Transcript Natural Agents of Change

Natural Agents of Change
• Earth’s surface changes
constantly. Natural processes
that occur on the Earth’s surface
change the shape of the land.
These processes usually occur
over a very long time.
• Features on the surface of the
Earth are called landforms.
• A mountain is an example of a
landform.
• Landforms are made of rocks. When rocks
are exposed to air and water at Earth’s
surface, they change. As rocks change, so
do the landforms.
• Rocks change all the time as forces act to
break them up. The two most important
natural forces are weathering and
erosion.
Weathering
• When a rock is broken down into smaller
pieces it is called weathering. A rock
weathers in response to changes in its
environment.
• Weathering can occur by three different
methods:
1. Mechanical weathering
2. Chemical weathering
3. Biological weathering
Mechanical Weathering
• Mechanical weathering is a process
where rocks are physically broken into
smaller pieces by wind, water, ice or
heat. The common product of
mechanical weathering is silt, a form of
very finely-ground rock.
• Examples of mechanical weathering is
everywhere. One famous example is the
Grand Canyon.
• Freezing and thawing cycles also
weather rock mechanically. When water
freezes, it expands. The ice crystals push
against the solid rock, weakening its
structure.
• When it warms up again, the ice crystals
melt and the pressure is released—but
the rock structure is weakened even more.
Each time the rock freezes and thaws, it
cracks a little more.
Chemical Weathering
• Chemical weathering is a process
in which the rocks are broken down
by removing or altering elements
that make up the minerals. The
most common form of chemical
weathering is from carbon dioxide
(CO2) in the air. When carbon
dioxide combines with rain, a
chemical change occurs.
• The end result of chemically
weathered rock is clay. Clay is
made up of finely ground rock
pieces that are a little larger
than silt.
Biological Weathering
• Biological weathering is
caused by living organisms. For
example, burrowing animals or
plant roots can break up soil
and rocks.
Erosion
• Erosion is the transport of soil or rock by
water, ice or wind. Erosion is the
movement of weathered rock, and not the
actual weathering itself. So, streams and
rivers not only weather rocks by carrying
water past the rock. They also transport
the fragments downstream (erosion).
Small fragments of rock and soil are called
sediment.
Erosion by Water
• Rivers move sediment by
carrying them in the
water or rolling them
along the bottom. This is
a form of water erosion.
Erosion by Wind
• Wind erosion occurs all over the Earth. It is
most noticeable in desert climates, where water
is scarce. The wind picks up small pieces of rock
fragments and carries them along until they
reach an obstacle, such as a hill. The fragments,
pushed by the wind, act as a sandblaster
eroding the hill slowly over time. The wind also
causes erosion by scooping up large areas of
loose soil and transporting them to another
location.
Erosion by Ice
• Ice on Earth’s surface
also causes erosion. Ice
erosion is usually the
result of glaciers. A
glacier is a large body of
moving ice. It flows
downhill slowly, acting
like a frozen river. A
glacier moves downhill
due to the force of
gravity. As it moves, it
picks up and carries any
loose material in its path.
Erosion by Gravity
• Gravity pulls everything
towards the center of the
Earth. It is constantly pulling at
rocks, soil, water and anything
on Earth’s surface.
• When a pile of rocks falls
down the side of the mountain
as one single block it is called
a landslide. Landslides erode
mountains and change their
shape very quickly.
Vegetation Affects Erosion
• The amount of vegetation in the area has a big
affect on how fast or slow erosion takes place.
Vegetation means plants, including trees, shrubs
and flowers. The roots of the vegetation reach
into the soil and hold it in place. The leaves and
limbs of the vegetation shield the ground from
wind. When vegetation is growing well, soil does
not erode quickly. When vegetation is removed
by fire, animals or humans, soil can erode
quickly.
The End!!!