OUR CHANGING EARTH

8.9C interpret topographic maps and satellite views to identify land and erosional features and predict how these features may be reshaped by weathering

ATL Skill: Critical thinking - Use models and simulations to explore complex systems and issues

GRAPHIC ORGANIZER:

WEATHERING, EROSION AND DEPOSITIONLet’s Review!

WEATHERING DEFINITION

• Weathering is the process of breaking down rocks into smaller pieces.

• Smaller pieces are called sediment

• Caused by agents such as wind, ice, water

2 TYPES OF WEATHERING

• Physical or Mechanical Weathering – the breakdown of rock into smaller pieces

• Does NOT change the composition of the rock

MECHANICAL OR PHYSICAL WEATHERING

Examples:

• Abrasion – particles are carried that scrape against existing rock.

• Ice Wedging from water freezing and expanding in cracks such as potholes on the street

• Exfoliation from extreme high temperatures causing rock to crack and flake off like an onion

PHYSICAL OR MECHANICAL WEATHERING

1. Abrasion by sand and other rock particles

2. Exfoliation - from extreme high temperatures causing rock to crack and flake off like an onion (thermal expansion)

3. Ice Wedging from water freezing and expanding in cracks such as potholes on the street

1 2 3

MECHANICAL OR PHYSICAL WEATHERING

More Examples:

Biological Agents -

• Roots from trees or other plants forcing cracks apart

• Animal actions such as burrowing loosening the ground

WEATHERING – 2ND TYPE:

Chemical Weathering – changes the actual chemistry of the rock

Examples of agents:

Oxidation - a reaction with oxygen

Carbonation such as in cave formation

Acid precipitation – rain or precipitation that is more acidic than usual

Biological – microscopic organisms

CHEMICAL WEATHERING

• Oxidation such as iron turning red and copper turning green

CHEMICAL WEATHERING

• Caves are formed by the dissolution of limestone. Rainwater picks up carbon dioxide from the air and as it percolates through the soil, which turns into a weak acid. This slowly dissolves out the limestone along the joints, bedding planes and fractures, some of which become enlarged enough to form caves

CHEMICAL WEATHERING

Plant acid breakdown of soil and rock

Acid rain dissolving statues

EROSION DEFINITION

• Erosion is the process that moves rock, sediment and soil from one place to another

EROSION

Agents of Erosion – these are the forces that cause erosion

• Moving water such as rain water, streams, rivers, and beach erosion

• Wind such as dust storms and general blowing of sediments

• Gravity such as what causes landslides and mudslides

• Glaciers/Ice - sliding erodes the rock surface underlying a glacier. Meltwater freezes in cracks, and pieces of bedrock are pried loose and incorporated into the ice (similar to frost wedging). These new pieces of rock grind against each other and the bedrock underneath.

EROSION

1. Moving water – carries the sediment, from small streams to large oceans

2. Wind – carries sediment and causes abrasion

1 2

EROSION – CAN BE SEEN ON SATELLITE IMAGES:

DEPOSITION DEFINITION

• Deposition – lays down rock, sediment and soil from one place to another

• Sediments, soil and rocks are added to a landform or land mass

• This is a CONSTRUCTIVE (building) process!

IN ACTION:

• In this example, the moving water is causing erosion in one part of the river

• When the water slows down (such as in a sharp turn), sediment is deposited or left behind

• Fast water carries more

• Slower water carries less

AGENTS OF DEPOSITION:

• Moving water – whenever water slows down

• Wind – wind carries sediment, areas of slow speeds means gets deposited!

River delta, alluvial fan

wind

AGENTS OF DEPOSITION:• Ice – As glaciers melt, they leave deposits behind. Moraines

are large chunks of broken rocks left on the edges of a receding glacier

• Gravity – things fall down ☺

INDEPENDENT PRACTICE: