You’re right, I was the backwards one.
It isn’t just a matter of the ice. Greenland sits atop 50 km of continental crust. If the ice melts the continent will rise above the sea as isostatic rebound occurs. It is already rising at up to 2cm a year due to the current melting. It could get a lot faster.
Going to take a few thousands years, but that is only a moment in geological time. Greenland has been part of a true continent for a few billion years.
The only reason we don’t notice is because the ice has pushed it down. But it hasn’t gone away. The idea that it is made up of a few disconnected islands is an idea based upon current sea levels rather than the reality of its geology. Choosing the current sea level to define the boundary is very arbitrary, and really not very useful except for human geopolitics. Geology tends to outlive such transient ideas and species.
This sounds like it could involve earthquakes.
Since we’re talking rebound over tens of millennia, the time-density of earthquakes will be low. And you’re more likely to end up with a long long list of small ones, not some Hollywood extravaganza where e.g. 20% of Greenland shoots skyward 100 meters over 2 minutes. That would be a planet ringing, ocean stirring kablooey.
and such a map is drawn for clarity of the big picture concept, not for using for detailed analysis of any one spot.
The lines aren’t even on the true even following the true location accurately..
But in many places, there is no such one single line… there are fracture zones. Like a shingle roof that is tearing apart, it still looks as one .. but its many.
What is drawn as the Nazca plate is more of a shingle roof…
The area of New Zealand has a history of being a minor plate , broken off Australia.
I have a problem with those maps showing Greenland/Antarctica without ice sheets. They depict landmasses as fractured archipelagos, but ice sheets are heavy, millions of tons. Plates are not made of rubber but they do have some elasticity; without all that weight, those submerged masses would rise up. Someone better in geology please correct me if I’m wrong.
That’s already been pointed out by @Francis_Vaughan four posts above yours.
Sure – if the ice was receding at a geological timescale, the rock below might rebound from the mantle at about the same timescale and we’d never see the archipelago scenario. But the ice is melting at an industrial scale. In 100 or 200 years, the map may well look like the illustrations above.
That will cause the land to rebound faster, at least at first. Isostatic rebound is not linear. When the ice first melts, it rebounds fairly fast and then slows over a very long time. So there might be some islands immediately after the melting, but within a few years, most of them may merge.
That would bring up the question of how fast is “fast” rebound? I would believe several feet a year, maybe - but not hundreds of feet. That sounds unrealistic. A mile or two of ice is heavy, but 10 miles of rock or more in the earth’s crust is a lot more mass by comparison.
In geology fast is only a few thousand years. It mostly goes in jumps of a few feet at a time every few hundred years. A jump like that is a major earthquake.
I would not expect the fast rebound to go in sudden jumps. The rebound that’s already going on, in Greenland and elsewhere, is steady, albeit very slow. I don’t think we’ve seen fast rebound, so perhaps my expectation is wrong.
@MrDibble may have some expertise here.
IMO, with some research but no expertise. …
My take is even “fast” rebound is multiple inches per year. Maybe an occasional earthquake, but not many. IMO no human will live long enough to see any material change in coastlines due solely to isostatic rebound during their lifetime.
This is especially true in a place, like Greenland, with significant bluffs & mountains and such. For two adjacent islands to merge due to rebound, the landmass has to go up more than the depth of the water between them was deep. In a place loaded with deep fjords and such, you’re gonna need a lot of landrise to bring the bottom of a fjord to the surface.
Contrast that with, e.g., much of the US east coast, where a meter of rise or fall between land and ocean can move coastlines far enough to matter a lot to coastal cities.
Further, if we melt the Greenland ice to expose these islands that folks are supposing will promptly merge, well, we just raised sea level by ~8 meters, so the amount of isostatic rebound needed to connect any two islands just increased by the same 8 meters.
If it’s the weight of ice holding things down, isn’t the weight of water also a factor slowing the rebound?
There are places (Gulf of Bothnia, Hudson Bay) where this would not be the case - where islands have merged or coastlines receded in a generation (and this is long after the initial fast rebound stage, when isostasy has settled somewhat).
But you’re right that Greenland doesn’t have that same shallow bay situation.
I’m not commenting on the speed land would rise if the ice sheet completely melts, but I don’t think this really follows (though IANA geographer). Fjords and glacial valleys only come into play at the edge of the ice sheet - the middle of the land mass the land, whether submerged or not, appears to be more level. Also in many places the rise in overall sea level might be more than counterbalanced by the dumping of glacial till.
So, after the ice sheet melts, all glacial debris is dumped and the sea level rises, I do not think it makes sense to assume that there might not be many places where there is an area of land a few metres above the new sea level, another one a mile away, and a bit of sea between them that is never more than a few metres deep.
Take Ireland, where exactly this scenario has happened on a smaller scale. It was completely covered by an ice sheet 25000 years ago that extended way out into the Atlantic (parts of the island are still rebounding, but not as fast as the sea is rising, and it’s not my concern here). Find Clew Bay on a map and zoom in on its eastern shore. Then find Strangford Lough and zoom in on its western shore. All those little islands are half submerged drumlins, left by the glaciers/ice sheet. The belt of drumlins extends all the way from Clew Bay to Strangford Lough, and I assume it is (or used to be) detectable under the sea as well. You can well imagine that if the land was rebounding fast enough, islands would still be appearing, joining together and then becoming part of the mainland. IMO there’s no reason to think this wouldn’t happen anywhere in the vast interior of Greenland.
On another topic that was being discussed here, tiny earthquakes related to isostatic rebound are apparently still recorded in Scotland on ancient fault lines. I’ve never noticed one.
ah, like you can see the islands in Chesapeake Bay disappearing as the continent adjusts to the relief of losing the ice sheets… which is a good example of how slow it is, USA is still adjusting to the loss of the ice.
But in the hypothetical Greenland case you could measure it, but its not fast … far slower than the ice is lost . Also it creates droop at the edge ? the middle of the land mass will rise more than the coast, because the coast is held by its connection to the unaffected crust.