Rakatu

Rakatu was a small island in the Aqua Magna sea and former home to the Jardel species.

History
It was brought into existence along with Spherus Magna through an unknown means. It was carried, along with the rest of the southern ocean, into space during the Shattering.

It was pulverized when the Great Spirit Robot fell from orbit, landing on the island and killing all but one of its natives.

Geology
Nothing is known at this point about its geology, but it is likely to be revealed soon.

Trivia

 * This is one point where the Altronia Continuity may in fact break Bionicle canon. It is said that it was an "endless ocean" on Agua Magna, but that was after the Robot fell, so it's truly unclear at this point wether or not the story did break canon at all.