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7

ALLUVIAL FANS and DELTAS 

Two of the most common landforms composed of alluvium (or sediment) are alluvial fans and deltas. They can be similar in shape, and are deposited for the same reason - an abrupt loss in competence in a stream. Alluvial fans are deposited on land and deltas are deposited in a body of water (lakes, oceans). 

Alluvial Fans

STS081.ESC.09162608 China

Alluvial Fans develop where a high-gradient stream leaves a narrow valley in mountainous terrain and comes out suddenly into a broad, flat plain or valley floor. Usually coarse material is deposited near the apex or top, of the fan, and finer material is carried to the base of the deposit. 

The image below is a fabulous example of an alluvial fan. Identify the present-day stream and outline the extent of the alluvial fan. How large is this alluvial? (You should be able to figure it out by using the scale.)

[[image]]

Transcription Notes:
Image on the bottom of an alluvial fan, is in black and white.