What is an alluvial fan? An alluvial fan is a cone of debris that builds up where a river flows out of a deep mountain valley onto a plain.

Fan

Alluvium fans highlighted by the yellow circles.

An alluvial fan is a large triangular area of material that has been dumped in a lake or the sea by a river. Another name for a very large alluvial fan is a delta.

Quite often these pieces of land are made of silt, which is fertile. Some of the biggest fans have been well know in history. The most famous of all is probably the Nile Delta, where the Ancient Egyptians got most of their food.

Video: A small fan forming. You might be able to find one of these on the edge of a lake near to you.

Explore these further resources...

(These links take you to other parts of our web site, never to outside locations.)

You can search in these books:

You can look in this topic for more books, videos and teacher resources:

Jump to Rivers toolkit screen

The toolkit screen link will take you to a library containing a selection of:
an i-topic, more books, pictures, videos and teacher's stuff related to the search word.

Fan