River Landscapes

Drainage Basin

A river's drainage basin is made up of a few different parts. These key terms are:

Drainage Basin - An area of land drained by a river and its tributaries.
Mouth - The part of the river that connects to a lake or the sea.
Source - Where the river originates.
Tributary - A smaller river that flows into other, larger rivers.
Watershed - The boundary of a river's drainage basin. Usually in higher land.
Confluence - Where multiple rivers meet.

Weathering and Erosion

Definitions:

Weathering - The break-down of rock in situ (at that place).
Erosion - The wearing away of the land by the action of rivers, ice, the wind and the sea.

The difference between weathering and erosion is that erosion involves movement, whereas weathering does not. Also, there are types of weathering - biological, chemical and physical. These are only the categories, as the types are:

Frost Shattering / Freeze-Thaw - Occurs when water gets into a crack in a rock, the water then freezes and expands; this causes the crack to open up, which results in the rock breaking apart.
Onion-Skin Weathering / Exfoliation - The rock is heated by the sun and it expands, then the rock cools down and begins to contract; this means that the rock has become weakened, then surface layers of the rock peel off.
Biological Weathering - Animals will dig into and burrow under rocks and into cracks, this causes the rocks to be undercut and it widens cracks; rocks are then loosened and broken up - which causes rocks to fall apart or collapse.
Chemical Weathering - Rain water contains weak acid and this acid attacks the rock, which causes rocks to dissolve or become weakened.

There are also erosion processes. These are:

Abrasion / Corrasion - The river picks up rocks and rubs them against the beds and banks of the river - this is called sandpapering.
Attrition - The rocks carried by the river are made smooth as they are crashed into one another.
Corrosion - Rocks dissolve in the water's weak acid.
Hydraulic Action - The force of the water crashes into the beds and banks of the river, breaking them up.

There is another set of processes within this category, which are known as the transportation processes. These processes are:

Saltation - Heavier material is bounced along the river bed.
Solution - Dissolved rock is carried invisibly.
Suspension - Light material is carried in the flow of the river.
Traction - Heavy material is rolled slowly along the bed.

	Created by Alex Collins about 9 years ago

Notes for revision - River landscapes.