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Surface Processes on Earth
Weathering, Erosion & Freshwater
Weathering and Erosion
• Weathering is the process of breaking down
rocks at or near the Earth’s surface.
• Erosion is the movement of sediments from
one place to another.
Weathering
Mechanical Weathering
Does NOT change the rock
CHEMICALLY
Natural processes just eat away
at (Erode) the surface
Mechanical Weathering
– FROST/ICE WEDGING: repeated thawing
and freezing of water in cracks of rocks
– UPLIFTING: when layers of rock above are
removed, the release of PRESSURE allows
the rock to expands and cracks
– Plant growth into cracks can split open
rocks
– EXFOLIATION: the action of EXFOLIATION
allows outer rock layers to be striped away
Chemical Weathering
• Occur when CHEMICAL REACTIONS take place
within the rock
– Eroded sediments are different chemically
– Erosion Increases with SURFACE AREA
Water, oxygen, carbon dioxide and acids can
cause chemical weathering
Chemical Weathering
Hydrolysis = water. Occurs in Silicate Minerals
Oxidation = oxygen. Occurs in Iron Minerals = RUST
Carbon dioxide. Combines with water to form a
weak CARBONIC acid
Acid Rain. Released by human activities that make
pollution.
Rate of Weathering
– Water-Soluble minerals weather easily (Like
salt melts into salt water)
– Different layers weather at different rates
Other Factors
• More surface area =
more weathering
• Topography (slopes,
hills, etc) allows gravity
push sediments
downhill faster than on
flat surfaces
Erosion
• Transportation of Sediment
Soils
Or as some call it..
Dirt
Soils
• Soil is made of
– Rock particles and minerals (sand, silt, clay)
– Humus is organic and provides PLANTS
with air and water
• Soil Texture depends on particle SIZE
Soil Horizons
• The layers of soil are called
the soil horizon
– TOP SOIL – Layer A: contains
NUTRIENTS and minerals and
is very dark
– SUB-SOIL- Layer B: high in clay
and is usually red or yellow in
color
– Layer C: Partially weather rock
Life in Soil
• Decomposers (such as fungi and bacteria)
break down ORGANIC MATERIAL
• Animals mix SOIL LAYERS and allow air and
water to pass through it.
• Humus = Plants produce litter and then
decay which returns nutrients to the soil.
Soil in the U.S.
• Polar (Alaska) – good drainage, no horizons,
permafrost
• Temperate (Eastern and Central U.S.) – vary greatly
– Grassland – fertile
– Forest – less fertile
• Desert (Western U.S.) – high in salts and little
organic/living material
• Tropical – can become infertile due to high rainfall
Soil Damage
• Loss of TOP SOIL
• Due to erosion
– Desertification
• Climate Change, Overgrazing, Cutting down FORESTS
Conservation
– Contour plowing
– CONSERVATION plowing
– Fallow (allowing fields to rest)
– CROP rotation
Karst Topography
• Groundwater contains some ACID usually CARBONIC ACID
– Acid gets there when carbon dioxide combines with water
Acid dissolves some types of
minerals
Calcites
Limestone
Acid leaves others
Quartz
Sandstones
Igneous rocks
Differential erosion causes KARST TOPOGRAPHY.
Features of Karst
•
•
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•
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Caves
Sinkholes
Stalactites – from above
Stalagmites – from below
Disappearing rivers
Karst Topography
Caves
Sink Holes
Stalactites
They hold TIGHT to the ceiling
Stalagmites
They MIGHT have fallen
Disappearing Rivers
Mass Movement by Gravity
• The downward movement of loose sediment
and weathered rock.
– Slide: moves as a block
– Flow: particles mix together
– Fall: falling freely
Creep
Slow, Steady, Downhill flow of sediment
Slump
Mass of sediment falls down
Mudflow
swiftly moving mixture of mud and water
Landslide
downhill movement of saturated topsoil
Avalanche
Landslides of snow (deep snow)
Mass Movement Caused by Wind
• Mass movement from wind includes
– Dust Storms
– Dunes Formation
Mass Movement by Glaciers
A glacier is a large moving mass of ice
The Water Cycle
Runoff
• Water moving along the surface will carry sediments.
• If surface is POROUS, then water can flow into the
ground.
• Plants slow erosion and allows more water into the
ground
• Light rains can allow more water into the ground
• Soil types affect absorption
Run Off & Porosity
Watershed
• All the land that drains into a stream or
river system is called the watershed.
Suspension:
particles carried
in water
Bed Load:
particles pushed
along by water in
a stream
Streams
• Stream channel: the pathway carved by a stream
• Stream banks: the ground bordering the stream on
either side
• Floods occur when streams or rivers rise over their
banks.
• Flood plain: the broad flat area on either side of
the stream banks.
• Meander: the bend and curves in a stream
Streams
Lakes and Freshwater Wetlands
• Lakes are depressions in the landscape that
collect and hold water.
• Eutrophication: the process by which lakes
absorb nutrients from the soil around them.
• Wetlands are land areas that are covered by
water for part of the year.
– Bogs
– Marshes
– Swamps
Groundwater and Infiltration
• Infiltration is when water on the surface
flows into the ground
• An aquifer is the area of ground water flow
through permeable rock
Groundwater
Groundwater
• Zone of Saturation – the depth to which
ground water completely fills all the pores
in the material.
– Upper boundary is the Water Table
– Permeability – how easily water passes
through
• Zone of Aeration – is the area above the
water table
Groundwater Systems
• Springs - Natural discharges of ground water
where ground water is blocked by
AQUICLUDES (Clay and Shale)
• Hot springs usually form near residual igneous
activity
• Geysers are explosive hot springs that erupt at
regular intervals.
Wells
• Wells are holes that are drilled or dug into the
ground to reach the aquifer
– Drawdown – the difference between the water table
level and the water level in the pumped well
– Recharge – the water filtering into the well from the
ground water
• Artesian well – a well in a CONFINED aquifer.