 WEATHERING:
the process by which rocks are
BROKEN down by the action of PHYSICAL or
CHEMICAL processes.
 2 Types of Weathering
1. MECHANICAL weathering: rocks are broken down
into SMALLER pieces without being chemically
changed. This is caused by several things.

Examples:
• ICE:
 FROST action – repeated freezing and thawing
 ICE Wedging: frost action where WATER seeps into cracks
during warm weather, then freezes, EXPANDS, and breaks
rock during cold weather.

Examples
• ABRASION: other rocks or sand rub and WEAR away
other rocks
• WIND - abrasion caused by the wind BLOWING
sediments
• WATER – abrasion caused by waves moving sediments
• GRAVITY: abrasion caused by rocks falling on other
rocks and from mountains and hills.
• PLANTS: ROOTS get into cracks, grow, expand, and
break rocks
• ANIMALS: animals burrow & cause abrasion by
BURROWING (digging)
• Wetting and Drying - causes clay minerals to
expand and contract, and salts may dissolve and
re precipitate.
• Sheet Joining - surface sheets of material
fracture and exfoliate because of pressure
release.
• Exfoliation - The peeling of rounded thin layers
from the rocks surface.
 The
rocks are
essentially torn apart
by physical force,
rather than by
chemical breakdown.
CHEMICAL weathering : rocks broken down into smaller piece
and are BROKEN DOWN by a CHEMICAL reaction.






WATER: (Hydrolysis) can chemically change
rocks over
millions of years
ACID RAIN: caused by PRECIPITATION (or
pollution)\
ACIDS IN LIVING THINGS: ex: LICHENS
produce acids that break down rock.
AIR- OXIDATION: OXYGEN in air reacts with
iron in certain rocks to make RUST (oxide).
Carbon Dioxide mixes with rain water to form
Carbonic Acid. It dissolves rock and caves form
underground.
Sulfuric Acid is pollution from factories that
dissolves in rainwater to weather metals and
rocks.
Lichens produce acid that break
down rock.
 This
depends on many things such as
CLIMATE, elevation, and composition
(what the rock is made of).




DIFFERENTIAL WEATHERING: when SOFTER rocks wear away
from the weather & leave the HARDER and more weatherresistant rocks behind (ex: Devil’s Tower – the softer part of the
volcano is gone, but the harder rock is left behind.)
THE SHAPE OF THE ROCK: the MORE rock that is exposed, the
MORE it will weather away.
CLIMATE:
• Chemical weathering happens FASTER in warmer, HUMID
climates
• Mechanical weathering happens faster in COOLER climates
where there is a lot of FREEZING & thawing
ELEVATION:
• HIGHER rocks weather away faster because they are exposed
to ICE, WIND & RAIN more
• The steeper the SLOPE of the mountain, the faster the
SEDIMENTS will flow downhill and the faster the ROCKS will
weather away

Mechanical Weathering:

Devil’s Tower: the softer outer
part of the volcano is gone, but
the harder rock is left behind

Chemical Weathering:

SOIL: a loose mixture
of MINERAL
fragments, ORGANIC
material, water, & air
that can support the
growth of
VEGETATION.

PARENT ROCK: a rock
formation that was the
SOURCE of soil






O, -humus (dark soil full of
nutrients from decaying
plants and animals)
A – topsoil
E- LEACHING occurs
(water drains nutrients
down)
B - collects NUTRIENTS
from upper layers
C- a lot of WEATHERED
bedrock—big chunks
R- bedrock
1. Humus:
2. Leaching:
1. TEXTURE: size of the sediments
SAND: has the LARGEST grains and water
moves through it easily
SILT: medium sized grain
CLAY: smallest grains and WATER does not
move through easily
http://www.iconn.org/presentations/CECA_Fall2007/Roche_files/slide0074_image027.jpg
 2.
STRUCTURE: soil sediments can CLUMP in
some areas and be loose in other areas
3. SOIL FERTILITY: the soil’s ability to
SUPPORT plant growth- Humus is great for
this
 4.
TEMPERATURE: plants can’t GROW if the
soil temperature is too high or too LOW
 5.
MOISTURE: depends on the soil’s texture

6. pH: influences which nutrients will be available to
plants
http://www.worsleyschool.net/science/files/pH/phscale.gif

7. Color:
• the DARKER the soil,
the more organic and
FERTILE
http://climatelab.org/@api/deki/files/190/=Biochar_dark_soil_betchkal.jpg
• reddish & yellow contain
IRON, but are also fertile
http://eusoils.jrc.ec.europa.eu/projects/soil_atlas/images/1-39%2028_img_2.jpg
• whitish contain SALTS &
are not fertile for farming
crops
http://www.wunderground.com/data/wximagenew/m/MikeTheiss
/140.jpg

TROPICAL RAIN FOREST SOIL: not very fertile, too
much LEACHING (water) from heavy rain, & too many
PLANTS soak up nutrients

DESERT SOIL: little RAIN, so little weathering occurs,
but no rain to wash away SALTS

TEMPERATE FOREST SOIL: BEST for crops &
weathering

ARCTIC SOIL: little water & COLD temperatures so
there is little decomposition to provide nutrients
A
method to PROTECT soil from
EROSION & nutrient loss
 WHY
DO WE NEED SOIL?
• For plant growth, for decomposers to live in
1.
CONTOUR
Plowing:
planting ROWS of
crops across
HILLS instead of
up & down to hold
soil in place
Minnesota."
Online Photograph. Britannica Student Encyclopædia.
3 Oct. 2008 <http://student.britannica.com/ebi/art-56029>.
2. Terracing:
changing a
steep slope into
a series of
FLAT stairs to
plant crops on
http://en.wikipedia.org/wiki/Image:Rice_terraces.png
3. NO-TILL
Farming: leaving
old, HARVESTED
plants lay on the
top of the field to
hold soil down
http://whyfiles.org/241GM_2/index.php?g=3.txt
Crop ROTATION:
planting crops in
DIFFERENT fields each
year so that the
NUTRIENTS of one field
are not used up right away
COVER Crops:
crops are planted in-between HARVESTS to
replace nutrients & cover the GROUND to
prevent erosion from wind & rain