2.4 External Forces Shaping the Earth

Wind and rain.

1. External ForcesExternal Forces
Shaping the EathShaping the Eath

2. Weathering
•Physical and chemical processes that change the
characteristics of rock on or near the Earth’s surface
•Breaks rock down into smaller pieces called sediment
(mud, sand, or silt)
•2 types
5.Mechanical Weathering
•The composition of the rock stays the same, it just
gets broken down into smaller bits

3. 1.Chemical
Weathering
•Rock is
changed into
new substance
•Rust, acid rain,
etc.

4. Erosion
•Weathered material moved by action of wind, water, ice,
or gravity
•3 types
4.Water erosion
•Water strips away material
•This can happen in rivers and streams by the current
eroding the banks and on coasts by waves eroding
the shores
•Eroded material becomes sediment
•In rivers, sediment is carried downstream and
deposited at its mouth and forms a delta

5. Nile Delta
Mississippi Delta

6. 1.Wind erosion
•Powerful winds erode soil and blow them hither and
thither.
•May form new landforms, such as dunes
•May also just get in your nose and ears in Lubbock

7. Iraq

8. 1.Glacial erosion
•Large masses of ice eroding the landscape –
glaciation
Building soil
•Weathering and erosion are part of the cycle of dirt (my
term)
•Soil gets stripped away and deposited
•Soil Factors
•See p. 45 in textbook