火山列岛 16

Across the South Pacific,

time continues to work its magic on rock.

Millions of years of erosion and sinking have reduced the volcanic mount of Maupiti

to little more than a hill.

Eventually, this hill will disappear too.

And when it does,

it will look like this - Mataiva,

a coral atoll.

Rising above the waves,

a coral atoll's reef surrounds a shallow lagoon.

Where there was once a mighty peak,

now there is only water.

There are thousands of atolls like Mataiva dotted around the South Pacific,

their size and shape determined by the original volcano.

Some atolls are round, their rings unbroken,

while others have been bent out of shape by ocean currents and earthquakes.

And a few span huge distances,

a testament to volcanoes whose size and power were once truly colossal.

Rangiroa in French Polynesia.

Over 30 miles wide,

its lagoon is so large that if you were floating in its centre,

you wouldn't see land in any direction.