泛滥之谜 24

More than 60 mountain rivers have flowed into Lake Tana

But only one river flows out, the Blue Nile.

Virtually dry just a few months ago

It has now become a very different river.

The highlanders call these falls Tis Lsat.

It means ''smoking fire''.

This, surely, is a force powerful enough

to carry the great flood thousands of kilometres to the deserts of Egypt.

Gathering speed and power, the floodwaters sweep on into the Blue Nile Gorge.

Well over a thousand metres deep

nearly 20 kilometres wide and over 600 kilometres long

this is Africa's Grand Canyon.

From all over the highlands, other huge rivers pour into the Blue Nile Gorge.

By the time it leaves Ethiopia

the Blue Nile will be 50 times the size it was in the dry season.

Now the Blue Nile is carrying 140 million tonnes of fertile soil.

For a million years

the Blue Nile has been carving this huge gash through the Ethiopian Highlands

grinding down the volcanic rock, grain by grain, to form the enormous gorge.