Mechanisms of Change in River Systems
- Rivers are dynamic systems that shape landscapes through three interconnected processes: erosion, transportation, and deposition.
- Each process plays a critical role in altering river channels and creating landforms.
These processes are interconnected and influence each other. For example, erosion provides the sediment that is transported and eventually deposited.
There Are 4 Main Mechanisms to Erosion
Definition
Erosion
Erosion is the process by which rivers wear away their beds, banks, and the surrounding landscape.
1. Hydraulic Action: The Power of Water
- Hydraulic action involves the sheer force of water dislodging material from the riverbed and banks.
- When water flows rapidly, it compresses air into cracks and crevices.
- As the pressure builds, the trapped air expands, causing the rock to break apart.
- Imagine a fast-flowing river crashing against a rocky bank.
- The force of the water pushes air into tiny cracks.
- Over time, this repeated pressure weakens the rock, causing pieces to break off.
2. Abrasion: The River’s Sandpaper
- Abrasion occurs when sediment carried by the river scrapes against the bed and banks, wearing them down.
- This process is most effective when the river is carrying a large load of coarse material, such as gravel or sand.
- Think of a river as a giant piece of sandpaper.
- As it flows, the sediment it carries grinds against the riverbed, gradually smoothing and eroding it.
3. Attrition: Breaking Down the Load
- Attrition refers to the process by which particles in the river collide with each other, breaking into smaller, rounder pieces.
- This reduces the size of the sediment as it moves downstream.
- Imagine pebbles tumbling in a river.
- As they collide, sharp edges break off, and the pebbles become smaller and smoother.
Solution: Chemical Erosion
- Solution (or corrosion) involves the dissolving of soluble minerals, such as calcium carbonate, in the water.
- This process is more pronounced in rivers with acidic water, which can dissolve rocks like limestone.
In areas with limestone bedrock, rivers can carve out features like caves through the process of solution.
TipRemember that solution is a form of chemical erosion, distinct from the physical processes of hydraulic action, abrasion, and attrition.
Transportation: Moving the Load
- Once material is eroded, it is transported downstream by the river.
- The method of transportation depends on the size and weight of the particles, as well as the river’s velocity.
Traction: Rolling Along the Bed
- This process requires high energy and typically occurs during periods of flooding or in the upper course of a river.
Definition
Traction
Traction involves the rolling or dragging of large particles, such as boulders and cobbles, along the riverbed.
During a flood, a river may have enough energy to roll large boulders along its bed through traction.
