Are cities sinking under their own weight?

Lily Holbrook sinks her teeth into the intriguing idea that cities may literally be on a downward spiral

Lily Holbrook
2nd March 2021
Image Credit: Sua Truong on Unsplash
As an ever-growing human population demands more living space to stay afloat in the modern world, new evidence suggests that there may be a new pressure facing our rapidly developing cities.

Faced with the alarming prospect of rising seas, many cities are already struggling to meet the monumental targets needed to ward off enduring environmental damage. Yet, in the wake of new research from geologist Tom Parsons of the United States Geological Survey (USGS), it is clear that rising sea levels are not the only factor drowning our hopes of coastal colonisation.

San Francisco may have experienced as much as 80 millimetres of sinkage over time

Approximately 10% of the global human population live in coastal areas less than 10 metres above sea level, with many more relying upon coastal areas for sustenance, livelihoods and recreation. But with more people migrating towards the sea and 70% of the world's population expected to live in large cities by 2050, Parsons makes it clear that the effects are beginning to take their toll:

"As global populations move disproportionately toward the coasts, this additional subsidence in combination with expected sea level rise may exacerbate risk associated with inundation."

According to Parsons' calculations of the San Francisco Bay Area, the city may have experienced as much as 80 millimetres (3.1 inches) of sinkage as it underwent vast urban development over time. Combined with a projected sea level rise of 300mm (11.8 inches) by 2050, there is no doubt that subsidence has become an additional cause for concern.

Image Credit: Joshua Sortino on Unsplash

Giving a nod to San Francisco which lies on the famous San Andreas fault where already lies a predisposition to devastating tectonic activity, Parsons writes in his paper:

"Anthropogenic loading effects at tectonically active continental margins are likely greater than more stable continental interiors where the lithosphere tends to be thicker and more rigid."

Moving away from San Francisco, there are a number of other cities facing immediate threats from rising sea levels, all of which may be exacerbated by subsidence: Miami, Rotterdam, Bangkok, Jakarta, Venice and Houston to name just a few.

There's virtually no scenario under which you can imagine Miami existing at the end of the century

Numerous factors may determine the extent of city sinking, from population density to local geology. Excessive groundwater pumping is another culprit, resulting in a change to the volume and pressure of the earth's surface which causes land to subside.

Speaking to Business Insider in 2018, environmental author Jeff Goodell said, "There's virtually no scenario under which you can imagine [Miami] existing at the end of the century," referring to it as "the poster child for a major city in big trouble." With rapidly rising sea levels wreaking havoc on Miami's infrastructure, homes and drinking water supplies, there are concerns that Florida's coastal city may have to raise its structures to stay afloat.

Image Credit: Ryan Parker on Unsplash

If humans have the power to make a literal physical depression on the earth's surface, the need to scrutinise other anthropogenic impacts becomes even more essential.

It is evident that humans have the power to make an impression - but it remains up to us whether that will be our blessing or our downfall.

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AUTHOR: Lily Holbrook
MA Media & Journalism student and science sub-editor for the 20/21 academic year.

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