As rising oceans threaten NYC, study documents another risk: The city is sinking | Hacker News Reader

As rising oceans threaten NYC, study documents another risk: The city is sinking

apnews.com

36 pointsLinuxBender21 comments

Previous discussion, https://news.ycombinator.com/item?id=35983475

  1-2 millimetres a year, or three quarters of an inch per decade, or two thirds of a foot per century..

  This is a non-problem for Manhattan, which has bedrock not that far down across the entire island..

  This is all based on the authors' estimations, not actual measurements or observations..

All buildings subside, because we can’t inject concrete and rebar down into the earth’s core. So long as they do so evenly (so not like the Tower of Pisa) it’s not a massive problem.

For alarming rates of ground subsidence, Mexico City subsides at 50cm a year and Jakarta at 25cm a year, due to excessive groundwater extraction.

I wish they'd actually link to the study. Most of NYC's skyscapers are in Manhattan, and are built in the areas where the Manhattan schist[1] is closest to the surface. The Bronx's geology is similar.

Brooklyn and Queens don't benefit from the same geology, and have always had flooding problems. Those flooding problems are going to get worse with sea rise, but neither borough has the same density of skyrises that Manhattan does. It's not clear without the study whether they accounted for that.

[1]: https://www.nycgovparks.org/parks/j-hood-wright-park/highlig...

Check it out for yourself: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022EF00...

My understanding is that Long Island (Brooklyn and Queens are the westernmost top of Long Island, for those not familiar with the local geography) is the remnants of the mountaintops of the Hudson Valley, that got scraped off during the last Ice Age and pushed into the ocean by the glaciers.

Which means the whole island is essentially built on landfill.

Oh, that article again. Even the article says "In New York City, buildings that exert the most downward pressure are skyscrapers, but most of these are anchored to bedrock (e.g., Barr et al., 2011). Hard rock elastic compression occurs instantaneously after a load is applied, meaning we do not expect to see ongoing subsidence under some of the largest loads unless the bedrock is heavily fractured." Parts of the outer boroughs are on fill, and they seem to be taking data that includes those areas and extrapolating it to the whole city.

There are cities and buildings in far worse shape. Venice, discussed yesterday, is about 400 meters above bedrock. SF's Millennium Tower was built on pilings that didn't go down to bedrock, and it is settling. It's places with shallow-slope river deltas that have the worst problems, because the ground is often sand and silt carried by the river and bedrock is a long way down. In the US, that's only New Orleans.

Hong Kong, though...[1] China has several major river delta cities.

Also, their map label for "Manhattan" is in New Jersey.

[1] https://www.mdpi.com/2072-4292/10/11/1738/htm

The schist thing is kind of a myth. A lot of the Lower Manhattan skyscrapers are built on landfill.

The skyscraper districts are where they are because of transport links; Downtown and Midtown are the places with the most access to all parts of the metropolitan area, because Downtown was the historic center with all the ferry landings and bridges, and Midtown because the rail terminals stopped there.

I wish they'd actually link to the study.

Tag the writer and the AP on Twitter and embarrass them for not including it. This works sometimes, and over time it nudges outlets towards including direct links.

FWIW: this appears to be the referenced study in these news articles. I found this study from The Guardian:

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022EF00...

Is it inaccurate to say that anywhere that is either adding weight above or reducing groundwater capacity below is sinking?

No problem! The sinking of the city will counteract the rising of the ocean.

Oh, wait...

just watching this headline rattle around the internet the last week or so has been hilarious.

This was discussed before - this is a fake study. They did math and modeling, but neglected to actually measure anything.

And they could have, long term GPS is accurate enough to do that.

Also aren’t most landmasses in the northern hemisphere still rising due to the weight of the glaciers being gone?

It's not so clear cut. In the South Baltic, Northern Germany is sinking while in the Gulf of Bothnia up north, ground is rising a lot because it's balancing or something. Or some parts of British Isles are rising while others are sinking. According to this, New York City looks to be relatively neutral: https://en.wikipedia.org/wiki/Post-glacial_rebound

The crust of the earth is floating on liquid rock. It's constantly moving, rising, sinking.

> The crust of the earth is floating on liquid rock.

This is a common misconception. Molten magma under the crust only exists in a few places, the crust by and large rests on the mantle, which is solid. The mantle is extremely thick, but below it eventually is the outer core, which is liquid.

OK liquid was the wrong word. Maybe ductile? The point is the mantle moves under the crust, and this drives plate tectonics. The crust of the earth is constantly shifting, rising, falling. Subduction and all the geological processes that formed the arrangement of the land masses as we know them are still happening.

I think plastic is the term used in geology, but it’s been a long time since my undergrad.

Ductile as I recall refers more to the ability to draw a material into wire.

> We show maps of observed deformation from InSAR and GPS data that demonstrate an average 1–2 mm/year subsidence rate across New York City (Figure 5), which is consistent with values calculated for post-glacial subsidence across much of the U.S. northeast coast

These articles are referencing this study published earlier this month: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022EF00...

I’ll have to read it in depth later but seems the researchers modeled the “subsidence” and compared it with GPS data spanning at least a decade.

Read the other comments in the thread, and the last time this was posted.

"which is consistent with values calculated for post-glacial subsidence across much of the U.S. northeast coast"

Or in other words the entire east coast is moving, and the weight of the buildings in NY add nothing?

Reply on news.ycombinator.com