Mechanical (physical)
Weathering
• The process of breaking down sediment
without changing the rocks chemical
composition.
• Frost wedging
Physical Weathering
Biological activity (Mechanical Weathering) –
(sometimes chemical)
Tree roots splitting
rock
Biological activity
Exfoliation (Mechanical Weathering)
• Uplift of under rock causes the top
hard rock, like granite, to split into
layers.
Thermal Heating & Contraction
Chemical Weathering
• The transformation of rock into
one or more new substances.
Oxidation
Chemical Weathering
– Oxidation : Elements reacting with Oxygen
ex. (Rust)
Hydrolysis
Feldspar +Water = Clay
Feldspar
A Clay Cliff
Acids
Lichen – Plant Acid
Sulfuric Acid &
Carbonic Acid
Acids (chemical weathering)
• Old tombstones made of marble will
weather due to the Carbonic Acid that is
in rainwater.
Dissolution
• Dissolving a rock in water
Carbonation
What can affect Mechanical and
Chemical Weathering?
Dissolving candy!!!! – I need a volunteer
Where does chemical weathering
occur the fastest????????????
• Warm and Moist!!!!!!
– Tropical rainforest
Where does mechanical
weathering occur the fastest???
• Wet & temperate (warm day / cold night)
• Frost Wedging!!!!!
Buffalo, NY
Erosion – The process of
moving weathered sediments
from one location to another.
The four major Agents of
Erosion are:
Gravity (Mass Movement)
Running Water
Wind
Glaciers
Types of Mass Movement (Gravity)
•
Water erodes more sediments than any other
agent of erosion, due to its great energy of
motion.
Deposition
•
When water flows downhill or wind slows
down it loses energy of motion, & drops
its sediments.
Large Sediment
Med Sediment
Small Sediment
http://www.classzone.com/books/earth_science/terc/content/visualizations/es1303/
es1303page01.cfm?chapter_no=visualization
Mass Movement
• Gravity causes loose
materials to move
down a slope. When
gravity alone causes
materials to move
down slope this
erosion is called
Mass Movement.
Mass Movements: Five Main Types
Slump
•
occurs when loose
materials or rock
layers slip
downward as one
large mass. It
happens because
the material under
the slump weakens.
Creep
• occurs when sediments
slowly move downhill.
As the ground freezes,
small sediments are
pushed up by the
expanding water in the
soil. As it thaws, the
sediments fall down
slope, often less than a
millimeter at a time.
Rockslides
• occur when large
blocks of rock break
loose from steep
slopes and tumble
quickly to the bottom.
• Fastest form of Mass
Movement
Talus
Mudflows
•
usually occur in relatively dry areas where
weathering forms thick layers of dry sediments.
When heavy rains or rapid ice thawing
happens, water mixes w/ the sediments &
forms a thick mud. Gravity causes this mud to
flow downhill.
• All types of Mass Movement happen
where there are slopes. All are more likely
to happen after a heavy rain because
water makes the sediments heavier &
slippery.
Wind Erosion
Areas most prone to wind Erosion
Deflation
•
wind picking up and moving small sediments
such as clay, silt, and sand.
Sediment Transport by Wind
Abrasion
•
wind making sand
grains roll and skip,
bumping into other
grains and rocks.
The surfaces they
strike become pitted
and polished when
small fragments are
broken off.
(sandblasting)
Glen Canyon, AZ
Wind Deposition
• Loess
• Dunes
Loess
• very fine sediment particles eroded by
wind that become packed together,
creating a thick deposit. They are found
in the farmlands of the U.S., especially
the Mississippi River area.
Dunes
•
sediments blown by wind that encounter a
barrier such as a plant, rock or some other
obstacle and pile up behind it. These are the
most common type of wind deposits.
Small scale
Large scale
Dune Movement
Running Water Erosion
Sheet Erosion
Occurs when rainwater flows over a relatively
flat area to lower elevations carrying
sediments with it. The sediments left behind
cover the soil like a sheet.
Rill Erosion
Begins when a
small stream
forms after a
heavy rain. Water
can carry away
plants & soil,
leaving a scar.
Gully Erosion
begins when a rill channel becomes broader &
deeper. Large amounts of soil are removed from
the area.
Most Famous Gully
Grand Canyon
Sediment Transport by Streams
Alluvial Fan
a type of deposit shaped like a triangle that
occurs when a river drops sediments on a
floodplain. (land)
Delta
A type of Alluvial fan
when the sediments
are into a large body
of water (lake, gulf or
ocean)
ex. (Mississippi delta)
Vegetation Affects Erosion
• Roots hold soil in place!!!!!!!!!!!!!!!!!!!!!!!!!
Things people can do to reduce erosion
Build terraces.
Terraces are broad,
step-like cuts made
into the side of a
slope.
Things people can do to reduce erosion
Plant vegetation
No till farming
Wind Breaks (fences/trees)
Video - dustbowl
•
Erosion can be slowed, but never stopped
completely.
Rivers
River systems are referred to as
dendtritic, like tree branches.
Tributaries
Small streams
branching off of
larger streams.
Where do streams get their water supply?
• Surface water runoff
• Groundwater (base flow)
Water has to go somewhere! It
always follows the path of least
resistance (generally downhill).
Drainage basin
• the land area from which a stream gets its
water.
Mississippi Drainage Basin
Stream Characteristics
Gradient: The slope or
steepness of a
stream channel.
Affects stream
velocity and
bedload (sediment
deposition) size.
Discharge
• The amount of water passing a point over a period
of time.
Which has a greater discharge?
Stages
of
Stream
Development
Erosion of Deformed Sedimentary Rock
Stages of River Development
• Young streams flow fast
through steep valleys.
• They are found in mountainous or
hilly regions and may have white
water rapids and waterfalls.
• They have high levels of energy
and erode the stream bottom more
than the sides.
Mature Rivers
– Mature rivers flows down a
more gradual slope with
curves called meanders.
The floodplain
Old-stage rivers flow very slowly
through a very broad, flat floodplain
that is curved.
• A river in this stage mostly
erodes its sides causing
changes in its meanders, like
the Mississippi.
• Meanders can eventually be
cut off forming Oxbow lakes.
Erosion of Deformed Sedimentary Rock
Meanders (old rivers)
Meanders
Old Mississippi
Meander
Oxbow Lakes (Old Rivers)
Oxbow Lake Formation
Young stream
Mature stream
Old stream
http://www.dkimages.com/discover/previews/774/206778.JPG
Quiz – Water/Wind/Glacier Erosion
1.
2.
3.
4.
5.
The beginnings of a stream is called a _.
Name the largest gully.
What is an Alluvial Fan?
Glaciers form this shape valleys.
Pieces of rock picked up by wind is
called ____.
6. Name two methods of reducing erosion’s
affects.
Shoreline and Sedimentation Changes