Rivers: Processes (ETD, HAAS)

Question 1

What are the 3 types of river processes?

Answer 1

ETD

1. Erosion
2. Transportation
3. Deposition

Question 2

What causes vertical and lateral erosion, what landforms are formed and where are they mainly found?

Answer 2

Vertical erosion: Due to a steep gradient, the water flows quickly, causing the channel to deepen to form a deep-sided V shaped valley. Found mainly in the upper course

Lateral erosion: Due to a gentler gradient, the water has a lower speed of flow, hence erosion occurs laterally as the channel widens, forming a broad and flat valley. Found mainly in the lower or middle course.

Question 3

What are the 4 types of erosion?

Answer 3

HAAS
1. Hydraulic action
2. Abrasion/Corrasion
3. Attrition
4. Solution/Corrosion

Question 4

Describe the erosive process of hydraulic action with mention of the erosive agent

Answer 4

Erosive agent: Fast flowing water

The action of flowing water hitting against the riverbed and banks as it surges into cracks and joints, further breaking and loosening pieces of rock and soil.

Question 5

Describe the erosive process of abrasion with mention of the erosive agent

Answer 5

Erosive agent: Rock fragments

The scraping and grinding of river load against the riverbed and banks as the water flows, causing the removal of materials from these locations

Question 6

Describe the erosive process of attrition with mention of the erosive agent

Answer 6

Erosive agent: Rock fragments

The breaking down of rock fragments into smaller pieces as they knock against each other when carried by water, causing materials to become rounded and smoother

Question 7

Describe the erosive process of solution with mention of the erosive agent

Answer 7

Erosive agent: Carbonic acid in river water

The chemical reaction of the acid in the water with minerals in the rocks causes them to dissolve and form a solution

Question 8

What are the 4 processes of transportation?

Answer 8

1. Traction
2. Saltation
3. Suspension
4. Solution

Refer to notes for drawing

Question 9

Describe the transportational process of traction

Answer 9

The rolling and sliding of larger sized materials as they are too heavy to be lifted

Question 10

Describe the transportational process of saltation

Answer 10

The bouncing and hopping of large particles or smaller materials that are too heavy to be suspended in water all the time

Question 11

Describe the transportational process of suspension

Answer 11

The process where fine particles are suspended and kept from settling down

++ Greatest proportion of river load
++ River will appear cloudy

Question 12

Describe the transportational process of suspension

Answer 12

The process when readily soluble rocks dissolve in river water and carried downstream as a solution

Especially common in tropical areas due to the organic acids from decaying plant matter

Question 13

What is the trend in deposition when it comes to particle size?

Answer 13

Coarser and heavier loads are deposited first then the lighter and smaller loads

Question 14

What are factors that can cause deposition to occur?

Answer 14

1. Change in VOF (Sudden increase in river load-> landslides; shallow channel; period of low precipitation; sudden entry to a large body of water”
2. Change in SOF (Obstructions in the river; sudden entry to a large body of water)

Question 15

What does the Hjulstrom diagram show?

Answer 15

The different speeds at which particles of different sizes will require for erosion, transportation and deposition.

Question 16

Is it a fixed rule that the larger the particle, the greater the speed required for ETD?

Answer 16

No. Smaller particles are more adhesive.

Hence, higher speeds are needed for erosion (non-porous; tend to stick in clumps) and transportation (adhesiveness makes them deposit easily)