Weathering and Erosion

Unit 3

Chapter 7

Weathering – the process by which rocks are broken up into smaller pieces by the action of water, the atmosphere and living organisms.

Erosion – the process by which particles of rock are transported by moving water, wind or ice.

                                                                                                                        

“Weathering”

“Erosion”

Weathering

There are 2 main types of weathering:

1. Mechanical (physical)

2. Chemical

Mechanical Weathering The process of breaking rock into smaller

pieces by mechanical or physical means is called mechanical weathering.

Causes (agents) of mechanical weathering:

• Ice wedging – freezing and thawing of water

• Plant weathering – roots press into cracks in rock, slowly widening the crack over time.

• Animal weathering – animals burrow into soil

• Temperature change – uneven heating of rock causes expansion and cracking

• Water abrasion – streams of water carry particles of rock that wear away other rock.

• Wind abrasion – the wind will carry tiny particles of rock that wear away other rock.

Chemical Weathering

Weathering that changes the chemical composition of rock is called chemical weathering.

What are the causes (agents) of chemical weathering? • Water• Oxygen • Carbon dioxide

Water – H2O

1. Can dissolve many minerals.

2. Can react with silicate minerals. (hydrolysis)

3. Can combine with gases in the air to form acids that can dissolve minerals.

4. Water can serve as a medium for other reactions to occur.

Oxygen – O2

Will cause oxidation or rust, iron in rocks will combine with the oxygen in the air and form rust.

___Fe3O4 + ____O2 ___Fe2O3

Carbon dioxide – CO2

Can produce carbonic acid that will dissolve limestone.

___H2O + ____CO2 ___H2CO3

Erosion

The action of picking up and moving materials is called erosion. Think of erosion as the dump truck that moves material.

• Erosion will move weathered material. • The end stage of erosion is called

deposition where material is dropped off.• Deposition creates new landforms.

• The four main agents of erosion are:1. Gravity2. Water3. Wind4. Ice

Special Types of Erosions

Mass Movement – when gravity moves rock or soil down a slope.

• Landslides – rapid movement of large amounts of rock and soil. (heavy rains and steep slope help this happen)

• Mudflows – fine sediments collected in thick layers, when heavy rain falls, these turn to mud and can flow rapidly.

• Creep – gradual downslope movement of soil. (SLOW)

• Slump – weak layers of underlying material move down slope as a single unit. (water and gravity help)

Water Erosion – moving water can carry many particles and of varying sizes based on the velocity of the water (ESRT page 6)

• Rills• Gullies• Streams• Rivers (young, mature, old)• Delta• Alluvial fan• Floodplain• levee

Wave Erosion – sand is continuously eroded and deposited along the shore by waves and currents.

• Spit

• Sandbar

Ice Erosion – glaciers are like huge bulldozers that can move large amounts of material at a slow pace. Many landforms in NYS have been formed by the movement of glaciers.

2 types of glaciers:

1. Valley glaciers (alpine)

2. Continental glaciers

Glaciers that form in high mountain valleys are called valley glaciers.

Glaciers that cover large areas in polar regions are called continental glaciers.

How do glaciers form?

When the snow becomes so deep that it cannot melt in the summer, a glacier is born. As the layers of snow pile up, the pressure on the layers below becomes so great that ice forms, creating the glacier.

• Glaciers ride on a thin layer of water due to the pressure of the ice [melting on bottom of ice mass]

• Glaciers move due to gravity.

Soil Texture