1. Unit 2: Surface Processes and the Hydrosphere
Lesson 6: Processes and Features of Erosion
(Heath Earth Science – Pg )

2. Today’s Objectives
Relate the processes associated with weathering and erosion to the resulting features, including:
identify the processes (e.g., abrasion, dissolution) by which glaciers, running water, wind, and wave action erode rock and sediment
differentiate between erosional and depositional features formed by glaciers, running water, wind, and wave action

3. Types of Erosion Erosion can be carried out in many different ways
Today we will look at 4 different processes of erosion:
1) Glacial Erosion
2) Running Water Erosion
3) Wind Erosion
4) Wave Erosion
In addition to looking at these processes, we will also identify some features created by erosion, as well as features formed by deposition

4. Erosional vs. Depositional
The incorporation and transportation of material by a mobile agent, such as water, wind, or ice
Deposition:
The process by which materials are added to a landform after being transported by a mobile agent

5. Glaciers – Chapter 11
A glacier is a thick mass of ice originating on land from the compaction of snow that shows evidence of flow
Two main kinds of glacier:
Valley glacier (alpine glacier)
Occur in all parts of the world where mountains stretch above the snow line
,000 meters long, meters thick
Continental glacier (ice sheet or ice cap)
Occur in polar areas where the snow line is close to sea level
Up to 12.5 million km2, up to 5 km thick!
Glacier Simulation

6. Advancing vs. Receding Glaciers
Accumulation zone: Area of glacier where accumulation > melting
Ablation zone: Area of glacier where melting > accumulation
Firn (snow) line: line where melting = accumulation
When the amount of snow falling in the accumulation zone is larger than the amount of snow melting in the ablation zone, the glacier will advance
When the opposite is true, the glacier will recede
Advancing glaciers will create erosional features
Receding glaciers will create depositional features

7. Glacial Erosion - Abrasion
Glaciers erode the bedrock largely by using pieces of rock as cutting tools
These pieces are dragged over the bedrock by the forward movement of the glacier, in a process called abrasion
The scratches left behind on the rocks are called striations

8. Glacial Erosion - Plucking
Another process of glacial erosion is plucking
Plucking occurs when melt-water beneath the glacier penetrates cracks in the bedrock, then freezes to the rock (video)
As the glacier moves forward, the rock is pulled from the ground

9. Glacial Erosional Features
You should be able to name and recognize the following erosional features, and how they are formed:
arete, cirque, horn, hanging valley, U-shaped valley, roches moutonnees, fjord, tarn

10. Glacial Erosional Features

11. Glacial Deposition
Once a glacier begins to recede, the material from beneath, within, or on top of the glacier will be left behind
This material will form many features called depositional features
You should be able to name and recognize the following depositional features, and how they are formed:
Till, moraine, outwash plain, drumlins, eskers, kames, kettles, and erratics

12. Glacial Depositional Features

13. Glacial Depositional Landforms

14. Homework Complete the homework package that you are given!
Due: Next class
Next day: We will continue discussing erosion and erosional/depositional landforms
Soon: Unit Test!

15. Running Water Erosion – Chapter 10
Another agent of erosion is running water
Running water transports sediment in three ways:
Solution
Suspension
Bed load

16. Running Water Erosion Solution: Suspension:
Material that has dissolved from the bedrock are carried in solution
Minerals such as calcium and magnesium are often carried in solution
Suspension:
When a river looks muddy, it is carrying material in suspension
Suspended material includes clay, silt, and fine sand
Are kept from sinking because of turbulence
Faster moving water can keep more material in suspension

17. Running Water Erosion Bed load:
Sand, pebbles, and boulders that are too heavy to be transported in suspension may be moved along the stream bed
Very common during floods
Boulders and pebbles roll or slide along the riverbed
Sand grains jump and bounce along the bottom
Sediment moved along the stream bed is called the bed load

18. Running Water - Abrasion
Much like in glaciers, weathering and erosion by running water also involves abrasion:
Sand, pebbles, and even boulders carried as load in the water will grind and hammer away at its bed
Over time, this abrasion causes rock to be worn down and rounded: this rock is known as river rock

19. Erosional Features – V-shaped Valleys
Running water wears away and erodes the surface, of mountains they flow down creating river valleys
River valleys are typically V-shaped:
High speed water easily scours away the streambed
Upper valley walls are widened by weathering and erosion

20. River Valley Drainage Patterns
Topography influences the shape of the rivers drainage system

21. Erosional Features - Potholes
Streams running over irregular beds develop small circular currents called whirlpools
As whirlpools develop, sand, pebbles, and small boulders abrade the streambed, grinding out deep oval or circular holes called potholes

22. Depositional Features – Oxbow Lakes
Mature river valleys develop wider floors
Rivers are easily deflected from side to side, forming meanders
As a meander gets larger and larger, the curve can become a loop and break through its bank
This is called a cutoff
Result is an abandoned meander, or oxbow lake

23. Depositional Features – Oxbow Lakes

24. Depositional Features - Levees
In times of heavy rain, rivers may overflow their banks and cover part of the valley floor
This part of the valley floor is called the flood plain
As water flows over the river bank, it slows down and releases some of its sediment load
Largest, heaviest sediment is released first
Finer sediment released last
This larger sediment forms a “wall” or levee on each river bank, a natural form of flood protection

25. Depositional Features - Levees

26. Depositional Features - Deltas
When a river meets the sea, or a lake, the velocity of the water slows down dramatically
As it slows, the fine sediment in the suspended load will be deposited at the mouth of the river, forming a delta

27. Depositional Features – Alluvial Fans
Similar to a delta, but occur in dry regions where a steep mountain stream meets flat, dry land at the bottom of the mountain
Again, water velocity slows down greatly, sediment load is dropped forming a fan-shaped deposit, called an alluvial fan
Different from a delta in that:
1) formed on land, not in water
2) sediment is coarse sand and gravel instead of fine sediment
3) surface is sloping, not flat

28. Depositional Features – Alluvial Fans

29. Homework
You should be able to identify and explain the following erosional/depositional features formed by running water: delta, alluvial fan, oxbow lake, pothole, levee, v- shaped valley

30. Wind Erosion – Chapter 12 Another agent of erosion is wind
Just like running water and ice, abrasion is a process of wind based weathering and erosion
High winds pick up sand particles, which grind away at rock features the wind blows into

31. Erosional Features - Ventifacts
Boulders and rocks that have been shaped by sand blasting winds, are called ventifacts
Have one or more sides that have been worn away by sand blasting

32. Wind Erosion Another effect of wind erosion is deflation
Deflation describes the removal of loose rock particles by wind
Usually sand, silt and clay will be blown away first, leaving behind pebbles and boulders
Material carried away by wind and deposited elsewhere is called loess
Such a surface is known as desert pavement
The heavy surface material of desert pavement protects the material beneath from further deflation

33. Erosional Features – Desert pavement

34. Erosional Features - Blowouts
In some areas where larger materials are not present, blowouts are common
A blowout is a hollow resulting from the removal of huge amounts of soil due to deflation

35. Depositional Features - Dunes
Hills of sand deposited by wind are called dunes, or sand dunes
Dunes form when deposited sand piles up against shrubs, boulders, or other obstructions
Found wherever there are strong winds and enough loose sand
If wind blows steadily from one direction:
Dunes have long, gentle slope on windward side
Short, steep slope on the leeward side
Dunes occur in many different shapes, dependent on the amount of sand available, strength and steadiness of winds, and amount of vegetation present

36. Depositional Features – DunesPg

37. Wind Depositional Features - Crossbedding
Over time, winds can change direction, reversing direction of the dunes
As older dunes get buried, pressure builds turning them into stone
This process creates another feature, called crossbedding

38. Homework
You should be able to identify and explain the following erosional/depositional features formed by wind: dunes, cross-bedding, blowouts, desert pavement, ventifacts

39. Wave Erosion – Chapter 12 One last agent of erosion is wave action
Waves repeatedly pounding against the coast, along with abrasion, can create numerous erosional and depositional landforms

40. Anatomy of a Wave
Wave height is the difference between its high point (crest), and its low point (trough)
Wavelength is the distance from one crest to the next
The period of a wave is the amount of time it takes one wavelength to pass a given point
Almost all waves are generated by wind

41. Erosional Processes – Longshore drift
As waves strike the coast at an angle, sediment is picked up at an angle, then dropped as the water follows gravity back to the ocean
This causes sediment to migrate down the coast, a process called longshore drift

42. Erosional Features – Sea Stacks and Sea Arches

43. Erosional Features – River rocks, Undercutting

44. Wave Depositional Features
Homework:
You should be able to recognize and explain the following erosional and depositional features created by wave action:
Sea arch, sea stack, tombolo, spit, beach, sandbar