1. Ch.13, Sec.2 – Stream Erosion & Deposition
- running water is the most effective agent of erosion
- gravity draws surface water downhill, which allows the water to erode soil and rock materials
- rivers also eventually leave their eroded materials behind, which we refer to as deposition

2. Ch.13, Sec.2 – Stream Erosion & Deposition
How Streams Weather and Erode Material
- running water breaks up the bedrock over which it flows primarily by mechanical means
- rapidly flowing water has a lifting effect that can split off and move rock fragments
- however, most erosion occurs when running water abrades (abrasion) & hammers away at its bed using sand, pebbles, and boulders as cutting tools

3. Ch.13, Sec.2 – Stream Erosion & Deposition
- cutting tools are involved in the formation of potholes, which are circular basins created by the erosion of swirling water and sediments
- running water’s chemical weathering of bedrock consists of dissolving soluble minerals
- water dissolves calcite cements found in rocks, which leaves sand particles left behind to become transported & deposited by rivers

4. Ch.13, Sec.2 – Stream Erosion & Deposition
How Streams Transport Material
- the eroded rock and soil materials that are transported downstream by a river are called its load
- the load can be carried in three ways: in solution, suspension, & its bed load
- suspended materials do not dissolve in water, but the movement of the water keeps them from sinking to the river bed

5. Ch.13, Sec.2 – Stream Erosion & Deposition
- rivers also transport materials in its bed load, which consists of sand, pebbles, or boulders that are too heavy to be carried in suspension
- most of the load carried by the world’s rivers is carried in suspension

6. Ch.13, Sec.2 – Stream Erosion & Deposition
- two measures are used to describe the ability of a stream to transport materials: competence & capacity
- competence is a measure that describes the maximum size of the particles a stream can carry
- capacity is a measure of the total amount of sediment a stream can carry
- because the velocity and discharge of a given stream are not constant, the competence & capacity of a stream are not constant

7. Ch.13, Sec.2 – Stream Erosion & Deposition
Stream Deposition
- a river will deposit a part of its load of sediment when either its velocity or its discharge decreases
New Orleans, Louisiana
Mississippi River Delta
- the greatest decrease in a river’s velocity occurs when it empties into a sea or a lake
Mississippi River emptying into the Gulf of Mexico

8. Ch.13, Sec.2 – Stream Erosion & Deposition
- a river’s discharge may decrease if it’s flowing through a dry region, but it may also increase if it’s flowing through a humid region (e.g. Amazon River & Gila River)
Amazon River in Brazil – much greater amount of water because of the excess rain being precipitated
Gila River in Arizona – much less amount of water because of the water being evaporated because of the dry heat

9. Ch.13, Sec.2 – Stream Erosion & Deposition
Depositional Features
- a delta is a fan-shaped deposit that forms when a river flows into a quiet or large body of water, such as a lake, an ocean, or an inland sea
Nile River delta in Egypt
Mississippi River delta in Louisiana