Author: Cara Giaimo / Source: Atlas Obscura
Every once in a while, Josh Calder goes out to Rock Creek in his home city of Washington, D.C., and peers across the water at a little gravel bar. The small spit used to barely be visible at all, but it’s growing more robust, and vegetation has started cropping up there.
When Calder swings by, he’s checking to see if a specific alchemy has occurred. He’s waiting for it to become an island.If you close your eyes and picture an island, what do you see? In the popular imagination, the word conjures up somewhere stable, contained, and understandable: maybe a little rocky outcropping covered with gulls, or a round disc of sand with a single palm tree. In reality, experts say, things are a bit more like that gravel bar: shifty, complicated, and full of gray areas. If you want to get to know islands, it helps to start by asking yourself what the heck they are.
The geographer Stephen Royle, who has published various books about islands, has a simple definition at hand. “An island is a body of land surrounded by water, above water at high tide, and smaller than a continent,” he says. David Clague and Rosemary Gillespie, co-editors of the Encyclopedia of Islands, take a slightly wider view. “I think [of islands] in terms of isolation from the surrounding area,” says Clague. “They’re bits of real estate with some boundary that prevents or severely inhibits exchange of [animal and plant life].” Under this definition, underwater volcanoes can be islands.
So can mountaintops, which often house plants and animals that wouldn’t be able to survive at lower elevations.But thinking about islands is tricky. As soon as you reach the solid ground of one answer, more questions spread out ahead of you in an endless archipelago. Say you take Clague and Gillespie’s broad ecological definition. In that case, what counts as isolation? Start considering this query at different physical scales, and the possibilities proliferate: “Water-filled tree holes can serve as islands for many invertebrates,” Gillespie points out, “and an animal’s body is an island to the parasites it contains.” (Maybe it’s time to revise our adages: No man is an island, except to his own gut flora.)
This may tempt you to hop back to that first, more traditional answer, in which an island is a body of land surrounded by water. That definition comes with an upper limit—“smaller than a continent.” But now we have to define the lower one: how big does an island have to…
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