Rivers Flashcards
Abrasion
A type of erosion involving rock particles being scraped against, and wearing away, the surface of other rocks.
Attrition
A type of erosion involving rock fragments being ground together to become smaller, smoother and more rounder.
Braiding
A braided river is a type of river that form a network of many branches within a channel.
Confluence
When two or more flowing bodies of water join together to form a single channel.
Corrosion
When water gets in cracks or holes in material and dissolves the rock through chemical changes.
Erosion
The wearing away of material.
Drainage/river basin/watershed
The area of land drained by a river and its tributaries.
Fault
A fracture or zone of fractures between two blocks of rock.
Floodplain
An area of flat land alongside a river.
Gorge
A narrow valley with steep, rocky walls found further down a river from a waterfall. A gorge is formed as a waterfall moves backwards from erosion.
Hydraulic action
When water enters cracks in rocks and compresses the air, which dislodges the rock and erodes it.
Impermeable
Something water cannot pass through.
Interception
When precipitation doesn’t reach the soil and is instead caught by the canopy.
Infiltration
The process by which water enters the soil.
Lower course
The final section of a river, where it flows into another body of water.
Middle course
The second section of the river, between the upper and lower course.
Mouth
The place where the river enters the larger body of water, found at the end of the lower course.
Oxbow lake
The remains of meanders in rivers, stillwater lakes.
Porous
Porous rocks contain empty spaces in which fluids can be stored.
Rapids
Areas of fast-flowing, shallow water in a stream.
Plunge pool
A pool at the bottom of a waterfall caused by erosion.
What are some characteristics of the Upper Valley?
- Vertical erosion with hydraulic action, abrasion and attrition being the dominant processes.
- Traction and saltation at high flow.
- Load size is large and angular.
- V shaped valleys.
- Begins with the source.
What are some characteristics of the Middle Reaches?
- Channel is deeper and wider.
- Vertical erosion decreasing in importance, more lateral erosion and deposition.
- Suspension is the main mode of transport.
- Load is becoming smaller and less angular.
What are some characteristics of the Lower Reaches?
- Channel is at its widest and deepest, and may be tidal.
- Deposition more important than erosion.
- Fine material deposited.
- Large amount of load but the size is very small and very rounded.
- Ends in the mouth.
How is a waterfall formed?
There is a layer of hard rock on a layer of soft rock. The water erodes the soft rock below the hard rock, and creates a plunge pool and an overhang. The overhang eventually collapsed from its weight, erosion and weathering. The collapsed rocks are used as abrasion and erosion tools. The waterfall retreats back upstream to create a gorge.
How are meanders formed?
They are formed by deposition and erosion. The river encounters an obstacle, and has to change paths to get around it. The faster current is on the outside bend, the slower one on the inside bend. The outside bank is undercut from erosion, and the material is deposited on the inside of the bend. This forms a river cliff and a slip-off slope.
How are oxbow lakes formed?
They are formed when the meander neck becomes narrowed from erosion, and then the river breaks through the neck. Deposition then blocks off the meander.
How are floodplains made?
The river is kept within bounds by the banks. When a flood occurs, the river overflows onto the valley plain surrounding. Smaller deposition is carried further, while larger deposition is not carried far, as energy and speed are lost. The layers of successive flood material build up, and the levees increase in height.
