Transcript Mechanical weathering

Weathering
The breaking down of rock into
smaller and smaller pieces.
Mechanical Weathering
• Mechanical weathering is the
breakdown of rock into smaller pieces by
physical means.
Weathering
Mechanical
Weathering
Chemical Weathering
Ice Wedging
Water
Abrasion – Wind,
Water and Gravity
Acid Precipitation
Plants
Acid in Groundwater /
Living Things
Animals
Oxidation - Air
Ice Wedging
Ice wedging is a process by which water
flows into cracks in rock and expands as it
freezes, enlarging the cracks.
Ice Wedging Animation
Root Wedging
The roots of plants can grow into cracks in
rocks, and the roots can enlarge the
cracks as they grow.
Abrasion
Gravity, water, and wind are agents of
abrasion in mechanical weathering.
Sphinx
Cleopatra’s Needle
Plants and Animals
The activities of plants and animals can
mechanically weather rock.
Burrowing animals for example
Chemical Weathering
Chemical weathering is the
breakdown of rock into smaller
pieces by chemical means.
Water can dissolve some rocks
and minerals.
Acid Precipitation
Sulfuric and nitric acids from pollution can
cause chemical weathering.
Rain and snow are naturally acidic and
contain carbonic acid.
Sulfuric Gases from Volcanoes also add to
acid precipitation.
Acid in Groundwater
Natural acids found in air and water are
produced by plants can cause chemical
weathering.
Limestone contains calcite which is
reactive with acid.
Caves form this way.
Acids in Living Things
Lichens produce organic acid.
Oxidation can cause chemical weathering
when oxygen combines with iron and other
metallic elements. (Rust)
Differential Weathering
The process by which softer less weather
resistant rocks weather and wear away
leaving harder more weather resistant
rocks behind.
Rates of Weathering – Section 2
The rate at which weathering occurs
depends partly on the composition of the
rock being weathered.
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If the minerals have higher hardness values
then they will weather slower than softer
minerals.
Rocks with a lot of quartz (7) will last longer
than rocks with a lot of talc (1).
Differential Weathering
The elevation changes around here are due to
DIFFERENTIAL WEATHERING.
Rocks weather at different rates due to the
different hardness of the minerals.
Sandstone
Shale
Limestone
Erosion carries sediment away after the rocks is
weathered.
Surface Area
The greater the surface area of a
rock is, the faster the rate of
weathering.
The only part of the cubes
available to be weathered are the
“faces”.
1. Has 6 faces to weather.
2. Has 48 faces to weather.
3. Has 384 faces to weather.
Which one will weather the fastest?
The one with more surface area (3.)
The Shape of Weathering
Page 253.
Which pile of rocks will weather quicker?
They may be the same volume of material
but one will definitely weather quicker.
Why?
Weathering and Climate
Different climates promote
different rates of weathering.
What climates are worse for
weathering?
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Hot and dry climates (New Mexico)
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OR
Wet and humid climates (Florida)
Why?
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Oxidation (rusting) – occurs quicker
in moister environments.
Weathering and Elevation
Factors that affect weathering:
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Water, ice, ice wedging.
Plants, animals
Oxidation
Look at the factors and think about how
each would relate to elevation.
How does elevation affect weathering?
Weathering usually occurs at a faster rate
at higher elevations.
From Bedrock to Soil
Soil – a loose mixture of small mineral
fragments and organic material.
Everything above the “bedrock”
Sources of Soil
Soils are made from weathered rock
fragments. The rock that creates the soil
is called the “parent rock”.
A soil derived from granite will be different
than a soil derived from limestone.
If the soil stays over top of the parent rock
it is known as “residual soil”.
Residual soils rest on top of their parent
rock, and transported soils collect in areas
far from their parent rock.
Sources of Soil
LIMESTONE
GRANITE
Living things also add to soil…..
Soil also contains organic material.
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Organic – material derived from living things.
Humus – very small particles of decayed
plant and animal material.
(HYU muhs) or (Hugh mus) not (hum mus)
20% - 30% humus is considered very
good soil for growing plants.
LEACHING
Soil and Climate
Tropical Climates – humid and a lot of rain
Soils are very good for growing plants
 Lot of humus (20%-30%)
However, lots of rain leaches the material downward and create
a very thin soil.
Any removal of vegetation will cause topsoil to erode away and
be lost.
Soil and Climate
Desert Climates – very dry
Low rate of chemical weathering.
Water moving through the ground will evaporate
as it reaches the surface leaving “salts” behind.
Too much salt is toxic to plants.
Salt Flats
Soil and Climates
Temperate Climates – “us” – both chemical and
mechanical weathering occur.
Not enough rain to leach out nutrients so you
have thick fertile soils.
Breadbasket – able to grow wide variety of
plants.
Soil and Climates
Arctic Climate – much like desert climates, arctic
areas can have very little precipitation. “Cold
Deserts”
Less chemical weathering and slow soil
development. Very few plants can survive in this
environment.
Soil Conservation
Soil Conservation – the various methods
used to take care of the soil.
Importance of soil
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Plant Health – better soil = better plants
Housing – burrowing creatures live there.
Storage – soil holds water
Preventing Soil Erosion
Erosion – the process by which wind and
water transport soil and sediment from one
location to another.
Soil Conservation
Soils need to be
protected from nutrient
depletion and erosion
through the use of soil
conservation methods.
Cover Crops
Farmers can plant crops between harvests
to protect their soil.
Crop Rotation
Growing the same crop
will deplete the soil
quicker. Alternating
crops allows a farmer to
prolong the life of the soil.
Contour Plowing
Contour plowing follows the lay of the land
like a topographic contour on a topo map.
This prevents soil from eroding during
heavy rains.
Terracing
Creating small flat areas out of steep
hillsides for planting crops.