Hiroshima residents living nearby first noted that the island seemed to be getting smaller after every storm or typhoon.
The island's soft rock, a material called tuff that is primarily composed of densely compacted volcanic ash, is an ideal habitat for the booming population of nanatsuba-kotsubumushi, Okimura said.
(Related photo: "Giant Jellyfish Invade Japan" [January 19, 2006].)
Through normal weathering, it would usually take thousands of years for the elements to reduce an island the size of Hoboro to debris, he noted.
Geological Oddity
But some experts have estimated that, at the current rate, the island may be gone within a century.
"This is a quite fascinating bio-erosion phenomenon that I've never seen anywhere else," said Akihiro Kano, an associate professor of historical geology at Hiroshima University.
"From Professor Okimura's evidence, it is obvious that these creatures are promoting the erosion of this island at a very rapid pace.
"By looking at the older images of the island and comparing them with the way it looks today, the scale of the changes is incredible," he added.
"Also, I don't think there has been another case of such a high density of these creatures, so there must be some interesting reasons for that we can learn more about."
What's more, Hoboro appears to be something of a geological oddity, Okimura said, with no other islands in the immediate area made of the same material.
Although he prefers not to put a time scale on the island's destruction, Okimura added that it's unclear where the burrowing creatures will go when Hoboro does ultimately disappear beneath the waves.
Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
|
SOURCES AND RELATED WEB SITES
|
