Geology Chapter 10

Drainage basins

The total area drained by a stream and its tributaries, separated by divides.

Dendritic pattern

A stream pattern that develops on uniform rock, resembling branches of trees; the most common stream pattern.

Rectangular pattern

A stream pattern that develops on regularly jointed rock, characterized by angles close to 90 degrees.

Radial pattern

A stream pattern that forms on conical mountains, with streams radiating outward.

Trellis pattern

A stream pattern that indicates the erosion of folded sedimentary rocks, featuring parallel main streams with short tributaries.

Key factor in controlling sediment erosion

Stream velocity.

Factors affecting stream velocity

Gradient, channel shape and roughness, discharge.

Gradient

The slope of a stream.

Channel shape and roughness effect on stream velocity

They increase or lessen friction, affecting the speed of the water.

Discharge

The volume of water that flows past a specific point in a unit of time.

Methods of stream erosion

Hydraulic action, abrasion, and solution.

Hydraulic action

The ability of flowing water to pick up and move sediments.

Abrasion

The grinding away of the streambed and its sediments.

Solution (in terms of stream erosion)

The process where water dissolves rock and absorbs soluble materials.

Ways streams transport sediments

Bed load, suspended load, and dissolved load.

Bed load

Large or heavy sediment particles that travel along the streambed.

Traction

The movement of bed load by rolling, sliding, or dragging.

Saltation

The short leaps or bounces of sediment particles in a stream.

Suspended load

Sediment light enough to remain lifted above the streambed.

Dissolved load

Soluble products resulting from chemical weathering carried by the stream.

Formation of potholes

Caused by the abrasion of hard rock on the streambed.

Bars in a stream

Deposits that form in the middle of streams.

Meanders are created when

A laterally eroding stream shifts across its floodplain.

River velocity is higher on the

Outside of the curve.

Natural levees are built by

Flood deposition occurring beside streams.

Deltas form when

A stream flows into standing water.

Alluvial fans form

Especially in dry climates at the base of mountains as a stream's channel widens and velocity decreases.

Downcutting

The process of deepening a valley by the erosion of the streambed.

Graded stream

A stream that maintains a delicate balance between its transporting capacity and the available load.

Lateral erosion

The process of erosion and undercutting of stream banks.

What widens a valley?

Lateral erosion.

Headwater erosion

The slow uphill growth of a valley above its original source through gullying and sheet erosion.

Stream terraces

Formed by erosion of rock or uplift, cutting into old floodplains.

Incised meanders form when

1. River meanders are cut vertically downward following uplift;

2. Lateral erosion and downcutting occur.