"It's appeared on an ornamental coin, it was visited by Sir Walter Scott, it inspired a short story by James Fenimore Cooper, it was depth-charged by the U.S. military who mistook it for a Libyan submarine."
BLDGBLOG has a lyrical post up about the disappearing island of Ferdinandea. The semi-mythical Italian island is actually the tip of an underwater volcano, whose occasional fits of gas and cresting rocks were once mistaken for sea monsters. Ferdinandea appears only occasionally above the surface of the sea, but when she does rise, nearby nations get very excited.
For example, during Ferdinandea's brief appearance in 1831, the Italian, British, Bourbon and French navies all scrambled to plant a flag and call Ferdinandea their own (the French actually called the island Julia).
And although Ferdinandea has remained submerged for more than a century now, in 2000, local Sicilians sent divers to plant a 150kg marble plaque and a Sicilian flag on the underwater island. Just in case of argument, the plaque's inscription reads, "This piece of land, once Ferdinandea, belonged and shall always belong to the Sicilian people".
The sentiment here isn't nationalism, it's avarice. When Ferdinandea does surface, whoever owns the land will own the surrounding waters. In the 19th century, European empires hoped the island would be a good stop on the Mediterranean trade routes. Today, the most valuable part of the sea is not how you get across it, but what lies beneath: oil.
Sounding for deep sea hydrocarbons is one of the last frontiers for the energy industry, which makes the ocean floor surprisingly hot real estate. Of course, you can't buy the high seas; only dry land can be legitimately owned and sold. But even the barest jutting rock may come with a lot of potentially lucrative sea-space.
Consider the Pacific island nation of Kiribati (soon to be submerged, too). It's a small and mostly insignificant sprinkling of beaches, but its exclusive maritime zone is huge. The 100,000 Kiribatians who live there own a slice of ocean that’s as big as India (population: 1,210,193,422).
More than half of the world’s oil resources are already depleted, so disappearing islands and the border changes they entail can put fuel-hungry nations on edge. In 2009, a Mexican-owned island called Bermeja disappeared from the oil-rich Gulf of Mexico. Locals immediately accused the American C.I.A. of torpedoing it.