火山列岛 10

Measured from the sea floor,

The wekiu's home is the tallest mountain in the world,

about a kilometre taller than Everest

But it won't hold this record forever

After millions of years of growth,

This mountain is slowly but surely losing height

At a rate of 20 centimetres every 100 years

In fact, it's so massive that it's buckling the sea floor beneath it

And sinking into the ocean

Mauna Kea's future can be glimpsed in the Society Islands of French Polynesia

The peaks of these islands once rose much higher than this from the ocean floor

It's been almost 2 million years since their volcanoes first broke through the ocean

But erosion is washing away their volcanic cores

Now the only growth occurs just below sea level,

On what was once the mountain's sloping flanks

In the shallow waters around an island's base,

Coral reefs rise towards the surface