Transcript External Forces Shaping the Earth

External Forces Shaping the Earth
Chapter 2: Section 4
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.
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
earth’s surface.
Sediment: broken rock which can be identifiable as
either mud, sand, or silt.
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.
Mechanical Weathering
Chemical Weathering
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.
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 V—shaped
valley.
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.
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.
Building Soil
Weathering & erosion help in forming soil.
Soil is the loose mixture of weathered rock,
organic matter, air, & water that supports plant
growth.
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.
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.