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Erosion Powered By Docstoc
Erosion happens when running water, wind, waves or
glaciers pick up things like dirt and rocks from the
earth’s surface and moves them around.

But if the dirt or rock is just loosened, or
worn down, but doesn’t move, it’s just
called Weathering.

  There are two kinds of Weathering.
•Mechanical Weathering
Physically breaking down rocks
into smaller fragments without changing
the chemical makeup of the minerals in
the rocks. Like pebbles being worn down
into sand.
 •Chemical Weathering
Chemically breaking down of at least
one of the minerals in the rock. Water
can react with carbon dioxide to make
carbonic acid. This acid reacts with the
mineral calcite in limestone and can
cause it to become stalagtite in cave.
      Mechanical Weathering
 Forces like these can all cause Mechanical Weathering

Growing        Expanding                       Crystal
Plants         Ice                             Growth

              Plant Roots

Plant Roots grow into the cracks of rocks
and cement looking for water and nutrients.
When these roots get big enough, they force
the concrete or rock apart. The crack gets
bigger as the plant grows.
 Ice Can Do the Same Thing
In cold weather, water
freezes on a rock
and forces the rock apart
creating all sorts of

Then when it gets warm,
the ice melts leaving dry
cracks, making the rock
weaker and easier
to break apart.
 Beaches are Formed by Weathering

Sand is made by the
gradual process of
pebbles being
broken up into
smaller and smaller
pieces by the motion
of waves.

                     Sand Blasting
   Another type of mechanical weathering is
   called Sandblasting.
When wind blows sand at high
speeds, it forces particles to
smooth and reshape rocks and
even buildings. The effect is
similar to that of using

Workers have found
Sandblasting to be
very helpful in smoothing
surfaces when building.
 Example of Chemical Weathering
1. Water H2O and
   carbon dioxide CO2 are separate.
2. Water H2O and
   carbon dioxide CO2 mix together.
3. The chemical composition changes and becomes
   Carbonic Acid. H2CO3
4. Carbonic Acid mixes with the calcite in the Limestone Rock and makes a
   new chemical composition, Stalagtites.

H O and C O2      Mix together     New Chemical        Mixes with limestone
 2                                                     becomes Stalagtites
                                   H2 3                                       Q5
Chemically Weathering Causes Rust
When iron reacts
with oxygen in
the air and
water, it
becomes Iron
oxide through a      A rusted bolt


Chemical Weathering Causes Tarnish

The Statue of Liberty
is made out of copper,
which is the color of a
penny. After many years,
 the oxygen in the air and
 water causes oxidation,
 chemical reaction and
 produces a green tarnish
 on the copper.

 Erosion happens
when running water,
wind, waves or even
glaciers pick up things
like dirt and rocks
from the earth’s
surface and move
them around.
                 Erosion by Water
• Rivers, rain, and the ocean
  wear down surfaces and carry
  away soil and rock.

• The soil and rock eventually
  become sediment that ends up
  back in the water settling at the

• This sediment eventually
  becomes sedimentary rock.

     Erosion (movement of rock and dirt) can cause…
 Flood Plains                        River Deltas are
 cut deep into                       triangular shaped
 the banks of                        deposits of sediment
 a river from                        at the mouth of a
 flooding water.                     river going into the

Sand bars
are formed
when the ocean
currents carry
sand off shore.

        Over Millions of Years
Over millions of years
erosion can make
fantastically deep
canyons… Like the
Grand Canyon.

It can even change
the shapes of continents
but it takes millions of years.
             Glacier Erosion
                           As glaciers move
                           very slowly, they
                           gradually pick up
                           loose materials from the

Pieces of rock caught
on the glacier’s surface
grind away at mountain
walls and valleys as
they move.
How Much Erosion Happens Depends on 4 Things

1. Slope
 The steeper the slope of a hill, the easier water or
  wind can move loose dirt and rocks because of
  gravity. Like a rock rolling down a hill.

 Plant roots hold
 soil or sand
 together against
 the effects of wind
 and water.

2. Soil Texture
    The tinier the texture of the rocks, like sand,
    the easier water or wind can move loose dirt.

 Just like when you
 move water around in a
 pond, the tiny pieces of
 dirt mix with the water
 and make it look muddy
 but the big ones stay at
 the bottom.

3. Cover
 If there is no cover on the ground, like grass, crops or plants, dirt will
  be carried away easily from wind or water.

After a farmer plows the
land and the dirt is all
mixed up, soil can easily
move away with wind or
water and cause erosion.

4. The speed
 The speed of the wind or water affects the amount
 of sediment that can be carried.

      Erosion and Weathering
     Cause Very Slow Changes
       in the Earth’s surface.

             But Rapid Changes
             Can occur from….

•Mudslides   •Volcanic Eruptions • Earthquakes

  Earth Is Constantly Rebuilding
   If slow and rapid changes are wearing the
   surface of the earth down, why isn’t the
   earth level and flat?

Because other forces keep building the surfaces up and down.


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