Ciudad de México Has Been Sinking (Not Me)

Hey, look, Mexico City!

Oooh, pretty colors! What could they mean? Foilage? Population density? Availability of huarachas?

Um, no.  They indicate the rate at which Mexico City is sinking thanks to groundwater extraction.

Not entirely surprising given Ciudad de México (aka Tenochtitlan) was built on a lake. Here we see it in 1580.

Cool islands!

(Hey, that sure looks familiar.)

(Good thing we don’t impose Aztec handball consequences on the Giants or the Sharks.)

Anyway, you build on fill and your city sinks. We here are familiar with the concept.

So, back to this image taken by TerraSAR-X, a German radar satellite: green equals no change, while yellow and red indicate increasing subsidence for the city built upon the bed of a lake.

But how much change?

“…within this imaging period, the ground has sunk by as much as 10 centimetres in some places as a result of the water extraction”

Uh oh. 10 cm equals nearly 4 inches.

Over what period of time?

“…between 20 September 2009 and 30 January 2010”

Parts of Mexico city sunk FOUR INCHES in FOUR MONTHS. One inch. Per month.

“What is particularly noticeable even to anyone on a short visit is the subsidence in the city centre, where two of its most famous landmarks, the Bellas Artes Opera House and the cathedral in the main square, are sinking rapidly,” says Michael Schmidt, coordinator at Conobio, the National Commission for the Exploration and Use of Biodiversity, in Mexico City. “When you look at the cathedral from the front, you can immediately spot that it is leaning.”

Hey, I have an idea — stop pumping so much water.

Even if pumping stopped and the sedimentary layers absorbed moisture again, they would not return to their original thickness,” says geologist Christian Minet of the DLR Institute for Remote Sensing Methodology.

Oh dear.

“Instead, steep and deep groundwater funnels would be formed in the Mexican capital – with the result that various districts in the city would subside. This means that at its front, over the fine-grained marine sediment, the cathedral is sinking, but, on the other hand, the rear part is standing on parts of a former Aztec temple.”

Plan B: build everything on top of former Aztec temples.