Bifurcation: The secret giant islands formed when rivers split

The article that follows that one is also very interesting and worth reading. It shows how a coastline that existed 100 million years ago and cut through modern day Alabama is still visible in demographic and election maps. (By a crazy coincidence, I just dug up that article and sent it to someone not even half an hour ago, since we were talking about geology and I remembered reading it. Then I go to HN and see this posted.)

1. https://starkeycomics.com/2021/06/11/how-a-coastline-100-mil...

This is not to take away from the fun of investigating and identifying these ‘bifurcation islands’, but on the question of whether they qualify as ‘islands’:

> Like a delta island, it is surrounded entirely by sea and rivers. As an area of land separate from a continent, permanently and entirely surrounded by water, it seems to fit every definition of an island I can find.

I agree that by ‘Air Bud’ rules these qualify as islands (‘ain’t no rule says an island can’t have one end halfway up a mountain and the other at sea level’) but I think there is a reason why we don’t instinctively feel like they qualify as ‘proper islands’.

Specifically, I think the instinctive definition of an island is that it emerges from the water surrounding it at a consistent elevation. It has a shoreline that is broadly level.

The delta islands that he identifies as being basically the same as bifurcation islands are typically surrounded by tidal water on all sides so their shoreline is all at sea level.

Counterpoint, though: Goat Island, which is in the middle of Niagara Falls, and has one end at the elevation of Lake Erie and the other at the lower elevation of Lake Ontario. Does this feel like a ‘proper island’? I know in my mind I sort of struggle to think of Goat Island as being an island, not two islands that happen to be right next to one another… but I can adjust my mental definition of island to account for it; but extending it to the continent-spanning bifurcation islands still feels too much of a stretch.

This is like the ‘dwarf planet’ problem - there wasn’t a good way to make Pluto a planet without making a lot of things that definitely aren’t planets also count as planets.

Is there a good way to make Goat Island an island, without also making the bifurcation islands into islands?

Also… Australia is clearly an island by this definition. But then so is Antarctica.. and the entire Americas. And the Eurasian/African supercontinent…

> The Missouri is the largest tributary of the Mississippi River, which flows into the Gulf of Mexico

He must mean longest. This chart[0] shows that the Ohio is by far the largest tributary of the Mississippi by volumetric flow, and also shows the Atchafalaya bifurcation. However, the wiki articles for the Missouri[1] and Ohio[2] show average discharges into the Mississippi of 87,520 cu ft/s and 281,000 cu ft/s, respectively. Not as great a difference as the first chart [0] shows, but still significantly different. Even more interesting, since the Missouri drainage basin is about 2.5x larger.

[0]https://en.wikipedia.org/wiki/Mississippi_River#/media/File:...

[1]https://en.wikipedia.org/wiki/Missouri_River

[2]https://en.wikipedia.org/wiki/Ohio_River

The parting of the waters in the USA is such an interesting landmark for just how uninteresting it actually is in person. Looks like any other split in a forest river, only thing that marks it is a sign on a tree that you can only get to after a long wilderness hike.

https://en.wikipedia.org/wiki/Parting_of_the_Waters

https://www.anotherlongwalk.com/2022/07/day-119-parting-of-w...

I though this about running multiple nvme disks on single PCIE slot. https://www.asus.com/support/faq/1037507/

Most of the population of Bangladesh lives on what is technically an island created by the forking of the Brahmaputra, whose distributaries rejoin 150 miles away (as the crow flies). https://en.wikipedia.org/wiki/Brahmaputra_River#Bangladesh

As always, there's an xkcd for that: https://xkcd.com/2838/

Very cool, I just learned about these recently. I wonder, at what point does something become not eligible to be an island? Like, that biggest island looks like almost half of North America. Doesn't that make the other half an even bigger island?

It’s surprising how common this is.

Other examples: https://en.wikipedia.org/wiki/River_bifurcation#Examples

Bifurcation occurs at the Great Lakes, where the Mississippi flows into the gulf and the St. Lawrence empties into the Atlantic. This forms the “great loop”, a circumnavigation course known by many power boaters . This makes about half of the United States and island by your definitions.