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

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

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

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

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

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

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

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

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