Transcript Deposition, Weathering , and Erosion - ESC-2

Deposition,
Weathering, and
Erosion
Weathering
What Caused This?
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Effects of Weathering
• Weathering is a process that breaks
down rock and other substances at
Earth’s surface
– creates soil
– softer rock weathers faster
– weathering is fastest in hot and wet
climates
Types of Weathering
• Mechanical Weathering
• Chemical Weathering
What is Mechanical Weathering?
• Breakdown of rock into smaller pieces
without any change in the chemical
composition of its minerals.
– Sometimes called “physical” weathering
– Rock is torn apart by physical force, rather
than by chemical breakdown.
Mechanical Weathering
• Works very slowly
• There are different types
– ice wedging
– exfoliation
– thermal
– biotic
Mechanical - Ice Wedging
 Ice Wedging
– Water fills joints of rocks and freezes
– Freezing expands the water by 10%
– Repeated freeze and thaw cycles
over the years causes rock to break
along joint
Mechanical - Exfoliation
• Exfoliation or unloading
–Rock breaks off into leaves or
sheets along joints which are
parallel to the ground surface
Mechanical - Thermal
• Thermal expansion
– Repeated daily heating and cooling of rock
– Different minerals expand and
contract at different rates causing the
rock to split
Mechanical - Biotic
• Biotic – means life
– Weathering caused by living
organisms
– Plant roots, digging animals, microscopic
plants and animals, algae and fungi.
Mechanical Weathering
What is Chemical Weathering?
• Breakdown of rock into smaller pieces
because of change in the chemical
composition of its minerals.
– Chemical reactions break down the bonds
holding the rocks together, causing them to fall
apart.
– Chemical weathering occurs in all types of
rock but smaller rocks are more susceptible
because they have a greater amount of
surface area.
Chemical Weathering
• Types of chemical weathering
•
•
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•
•
Oxidation (oxygen)
Hydrolysis (water)
Carbonation (carbon dioxide)
Biotic (living organisms)
Acid rain
Chemical - Oxidation
• Oxidation - oxygen combines with
other elements in rocks to form new
types of rock.
– Causes a “rusting” of the rock, often
causes a color change in the rock
Chemical - Hydrolysis
• Hydrolysis - water combines with the
substances in rocks to form new types
of rock
– New substances are softer than the
original rock types
Chemical - Carbonation
• Carbonation – Carbon dioxide is
dissolved in water making carbonic
acid, which eats away at the rock
– Weak acid is formed when carbon dioxide
in the air mixes with rain. This is the same
acid found in soft drinks.
Chemical - Biotic
• Organisms - living organisms can cause
changes in the chemistry of rock
– Plants lower the local pH to make it more
acidic
– Bacteria act as catalysts in various
geochemical processes
Chemical Weathering
Weathering by Water
• Most important agent of chemical weathering
• It can dissolve rock and minerals in rock
Weathering by Waves
• Waves weather the land:
– Mechanical weathering
• Broken down into smaller pieces
– Chemical weathering
• Dissolved in water
Weathering by Waves
Weathering by Wind
• Wind weathers the land by mechanical
means
– Abrasion
• Very slow process
Weathering by Wind
Erosion
What Caused This?
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below_Hay_Bluff_-_geograph.org.uk_-_1074175.jpg
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Seminole_Canyon.JPG
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ntian_Clay_Beds_-_geograph.org.uk__1776748.jpg
Erosion
• Movement of weathered rock and soil
to a new location.
– gravity
– water
– glaciers
– waves
– wind
What Is Gravitational Erosion?
• downward movement of rock and
sediments, mainly due to the force of
gravity.
Erosion by Gravity
• Gravity can erode
landscapes
–
–
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–
Landslides
Mudflow
Slump
Creep
Erosion by Water
• Moving water is the strongest agent of
erosion that has shaped Earth’s land
surface
• Erosion by water starts with rain. As
the rain runs downhill, it carries soil
rock and other material with it
Erosion by Water
• The rate depends on amount of rain,
vegetation, type of soil, shape of land,
and how people use the land
• As water moves fast, it picks up
sediment
• As water slows down, it drops
sediment
Water
What Is Glacial Erosion?
• moves and carries rocks, grinding the
rocks beneath the glacier
– Glaciers pluck and abrade to cause erosion
Erosion by Glaciers
What Is Wave Erosion?
• Waves - relentless pounding of waves that
erodes the weaker, softer rock
– Can take over 100 years to erode a rock to
sand
Erosion by Waves
• When waves hit rocky coastlines, the
impact can break off pieces of the rock
• The sand and sediment in the waves
can also act like sandpaper and wear
away rock
Waves
What Is Wind Erosion?
• wind picks up surface material and
moves it, weakest agent of erosion
– responsible for creating great deserts like the
Sahara Desert and Gobi
Wind
Deposition
Deposition
• laying down (dropping) of
sediment carried by wind, water,
or ice
Deposition by Water
• Water is the strongest agent of
deposition.
• Rivers deposit soil and sediment on
their flood plains and deltas
• Good farmland is usually based on land
where sediment was deposited by
water
Deposition by Water
Water Deposition
Deposition by Glaciers
• When a glacier melts, it deposits the
sediment it eroded from the land
• This deposition can create new
landforms and deposit sediment in new
areas
– Till – material deposited on the land’s
surface
– Moraine – ridge at the edge of a
glacier
Glacier Deposition
Deposition by Waves
• Waves shape coastlines by depositing
sand on the beach
• The type of sand is determined by the
sediment on the ocean floor
– White sand
– Black sand
Deposition by Waves
Deposition by Wind
• Wind is the weakest agent of
deposition
• When it drops the sediment it is
carrying, it can form dunes or mounds
Deposition by Wind
• Wind, water, and waves work together
in the processes of deposition,
weathering, and erosion
What’s the Difference?
• WEATHERING - think weather wearing
rock down
• EROSION - think of a road and traveling
• DEPOSITION – think of depositing money
in a bank