Weathering

1

• Weathering Erosion

2
Weathering and Erosion

• Weathering is the break down of rocks that have
  been exposed to the atmosphere
• Once the rocks are broken down, the pieces are
  transported from one place to another. This
  process is called erosion
• Erosion is caused by wind, moving water (streams,
  waves, ocean currents), ice (glaciers), and by
  gravity.
• Most erosion that takes place on Earth is caused
  by moving water

3
Types of Weathering

•   Mechanical weathering rocks are broken down
  into smaller pieces without changing their
  composition (doesnt change what theyre made of)

• Chemical weathering - rocks break down as their
  minerals change in composition (they become
  different substances)

4
Types of Mechanical Weathering

• Ice wedging/frost action
• water enters small cracks in the rock
• When it freezes, it expands and forces the crack
  to open more
• The process repeats over again until the rock
  breaks apart

5
(No Transcript)
6
Eventually, the rock splits from repeated frost
action!
7
Types of Mechanical Weathering

• Wetting and drying
• breaks up rocks that are made from clay
• When they are wet they expand, and they shrink as
  they dry
• As this repeats over and over, the clay becomes
  weak and cracks (think of all the projects you
  have made out of claythey all crack and fall
  apart)!

8
(No Transcript)
9
(No Transcript)
10
Types of Mechanical Weathering

• Exfoliation
• soil and rock is removed (glaciers or uplifting),
  exposing rock found deep underground
• This releases the pressure causing the surface of
  the rock to expand and eventually crack

11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
Types of Mechanical Weathering

• Plant Roots
• The deep roots of trees often break apart rocks
• Lichen Moss
• These low to the ground plants can grow on rocks
  and eventually break them apart

15
(No Transcript)
16
Types of Chemical Weathering

• Hydrolysis
• water (hydro) reacts with minerals such as
  feldspar and form clay

17
(No Transcript)
18
Types of Chemical Weathering

• Oxidation
• oxygen reacts with some minerals, especially
  those containing iron (magnetite) to form rust
  (called iron oxide)
• This occurs faster with water!

19
Chemical weathering of basalt
20
Iron Banding in Basalt
21
Oxidative weathering of mineral deposits (new
deposits are white/yellow, weathered deposits are
reddish-brown)
22
Types of Chemical Weathering

• Carbonic acid
• carbon dioxide (CO²) dissolves in water to form
  this acid
• can cause minerals to dissolve, especially those
  containing calcite

23
Gnarled Rock a formation of limestone
chemically weathered by acid rain
24
(No Transcript)
25
Factors which affect rates of weathering

• Rocks resistance to weathering (HARDNESS)
• Amount of surface area
• Climate
• Chemical weathering occurs faster in warm, wet
  climates
• Mechanical weathering occurs faster in cold or
  dry climates

26
The central area of rock was less resistant to
weatheringthus the arch was formed!
27
(No Transcript)
28
Surface Area

• Greater surface area increases the rate of
  weathering
• Surface area is the amount of rock surfaces
  exposed to the atmosphere
• Weathering creates more surface area

29
(No Transcript)
30
Dry Climate Mechanical Weathering!
Devils Marbles, Australia Mechanical
weathering from wind and sand!
31
Warm Climate Chemical Weathering
Parthenon Athens, Greece
32
(No Transcript)