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Transcript
Rocks on the Earth’s
surface undergo
changes in appearance
and composition
Weathering: Physical or chemical
changes in rock material exposed
at surface
1. Mechanicalphysically change rock into
smaller pieces
2. Chemicalbreakdown of rock by changing
its chemical composition
Types of Mechanical
Weathering
1. Exfoliation- process
where sheets of rock
peel or flake away
Example of exfoliation:
Types of Mechanical
Weathering
weathering
2. Frost wedging- occurs
when water seeps into
rocks and freezes
Ice
wedging
Types of Mechanical
Weathering
weathering
3. Biological activityroots of plants and
burrowing animals
weather away rock
Weathering by plants
Weathering by sandmartins
nesting in cliff
Types of Mechanical
Weathering
weathering
4. Abrasion- collision of
rock with one another
resulting in breaking
and wearing away.
• Abrasion refers to the breaking and
grinding away of solid rock by collisions
with moving particles.
• Abrasion takes place in many
environments:
– fast-moving streams
– beaches subject to storm waves
– desert environments with high winds
– beneath glaciers that are loaded
with fragments of rock.
Water-carried particles
eating away at the rock
Storm waves have eaten
away at the shoreline
The ocean waves have eroded
this beach leaving behind a
cliff as the soil was washed
away
Observe the effects of
mechanical
weathering.
Types of Chemical
Weathering
1. Hydrolysis:
Change in composition
of minerals when they
react with water
Feldspar combines with H2O to
form a common clay called kaolin
Types of Chemical
Weathering
2. Carbonation –
When some minerals come
in contact with carbonic
acid, they form a new
product
Stalactites caused by
carbonation
Limestone
is eaten
away by
acid and
deposits as
it drips
from ceiling
of cavern
Types of Chemical
Weathering
3. Oxidation –
When metallic elements
combine with oxygen
Oxidation =
rust!
Types of Chemical
Weathering
4. Acid
Precipitation
“acid rain”
Types of Chemical
Weathering
5. Plant acids – plants
secrete acids that
erode away the rock
Lichens and
mosses grow
on rocks and
secrete
weak acids
that dissolve
the surface
Rate of
weathering
depends on
4 things…
1. Rock composition
• Igneous and
metamorphic rocks
don’t weather easily
• Sedimentary rocks do
2. Amount of exposure
• More exposure it receives,
faster it will weather
• Amount of time and
amount of surface area
exposed is also important
3. Climate
• Slow in very hot / very
cold climates
• Fairly rapid in warm,
humid climates
Cleopatra’s needle after only
one century in New York City
4. Topography
• Elevation or slope of
surface where rock is
located affects rate of
weathering
Results of Weathering:
• Humus
• Soil
• Bedrock
• Regolith
Humus
• Dark, organic material,
remains of animals and
plants
Humus:
Soil
• Complex mixture of
minerals, water, gases,
and remains of plants
and animals
Regolith
• A layer of weathered rock
fragments
• (covers much of Earth’s
surface)
Bedrock
• Solid, unweathered
rock that lies beneath
regolith
Bedrock
Bedrock
Composition of Soil:
Soil Texture:
• The proportion of different
soil particle sizes
• Influences the soil’s ability
to support plants
•Consists of 3 main types
classified by particle size
Soil Composition
1. Clays: less than .0002 mm
in diameter (feldspar)
2.Silts: between .0002mm
- .06mm
3.Sand: between .06mm – 2
mm (granite)
The portions of clay,
silt, and sands depends
on the parent material
Parent material
or “parent rock”
is the rock from which the
soil was weathered.
CLAY
SILT
SAND
Soil Texture Diagram
Loamy soils
are the best
for growing
plants
Soil profile:
• A cross-section in which the
layers of the soil and
bedrock can be seen
• Each layer is called a horizon.
• In fully developed residual
soil, there are three horizons
A
Humus &
Topsoil
B
C
R
Parent Rock
Subsoil
Regolith
A horizon
(topsoil)
• mixture of organic and small
rock particles
B horizon
(subsoil)
•contains minerals and clay
C horizon
(regolith)
•partially
weathered
bedrock
Types of Soil
• Climate is most
important factor
influencing soil
formation
Tropical (wet & warm)
climate:
• Laterite soil (thick and
infertile)
*rain always is washing
away the A horizon but
constant rotting
vegetation covers the B
Horizon
Laterite
Desert (dry) Climate
• Forms soils from
mechanical weathering
• Soil is thin and mostly
of regolith
Temperate climates
• Temperatures range from
cool to warm
• Rain fall is not excessive
• Two types of soil are
found dependent on
amount of rainfall:
Soil types in temperate
climates:
2. Pedalfer – soil formed if an area
receives 65 cm or more of rain
per year (clay, quartz, iron)
-found in places east of the
Mississippi
3. Pedocal – soil formed if rainfall
is less then 65 cm a year
(calcium carbonate)
Pedalfer
Pedocal
Soil and Topography
• The configuration of
the land (topography)
plays a role in soil
formation.
Thinner on slope
because water erodes
soil & deposits it down
the slope
Tends to be
thicker here
(deposited)
Mass Movements
• The transfer of rock and soil
down slope due to gravity
• The combined actions of
weathering and mass movement
produce most landforms
• Streams and valleys are the most
common landforms on earth
• Most mass movements end up in a
stream or valley
1.Water – heavy rain and snow saturate
the ground
2.Oversteepened Slopes – angles 25
to 40 degrees will hold loose particles. If
the slope is greater than 40 degrees slips
become less likely.
3.Removal of Vegetation – plant
roots stabilize
4.Earthquakes
talus: a pile
of rock
fragments
that
accumulates
at the base
of the slope
in piles
Geologists classify mass
movements based on 3 things:
1.Kind of material that moves
2.How it moves
3.Speed of movement
1. Rockfall: rocks or rock
fragments fall freely through
the air
•is the most rapid
•Common on steep slopes &
can trigger other mass
movements
2. Slide: a block of material
moves suddenly along flat,
inclined surface
Slumgullion landslide
Hinsdale County, Colorado
700 years old and still moving
Rockslide: slides including segments of
bedrock
3. Slump: downward movement of
a block of material along a curved
surface
•Leaves a crescent-shaped cliff
A slump is a type of slope failure which involves
the rotational movement of soil or rock
4. Flows:
mass
movements
of materials
containing
large amount
of water
Earthflow –
moves slowly
Mudflow – moves quickly
5. Creep: slowest type of mass
movement. (freezing & thawing)