Erosion and Soil Depostion

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Erosion and Soil Depostion

• Chapter 8

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Section OneChanging Earths Surface
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Erosion

• Erosion moves sediment from one place to another

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• While deposition lays down sediment in new
  locations.

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What are the forces which cause erosion?
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• The force of gravity.

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• The force of running water.

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• The force of glaciers.

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• The force of waves.

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• And the force of wind.

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What Do You Remember?

• What does erosion do?
• moves sediment from one place to another
• What does deposition do?
• lays down sediment in new locations.
• What are the forces which cause erosion?
• Gravity, water, glaciers, waves, and wind.

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Section 2 Water Erosion

• Moving water is the major cause of erosion on
  Earths surface.

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Runoff and Erosion

• Runoff is water which moves over the land,
  carrying soil particles with it.

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• The amount of erosion caused by runoff can depend
  on how much plant life is there to hold the soil.
  With very little plant life, a desert can have
  high runoff and erosion.

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• Because of gravity, runoff and the soil in it
  carve little grooves called rills.

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• As rills flow into one another, they grow larger
  and form gullies.

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• Gullies join together to form streams. While
  gullies only flow when it rains, streams flow all
  the time.

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• A stream grows into a larger stream by receiving
  water from tributaries.

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Together, all these streams, from tiny rills to
great rivers, form a system that drains the land.
A drainage basin is a land area where all this
water collects.
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What Do You Remember?

• What is the major cause of erosion on Earths
  surface?
• Moving water.
• What is water which moves over the land, carrying
  soil particles with it?
• Runoff
• Describe the system by which water is moved from
  small to large.
• Rills to Gullies to Streams which are Tributaries
  to Larger Streams, which run to a Drainage Basin.

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Rivers have features which are caused by erosion.
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• Near its source, a river flows quickly and
  follows a straight, narrow course. The steep
  slopes along the river erode rapidly and we see a
  deep,
• V-shaped valley

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• Waterfalls occur where a river meets an area of
  rock that is very hard, followed by softer rock.
  The soft rock wears away more quickly, creating a
  waterfall.

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• Lower down on its course, a river usually flows
  over more gently sloping land. It spreads out and
  erodes the land, forming a wide river valley.

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• A wide, flat area of land along a river is called
  a flood plain. A river can cover the flood plain
  during floods.

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• A river can have meanders, which are looplike
  bends in the river caused by uneven erosion.

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• Sometimes a meandering river forms an oxbow lake.
  This is a meander that has been cut off from the
  river when the water level drops.

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Complete River System
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What Features Do You Remember?

• High in the mountains near the rivers source
  are
• deep, V-shaped valleys.
• When the river runs over hard rock, then soft
  rock?
• Waterfalls
• When it flows over gently sloping land?
• Wide river valleys
• When it comes to a wide, flat area of land?
• Flood plains
• Looplike bends in the river caused by uneven
  erosion?
• Meanders

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River Deposits

• As water moves, it carries sediments with it. Any
  time moving water slows down, it drops some of
  the sediment.

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• Soil deposition creates new landforms, such as
  alluvial fans, which is a wide, sloping deposit
  of sediment.

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• Sediment deposited where a river flows into an
  ocean or lake builds up a landform called a
  delta, which can take a variety of shapes, like
  this birds foot delta.

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What Do You Remember?

• What happens when water flow slows down?
• The water drops its sediment.
• What are wide, sloping deposits of sediment?
• Alluvial fans
• When a river flows into an ocean or lake,
  sediment builds up at the mouth. What is this
  landform called?
• A delta

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Groundwater Erosion and Deposition
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• Not all rainwater goes to runoff or evaporates.
  Some of it soaks into the ground. This
  underground water is called groundwater.

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Underground water combines with carbon dioxide to
form a weak acid, which can dissolve limestone.
These hollowed out pockets in the underground
stone become caves.
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• Inside the caves, water containing dissolved
  limestone drips from the roof, forming
  stalactites (which hang down) and stalagmites
  (which grow up from the cave floor).

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• Sometimes the ground above a cave can collapse,
  creating a depression called a sinkhole.

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What Do You Remember?

• What is water that soaks into the ground?
• Groundwater
• How do caves form?
• Water combines with carbon dioxide to form a weak
  acid, which dissolves limestone.
• What are the deposits of dissolved limestone in
  caves called?
• Stalactites (ceiling) and Stalagmites (floor).
• What is the name for a collapsed cave?
• Sinkhole

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Section 3 The Force of Moving Water
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• A rivers moving water has energy, and we can use
  this energy to create power.

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There are two kinds of energy Potential Energy
and Kinetic Energy.
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.
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• As water moves down from a higher slope, its
  potential energy is released into kinetic energy.

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• This released energy picks up sediment, pebbles,
  and even rocks, which wear the riverbed away
  with a grinding action. This is called abrasion.

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• The power of a river depends on how steep it is
  (slope), how much water is flowing (volume) and
  the shape of its streambed.

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A streambed can be full of boulders and other
obstacles. All these rough surfaces can increase
friction, which causes the water to move every
which way. This is called turbulence.
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What Do You Remember?

• What are the two kinds of energy?
• Potential and Kinetic
• Water at a high place has which kind of energy?
• Potential
• Water flowing downhill has which kind of energy?
• Kinetic
• Moving water can be used to create
• Power
• The grinding action of pebbles and rocks on the
  riverbed is called
• Abrasion
• What are the three features which determine the
  power of a river?
• Slope, volume, and shape
• River obstcles like boulders create more
  friction, which increases
• Turbulence

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Section 4 Glaciers
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• A glacier is any large mass of ice that moves
  slowly over land.

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There are two kinds of glaciers

• Valley Glaciers, which are long, narrow glaciers
  which forms when snow and ice build up high in a
  mountain valley.

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• Continental Glaciers, which cover much of a
  continent or large island. They cover 10 of the
  earth today.

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Many times in the past, continental glaciers have
covered large parts of Earths surface. These
times are known as the ice ages.
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• Although glaciers move slowly, they are a major
  force of erosion.

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• The glacier flows over the land and picks up
  rocks. This is called plucking. As the rocks
  are dragged across the land they gouge and scrape
  the bedrock. This is called abrasion.

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When the glacier melts, it deposits the
sediments, which are called till. The till at
the edge of a glacier forms a ridge, which is
called a moraine A terminal moraine is the
farthest point reached by a glacier.
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• Continental glaciers can scoop out huge basins.
  The Great Lakes were formed by glaciers of the
  past.

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What Do You Remember?

• What is a glacier?
• A large mass of ice which moves over the land.
• What are the two kinds of glaciers?
• Valley glaciers and Continental glaciers.
• What is an ice age?
• A time when glaciers covered huge amounts of
  Earth.
• What are the two things glaciers do to change the
  surface of earth?
• Plucking and Abrasion
• What are sediments left by glaciers called?
• Till
• What is the ridge of sediment at the edge of a
  glacier?
• Moraine
• What is the farthest point of sediment left by a
  retreating glacier?
• Terminal Moraine.

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Section 5 Waves
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The energy in waves comes from wind that blows
across the waters surface.
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• The energy from waves can break apart rocks. Over
  time, waves can make the small cracks in the
  rocks larger. Eventually, pieces of the rock
  break off.

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Waves also erode land by abrasion. When a wave
hits land, the sediment in it is carried forward
by the wave and wears away rock like sandpaper
wearing away wood.
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Waves not only erode the land, but they also
deposit sediment.
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As waves reach the shore, they drop the sediment
they carry, forming a beach

• .

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What Do You Remember?

• What causes waves?
• The pressure of wind across the surface of water.
• What causes waves to break on the beach?
• The friction of the land slows down the bottom
  water, but the top water keeps moving forward.
• What are the two ways that waves erode land?
• They hit rocks and cause cracks, and they abrade
  the rocks with their sediment like sandpaper.
• What deposits do waves leave?
• Sandy beaches.

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Section 6 Wind
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• Wind is actually the weakest force of erosion.
  Water, ice, and waves are much stronger agents.
  But wind can be a powerful shaping force if there
  are no plants to hold the soil in place.

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• Wind picks up the smallest particles of sediment.
  The stronger the wind, the larger the particles
  it can pick up. This sweeping away of earth is
  called deflation.

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• When the wind slows down, or some obstacle traps
  the windblown material, sand dunes form. These
  are formed by the coarser particles blown by the
  wind.

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The finer particles in the wind are carried very
far away from their source. These are particles
of clay and silt and can create rich farmland.
This windblown material is called loess.
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What Do You Remember?

• When can wind be a powerful force for shaping
  earth?
• When there are few or no plants to hold the soil.
• What is the sweeping away of particles by wind?
• Deflation
• How are sand dunes formed?
• The wind-carried particles are trapped by
  obstacles or the wind slows down and drops the
  particles.
• What are the finer particles which can be carried
  long distances before they fall?
• Loess