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Weathering Erosion Weathering


									Weathering & Erosion
    What is weathering?

Weathering is a set of physical,
     chemical and biological
   processes that change the
physical and chemical properties
 of rocks and soil at or near the
         earth's surface.
        More about weathering

   Definition – the breakdown of rock to
    form sediment [very small pieces of
     Weathering happens to rocks that are
     Weathering is part of the Rock Cycle
      There are three types of
 Mechanical [sometimes called physical]
 Chemical

 Biological
Mechanical weathering breaks rocks
     down into smaller pieces.

Types of mechanical weathering include
frost wedging, exfoliation, and thermal
Chemical weathering breaks rocks down
  chemically adding or removing chemical
  elements, and changes them into other
 Chemical weathering consists of chemical
  reactions, most of which involve water.
Biological weathering is the breakdown
   of rock caused by the action of living
  organisms, including plants, burrowing
           animals, and lichens.

 A lichen is a combination of fungus and algae,
   living together in a symbiotic relationship.
 Lichens can live on bare rock, and they break
     down rocks by secreting acids and other
Click to watch and learn about
     Let’s investigate
mechanical weathering first.
In mechanical weathering, a rock is
  broken down into smaller pieces
    without changing its mineral
Enchanted rock
   is a huge
  example of
close to home.
Observe photographs of the
different types of mechanical
Review mechanical
  Now, let’s look at
chemical weathering.
In chemical weathering, a rock
  is broken down by chemical
    reactions that change its
    mineral composition and
      physical and chemical
 Chemical weathering happens
when the minerals that make up
 a rock are changed, leading to
  the disintegration of the rock
 Chemical weathering happens
      quickly in warm, moist
  environments because water is
     needed for the chemical
The warm weather speeds up the
Not all minerals are prone to chemical
  weathering. For example, feldspar
 and quartz, are common minerals in
 the rock granite, have very different
    levels of resistance to chemical
 Quartz doesn’t weather very easily,
 but feldspar does. Over a long time,
     it chemically changes into clay
Review chemical weathering:
Biological weathering involves
 processes that can be either
chemical or physical in nature.

Biological weathering can be
 considered special types of
   mechanical or chemical
Biological weathering – What is it?
       Some biological weathering
            processes are:
   1. Rocks can break because of animal
   2. Tree roots grow into cracks and widen
    them, which helps physical weathering.
   3. Bacteria, lichens and other organisms
    secrete acidic solutions, which helps
    chemical weathering.
Read about biological weathering
 and view photographs to help
   understand the processes.
 Lichens on
rocks cause
Plants growing in rocks break the
          rocks apart.
Review biological weathering:
      Chapter Book Assignment

   Complete the handouts
   Chapter 23: Section 1-3
   Crossword Puzzle
Now let’s move on to
         What is erosion?

Erosion is defined as the removal and
   movement of earth materials by
            natural agents.
Some of these agents include glaciers,
 wind, water, earthquakes, volcanoes,
  tornadoes, hurricanes, mud flows,
            and avalanches.
 How are erosion & weathering
     Weathering involves two
      [mechanical, chemical]
that often work together to break
    down rocks. Both processes
  occur in place. No movement is
       involved in weathering.
As soon as a rock particle (loosened
     by one of the two weathering
      processes) moves, we call it
       erosion or mass wasting.
 Mass wasting is simply movement
       down slope due to gravity.
Rock falls, slumps, and debris flows
  are all examples of mass wasting.
We call it erosion if the rock particle
   is moved by some flowing agent
        such as air, water or ice.
  In a nutshell: if a particle is
    loosened, chemically or
    mechanically, but stays
  put, we call it weathering.
Once the particle starts moving,
       we call it erosion.
What are the different types of
 Water is the most important
 erosional agent and erodes
most often as running water in
      streams or rivers.
 Water in all its forms is erosional.
  Raindrops create splash erosion
   that moves tiny particles of soil.
Water collecting on the surface of the
soil collects as it moves towards tiny
 streams and creates sheet erosion.
Observe river erosion causing
  Erosion by wind is known as
 aeolian erosion (named after
Aeolus, the Greek god of winds)
 and usually occurs in deserts.
 Aeolian erosion of sand in the
desert is partially responsible for
 the formation of sand dunes.
Painted Desert National Monument
The erosive power of moving ice is
    actually a greater than the
  power of water. However since
  water is much more common, it
    is responsible for a greater
 amount of erosion on the earth's
 Glaciers cause erosion two ways -
   they pluck and abrade. Plucking
takes place by water entering cracks
   under the glacier, freezing, and
 breaking off pieces of rock that are
then moved by the glacier. Abrasion
cuts into the rock under the glacier,
  scooping rock up like a bulldozer
  and smoothing and polishing the
            rock surface.
Athabasca Glacier - Jasper, Canada
Waves in oceans and other large
  bodies of water cause coastal
  The power of ocean waves is
awesome; large storm waves can
produce 2000 pounds of pressure
per square foot. The pure energy
of waves along with the chemical
   content of the water is what
 erodes the rock of the coastline.
Wave action in Calvert County Maryland
Watch wave erosion
Observe landscapes formed by
Let’s look at some erosion
       close to home.
 Remember the flood of 2002?
   Click the arch to jog your
Clicking on the picture will take you to
a website with several photographs of
the erosion that took place at Canyon
         Lake during the flood.
 Click on the pictures to see a larger
    Observe each photo – they are
    Review weathering & erosion
  vocabulary with online flashcards.

Note: Some of the terms on the cards
   have not been covered during this
 lesson. Read them anyway; it never
   hurts to expand your vocabulary!
          The End!

Double check your answers & turn
            them in!
Unless otherwise noted, the
source for all photographs in
     this presentation is

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