Mexico City
The above photo was not taken in Mexico City, but in the nearby city of Puebla. Due to poor air quality in Mexico City, it is rare to see the twin volcanos of Ixtaccihuatl and Popocatapetl (pictured above), but this photo illustrates some of the many geologic hazards that threaten the capital of Mexico. Some of the hazards are subtle while others are potentially catastrophic, including the 1985 earthquake which paralyzed the capital for over a week. Since then, the world economy has become increasingly integrated so that many economists cite a similar disaster today as a "black swan" event. The importance of Mexico City cannot be understated - it is not only the country's seat of government, but it is also the country's economic nerve center, responsible for a third of Mexico's GDP, and a global center for trade and commerce. Similar to how the Fukushima earthquake in Japan froze the world economy and nearly tipped the globe into a second recession, a major geologic event that paralyzes Mexico City could also paralyze the world economy. Since the globalization of Mexico's economy, the world has become dependent on products and components made in Mexico. The U.S. would be especially be vulnerable because many of the goods and components that keep the American economy running are made in Mexico. The sudden halt of these goods and components would paralyze key U.S. industries just as the 2011 earthquake in Japan throttled U.S. manufacturing when the sudden dearth of Japanese components forced the temporary shutdown of U.S. factories and layoff of their workers.
Although many perceive Mexico City as an urban nightmare (by some measures, it is the second largest city in the world), those who actually visit the capital find it incredibly fascinating, surprisingly friendly, and endlessly fun. The city offers an endless diversity of attractions ranging from top notch museums, imaginative fusion cuisine, a fantastic night club scene including a scene that caters to gays, and ancient buildings ranging from Spanish colonial cathedrals to the timeless pyramids of Teotihuacan. Its long history as not only the capital of Mexico, but also the capital of the Aztec Empire has earned it the nickname Rome of the Americas. Interspersed among Mexico City's attractions are signs that the city is vulnerable to geologic hazards. Come see this amazingly dynamic city and how it copes with life in an embattled geologic environment.
Although many perceive Mexico City as an urban nightmare (by some measures, it is the second largest city in the world), those who actually visit the capital find it incredibly fascinating, surprisingly friendly, and endlessly fun. The city offers an endless diversity of attractions ranging from top notch museums, imaginative fusion cuisine, a fantastic night club scene including a scene that caters to gays, and ancient buildings ranging from Spanish colonial cathedrals to the timeless pyramids of Teotihuacan. Its long history as not only the capital of Mexico, but also the capital of the Aztec Empire has earned it the nickname Rome of the Americas. Interspersed among Mexico City's attractions are signs that the city is vulnerable to geologic hazards. Come see this amazingly dynamic city and how it copes with life in an embattled geologic environment.
When you first arrive in Mexico City, you may feel a bit winded, especially when climbing a set of stairs, as if you were more out-of-shape than usual. Don't worry, it's the altitude! At 2,200 meters, it is the highest capital in North America. In futbol (soccer), it gives the Mexican national team a huge advantage during World Cup qualifying matches. Its biggest rival for the qualifying rounds is the U.S. and while the U.S. has beat Mexico 2 out of 3 times on neutral playing grounds, it has yet to win in Mexico City after 19 matches.
Mexico City is the highest venue ever for the Summer Olympics which was held in 1968, and the thin air led to some peculiar results. The high altitude led to poor time results for endurance events like the marathon and other long distance categories. However, the thin air led to many records for events where air resistance is a factor such as the long jump, javelin, and short distance track events.
Mexico City is the highest venue ever for the Summer Olympics which was held in 1968, and the thin air led to some peculiar results. The high altitude led to poor time results for endurance events like the marathon and other long distance categories. However, the thin air led to many records for events where air resistance is a factor such as the long jump, javelin, and short distance track events.
Mexico City is located in the southern portion of a region known as the Mexican Altiplano (high plain), a mountainous region whose relief ranges from 1,000 to 3,000 meters high (the highest mountain in Mexico, Orizaba, rises to 5,600 meters in the Altiplano). The Mexican Altiplano was created by subduction along the country's Pacific coast and is geologically unstable with frequent earthquakes and volcanic activity. The source of the 1985 Mexico City earthquake was at this subduction zone. This same instability is also why the Altiplano is rich in minerals, a key reason why Mexico was a hub of the Spanish American colonies. Even today, mines throughout the Altiplano produce large quantities of silver, gold, copper, and other metals.
Mexico City's hazards are three-fold: volcanos, earthquakes, and subsidence. The latter two are closely inter-related. As it turns out, the capital is built over a former lake known as Lake Texcoco. Prior to the arrival of the Spanish, the Aztecs built their capital on an island in the middle of this lake known as Tenochtitlan. Tenochtitlan's central square is located where today's Zocalo (pictured on left) is today, considered the center of the Mexican nation. Many of the city's streets are built along the same streets of Tenochtitlan.
Over the years, nearly 60 meters of soft, spongy mud accumulated on the bottom of Lake Texcoco which formed the foundation for Tenochtitlan and Mexico City. When the Aztecs built their pyramids in Tenochtitlan, they began to sink into the mud below. As they sank, they continued to build on top of the sinking structures below.
Over the years, nearly 60 meters of soft, spongy mud accumulated on the bottom of Lake Texcoco which formed the foundation for Tenochtitlan and Mexico City. When the Aztecs built their pyramids in Tenochtitlan, they began to sink into the mud below. As they sank, they continued to build on top of the sinking structures below.
You can see what's left of Lake Texcoco in the southern part of the city in an area known as Xochimilco. As Mexico City grew, the lake was backfilled until all that is left is in Xochimilco. Compounding the problem of building on soft sediment was groundwater withdrawal. Mexico City is located in a desert with little surface water resources to tap into. They therefore drilled wells and pumped water out of the ground to serve the city's ever-growing demand. This caused water levels in the subsurface to drop. The dewatering of the soft sediments caused them to shrink and the ground surface to drop. This drop of the surface didn't occur evenly, but differentially so that buildings on the surface started to tilt at weird angles.
On the left, you can see how the buildings are tilted in different directions as they sink differentially into the soft mud. A resident of one of these buildings complained that his entire building suffers from constant plumbing issues.
Mexico City's skyscrapers are also built on the soft muds of Lake Texcoco, but unlike the Spanish colonial buildings, they are built on pilings that extend about 60 meters down to the more solid basalt bedrock underneath the Lake Texcoco sediments. This gives them a solid foundation and prevents them from sinking into the soft muds.
Groundwater withdrawals have been curbed to a more sustainable level and the city has started importing water from adjacent valleys. It is hoped that this help slow the sinking of buildings in the Historic Center around the Zocalo.
Mexico City's skyscrapers are also built on the soft muds of Lake Texcoco, but unlike the Spanish colonial buildings, they are built on pilings that extend about 60 meters down to the more solid basalt bedrock underneath the Lake Texcoco sediments. This gives them a solid foundation and prevents them from sinking into the soft muds.
Groundwater withdrawals have been curbed to a more sustainable level and the city has started importing water from adjacent valleys. It is hoped that this help slow the sinking of buildings in the Historic Center around the Zocalo.
The Metropolitan Cathedral, one of Mexico's most important landmarks, was in danger of collapsing since different parts of the church were sinking at different rates. In the 1990s, engineers excavated underneath the cathedral and stabilized the foundation so that the entire cathedral would sink uniformly. Restoration has been carried out at other important structures, but because it is a very expensive endeavor, there are no plans to restore every Spanish colonial building in the city.
Mexican engineers are considered the world's leading experts on restoring sinking historical structures. The Italian government consulted with them on restoring Venice as well as the Leaning Tower of Pisa.
Mexican engineers are considered the world's leading experts on restoring sinking historical structures. The Italian government consulted with them on restoring Venice as well as the Leaning Tower of Pisa.
The deadliest hazard in the city are earthquakes. This hazard is closely related to the dangers posed by soft muds. During an earthquake, these muds can amplify earthquake waves to be much more destructive than when they travel through solid rock. Take a pan of baked brownies and a pan of warm jello next to each other and shake them. Which shakes more violently? The sediments underlying Mexico City have the same properties as that warm jello. The epicenter for the 1985 earthquake was 250 km away and none of the communities between the epicenter and the capital sustained significant damage. However, when the waves reached Mexico City, the soft mud amplified those waves much like warm jello does when you shake it.
The buildings most damaged were the ones between 10 and 15 stories high (similar to the ones seen here). These buildings were not high enough to warrant pile foundations on the bedrock below which are necessary for skyscrapers, but high enough that intense shaking amplified by the soft mud would cause them to swing beyond their design limits. Interestingly, the Spanish colonial buildings which are the city's oldest buildings, sustained relatively little damage. This was due to their low center of gravity which minimized swinging during the most intense shaking.
Mexico City's 1985 earthquake shocked earthquake engineers in the U.S. They had previously coordinated with Mexican officials to streamline and improve building codes to make earthquakes more survivable. However, what they found was that many of the buildings destroyed in Mexico City were built identically to many buildings in the U.S. Thus, many U.S. buildings were at serious risk in a major earthquake. Of particular worry were not just buildings in California, but buildings in the midwestern U.S. where a M8 earthquake is believed to be possible in the near future.
The buildings most damaged were the ones between 10 and 15 stories high (similar to the ones seen here). These buildings were not high enough to warrant pile foundations on the bedrock below which are necessary for skyscrapers, but high enough that intense shaking amplified by the soft mud would cause them to swing beyond their design limits. Interestingly, the Spanish colonial buildings which are the city's oldest buildings, sustained relatively little damage. This was due to their low center of gravity which minimized swinging during the most intense shaking.
Mexico City's 1985 earthquake shocked earthquake engineers in the U.S. They had previously coordinated with Mexican officials to streamline and improve building codes to make earthquakes more survivable. However, what they found was that many of the buildings destroyed in Mexico City were built identically to many buildings in the U.S. Thus, many U.S. buildings were at serious risk in a major earthquake. Of particular worry were not just buildings in California, but buildings in the midwestern U.S. where a M8 earthquake is believed to be possible in the near future.
An occasional hazard throughout the Altiplano are volcanos. There are two types of volcanos that present two different types of hazards in Mexico: basaltic and dacitic. Basaltic volcanos usually form cinder cones and unleash extensive fluid lava flows that can destroy a lot of property, but rarely result in any casualties. Seen on the right is the cathedral of San Juan Parangaricutino which was covered in lavas unleashed by Paracutin whose cone you can see in the background. Even though the entire town was destroyed, there were no casualties.
The other type of volcanism, dacitic, are associated with high stratovolanos and produce some of the deadliest types of eruptions. El Chichon in Chiapas is such a volcano and an eruption in 1982 killed nearly 2,000. Elsewhere around the world, Vesuvius, Mt. Saint Helens, and Krakatoa are similar dacitic volcanos that erupted in historic times.
The other type of volcanism, dacitic, are associated with high stratovolanos and produce some of the deadliest types of eruptions. El Chichon in Chiapas is such a volcano and an eruption in 1982 killed nearly 2,000. Elsewhere around the world, Vesuvius, Mt. Saint Helens, and Krakatoa are similar dacitic volcanos that erupted in historic times.
Mexico City is located at the heart of a volcanic region in which both types of volcanism occur. When viewing the city from the air, you can see that some of the districts lie inside the craters of volcanic cones. Volcanic eruptions have occurred within historic times, but none have occurred since Mexico City expanded to cover the entire Valley of Mexico in the 20th Century. Seen on the left are young basalt flows on the campus of the National Autonomous University of Mexico (known as UNAM). These flows, known as pahoehoe, flow passively and slowly.
The greatest threat to Mexico City are the large stratovolcanos to the southeast. Stratovolcanos, associated with dacitic-type eruptions form the most beautiful mountains in the world, Mt. Fuji and Mt. Rainier being good examples, but they are also among the deadliest. Their eruptions can be catastrophic unleashing glowing avalanches - massive clouds filled with ash at the melting temperature of rock (about 600 degrees C) that incinerates everything in their path, and mudflows that follow valleys and bury everything in a wet, heavy ash resembling something like concrete. Nearby Mexico City are two stratovolcanos: Popocatapetl and Ixtaccihuatl. The former, known as El Popo, is seen on the right during a minor eruption.
El Popo (seen on the right of this photo with Ixtaccihuatl on the left) is far enough from Mexico City that it does not pose a major threat as far as mudflows and glowing avalanches are concerned. A third hazard associated with stratovolcanos, however, is spontaneous collapse and this could pose a threat to the capital. If you look at the photo of Popo in the top of this page, you will notice how steep its slopes are. Stratovolcanos grow from the accumulation of debris around its central vent. Over time, they can grow very high and very steep with slopes that become increasingly unstable. The movement of magma within the volcano as well as seismic activity can cause the slopes to bulge and become even more unstable. The end result is a collapse of large section of the volcano (this is what triggered the Mt. St. Helens eruption in 1980). This collapse results in an enormous landslide that can travel at speeds exceeding 400 km/hr and travel tens of kilometers away, far enough to reach Mexico City. These events are often triggered by an earthquake or volcanic eruption, but they can also occur with no trigger at all, meaning that there may be no time to evacuate people. Geologists studying Popo's past have found that it has collapsed in the past including one that sent debris 70 km to the south. However, it is important to point out that these are low probability events and the chances of such an event occurring in the near future is very low. What worries Mexican officials more than anything else is a prolonged period of activity in which a major eruption seems imminent but never actually occurs, or occurs after everyone gets volcano fatigue and ignores the warnings. Such a scenario may not paralyze the Mexican economy, but could slow it down and tip it into recession.
Mexico City has had more than its fair share of problems ranging from water supply, geologic hazards, political problems, urban issues, and so on. Yet it somehow responds to each of these problems with resourcefulness and imagination. The city reinvented itself after the 1985 earthquake and it continues to evolve as Mexico becomes increasingly connected with the rest of the world. Were some geologic disaster to strike the city in the future, I have no doubt that it will bounce back and transform itself into something more fascinating and interesting.
Logistics
Although generally safe and easy to get around, there are a few caveats to know about when traveling in the city. The best way to get around is the Metro which is cheap, safe, and easy to use - it even has a stop at the airport. However, certain lines can get really crowded during rush hour, football game days, and so on. Unless you have nerves of steel, a private car is not recommended. Although taxi crime is becoming less common, you should use only taxis called by your hotel or at an official taxi stand (if you can't find one right away, there is always one at a Sanborns restaurant, about as plentiful in Mexico as Starbucks is in the U.S.). Aside from the government-operated Metro bus, avoid using privately operated buses, especially in the northern part of the city.
Crime is generally limited to pick-pocketing and scams if you stick to the areas frequented by tourists, but you should also take the same precautions you would in any large city - avoid walking alone at night, keep your valuables in secure areas (such as a waist belt), and don't leave any valuables sitting in the open in your hotel. The high altitude of the city poses a couple of risks: you may feel a little winded when walking around and you should bring sun screen since your skin will burn in as little as 20 minutes in the intense sun.
Because Mexico City is located almost literally in the center of Mexico, the selection of trips out of the city is infinite. The country also has an excellent long distance bus system which services just about every remote corner of the country. Recommended trips that make a great day trip from the capital (besides those mentioned above) include Puebla, Nevado de Toluca, Tepoztlan, the monastaries around Popocatapetl, and Cuernavaca.
Crime is generally limited to pick-pocketing and scams if you stick to the areas frequented by tourists, but you should also take the same precautions you would in any large city - avoid walking alone at night, keep your valuables in secure areas (such as a waist belt), and don't leave any valuables sitting in the open in your hotel. The high altitude of the city poses a couple of risks: you may feel a little winded when walking around and you should bring sun screen since your skin will burn in as little as 20 minutes in the intense sun.
Because Mexico City is located almost literally in the center of Mexico, the selection of trips out of the city is infinite. The country also has an excellent long distance bus system which services just about every remote corner of the country. Recommended trips that make a great day trip from the capital (besides those mentioned above) include Puebla, Nevado de Toluca, Tepoztlan, the monastaries around Popocatapetl, and Cuernavaca.