Measured from the sea floor,
The wekiu's home is the tallest mountain in the world,
Sbout 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