Lecture 19

Question 1

Geomorphology

Answer 1

Study of landforms, including processes that shape them.
Tectonic processes build up landscape (uplift).
Erosional processes wear it down (denudation).
Depositional processes also build up landscape.

Question 2

Powell

Answer 2

Best known for leading the first group down the Grand Canyon. Led US Geological Survey.
Was contributor for geography, geology, and anthropology.

Question 3

Base level

Answer 3

Idea introduced by Powell.
Streams can erode to a certain level; sea level is ultimate base level.
Local base level; resistant rock. Like dams.

Question 4

Gilbert

Answer 4

Worked with Powell in USGS. Many contributions to geomorphology.
Thought in terms of systems; landforms tend to equilibrium.
Theory of Graded River.

Question 5

Graded River Theory

Answer 5

Stream adjusts its slope to be able to transport available sediment, with no extra energy.
Energy of stream based on discharge of slope. Sediment delivered by tributaries and erosion of slopes.
Discharge and sediment supplies are constant.

Question 6

Davis

Answer 6

Dominated geomorphology in the first half of 1900s.

Studied landscape change over millions of years. Evolution of landscapes; cycle of erosion.

Question 7

Cycle of erosion

Answer 7

Simple humid version - flat surface at base level (peneplain) undergoes rapid uplift - now above base level.
SEE CHART.
Cycle takes millions of years. Uplift can occur anytime.

Question 8

Kinetic energy

Answer 8

Based on mass and speed.

Question 9

Potential energy

Answer 9

Not used now, but can be used in the future.

Anything above base level has potential energy.

Question 10

Q=AV

Answer 10

Discharge defined as cross sectional area times average velocity.
If you change A or V, the other has to adjust, as long as Q stays the same.

Question 11

Laminar flow

Answer 11

Slow water may move in a straight line.

Question 12

Turbulent flow

Answer 12

More chaotic flow, typical in a stream.

Question 13

Factors affecting velocity

Answer 13

Channel slope; steeper = faster (positive).
Discharge; more mass, more away from bed (positive).
Depth of flow; less friction if deeper (positive).
Roughness of channel; more friction (negative).

Question 14

Positively related variables

Answer 14

Variables that change the same direction.

Question 15

Negatively related variables

Answer 15

Variables that change in opposite directions.

Question 16

Shear stress

Answer 16

AKA tractive force.
Friction transfers some energy from water to bed. High erosion shear stress makes sediment move.
SEE CHART.

Question 17

Stream load

Answer 17

Sediment carried by stream.
Bed load; large particles roll along bed or bounce (saltation).
Suspended load; small particles stay up above bed.
Dissolved load; products of chemical weathering, in solution.

Question 18

Competence

Answer 18

Size of largest particle stream can carry at a given discharge.

Question 19

Capacity

Answer 19

Amount of sediment stream can carry at a given discharge.

Question 20

Types of erosion

Answer 20

Hydraulic action; flowing water picks up loose material.
Bank caving; sides of channel can fall into flow.
Abrasion; colliding particles break down (size decreases downstream, become more rounded).
Corrosion; chemical weathering in stream, rocks dissolve.

Question 21

Factors affecting deposition

Answer 21

Dissolved load stays in water, but if velocity decreases, solid particles fall out.
Decreases velocity by; reduce slope, reduce discharge, decrease depth, enter standing water. OR exceed competence of capacity.

Question 22

Erosional landforms

Answer 22

Created by removing material and the landform is what’s left.

Question 23

Depositional landforms

Answer 23

Created by depositing sediment and building up the landform.

Question 24

Waterfalls

Answer 24

Created by erosion. Resistant rock layer over a weak rock layer. Water flows over strong rock and erodes and the edge of it. Migrates upstream.

Question 25

Deltas

Answer 25

Deposition as stream enters ocean or lake. Stream often changes course, due to deposition (distributary channels).

Question 26

Alluvial fans

Answer 26

Found along mount fronts, typically in deserts. Stream leaves canyon, spreads out and slows down - deposition. Distributary channels like deltas.

Question 27

Alluvium

Answer 27

Stream deposited sediment. Streams near base level erode wide valley that often get a layer of alluvium on either side of the stream.

Question 28

Floodplains

Answer 28

The flat surface next to the channel that occasionally gets flooded, each flood deposits more sediment.
Flooding about every 1.5-2 years.

Question 29

Meandering channels

Answer 29

Faster moving water tends to spiral down the channel.
Reasoning not well understood.
Some waters moves faster and slower. The faster water is close to side of the stream you where you will get erosion, and slower water is deposition.

Question 30

Cut bank

Answer 30

Occurs where erosion is happening and there is a steep drop off into the water.

Question 31

Point bar

Answer 31

Occurs where deposition of sediment is and leads to a gentle drop off into the water.

Question 32

Braided channels

Answer 32

Found where discharge varies and high sediment loads -graded glacial streams and deserts.
Can’t carry all the sediment, so it deposits some in bars (islands).
Bars decrease cross sectional area, so velocity increases (Q=AV). Another way streams move toward graded state.

Question 33

Drainage network

Answer 33

Series of connected streams (main stream and its tributaries).

Question 34

Drainage basin

Answer 34

Area (valley) drained by a drainage network.

Question 35

Divide

Answer 35

Boundary of drainage basin; high point between networks.

Question 36

Exterior drainage basin

Answer 36

Flow exits basin at one point, most common.

Question 37

Interior drainage basin

Answer 37

No outlet, flow accumulates in low spot (playa).

Question 38

Longitudinal profiles

Answer 38

Slope of channels tends to change in downstream direction - steeper in headwaters, less steep at mouth.