I guess if anything, it and Indian Island should be one V-shaped island?
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What about Grand Island, just upriver?
I got the impression that Rhode Island was the islandy part, and Providence plantations was the mainlandy part, and that the state was the combination of the two, and over the years the “and Providence Plantations” part was just dropped from common usage.
On the map it still looks like an island to me: I think it would have to be an order of magnitude or greater size and elevation drop before I started to rethink this. I say “on the map” because the last time I was on Grand Island it didn’t feel like I was on an island, but I was deceived due to the smallness of the Niagara branch I had to cross.
The situation I was addressing was more along the lines of lakes which drain into multiple watersheds. I think there is even one in Canada that drains into multiple oceans. That’s where my “elevation” rule comes into play. If the rivers were replaced with identically-sized sea-level straits, then I would think the separate chunks of land to be islands, but since they are downward-flowing rivers, I don’t consider the pieces of land cut off from each other.
glowacks - good call on the Casiquiare Canal (which I’d never heard of).
I agree that’s a tough one - it’s all-natural (unlike the Chicago River), navigable and permanent, yet, as you say, no-one has ever claimed that north-eastern South America is an island because of it.
On the other hand I note that no-one has challenged Rene-Levasseur Island. I contend that it meets SlackerInc’s definition of “looks like an island on the map” - if you set the scale to show the whole island, you can see a clearly-defined boundary ring of water around it, even though the water is much narrower than the island.
But the we’re back in the game of arbitrary definitions - if Grand Island is an island, then is Alney Island an island? If not, what is the fundamental distinction?
While I was looking up Rene-Levasseur I found a reference to Soisalo “generally considered to be Finland’s largest island” - and yes, it took me about 10 minutes with Google Maps to find the boundary.
The whole Finnish lakeland is designed to drive hydrographers insane - there are thousands of (often-interlinked) lakes, multiple bifurcations some of which ultimately reach the sea hundreds of miles apart and the whole thing merges into the Baltic via the Turku archipelago - and good luck defining where the mainland ends and the archipelago starts.
So any definition we come up with is going to fail for pathological edge cases.
The fact that there’s no English word for “a piece of land completely surrounded by rivers (or lakes)” other than “island” suggests that anyone who has ever defined such places has defined them as islands. If they aren’t islands, what would you call them?
The more I think about it, the more I like Ludovic’s definition, although applied more tightly. If the water all around a piece of land is at the same level, it’s an island—even in cases (which probably aren’t that numerous) where it fails my eye test. Put another way: if it’s a legit island, it should be possible conceptually to remove all water from the world and then fill it back in, starting from the deepest trenches of the ocean, and at some point as “sea level” rises (without the water cycle of precipitation and evaporation) the island in question should be visible with the exact same shape. In the case of “islands” which are sections of mainland bounded by rivers, this will almost never be the case. And then we don’t have to call Finland an archipelago.