Download Chapter 8

Chapter 8
Part 1
Weathering, Soils
and
Mass Movement
GRB Pages 62 - 71
Weathering and Erosion
• Weathering - Def. - 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.
• VIF - Most erosion that takes place on
Earth is caused by moving water
2 Types of Weathering
Mechanical weathering
– rocks are broken
down into smaller
pieces without
changing their
composition (what
they’re made of).
AKA - physical weathering
Chemical weathering
– rocks break down
as their minerals
change in
composition (they
become different
substances).
Types of Mechanical
Weathering - #1
• 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.
Mt. Brewster – looks solid, right?
Close up shows jagged rocks from FROST wedging!
Eventually, the rock splits from
repeated frost action!
Types of Mechanical
Weathering - #2
• Abrasion
– It is the physical
wearing down of
rocks as they rub or
bounce against
each other. This
process is most
common in windy
areas, under
glaciers, or in
stream channels.
– It can also happen
during rock slides
Types of Mechanical
Weathering - #3
• 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
clay…they all crack and
fall apart)!
Types of Mechanical
Weathering - #4
• 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.
Types of Mechanical
Weathering - #5
• Plant Roots
– The roots of trees
often wedge in
between cracks
in rocks and force
apart rocks even
further!