Weathering
You will need your journal and a writing utensil
What do you think caused this?
http://en.wikipedia.org/wiki/File:KharazaArch.jpg
http://commons.wikimedia.org/wiki/File:Toad_Rock_-_geograph.org.uk_-_767454.jpg
Weathering
• Weathering is the
breakdown of rock and
other substances at the
Earth’s surface
• Two main types of
weathering:
• Mechanical
• Chemical
Some things in nature that cause weathering
• Water running over rocks, causing the rocks to hit one
another and break into smaller pieces
• Plant roots growing into rocks
• Water in cracks in the rock freezing and expanding
• Wind carrying sand that wears away rock
• Carbon dioxide dissolved in water forming an acid that eats
holes in the rock
Mechanical or Physical Weathering
• Mechanical weathering – when rocks are broken
apart by a physical force.
• During mechanical weathering, no new
substances are produced. The rock gets smaller,
but it stays the same kind of rock.
Examples of Mechanical Weathering
Ice Wedging
Release of Pressure
Abrasion
Plant and Animal Action
New Mexico's Bisti Badlands have been carved by millions of years of
mechanical weathering. Mechanical weathering is the process of
atmospheric forces, such as rain and wind, wearing away rock and soil.
Photograph by Dawn Parker, MyShot
Via National Geographic
Ice Wedging – when water freezes in a crack
of a rock it expands and pushes the walls of
the crack apart eventually breaking the rock
Frost Action or ice wedging slowly breaks up this
sedimentary rock into unusual shapes.
Release of Pressure
Rocks break off into
sheets along joints
which are parallel to
the surface; caused by
expansion of rock due
to uplift and removal
of surface material
that originally buried
the rock
ABRASION is the process of sand and other rock particles,
such as sediment, are carried by wind, water, or ice over an
exposed rock surface.
This is a picture of a glacier
which carves out a Ushaped valley where it
flows dragging rocks and
boulders along the way.
These rocks have been blasted by wind and
sand causing them to become rounded.
WIND ABRASION
This rock has
undergone abrasion
from the pond water's
sediments for a while.
Plant and Animal Action
Growth of Plants
Biological Weathering
Action of animals
• When animals, and some
insects as well, burrow in
the ground, they loosen
and break apart rocks in
the soil. Moles, gophers,
prairie dogs, ants, and
even earthworms cause
this to happen.
Discovery Education – Physical
Weathering video segment
• http://app.discoveryeducation.com/player/view/assetGuid/F3
E2749C-D871-4EBA-930F-F30574A4CF79
Chemical Weathering
• Chemical weathering is the process that breaks down rocks
using chemical changes.
• These changes either break down the rock or weaken the rock to
allow for physical weathering.
• The main agents of chemical weathering are water, oxygen and
weak acids.
• It can remove certain minerals from rocks
• It can change the minerals into new substances
Examples of Chemical Weathering
Oxidation
Dissolution
Carbonation
Acid Rain
Oxidation
• Iron in rock can react
with oxygen and water to
form rust, making the
rock reddish and
crumbly.
New substances due to oxidation:
– rock softer than original
– easier for other forces to break rock apart
– “rusting” of the rock
– color change in the rock
Dissolution
• Dissolving a rock in
water is yet another
form of chemical
weathering, called
solution
• Solution occurs
when compounds
are dissolved into
water.
• Halite, gypsum,
and limestone are
most susceptible to
solution.
Carbonation
• CO2 dissolves in rain water
and creates carbonic acid
• Carbonic acid easily weathers
limestone making holes in the
rock
• Rocks such as limestone and
dolomite can be entirely
dissolved, leaving extensive
caverns.
• In states with bedrock
composed of calcite, such
as Florida this process
can cause extensive
damage to structures
above.
• Often, caverns are cut out
of the rock, the structures
on top are heavy, and
everything on top
collapses into the cavern,
leaving what is called a
sinkhole. This sinkhole
can swallow many houses
at a time.
Living
organisms
Lichens
1908
to
1969
Acid rain has eaten away this
limestone statue.
Acid Rain
Discovery Education – Chemical
Weathering video segment
• http://app.discoveryeducation.com/player/view/assetGuid/F3
E2749C-D871-4EBA-930F-F30574A4CF79
Exit Ticket
• Today I learned that there are two types of weathering ______________________ and _________________.
• An example of each type • Mechanical - _______________________
• Chemical - _______________________