What are alluvial fans, and why are they common in desert ...

[vicotolentino]

What are alluvial fans, and why are they common in desert mountain ranges? What will be an ideal response?

Question 2

Why are flash floods and sheet flows common in deserts? What do these events have to do with
  erosion in the desert? What will be an ideal response?

[CourtneyCNorton]

Answer to Question 1

Alluvial fans form when sediment-laden streams flow out from the generally straight steep mountain
fronts, usually during an intense storm. When the stream hits the valley floor, its gradient goes from
steep to shallow, and it deposits its sediment load. The sediment spreads out laterally, forming a gently
sloping and poorly sorted fan-shaped deposit.

Answer to Question 2

Although deserts receive little rain, what they do get often comes in heavy, localized cloudbursts. The
ground cannot absorb all of this water because of the abundance of regolith and the hardness of the soil
surface. The lack of vegetation allows runoff to be rapid especially on slopes. Water runs quickly into
dry stream channels, resulting in flash floods and sheet flows. Streams carve steep gullies and
overflow their banks. A tremendous amount of sediment is transported rapidly, and very little is moved
at other times.