Stream and River DepositsStream and River Deposits

Chapter 11 Section 2Chapter 11 Section 2

The Ability to ErodeThe Ability to Erode

• GradientGradient: Measure of change in : Measure of change in elevation over a certain distanceelevation over a certain distance

• DischargeDischarge: The amount of water a : The amount of water a stream or river carriesstream or river carries

• LoadLoad: The material carried by a stream: The material carried by a stream

GradientGradient

• The steeper a stream is the more The steeper a stream is the more erosive energy it haserosive energy it has

DischargeDischarge

• The more water a river will discharge The more water a river will discharge the more erosive power it will have.the more erosive power it will have.

LoadLoad

• Load is affected by speed.Load is affected by speed.

– Fast = large particlesFast = large particles– Slow = Smaller particlesSlow = Smaller particles

Stages of a RiverStages of a River

• Rivers go through a “life cycle.”Rivers go through a “life cycle.”

• YouthfulYouthful

• MatureMature

• OldOld

YouthfulYouthful• Youthful riversYouthful rivers have a steep gradient, have a steep gradient,

a steep and narrow channel, and a steep and narrow channel, and many waterfalls. The channel will many waterfalls. The channel will erode deeper, rather than wider.erode deeper, rather than wider.

MatureMature

• Mature Rivers Mature Rivers have a gradient that is have a gradient that is not as steep as a youthful river. They not as steep as a youthful river. They have few falls and rapids. They will have few falls and rapids. They will erode wider rather than deeper.erode wider rather than deeper.

OldOld

• Old rivers have a low gradient and Old rivers have a low gradient and little erosive energy. They deposit little erosive energy. They deposit rather than erode.rather than erode.

Rejuvenated RiversRejuvenated Rivers

• Rejuvenated rivers are mature rivers Rejuvenated rivers are mature rivers that have a steeper gradient due to that have a steeper gradient due to land rising because of tectonic land rising because of tectonic activity.activity.

DepositionDeposition

DeltaDelta• Rivers slow down when they empty Rivers slow down when they empty

into a large body of water.into a large body of water.

• This often causes a fan-shaped This often causes a fan-shaped pattern of deposits called a delta.pattern of deposits called a delta.

Deltas (cont.)Deltas (cont.)• These deltas cause the coast line to These deltas cause the coast line to

grow. grow.

• Deltas are made of mostly mud. Deltas are made of mostly mud. Some of the mud particles come Some of the mud particles come from very far away.from very far away.

Alluvial FansAlluvial Fans• When a fast-moving When a fast-moving

mountain stream mountain stream flows onto a flat plain, flows onto a flat plain, the stream slows very the stream slows very quickly.quickly.

• The deposition forms The deposition forms an alluvial fan.an alluvial fan.

• Alluvial fans form on Alluvial fans form on dry land.dry land.

How do rivers deposit How do rivers deposit sediment?sediment?

• Rivers pick up weathered sediment Rivers pick up weathered sediment during erosion. during erosion.

• Then the sediment is dropped off or Then the sediment is dropped off or laid down.laid down.

• This happens when the speed of This happens when the speed of water decreases.water decreases.

Meandering RiversMeandering Rivers

• Constantly erode material - Cut bankConstantly erode material - Cut bank

• Constantly deposit material - Point barConstantly deposit material - Point bar

• Change their channel course graduallyChange their channel course gradually

• Create floodplains wider than the Create floodplains wider than the channelchannel– Very Fertile soilVery Fertile soil– Subjected to seasonal floodingSubjected to seasonal flooding

Formation of MeandersFormation of Meanders

Point bar deposits

Cut bank erosion

Point bar deposits

}Meander loop

Formation of an Oxbow

Meandering streamflowing fromtop of screento bottom

Maximum erosion

Maximum deposition

Oxbow Lake

Oxbow cuttoff

Meander scars

Flood PlainsFlood Plains• When there is a sudden increase in the When there is a sudden increase in the

volume of water flowing into a stream, it will volume of water flowing into a stream, it will overflow.overflow.

• This is caused by a SUDDEN increase in This is caused by a SUDDEN increase in precipitation or rapid snow melt.precipitation or rapid snow melt.

• The area around a river that forms from The area around a river that forms from sediments deposited during a flood is called a sediments deposited during a flood is called a floodplainfloodplain..

• Each flood adds another layer of sediment.Each flood adds another layer of sediment.

Good FarmingGood Farming• Floodplains are good for farming Floodplains are good for farming

because the periodic floods bring in because the periodic floods bring in new, rich soil.new, rich soil.

ReviewReview

1.1. What is the difference between a What is the difference between a delta and an alluvial fan?delta and an alluvial fan?

2.2. Why are floodplains bad?Why are floodplains bad?

3.3. Why are flood plains good?Why are flood plains good?

4.4. What causes sediment to be What causes sediment to be deposited.deposited.

5.5. What is the relationship between What is the relationship between weathering, erosion, and weathering, erosion, and deposition?deposition?