<p>While the weight of the population removed might not have much effect, stopping the removal of groundwater could potentially have a fairly large effect on the height relative to sea level. Lots of places are subject to &quot;land subsidence&quot;, which is the vertical sinking of land due to groundwater removal and subsequent settling. The most notable example I have heard about recently is Jakarta, but other arid places also suffer from it. The east coast doesn't count as arid, but the USGS claims that 45 US states suffer from it, so it stands to reason that some of those are on the East coast</p>
<p><a href="https://www.usgs.gov/special-topics/water-science-school/science/land-subsidence#overview" rel="noreferrer">https://www.usgs.gov/special-topics/water-science-school/science/land-subsidence#overview</a></p>

CC BY-SA 4.0
2022-12-08T00:27:50.513Z
Yes. I've heard of that living in California with droughts, we have the issue here.
Alexis Wilke
CC BY-SA 4.0
2022-12-08T21:18:31.820Z
My understanding is that subsidence due to groundwater removal (up to 20 feet in some parts of California) is largely (or even entirely) irreversible. Stopping the further removal of groundwater therefore simply retains the status quo, meaning the effect on elevation relative to sea level would be approximately zero.
njuffa
CC BY-SA 4.0
2022-12-09T21:36:28.463Z
I would expect some rebound with water extraction ceasing but highly dependent on the local subsoil characteristics; lots of it - most? - will be too compacted. Groundwater replenishment as a cause of land rise seems likely to have only small and localized effects. Loss of mass from groundwater loss ought to have a similar gravity effect (direction) on ocean water and coastal sea levels as ice loss - apparent (but not actual) land rise. Isostatic (actual) rise and from lost and regained mass will have a slow, delayed effect.
Ken Fabian
CC BY-SA 4.0
2022-12-07T21:37:02.263Z
2022-12-07T21:37:02.263Z
Tom Pridham
<p>The mass of human bodies across the US East coast (about 120 million for the East coast States) is very small compared to Greenland ice mass loss, which (according to Grace Satellite data) has averaged 273 billion metric tons per year since 2002 - about 5 trillion tons over the last 20 years, ie about 1/40,000th based on a generous body mass of 100kg (it is closer to 80kg) if my arithmetic is correct. (I had to edit because my arithmetic <em>wasn't</em> first time around).</p>
<p>I don't know if that would make a <em>measurable</em> difference to the gravity effect of land masses on nearby sea levels - that depends on how accurate the measurements - but it won't be <em>significant</em>.</p>
<p>The mass of buildings, cars trucks, machinery would be larger than that but a lot of that mass would be made out of materials like gravels and sands that were mined locally. Again, it won't be significant.</p>
<p><a href="https://i.sstatic.net/pwc3y.png" rel="noreferrer"><img src="https://i.sstatic.net/pwc3y.png" alt="Greenland Ice Mass Loss" /></a></p>

CC BY-SA 4.0
2022-12-07T00:50:33.813Z
To add to this, the average weight of [Americans in 2020](https://news.gallup.com/poll/328241/americans-average-weight-holds-steady-2020.aspx) was 181 lb (82 kg). With 120 M Americans on the east coast, their total weight would be 9.84 Mt. The amount of ice lost in Greenland each year (273 Gt) is 27 744 times the weight of people of the US east coast. The weight of people on the US east coast is insignificant by comparison.
Fred
CC BY-SA 4.0
2022-12-07T01:27:25.507Z
@Fred - sounds like my 1/40,000th of what Greenland lost over 2 decades is a significant overestimation.
Ken Fabian
CC BY-SA 4.0
2022-12-07T18:26:22.103Z
If [Wikipedia](https://en.wikipedia.org/wiki/Biomass_(ecology)) is accurate, 273Gt is about half the world's multicellular biomass, and humans account for about 65Mt. US east coast humans are about 1.5% of that by number, surely more by weight (relatively few children, and fatter adults) but I think less than Fred's estimate which IIUC multiplies adult weight by population. Also, if there were no humans in the region but with an otherwise unchanged environment, there would probably be a lot more plants, ants, etc. so the local biomass would probably be heavier (but still negligibly so)!
Gilles 'SO- stop being evil'
CC BY-SA 4.0
2022-12-06T22:06:28.750Z
2022-12-06T22:18:19.627Z
2022-12-06T22:18:19.627Z
Ken Fabian
<p>I watched a documentary about research on the coasts of Greenland where the sea level has <em>fallen</em>. According to the research, this is because a lot of the glaciers have melted, resulting in less weight on the land and a upward push by the magma under Greenland.</p>
<p>I'm wondering whether the US East Coast could also rise if all the people living there were to move away far enough for the weight to decrease. Since there are some 100 million people living there, I would imagine that's a lot of weight. However, I am thinking that since the inland US is part of a large continent, the magma would not be able to push it up like a &quot;small&quot; island like Greenland.</p>
<p>Do we currently have sufficient metrics to calculate such movements with fairly good accuracy?</p>
<p>Here is an article for reference:
<a href="https://www.sciencenews.org/article/jacky-austermann-climate-sn-10-scientists-to-watch" rel="nofollow noreferrer">https://www.sciencenews.org/article/jacky-austermann-climate-sn-10-scientists-to-watch</a></p>

CC BY-SA 4.0
2022-12-06T21:29:07.857Z
Some thoughts: 1/ this phenomenon is called "isostatic rebound" and has nothing to do with magma (the mantle is solid); 2/ you don't need an island to see the effect, it also occurs in Scandinavia for instance; 3/ we are talking kilometer thick of ice (order of magnitude), so about one million kilograms per square meter. Assuming the average American weighs 100 kg (for the sake of simplicity), you'd need 10,000 people per square meter to get the same effect. New York has 10,000 people per square kilometer.
Jean-Marie Prival
CC BY-SA 4.0
2022-12-07T10:29:44.220Z
Push up of magma does not make sea level fall, it only changes relative coast height. What *is* going on is that the big mass of ice was pulling water towards Greenland (higher sea level close by, lower sea level further away), and with that mass diminishing this effect becomes less, lowering sea level close by.
Jan Doggen
CC BY-SA 4.0
2022-12-07T23:39:23.337Z
Relevant to your interests: https://xray-delta.com/2011/05/10/national-geographic-the-doomsday-machine/
Eric Lippert
CC BY-SA 4.0
2022-12-08T12:28:06.963Z
Related: [What would happen if everyone on earth stood as close to each other as they could and jumped, everyone landing on the ground at the same instant?](https://what-if.xkcd.com/8/)
Stef
CC BY-SA 4.0
2022-12-08T21:14:17.187Z
"I would imagine that's a lot of weight": you could also estimate it, and compare with the weight of a layer of ice on the area that you're considering
njzk2
CC BY-SA 4.0
2022-12-08T22:06:46.467Z
@JanDoggen "the big mass of ice was pulling water towards Greenland" Are you asserting that the mass of Greenland's ice was exerting gravitational pull on the surrounding water making local sea level higher than the mean, rather than the mass of ice pushing down on the land mass, being the primary driver of relative coast height changes?
Glen Yates
CC BY-SA 4.0
2022-12-08T22:09:57.327Z
@njzk2: …or, for a quick and visually striking ballpark estimate, just note that the average density of ice is roughly the same as that of humans. (Both float mostly submerged in water.) The US East Coast may be densely populated, but it's _not_ covered in a layer of human bodies several kilometers deep.
Ilmari Karonen
CC BY-SA 4.0
2022-12-09T10:18:17.217Z
@GlenYates Correct, but I'm not asserting, I'm taking that from others. Google "greenland sea level gravitational effect"
Jan Doggen
CC BY-SA 4.0
2022-12-09T12:16:54.030Z
The North American continent is *still* [rebounding from the thaw of the last glacial period](https://lakeheadca.com/events-education/geology/glacial-lakes-history-1#:~:text=Once%20the%20glaciers%20retreated%2C%20the,%22isostatic%20rebound%22%20by%20geoscientists.)which is causing their shores to slowly move from Canada to the U.S., ever so slightly.
RBarryYoung
<climate-change><plate-tectonics><sea-level>
Would the US East Coast rise if everyone living there moved away?
Alexis Wilke
# Would the US East Coast rise if everyone living there moved away?

(Asked by: username_0 on 2022-12-06)

I watched a documentary about research on the coasts of Greenland where the sea level has *fallen*. According to the research, this is because a lot of the glaciers have melted, resulting in less weight on the land and a upward push by the magma under Greenland.

I'm wondering whether the US East Coast could also rise if all the people living there were to move away far enough for the weight to decrease. Since there are some 100 million people living there, I would imagine that's a lot of weight. However, I am thinking that since the inland US is part of a large continent, the magma would not be able to push it up like a "small" island like Greenland.

Do we currently have sufficient metrics to calculate such movements with fairly good accuracy?

Here is an article for reference:
<https://www.sciencenews.org/article/jacky-austermann-climate-sn-10-scientists-to-watch>

**Tags:** climate-change, plate-tectonics, sea-level

> **Comments:**
> **username_1**: Some thoughts: 1/ this phenomenon is called "isostatic rebound" and has nothing to do with magma (the mantle is solid); 2/ you don't need an island to see the effect, it also occurs in Scandinavia for instance; 3/ we are talking kilometer thick of ice (order of magnitude), so about one million kilograms per square meter. Assuming the average American weighs 100 kg (for the sake of simplicity), you'd need 10,000 people per square meter to get the same effect. New York has 10,000 people per square kilometer.  
> **username_2**: Push up of magma does not make sea level fall, it only changes relative coast height. What *is* going on is that the big mass of ice was pulling water towards Greenland (higher sea level close by, lower sea level further away), and with that mass diminishing this effect becomes less, lowering sea level close by.  
> **username_3**: Relevant to your interests: https://xray-delta.com/2011/05/10/national-geographic-the-doomsday-machine/  
> **username_4**: Related: [What would happen if everyone on earth stood as close to each other as they could and jumped, everyone landing on the ground at the same instant?](https://what-if.xkcd.com/8/)  
> **username_5**: "I would imagine that's a lot of weight": you could also estimate it, and compare with the weight of a layer of ice on the area that you're considering  
> **username_6**: @username_2 "the big mass of ice was pulling water towards Greenland" Are you asserting that the mass of Greenland's ice was exerting gravitational pull on the surrounding water making local sea level higher than the mean, rather than the mass of ice pushing down on the land mass, being the primary driver of relative coast height changes?  
> **username_7**: @username_5: …or, for a quick and visually striking ballpark estimate, just note that the average density of ice is roughly the same as that of humans. (Both float mostly submerged in water.) The US East Coast may be densely populated, but it's _not_ covered in a layer of human bodies several kilometers deep.  
> **username_2**: @username_6 Correct, but I'm not asserting, I'm taking that from others. Google "greenland sea level gravitational effect"  
> **username_8**: The North American continent is *still* [rebounding from the thaw of the last glacial period](https://lakeheadca.com/events-education/geology/glacial-lakes-history-1#:~:text=Once%20the%20glaciers%20retreated%2C%20the,%22isostatic%20rebound%22%20by%20geoscientists.)which is causing their shores to slowly move from Canada to the U.S., ever so slightly.  

---

## 2 answers

### Answer by username_11 on 2022-12-06. Score: 17 | Accepted answer

The mass of human bodies across the US East coast (about 120 million for the East coast States) is very small compared to Greenland ice mass loss, which (according to Grace Satellite data) has averaged 273 billion metric tons per year since 2002 - about 5 trillion tons over the last 20 years, ie about 1/40,000th based on a generous body mass of 100kg (it is closer to 80kg) if my arithmetic is correct. (I had to edit because my arithmetic *wasn't* first time around).

I don't know if that would make a *measurable* difference to the gravity effect of land masses on nearby sea levels - that depends on how accurate the measurements - but it won't be *significant*.

The mass of buildings, cars trucks, machinery would be larger than that but a lot of that mass would be made out of materials like gravels and sands that were mined locally. Again, it won't be significant.

[![Greenland Ice Mass Loss](https://i.sstatic.net/pwc3y.png)](https://i.sstatic.net/pwc3y.png)

> **Comments:**
> **username_12**: To add to this, the average weight of [Americans in 2020](https://news.gallup.com/poll/328241/americans-average-weight-holds-steady-2020.aspx) was 181 lb (82 kg). With 120 M Americans on the east coast, their total weight would be 9.84 Mt. The amount of ice lost in Greenland each year (273 Gt) is 27 744 times the weight of people of the US east coast. The weight of people on the US east coast is insignificant by comparison.  
> **username_11**: @username_12 - sounds like my 1/40,000th of what Greenland lost over 2 decades is a significant overestimation.  
> **username_13**: If [Wikipedia](https://en.wikipedia.org/wiki/Biomass_(ecology)) is accurate, 273Gt is about half the world's multicellular biomass, and humans account for about 65Mt. US east coast humans are about 1.5% of that by number, surely more by weight (relatively few children, and fatter adults) but I think less than username_12's estimate which IIUC multiplies adult weight by population. Also, if there were no humans in the region but with an otherwise unchanged environment, there would probably be a lot more plants, ants, etc. so the local biomass would probably be heavier (but still negligibly so)!  

---

### Answer by username_9 on 2022-12-07. Score: 7

While the weight of the population removed might not have much effect, stopping the removal of groundwater could potentially have a fairly large effect on the height relative to sea level. Lots of places are subject to "land subsidence", which is the vertical sinking of land due to groundwater removal and subsequent settling. The most notable example I have heard about recently is Jakarta, but other arid places also suffer from it. The east coast doesn't count as arid, but the USGS claims that 45 US states suffer from it, so it stands to reason that some of those are on the East coast

<https://www.usgs.gov/special-topics/water-science-school/science/land-subsidence#overview>

> **Comments:**
> **username_0**: Yes. I've heard of that living in California with droughts, we have the issue here.  
> **username_10**: My understanding is that subsidence due to groundwater removal (up to 20 feet in some parts of California) is largely (or even entirely) irreversible. Stopping the further removal of groundwater therefore simply retains the status quo, meaning the effect on elevation relative to sea level would be approximately zero.  
> **username_11**: I would expect some rebound with water extraction ceasing but highly dependent on the local subsoil characteristics; lots of it - most? - will be too compacted. Groundwater replenishment as a cause of land rise seems likely to have only small and localized effects. Loss of mass from groundwater loss ought to have a similar gravity effect (direction) on ocean water and coastal sea levels as ice loss - apparent (but not actual) land rise. Isostatic (actual) rise and from lost and regained mass will have a slow, delayed effect.  

---

