Modern Mexico City, a thriving capital of 7,000,000 people, faces an unusual problem. It is?
Modern Mexico City, a thriving capital of 7,000,000 people, faces an unusual problem. It is built on an ancient lake bed and the land beneath the city is slowly but surely sinking.
Mexico City is the only great Metropolis in the World not located at or near the edge of a river, lake or other large surface of water.
In fact, the city is located above a huge deposit of water. Under relatively hard crust some five to six feet deep, the soil under the city is impregnated with water and the thousands of buildings and homes actually stand on a gigantic, very soft and extremely fine-grained water soaked sponge.
Millions of years ago, this lake in the Valley of Mexico extended above ground and filled the entire Volcano-ringed basin. In time, the Aztecs built a water-surrounded city in the centre of the lake with Venice-style canals as their main Avenues. Later, the Spaniards conquered the area, drained the canals, emptied the water from the Valley and built their own city. Today,s Texcoco Lake and Xochimilco are all that remain of the Lake that once covered the Valley..
But, always lurking under the surface and extending downwards for thousands of feet, is the great buried lake of Mexico. It was in 1938 that the expanding city had to tap this supply for the first time and hundreds of wells started to pump millions of gallons of water -- and the entire valley surface started to sink. The peak rate was reached in 1950 when it was found that the City was sinking at a rate of nearly 14 Inches year. It was then that the engineers sounded the alarm.
The warning was plain to see. If the fall continued, damage to sewers and water main would be irreparable and building would tilt, crack and fall. Experts pointed to the Independence Monument on the Plaza de la Reforma. Originally built on piles driver 25 meters into the hard stratum, its base has now risen over 12 feet (4 metres) above street level.
The answer was obvious and swift. The City Government began an anti-well campaign, prohibited t he drilling of new wells and closed down existing ones. Finally, in July 1953, the Lerma River Water Works piped a new supply into the city and all existing wells were closed down. The result was equally dramatic. From the peak sinking rate of 14 inches, the sinking has showed down to about four centimetres (2 inches) per year -- the rate it was before 1938.
Building -- which have also to be earthquake-proof in this land of tremors and quakes -- are built on "floating" foundations which is the reason why the 44-storey Latin American Tower has never toppled following the movements of the quakes. The slightest change is automatically corrected by inbuilt gyroscopes.
But as long as the sinkage continues, the city problem remains. Buildings have to be shored up, gaps appear at the base of modern concrete building, pavements rise and fall or have to be adjusted to front entrances by workmen, crack appear in the pavements. An just to add to the problem, Mexico City has a smog problem to match any other city in the world. In fact, it ranks the seventh - worst in the world.