Transcript Erosional Forces

Forces That Shape Earth’s
Surface
Weathering
• Weathering is the breaking down of the
materials of Earth’s crust into smaller
pieces.
• There are two types of weathering:
1. Physical weathering
2. Chemical weathering
• Physical weathering – is the processes that
mechanically break up rocks into fragments,
such as the movement of water, wind and ice,
and frost action. Physical weathering is also
known as mechanical weathering.
• Chemical weathering – is the breaking
down of the materials in rock through
chemical alteration of those minerals.
Chemical weathering involves
reactions between air and
water and minerals in rocks.
An example of chemical
weathering occurs when certain
metallic elements combine with
oxygen to form oxides. This is
known as oxidation. The most
familiar oxidation form is the
“rusting” of iron in rocks or soil
that produces a reddish brown
stain of iron oxide.
Erosion
• Erosion is the carrying away of pieces of
weathered rock by gravity, water, wind, and
ice. Piece by piece erosion can carry away a
bolder, a hill, or even a whole mountain
range!
Erosional Forces:
• Gravity
• Glaciers
• Wind
• Water
• What is the greatest agent of erosion?
Water
Erosional Forces
• These agents of erosion can only move
material when they have enough
energy to move the object.
• Another thing they have in common is
they will deposit, or drop, the material
they carry when they have lost the
energy.
Gravity as a force:
• Gravity is the force which Earth has on
all objects.
• It pulls boulders, soil and everything
else to the lowest point possible.
• When gravity moves materials
downslope this is then called mass
movement.
Some mass movements are slow:
Some mass movements are fast:
Erosion by slump
• Slump - a type of mass movement that
occurs when a mass of material moves
down a curved slope.
Erosion by Slump
Erosion by Creep
• Creep is the slow movement of soil
downslope that causes fence poles,
telephone poles to tilt in the direction of
movement.
Erosion by Rock Slides
• Rock slides happen when layers of rock
slip downslope suddenly.
• Rock slides can be very fast and very
dangerous
• Very common in mountainous areas.
Erosion by Rock
Slides
Erosion by Rockfalls
• Rockfalls occur
when material free
falls through the air.
Glaciers as Agents of Erosion
• A moving mass of ice and snow is
called a glacier.
• Glaciers form when snow and ice build
up faster than they melt.
• There are two types of glaciers:
– Continental glaciers and
– Valley glaciers
Continental Glaciers
• Continental glaciers cover large parts of
continents such as Antarctica.
Valley Glaciers
• Valley glaciers are found in mountain
regions all around the world. They begin at
the top of the mountain where it is snows all
year and the temperatures are always below
freezing.
Glaciers
• About 18,000 years ago glaciers
covered 28% of the Earth’s surface.
• Since that time they have been melting
and now cover about 10% of the Earth.
• Greenland and Antarctica are almost
completely covered in ice.
Glacier Erosion
• Glacial plucking is a process
that occurs when moving
glacier picks up loosened
rock particles.
Glacial Plucking of Rocks
Wind Erosion
• Wind is a very powerful force in
erosion.
• Through blowing away silt and
clay by deflation or by eroding
down rocks by abrasion.
Deflation or blowing away of other material by wind.
Abrasion: Wind-blown sediment strikes a surface.
Sandstorms
Are strong winds that carry sand particles
through the air.
Dust Storms
A strong wind storm that fills the air with
thick dust.
Windbreaks
Hedge or fence of trees designed to lessen
the force of the wind and reduce erosion
Roots
Vegetation is planted to reduce soil erosion.
Plants with fibrous root systems, such as
grasses, work best at stopping wind erosion.
Dust Bowl of the 1930’s
The End