Unit 2: Surface Processes and the Hydrosphere

Lesson 6: Processes and Features of Erosion(Heath Earth Science – Pg. 190-202)

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

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

Erosional vs. Depositional Erosion:

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

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

2000-100,000 meters long, 100-1000 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

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

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

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

Glacial Erosional FeaturesYou 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

Glacial Erosional Features

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

Glacial Depositional Features

Glacial Depositional Landforms

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!

Running Water Erosion – Chapter 10 Another agent of erosion is running water Running water transports sediment in

three ways: Solution Suspension Bed load

Running Water Erosion Solution:

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

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

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

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

River Valley Drainage Patterns Topography influences the shape of the

rivers drainage system

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

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

Depositional Features – Oxbow Lakes

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

Depositional Features - Levees

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

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

Depositional Features – Alluvial Fans

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

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

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

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

Erosional Features – Desert pavement

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

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

Depositional Features – Dunes

Pg. 213-214

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

Homework You should be able to identify and explain the

following erosional/depositional features formed by wind: dunes, cross-bedding, blowouts, desert pavement, ventifacts

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

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

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

Erosional Features – Sea Stacks and Sea Arches

Erosional Features – River rocks, Undercutting

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