Not enough straight land wide enough and long enough for even an airport runway!
Lots of time, these coral islands were started on top ofsubmerged volcano that is slowly still going under.
Would an original caldera (partially collapsed) account for the twin "arc's" that make up the current island?
Good question. Without knowing more, I'd stake a first guess on uneven erosion, but it's not unknown for volcanoes to have multiple craters.