And as the sandstone weathers, new grains break free.
Some of those grains may then accumulate
on a massive scale,
into a sand dune.
In a way, the static, stone mountain
becomes a moving mountain of sand.
But, moving mountains can be dangerous. Let me try and explain why.
Dry areas cover more than one third of the Earth's land surfaces.
Some are already deserts;
others are being seriously degraded by the sand.
Just south of the Sahara we find the Sahel.
The name means "edge of the desert."
And this is the region most closely associated with desertification.
It was here in the late '60s and early '70s
that major droughts brought three million people
to become dependent upon emergency food aid,
with about up to 250,000 dying.
This is a catastrophe waiting to happen again.
And it's one that gets very little attention.
In our accelerated media culture,
desertification is simply too slow