracks,
In the Iztapalapa mayor's office, one of the areas closest to the mountains, the deformations of the ground are not a surprise.
The fissures led to the creation of the Sinking and Fracturing Interactive Observatory, a center to monitor fractures which, in turn, allowed the recovery of land where its buildings were affected by fissures.
The cracks, in turn, also give rise to another big problem: the opening of the ground to the polluted waters of the surface.
The mixture of groundwater with corrupted water could affect access to drinking water in the city, a situation that would deepen the crisis that the capital is going through.
Last year, the head of government of the capital, Claudia Sheinbaum, acknowledged before the United Nations Organization that part of the population does not have "adequate" access to water.
That same year, the National Water Commission (Conagua) established an emergency situation in the face of drought.
Mexico was going through a situation in which there was less rainfall, which caused serious difficulties in recovering desirable levels in the aquifers.
The technician who looks at the fractures of the Metropolitan Cathedral smiles.
"No matter how much it is covered, the crack reappears, like that always," he says while the workers repair the damage that the earthquake has left on the monument and while the city continues with its settlement.
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