Definition

Noun: A fan-shaped deposit of sediment, typically gravel and sand, formed where a fast-flowing stream emerges from a steep, narrow mountain valley onto a flatter, broader plain. The sudden decrease in slope causes the stream to lose energy, spread out, and drop its sediment load.

Usage

The term is used in physical geography, geology, and earth sciences to describe a specific type of sedimentary landform. It is a technical term.

Examples

• Noun:
  • The hikers could see a large alluvial cone at the mouth of the canyon.
  • Geologists study the layers within an alluvial cone to understand past flood events.
  • The river deposited sediment, building a prominent alluvial cone where the valley widened.

Advanced Usage

• Alluvial cones are often associated with arid or semi-arid environments where flash floods are common.
• They are similar to, but typically steeper and coarser-grained than, alluvial fans. The terms are sometimes used interchangeably, though a cone often implies a steeper slope.

Variants and Related Words

• Alluvial fan (n): A more general term for a fan-shaped deposit; often larger and with a gentler slope than a cone.
• Debris cone (n): A similar landform composed primarily of coarse, angular rock debris.
• Sediment (n): Solid material, like sand or gravel, that is transported and deposited by water, wind, or ice.

Synonyms

• Alluvial fan (in many contexts)
• Debris cone (when composed of coarser material)

Related Terms (Not Phrasal Verbs)

• Deposition (n): The geological process of dropping or settling sediment.
• Fluvial (adj): Of or relating to rivers.
• Outwash plain (n): A different, glacially-related depositional landform.

Noun

1. a fan-shaped deposit where a fast flowing stream flattens out