Download weathering - Effingham Secondary School

SOCIAL STUDIES
GEOGRAPHY
SUBJECT TEACHER :
A ELLAN
Three types of weathering:
1. Physical weathering
2. Chemical weathering
3. Biological weathering
Physical Weathering / Mechanical
Weathering
 This happens when rocks are broken down into
smaller pieces through expansion and contraction.
 Rocks expand and contract due to temperature
changes.
 Physical weathering due to temperature changes
usually happens in areas where there is a large
temperature range (hot in the day and very cold at
night).
 There are TWO types of physical weathering that
happen as a result of expansion and contraction:
1.
Freeze-thaw weathering (Frost
shattering)
 Water is trapped in the joint (crack) of a rock.
 At night, when the temperature drops below 0°C
, the water that is trapped in the rock becomes
froze, it expands.
 During the day, as the temperature increases, the
water melts, causing the rock to contract.
 After some time, if this happens repeatedly, the
rock will weaken and eventually shatter into
pointed fragments.
 These pointed (angular) fragments are then
deposited at the foot of the slope and are known
as scree.
2. Exfoliation
 Repeated heating and cooling can cause the
outer layers of a rock to peel off in thin sheets.
Chemical weathering
 This happens when rocks are exposed to acid .
 Acid rain is the main cause of Chemical Weathering.
 As rain falls from clouds it absorbs the carbon dioxide
in the atmosphere . The water and carbon dioxide mix
to form an acidic rain.
 This acid from the rain enters the cracks of rocks
widening them. . The acid also dissolves or eats away
the rocks causing them to become weaker and break
apart.
1. Dissolved
 Rain water can dissolve limestone out of rocks.
 These rocks become weak and begin to break up.
 The limestone surface is called a limestone
pavement and is weathered to form grooves
called grikes and flat-topped ridges called clints.
 Limestone caves can also result when the
underground limestone is dissolved and removed
(for example, the Cango Caves in Oudtshoorn).
Honeycomb weathering
3. Plant acids
 Organic acids which are secreted (given off) by
plants result in rocks breaking down chemically.
(c) Biological weathering
 Caused by living animals
1. Growth of roots
 This is often the most
common type of
biological weathering.
 The roots of trees grow
into cracks and joints,
breaking rocks apart.
2. Animals burrowing
 Animals who burrow underground to make
home often disturb rocks, which can result in
rocks breaking up.
Location of weathering types
Weathering type
Physical (Exfoliation,
Pressure release)
Where it usually happens
Hot deserts
(there are big differences between daytime and
night time temperatures)
Freeze-thaw
Very cold areas
(daytime temperatures are above freezing point,
but night time temperatures drop below 0°C)
Chemical
In all areas where there is rain but more
commonly in hot areas where there is high
rainfall (because heat speeds up chemical
reactions)
Impact of human activities on
weathering
 Industries (factories), power stations and vehicle
emissions have significantly increased chemical
pollution in the atmosphere which has greatly
increased the rate of weathering.
 Acid rain, which is able to erode rocks such as
limestone, is caused by the increase of gases such
as carbon dioxide, nitrogen oxide and sulphur
dioxide. These gases increase the rate chemical
weathering processes.
 Acid rain causes limestone buildings to
deteriorate. It also causes metals to rust.
 Granite is a very strong rock so buildings which
are starting to deteriorate are given a granite
covering.
Now for an activity!!!
 Complete activity 3.1 and 3 .2 in your textbook .