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Transcript
WEATHERING
AND EROSION
CHAPTERS 14 & 18
WEATHERING
WATCH BRAIN POP
• The breaking down of
rock
• 2 types: mechanical and
chemical
MECHANICAL WEATHERING
• Rock is broken down by
physical means
• Types:
– Ice wedging (freezing and
expansion)
– Abrasion (collision of rocks by
wind, water, or gravity)
– Organic activity (plant roots,
digging of animals)
ABRASION
CHEMICAL WEATHERING
• Rock is broken down due to chemical interaction with
the environment
TYPES OF CHEMICAL
WEATHERING
• Oxidationelements in rock
combine with
oxygen, mostly in
rocks with iron
(rusting)
TYPES OF CHEMICAL
WEATHERING
• Hydrolysisreaction of
minerals in rock
to water, turns
rock into clay
TYPES OF CHEMICAL
WEATHERING
• Carbonation-carbon dioxide
dissolves in water and creates
carbonic acid (like in your soda!)
• This acid causes slow break down of
rock
TYPES OF CHEMICAL
WEATHERING
• Acid precipitationwater mixes with carbon
dioxide and other air
pollutants
• Weathers rock
• Air pollutants are often
from burning fossil fuels
RATES OF WEATHERING
DIFFERENTIAL WEATHERING: PROCESS BY WHICH SOFTER,
LESS WEATHER-RESISTANT ROCK WEARS AWAY AND LEAVES
HARDER, MORE WEATHER RESISTANT ROCK.
• Weathering occurs very slowly
• Rates depends on many factors:
– Rock composition
– Amount of exposure
– Climate
– Topography and elevation
– Human activities
– Plant and animal activities
ROCK COMPOSITION
• Rocks containing
calcite weather the
quickest
• Rate is determined by
what material holds
the sedimentary
grains together
AMOUNT OF EXPOSURE
• More exposure=faster weathering
• Larger surface area exposed=faster
weathering
• Fractures and joints create channels for
more exposure
CLIMATE
• Areas with alternating hot and cold
seasons have fastest rate of weathering
• Areas that are hot and dry have the
slowest rate of weathering
SOIL
WATCH BRAIN POP: SOIL
• Mixture of minerals, gases, water, remains of dead
organisms (humus)
• Soil profiles show layers of soil called horizons
• Humus
• Climate determines soil formation
SOIL PROFILE
EROSION
WATCH BRAIN POP
• Products of weathering are transported
• Soil erosion is caused by both natural and human
activities (such as some farming)
• Erosion keeps crops from growing and can cause
famine
• Roots of plants hold the soil in place
• Agents of erosion include: wind, water, gravity,
glaciers
GRAVITY AND EROSION
Mass movements caused by gravity:
 rockfalls and landslides-very fast
mvmt
 mudflows and slumps-rapid mvmt
 solifluction-slow, in cold regions
 creep-very slow mvmt
LANDSLIDES
SLUMP
Large block of soil and
rock becomes unstable
and moves downhill in
one piece-occurs on
very steep slopes
EROSION FROM WIND
• Sand grains get moved by a process called saltation
(bouncing of grains by wind or water).
EFFECTS OF WIND EROSION
• Deflation-removal of top soil and rocks
• Deflation hollows-holes left from deflation
• Ventifacts-rocks with smooth surfaces from wind
abrasion
WIND DEPOSITION
• Dunes are formed when the wind slows down and
drops the sand it is carrying
WAVE EROSION
• As wind moves over the
ocean, wind produces
waves and currents that
erode the coastline.
STRUCTURES FORMED FROM WAVE
EROSION
• Sea cliffs
• Sea caves, arches,
stacks
• Terraces
See pgs 452-453
STACKS
SHORELINE EROSION
• Force of waves will break off rock and
throw the pieces back on the shore
creating abrasion (mechanical weathering)
• Shoreline is also chemically weathered-air
and salt water are forced into cracks in the
rock
BEACHES
• A deposit of sediment
along the shore
• More sediment is
deposited than removed
FARMING AND EROSION
PREVENTION
• Contour Plowing
• Strip Cropping
• Terracing
• Crop Rotation
These techniques help reduce the erosion
caused by water flowing over the land.
CONTOUR PLOWING
TERRACING