External Forces Shaping the Earth

1
External Forces Shaping the Earth

• Chapter 2 Section 4

2
A Human Perspective

• In Egypt, a seasonal dry wind is called khamsin
  (fifty) for the number of days the season
  occurs. During Khamsin, wind-driven sandstorms
  kill and injure people, close businesses and
  airports, and strip topsoil and seed from the
  ground. Sandstorms are not limited to the desert
  areas of Africa and Southwest Asia. For instance,
  a five-hour storm recently blasted Jingehang,
  China, causing millions of dollars of damage and
  killing about 300 people. Sandstorms are among
  the external forces that change the shape of the
  earth and affect the lives of the people in their
  paths.

3
Weathering

• External forces, such as weathering and erosion,
  also alter landscapes and in some instances
  create the soil that is needed for plant life
  over many years or centuries.
• Weathering refers to physical and chemical
  processes that change the characteristics of rock
  on or near the earths surface.
• Sediment broken rock which can be identifiable
  as either mud, sand, or silt.

4
Two types of Weathering

• Mechanical weathering process of breaking rock
  into smaller pieces.
• Examples
• Ice crystals ice builts in a mts. It creates
  enough pressure to break the mt.
• Plants roots digs into the rocks and breaks it.
• Human activities break rock into smaller pieces
  road construction, drilling blasting in mining.

• Chemical Weathering it occurs when rock is
  changed into a new substance as a result of the
  elements in the air, water, minerals in the
  rock.
• Acid rain is believe to be speeding up the
  process.

5
Mechanical Weathering
6
Chemical Weathering
7
Erosion

• It occurs when weathered material is moved by
  action of wind, water, ice or gravity.
• For erosion to occur water must be present.
• Glaciers, waves, stream flow, or blowing winds
  cause erosion by grinding rock into smaller
  pieces.

8
Water Erosion

• As water flows in a stream or river, the motion
  picks up loose material and moves downstream
  the force will also break landform.
• Most streams erode both vertically
  horizontally it will cut a stream as it get
  deeper wider, forming a Vshaped valley.

9
Wind Erosion

• It is similar to water erosion because the wind
  transports and deposits sediment in other
  locations.
• Depending on speed of wind it can create new
  landform such as sand dunes or shape rock
  sculpted into new forms.
• It will eat always at a landform.

10
Glacial Erosion

• Is a large, long-lasting mass of ice that moves
  because of gravity.
• As a glacier moves it carries rocks and sediments
  underneath the snow forming new landforms.

11
Building Soil

• Weathering erosion help in forming soil.
• Soil is the loose mixture of weathered rock,
  organic matter, air, water that supports plant
  growth.

12
What makes good soil?

• Parent material the chemical of the rock before
  it decomposes affects it fertility.
• Relief higher mts. Erode easily do not produce
  soil quickly.
• Organisms plants, small animals like worms,
  ants, bacteria help to loosen soil supply
  nutrients for plants.
• Climate it needs to have a moist and cool
  climate.
• Time it varies, but 2.5 cubic centimeters per
  century.

13
The plus side of Volcanoes--Fertile Soil

• Volcanoes can clearly cause much damage and
  destruction, but in the long term they also have
  benefited people. Over thousands to millions of
  years, the physical breakdown and chemical
  weathering of volcanic rocks have formed some of
  the most fertile soils on Earth.