Download weathering - HBHS12Geo

WEATHERING
WEATHERING IS:
• The gradual breakdown of rock which lies
exposed to weather.
TYPES OF
WEATHERING
• Physical
• Chemical
• Biological
• Weathering
PHYSICAL
WEATHERING
Exfoliation
This occurs when rock that has been formed
at great pressures under the earths
surface is uplifted. As the tremendous
weight of the overburden on top of the
rock is weathered and the rock exposed,
the release in pressure from deep burial is
removed. Because of this layer after layer
of the rock peels off in curved slabs or
sheets. Dome shaped features are the
result of exfoliation.
Frost Action/Freeze-thaw
•Water seeps into small cracks in rocks.
When the water freezes it expands up to 9%
by volume creating great pressure. The
crack widens and allows water to seep
deeper into the rock. Eventually the rock
splits into smaller pieces.
BIOLOGICAL
WEATHERING
• This occurs when vegetation establishes
itself on top of thin soils. Root systems
grow through these soils and start to
invade the rock below the surface. As it
does so the roots find weaknesses in the
rock and exploit these weaknesses by
growing into them and act as a wedge to
break the rock apart.
Plant Roots--Physical Weathering
In the picture, plant roots have grown into the sedimentary rock creating cracks, and
causing some of the wall to collapse, exposing the inner rock. Mass movement of
weathered materials down slope often undermines the foundations of trees and causes
them to lean in the direction of the stream valley as seen on the right side of this photo.
CHEMICAL
WEATHERING
OXIDATION
• This occurs when certain metallic
elements combine with oxygen to form
oxides. The most common form is the
“rusting” of iron in rocks that produces the
reddish brown stain of iron oxide. The
simple oxidation reaction in iron is:
• Iron(Fe)+oxygen(O2)=iron oxide(Fe2O3).
• As the iron is removed from the rock it
becomes more susceptible to further
weathering
Oxidation--Chemical Weathering
This picture shows that chemical weathering has taken place by oxidation. When we
used the rock hammer to chop into the cream coloured clay layer in the bottom of the
stream, we saw that the original colour of the clay was blue. The blue colour is a result
of iron compounds containing ferrous iron. These compounds change to a cream
colour when the material reacts with oxygen in the atmosphere changing the iron to its
ferric form. Changing iron from its ferrous form to its ferric form is a typical oxidation
chemical reaction.