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Wearing Down Earth Surface

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					Wearing Down Earth’s Surface

   Unit C
   Chapter 6 Lesson 2
   C14 – C19
Objectives
   Identify destructive forces as processes that wear down
    Earth’s land features.

   Identify weathering as a destructive force.

   Recognize that weathering can be either mechanical or
    chemical

   Define erosion as the carrying away of weathered rock by
    water, wind, and glaciers.
Main Idea


   Destructive forces, such as weathering and erosion,
    wear down Earth’s surface features.
Vocabulary
   Erosion – (noun), destructive force in which pieces
    of rock are moved by water, wind, or moving ice.

   Sediment – (noun), small pieces of rock

   Weathering – (noun), destructive force that breaks
    down rocks into smaller pieces
Weathering
   A destructive force that breaks down rocks.

   Two types:

       Mechanical
       Chemical
Mechanical Weathering
   The breaking of larger rock into smaller rock called
    sediment
   Ice – water goes into cracks of rocks, freezes, and
    breaks rock apart.
   Moving air & Water – causes weakening of rock
    and it will crumble
   Living things – plant roots and burrowing animals
Chemical Weathering
   Rocks change into other materials
   Water is the main factor causing chemical
    weathering.
       Water dissolves minerals that make up certain rock
       Water dissolves certain chemicals from the air & soil to
        form a weak acid – which dissolves minerals
Cave Formation
                    Underground hollow areas
                     created by weathering
                    Weak acids seep into the
                     ground
                    Acid dissolves minerals in rock
                    Over time, holes produced in
                     the rock
                    At first full of water, but
                     eventually water drains
Limestone

   Many caves are made
    from limestone

   The minerals in limestone
    is easily dissolved by
    weak acid
Describe three ways that mechanical
weathering may occur?

     Water in the cracks of rocks, freezes, and busts
      rock into smaller pieces
     Wind or rushing water hitting rocks causes them to
      weaken and crumble.
     Plant roots breaks apart rock.
Why do many caverns form in
limestone?

    The minerals in limestone are easily dissolved by
     acids.
Erosion
   The carrying away of sediments by moving water,
    wind, or moving ice

   Common agent of erosion: Water moving down a
    river
River Valley Formation

                        Begins as a shallow
                         stream at higher
                         elevation
                        Stream grows and
                         carries sediment away
                        In time, the river cuts
                         a V-shaped valley
Frozen Water
                  Glaciers formed the rolling
                   plains and the Great Lakes.
                  Glaciers move down stream
                   toward the sea.
                  Move large amounts of rock &
                   soil.
                  They form hallows in the land
                   they erode. When they melt
                   they form lakes.
Ocean waves & Currents
   Crashing waves break down rock along coastlines.
   Sediments are dragged back and forth, slowly turning
    into sand.
   Wind & Waves erode the land.
   Sea caves may join to form a sea arch.
   Erosion may continue until arch falls creating a sea
    stack.
Weathering vs. Erosion
   Weathering                    Erosion

   Process that breaks down      The carrying away of
    rock into smaller pieces       sediments by moving
    called sediment                water, wind, or moving ice
Slow and Fast Changes
   Chemical weathering = takes thousands of years

   But, after a cave is formed, the weight my be to
    great causing a sudden collapse which forms a
    sinkhole.
Sinkholes

               Form very suddenly

               Land above weathered rock
                sinks into a hole.
Landslides
   Occur suddenly due to
    erosion

   Large movements of land
    that tumble down a steep
    slope.

   Mudslides, rock falls, &
    avalanches
Causes of landslides
   Gravity is the main cause
   Erosion from rivers, rain, glaciers, or ocean water
   These steepen the slope and loosen sediment
   A disturbance, such as an earthquake, can shake
    the rocks loose.
   Volcanoes can cause landslides also.
How are a sinkhole and a landslide
alike? How are they different?

   ALIKE                       DIFFERENT
   Occur quickly               Sinkhole is formed when
   Result of weathering &       rock above a cave falls
    erosion                      into the cave
   Gravity pulls sediment      In a landslide, rocks and
    downward                     soil tumble down a hill.
    What are the four forces that can
    combine to cause a landslide?
   Erosion loosens sediments making a steep slope
   Rain causes sediments to become heavy with water
   Earthquakes shake the sediments loose
   Gravity carries the sediments downhill
Turn to page C19 to answer the Review
questions.
Rocks break down during a destructive
process called what?

    weathering
This forms when agents of mechanical
weathering break rocks into smaller
pieces.

    sediment
Wind, water, and moving ice move
sediments during the process of
________.

    erosion
The rocky outer layer of Earth’s surface
is called the ________.

     crust
A ______ map shows the shape of
surface features and their elevations.

     topographic
A flat landform found at a high elevation
is called a ______.

     plateau
Earth’s crust consists mostly of

     A.   glaciers
     B.   Pressurized metals
     C.   magma
     D.   Solid Rock
Earth’s crust consists mostly of

     D. Solid Rock
List three causes of mechanical
weathering.

     Ice
     Wind
     Moving water
     Plant & animal activity
Describe how chemical weathering can
take place below Earth’s surface.

    Water seeps into deep cracks and dissolves minerals
     in rock.
    Acid rain seeps into cracks in rock and dissolves
     below the surface.
Wind, running water, and glaciers lead to erosion.
Which one moves sediments most quickly?
Which moves sediments most slowly? Which is
capable of moving the heaviest sediments?


   Fast-flowing water & high speed winds can carry
    small sediments quickly.
   Glaciers move most slowly, but are capable of
    carrying large amounts of sediment with them.

				
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