2. Weathering
The decomposition
and disintegration
of rocks in situ.

3. Decomposition
Refers to
chemical
weathering and
creates changes
in rock
substances
For Example:
Granite
decompose into
clay

4. Disintegration
• Produces smaller,
angular fragments of
the same rocks, such as
scree.
• No change in chemical
composition.
• For example: Granite
disintegrates into
smaller fragment but
rock type is still granite

5. Erosion
• Is the breaking
down and
removal of rocks
• agents of
erosion such as
rivers, glaciers
and the sea

6. Denudation
Weathering
and erosion
working
together
causing
landscape to
be worn down

7. Regolith
• a layer of loose material
covering solid rock.
• It includes dust, soil,
broken rock, and other
related materials and is
present on Earth, the
Moon, some asteroids,
and other terrestrial
planets and moons.

9. • Weathering and erosion depend on each other
• One could not exist very effectively without the
other
• Weathering break down a rock surface to produce a
pile of loose debris (Regolith)
• Erosion then removes the broken down rock
fragments often using the ‘weathered fragments’ as
‘tools’ for erosion.
• This exposes a fresh rock surface to the processes of
weathering and so the two processes continue

10. Three Types of Weathering
1. Physical Weathering
2. Chemical Weathering
3. Biological Weathering

11. Physical Weathering
• Disintegration of rock into smaller particles
by mechanical processes but without any
change in the chemical composition of the
rock
• Where is it likely to occur?
- devoid of vegetation
- deserts, high mountains, arctic regions
• End product- sands

12. Four main types of Physical /
Mechanical Weathering
1. Freeze-thaw action / Frost Shattering / Ice crystal
Growth
2. Salt crystalisation
3. Granular disintegration /Exfoliation
4. Pressure release

13. Freeze thaw action
1. When
water within
Continuation
the cracks
of alternate
freezes to
freezing and
ice, its
thawing will
volume
cause joints
expands as
and pores
much as 9%.
enlarge and
shatter.
2. This expansion creates a powerful
force called frost action or freeze-thaw
action, which can exceed the tensional
strength of rock.

17. Factors encouraging Frost Shattering /
Freeze Thaw action
• Rapid freezing with a minimum temperature
of -50C
• Frequent cycle of freeze thaw actions
• High degree of porosity or density of cracks in
a rock
• Presence of water

18. Salt-crystal growth (haloclasty)
• causes disintegration of rocks
• saline solutions seep into cracks and joints in the rocks and
evaporate, leaving salt crystals behind.
• salt crystals expand as they are heated up, exerting
pressure on the confining rock.
• may also take place when solutions decompose rocks
• Example: limestone and chalk  to form salt solutions of
sodium sulfate or Sodium carbonate, when the moisture
evaporates to form salt crystals.

19. Salt weathering of building Salt weathering of sandstone near
stone on the island of Gozo, Qobustan, Azerbaijan.
Malta

20. Insolation weathering / heating and cooling
• Expansion and
contraction of rock
particles resulting from
extreme variations in
temperature
• Significant in desert
area where diurnal
temperature range is
high (400C – 500C)

23. Pressure release
• It is not caused by element of the weather.
However, it does occur in situ
• Involve the disintegration of rocks to expand
• Pressure release can be caused:
i. Erosion of overlying rock
ii. When huge ice sheets melt at the end of a
glacial period

24. Pressure release:
• common in intrusive rocks that were
formed deep under ground.
• E.g. granite batholiths.
• When this rock is exposed to the surface
by uplift and erosion the rock expands and
sheet joints form parallel to the rock
surface.

26. What type of weathering?
W

27. What type of weathering?

28. What type of physical weathering?

29. Classwork
• Ross pg 51 – Noting activity