Download 4 Key Agents of Erosion

Topic 3 – Erosion
1. Erosion: the movement of rock and mineral grains from
one place to another.
Sediments come from larger rocks that have broken down
or worn away through weathering.
2. Weathering is the breaking down of rocks mechanically,
chemically, or biologically.
There are 3 Types of Weathering. Please read p. 373-374
for key pts. and examples below.
1. Mechanical Weathering
- The physical break-up or disintegration of rocks
Example: gravity causing rocks to fall and break apart; rocks
bumping together in a river, frost wedging, wind, water
(rain).
Mechanical Weathering is the part of the process
responsible for wearing away. Sedimentation is the part of
the process responsible for building up.
2. Chemical Weathering
- the breaking down of rocks and minerals through chemical
reactions
Example: Acid Rain – acidic rainwater caused by air
pollution dissolves some types of rock (ex. Limestone)
3. Biological Weathering
- the physical or chemical breakdown of rock caused by
living organisms such as plants, animals, bacteria, and fungi
Example: Tree roots getting into cracks in rock and wedging
the rock apart, acids produced by living organisms can
dissolve rocks
*The physical environment and natural processes such as
earthquakes and volcanic eruptions can also cause rocks
and the landscape to change.
3. 4 Key Agents of Erosion – p. 376
Glaciers, gravity, wind and water are the 4 Key Agents of
Erosion.
1. Glaciers – glaciers erode the land as they pass over it
(Striations – grooves left behind by rocks in a
glacier, erratics – large rocks left behind by a glacier,
moraines – piles of sediment in front of glacier, melt
water – washes away/moves sediment)
2. Gravity – responsible for rockslides and landslides; can
be unexpected (retaining walls, better drainage,
monitoring)
3. Wind – picks up loose sediment and wears away rock
through abrasion (plant vegetation, contour farming,
reduced tillage)
4. Water – most powerful cause of erosion (rivers,
meandering streams, heavy rain, coastlines) – break down
rocks, rocks can rub against each other, and be deposited
far downstream.
Define Abrasion- windblown particles of rock strike other
rocks and wear it down (ex. Like a sandblaster)
4. What is a Striation? P.376
- rocks frozen into glaciers scrape across the bedrock as the
glacier moves, leaving behind grooves in the bedrock
5. What is a Moraine? P.376-377
- eroded sediments get pushed in front of a glacier and piled
up along its sides in formations called moraines
6. What is an Erratic? P.377
- Large rocks left behind by a glacier, often many kilometers
from their source
7. Gravity is one force that is responsible for landslides and
rockslides. What can be done to prevent slides from
happening? Describe Frank Slide p. 377
- Adding retaining wall, improving drainage, monitoring
dangerous slopes
- In 1903, rock from Turtle Mountain in Alberta sent over
80 million tons of rock onto the town of Frank in less
than 100 seconds.
8. How does a V-shaped valley form?
- Rivers can cut straight into rock to form canyons, gorges,
and V-shaped valleys
* Topic 3 Review p. 380 - # 1-4