What is weathering by vmarcelo

VIEWS: 4,546 PAGES: 45

									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 rock]
   Weathering happens to rocks that
    are NOT MOVING
   Weathering is part of the Rock
    Cycle
There are three types of
weathering

 Mechanical [sometimes called
  physical]
 Chemical
 Biological
Mechanical weathering breaks rocks
down into smaller pieces.

Types of mechanical weathering include
frost wedging, exfoliation, and thermal
expansion.
Chemical weathering breaks
rocks down chemically adding or
removing chemical elements, and
changes them into other
materials.
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 chemicals.
Let’s investigate
mechanical weathering first.
In mechanical weathering, a rock is
broken down into smaller pieces
without changing its mineral
composition.
There are several different processes
  that cause mechanical weathering.

 Look on page 325 and 326 of your
 science book to discover how plants,
    animals, and ice wedging cause
        mechanical weathering.
 Observe the effects of
 mechanical weathering
Click on the link below and follow the
instructions to observe mechanical
weathering:
http://www.classzone.com/books/earth_scie
nce/terc/content/visualizations/es1201/es12
01page01.cfm?chapter_no=visualization
Observe photographs of the
different types of mechanical
weathering.

Click on the link below:
http://www.geosci.unc.edu/faculty/glazner/
Images/Weathering/weathering.html
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 properties
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
           reactions.
The warm weather speeds up
        the reactions.
 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
            weathering.
  Quartz doesn’t weather very
easily, but feldspar does. Over a
long time, it chemically changes
        into clay minerals.
Biological weathering – What is it?
Biological weathering involves
processes that can be either
chemical or physical in nature.

Biological weathering can be
considered special types of
mechanical or chemical
weathering.
Some biological weathering
processes are:

 1. Rocks can break because of animal
  burrowing.
 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.
Lichens on
rocks cause
biological
weathering.
Plants growing in rocks break the
          rocks apart.
Now let’s move on to
EROSION
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
different?

   Weathering involves two
            processes
    [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.
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.
 Click on the link below to
observe river erosion causing
waterfalls:


http://www.classzone.com/books/earth_scie
nce/terc/content/visualizations/es1305/es13
05page01.cfm?chapter_no=visualization
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 surface.
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. In abrasion, the glacier
   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 erosion.

 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:


http://www.classzone.com/book
s/earth_science/terc/content/vis
ualizations/es1606/es1606page
01.cfm?chapter_no=visualizatio
n
Observe landscapes formed by
erosion:


http://www.classzone.com/book
s/earth_science/terc/content/vis
ualizations/es1205/es1205page
01.cfm?chapter_no=visualizatio
n
   Runoff
 Runoff is water that doesn't soak into the ground or
  evaporate but instead flows across Earth's surface.
 Runoff does not happen randomly, it depends on several
  factors.
   For example, if light rain falls for several hours then runoff
     most likely won't form because the water will have time to
     evaporate. But, if heavy rain falls for less than an hour the
     water will not have time to evaporate or soak up and runoff
     will form.
   It also depends where the water falls. When it rains on a
     steep slope, gravity pulls the water down the slope,
     therefore it becomes runoff. It is runoff because it is
     roaming the Earth's surface having not been evaporated or
     soaked up.
 Runoff mainly causes three types of erosion: rill erosion,
  gully erosion, and sheet erosion.
Rill Erosion
 Rill erosion occurs
  when runoff flows
  and a small stream
  forms and carries
  away plants and
  soil leaving a scar
  or channel on the
  side of the slope. A
  rill is the channel
  left on the side of
  the slope.
Gully Erosion
 Gully erosion is
  when a rill channel
  becomes much
  deeper and wider
  which forms a
  gully. Gully erosion
  is basically rill
  erosion on a much
  higher level.
Sheet Erosion
 Sheet erosion is when
  water flowing into
  lower elevations loses
  energy and leaves
  behind sediments that
  cover the soil like a
  sheet.
 Floodwaters spilling
  our of rivers often flow
  in sheets and can
  cause sheet erosion.
Deposition
 As water moves through a river
  system, it loses some of its energy
  and slows down.
 As it slows, the water can no longer
  carry everything in it.
 As a result, the water drops sediment
  to the bottom of the stream.
 This process is called deposition.
Deltas and Alluvial Fans
 The sediments dropped by the slowing water
  (deposition) falls to the floor of the water or river
  bank.
 The collection of sediments from a lake or ocean is
  called a delta.
 The collection of sediments from a river from a
  mountain valley to a flat plain is called an alluvial fan.
 These sediments provide lots of nourishment for the
  vegetation around them.
   Agriculture around the Nile River and the Mississippi
      River depend on them.
The End…
 Use any remaining time to double
  check your worksheet
 Then, turn it in!

								
To top