Why Mexico City's Geography SUCKS

Imagine your house sinking 30 meters beneath where it is today, that would be a hole so deep. If you stood at the top and jumped in, it'd take about two and a half seconds for you to hit the bottom. Unfortunately, for millions of Mexicans, this is exactly what's going to happen to them very slowly, over the course, of the next few decades. And it's all because humans are really really prone to choosing objectively terrible locations to place their cities in, Mexico City in particular has some of the worst geography stats of any major city in the world, and this is why.

Let's rewind the geographical and historical clock back a little over 700 years ago, back then, the region's geography and reality was very different from today. The city didn't exist and in its place was a large lake called Lake Texcoco, wedged in a large valley surrounded by high mountains and volcanoes on all sides. Legend has it that for a hundred years before this, the nomadic Mexica tribe awaited the fulfillment of an ancient prophecy. They would eventually settle down and build the greatest city in the world, where the location would be determined wherever they saw an eagle eating a snake in its beak while perched atop a cactus.

Eventually this prophecy would be realized when the Mexica finally saw this exact vision in the most unlikely of places, for the greatest city the world would ever see, a small unpopulated and swampy island right here in the middle of Lake Texcoco, but undeterred by the formidable terrain, the Mexica kept true to their prophecy and began building their great city. And over the next two centuries, this small swampy island was continually enlarged by landfills and floating gardens until it eventually evolved into Tenochtitlan, the capital of the Aztec Empire and one of the largest cities in the entire medieval world.

By the time the Spanish arrived in 1519, Tenochtitlan was five times the size of London under Henry VIII, and at the time considering the Aztecs position on the tech tree, the city's geography didn't actually seem so bad, without being fortunate enough to have any pack animals like horses or oxen, and without having discovered any practical use of the wheel. The Aztecs had no other means available to them for transporting goods and conducting trade than by moving across the water on boats. Tenochtitlan's various canals easily facilitated this role, and when you combine that with a complex series of dams they built that provided abundant clean drinking water extremely rich infertile soil, and a highly defensible position surrounded by a literal moat. It's no wonder that the city became Mesoamerica's most successful, that is until the Spanish and Cortez arrived.

In 1519, Tenochtitlan was put under a brutal siege and under Cortez's direct orders, the Aztec dams across the lake were destroyed in order to turn Lake Texcoco salty and to deny the Aztecs inside of any access to clean drinking water, without their drinking water, and after a virulent smallpox epidemic, the Aztecs inside withered away, and the Spanish conquered and subsequently raised the city almost completely to the ground, brick by brick.

By the end of the 16th century, the once great city of Tenochtitlan's population had declined by over 90 percent, and atop the ruins, the Spaniards founded their new settlement called Mexico City. And this is when the big problems really began.

The Spaniards never rebuilt the Aztec dams and dikes and replaced them with more familiar streets and public squares, instead. On the plus side this allowed them to gradually reclaim more and more land from the lake to make more space for Mexico City's growing population and buildings. But on the other side, this meant that the city was expanding into a swamp that was surrounded by a lake, without any dam to keep out any of the lake's water, flooding therefore became a constant problem for Mexico City.

As it expanded and grew, including one particularly bad case in 1629, when the city flooded for five straight years, the Spanish crown even discussed moving the location of the city to a bit less geographically problematic place, but, evidently they thought, eh they just decided to stay and drain the lake even more and even more instead.

Under the Aztecs, Tenochtitlan's population was around 400 000 at its peak, and was basically just a small but very dense dot within Lake Texacoco. By 1900, the population here was actually pretty much the same. But the 20th century would see the city's population absolutely skyrocket. By 1950, the city had grown to cover 30 square miles and was home to over 3 million people. Today, Mexico City has grown from there to cover an area of approximately 3 000 square miles, and with nearly 22 million people. This enormous development in just a hundred years has effectively wiped out any trace of the former waters of Lake Texcoco, and covered it instead with a lake of concrete, and it's wreaked total havoc on the valley's environment.

Mexico City is in a region that receives even more rainfall than infamously rainy places like London or Seattle, but despite that, the city perpetually struggles to provide enough water for her citizens, without the waters of Lake Texcoco, the city has been forced to drill deeper and deeper into the below-ground aquifers in her ever-desperate quest for water. The problem here is that, the land beneath Mexico City is an ancient soft clay lake bed, and as Mexico City drills for more and more water, the clay weakens and crumbles. The water pressure within the aquifer supports the soil above it which in turn supports the city above it.

However, as the water is drained and removed, the soil above compacts this compaction combined with the lower water pressure pushing from beneath will slowly cause the city to sink over time. Rainwater can't easily get into the aquifers to replenish them because the land above is now absolutely covered in the concrete sprawling chaos of the world's sixth largest city, and as a result, Mexico City is trapped in a vicious geologic cycle. As the population grows, the demand for water further increases, but without the waters of the natural lake, she is then left with no other choice but to drill deeper into the below ground aquifers, which reduces the soil stability above and leads to the city sinking even further and further.

With the increased development above from the increasing population, rainwater can't get in to replenish the aquifers, and the soil's instability continues to get worse. Climate change even further exacerbates these already dire conditions since more heat and more drought in the region inevitably also means more evaporation and even more demand for the already scarce water supply, leading to even further drilling and of course, even further sinking.

Mexico City of course knows all of this, and through a complex series of canals and pipes, they now import about 40 percent of their water supply from other regions of Mexico. However these canals and pipes are wildly inefficient. The constantly shifting elevation causes pipes below the ground to routinely crack and burst while the struggling city government is rarely capable of mounting any kind of significant repairs, and as a result of that, for every one gallon of water that is pumped into the pipes of Mexico City, more than one third of it will simply be lost. The energy that's required to pump all of that water up to a city that's a mile and a half high in elevation in the mountains, is more than what the entire city of Puebla consumes, a city with roughly the same population as Philadelphia.

So as a result, Mexico City faces water shortages as if it were in the middle of a desert, despite receiving more rainfall than London. There isn't any easy or obvious solution for them to get out of this, but the city's sinking problem affects far more than just the water supply, since it affects some areas worse than others.

Roads will suddenly buckle and wobble, buildings tip over and look like they're about to collapse, the metro system in some areas will resemble more of a roller coaster, while the destruction caused by earthquakes is greatly amplified.

Mexico City is unfortunately located within a seismically active zone, and with most of the city's core located on the weak and silty clay lake bed, the soil will often behave more like a liquid during an earthquake, causing the buildings above to be even more greatly damaged than they otherwise would be. This is how in 1985 the Mexico City earthquake caused such catastrophic damage and loss in life to the city

Mexico City's rapid and unexpected population explosion in the 20th century caused other unnatural problems to crop up as well. By 1992, Mexico City was home to more than 50 000 industries, and more than 4 million motor vehicles. Due to the city's high elevation, a mile and a half above sea level, its oxygen levels are 25 percent lower when compared to a city that is precisely at sea level, and therefore fuels don't combust as efficiently.

Further, Mexico City is located within a high valley that's surrounded by tall mountains, which effectively keeps pollutants and exhaust trapped within without any place to go. This all meant that by 1992, the UN had labeled Mexico City as the world's most polluted city.

But 30 years later after a variety of methods, Mexico City has managed to get their air pollution levels down in the valley to about the same level seen in Los Angeles today, but air pollution continues to be the eighth leading cause of death within Mexico and causes about one in every 17 deaths in the country.

For the Aztecs seven centuries ago, settling on an island in Lake Texcoco not only fulfilled an ancient prophecy, but made perfect geographic sense with their understanding of technology and limited population at the time. In the current day though, it's one of the worst locations imaginable for the industrialized world's sixth largest city, and has caused countless problems for centuries. But it's too late now since pushing Mexico City somewhere else just isn't really feasible. Mexico City's countless geographic problems are just a fact of life now, and something that has to be lived with. Because in the end, nature will always win.

Mexico City's struggle against her environment has been one of the most massive and intimidating projects that humanity has had to have ever undertaken. As always, thank you for watching. Goodbye!