Alluvial fan facts for kids
An alluvial fan is a special shape of land made from soil and rocks. It looks like a fan or a triangle. These fans form when a fast-moving river or stream flows out of a narrow valley, like from a mountain range, and spreads onto a flat plain. As the water slows down, it drops the soil, sand, and rocks it was carrying, creating the fan shape.
Alluvial fans are often found at the bottom of mountains that are slowly wearing away. If there's a lot of rain, the area around an alluvial fan can sometimes flood.
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What is an Alluvial Plain?
An alluvial plain is a large, mostly flat area of land. It's built up over a long time by sediment (like mud, sand, and gravel) that rivers drop off. This happens when one or more rivers flow from higher ground, like mountains, onto a flatter area.
Alluvial Plains vs. Floodplains
It's easy to confuse an alluvial plain with a floodplain, but they are a bit different:
- A floodplain is the smaller area that a river floods during a specific time, like during a heavy rain.
- An alluvial plain is a much larger area. It includes many floodplains that have moved and changed over thousands or millions of years.
How Alluvial Fans Form
Alluvial fans are created by the power of moving water.
- When a river flows quickly down a steep slope, it picks up a lot of rocks, sand, and mud.
- As the river leaves the steep valley and reaches a flatter area, it spreads out and slows down.
- When the water slows, it can no longer carry all the heavy material. So, it drops the sediment, building up the fan shape.
- Over time, the river might change its path slightly across the fan, creating new channels and adding more layers of sediment.
Where Can You Find Alluvial Fans?
Alluvial fans are common in many parts of the world.
- They are often seen in dry or desert areas, like the Taklamakan Desert in China or Death Valley in the United States. In these places, water flows strongly only during rare rainstorms.
- You can also find them in mountainous regions where rivers flow from high peaks onto flatter land.
- Scientists have even found evidence of huge alluvial fans on other planets, like Mars, suggesting that water once flowed there!
Images for kids
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Alluvial fan in Death Valley
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Large alluvial fan in Death Valley showing a "toe-trimmed" profile
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Pebble bed in the New Red Sandstone
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Large alluvial fan at the base of the rim of Gale crater, Mars
See Also
In Spanish: Abanico aluvial para niños
