Weathering

Physical/Mechanical Weathering

The breakdown of the materials of Earth’s crust into smaller pieces.

Process by which rocks are broken down into smaller pieces by external conditions (wind, water, ice…)

Weathering & Erosion

5 Types of Physical

weathering

1. Frost heaving/wedging: water in cracks, freezes, & expands

2. Plant roots: grow in cracks causing the rock to break

3. Friction & impact: rocks breaking rocks

4. Burrowing of animals5. Unloading: overlying rock

eroded away creates exfoliation domes.

Chemical Weatherin

g

The 5 agents of chemical

weathering

The process that breaks down rock through chemical changes.

1. Water weathers rock by dissolving it

2. Oxygen combines with iron and forms rust

3. Carbon dioxide dissolves in rain water and creates carbonic acid

◦ Carbonic acid easily weathers limestone and marble

4. Living organisms◦ Lichens that grow on rocks produce

weak acids that chemically weather rock

5. Acid rain◦ Compounds from burning coal, oil

and gasoline react chemically with water forming acids in the clouds and are released when it rains

◦ Acid rain causes very rapid chemical weathering

Factors that affect weathering

Climate: Warm and wet Surface area Chemical composition of

rock

Erosion

4 Types of Erosion

The process by which water, ice, wind or gravity moves fragments of rock and soil.

1. Water: Rivers, streams, and runoff move soils, rocks and sediments around

2. Glaciers moving across the landscape

◦ rocks & boulder moved from place to place

◦ the glaciers carve into the land

3. Wind removing the different surfaces from one place and depositing it in another

4. Mass Movement of Land◦ Landslides◦ Mudslides◦ Slump: when part of a hill moves a

short distance down a hill)◦ Creep: slow movement of land down a

slope

Which rock layer appears to be the least resistant (weakest)?

Which rock layer appears to be the most resistant (strongest)?

Resistant rocks usually form steep cliffs and waterfalls, by sticking out further than the lower layers)?

Deposition

the process whereby these sediments are released by their transporting agents (dropped).

Most deposition happens in standing/still bodies of water (oceans/lakes).

Deposition is caused by the slowing down (loss of kinetic energy) of the agent of erosion.

Delta – a fan shaped deposit that forms at the mouth of a river/stream when it enters a larger body of water. This is seen under the water. The particles are horizontally sorted.