🟩 SECTION 2: RIVER EROSION PROCESSES

What are the four processes of river erosion?

The four processes are:

• Hydraulic action

• Abrasion, also called corrasion

• Attrition

• Solution, also called corrosion

Each process erodes material in a different way.

What is hydraulic action?

Hydraulic action occurs when the force of moving water acts against the riverbed or riverbanks and dislodges material.

Water may also force air into cracks in the rock. The pressure can weaken the rock and help break pieces away.

Example: Fast-flowing water strikes a riverbank and removes pieces of rock.

Memory tip: Hydraulic action = the force of water.

What is abrasion?

Abrasion occurs when rock fragments carried by moving water scrape, grind or wear away the riverbed and riverbanks.

As the fragments move along the channel, they act like tools that gradually wear down the rock surface.

Abrasion is also called corrasion.

Example: Stones carried by a river scrape against the riverbed and gradually wear it away.

Memory tip: Abrasion = rocks scrape the channel.

What is attrition?

Attrition occurs when rock fragments carried by a river collide with one another.

These collisions cause the fragments to break into smaller pieces and become smoother and rounder.

Example: Angular stones collide while travelling downstream and gradually become smaller and rounder.

Memory tip: Attrition = rocks collide with other rocks

What is solution?

Solution occurs when soluble minerals in rock dissolve in water and are carried away.

It is a form of chemical erosion.

Solution is also called corrosion in the terminology used in your material.

Example: Water dissolves soluble minerals from a rock surface and transports the dissolved material away.

Memory tip: Solution = minerals dissolve.

What is the difference between hydraulic action and abrasion?

Hydraulic action: The force of moving water dislodges material.

Abrasion: Rock fragments carried by the water scrape against the riverbed and banks.

Application:

If water strikes a riverbank and breaks rock away, think of hydraulic action.

If stones carried by the river scrape against the riverbed, think of abrasion.

What is the difference between abrasion and attrition?

Abrasion occurs when transported rock fragments wear away the riverbed and banks.

Attrition occurs when transported rock fragments collide with one another and wear each other down.

Exam tip: Be precise about what is being worn away.

• Abrasion: the channel.

• Attrition: the particles themselves.

What is the difference between solution and the other three river erosion processes?

Solution is a chemical process because soluble minerals dissolve in water.

The other three processes involve physical action:

• Hydraulic action: force of water.

• Abrasion: rock fragments scrape the channel.

• Attrition: rock fragments collide with one another.

Key distinction: Solution involves dissolved minerals rather than simply breaking or scraping rock.

A river carries stones that scrape against its bed. Which erosion process is occurring?

Abrasion.

The stones are being transported by the river and are scraping against the channel, wearing away the riverbed.

A river carries angular stones that collide and become rounded. Which erosion process is occurring?

Attrition.

The stones collide with one another and gradually become smaller, smoother and rounder.

Water strikes a crack in a riverbank and forces pieces of rock away. Which process is occurring?

Hydraulic action.

The force of the moving water acts against the rock and dislodges material.

Water dissolves minerals from a rock surface. Which process is occurring?

Solution, also called corrosion.

The minerals dissolve in the water and are carried away.