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WeatheringEssential Vocabulary
Weathering & Natural Erosion weathering – the processes
that breaks down rocks, soils, or minerals at Earth's surface. Types of weathering are mechanical and chemical.
mechanical weathering – type of weathering where rocks are physical broken down into smaller pieces.
chemical weathering – process that breaks down rock through chemical changes
Good to Know
Weathering and erosion work
together continuously to wear down
and carry away rocks at the Earth’s
surface.
Geologists make inferences based
on the principle of
uniformitarianism. That is a big
word that means the same
processes that operated today
operated in the past.
This means that, over time, even
the biggest, hardest rocks are
broken down by weathering.
abrasion – the grinding away of rock by rock particles carried by water, ice, wind, or gravity.
How to Know Mechanical Weathering When You See It?
Good to Know
The causes of mechanical
weathering include
freezing and thawing,
release of pressure, plant
growth, actions of animals,
and abrasion.
Weathering & Natural Erosion
ice wedging – process that splits rock when water seeps into cracks, then freezes and expands.
release of pressure– as erosion removes surface material, pressure is reduced on the rock, causing outer sheets to flake off (like onion layers)
animal actions – burrowing animals (moles, gophers, prairie dogs, and some insects) loosen and break apart rocks in the soil.
Good to Know
The causes of mechanical
weathering include freezing
and thawing, release of
pressure, plant growth, actions
of animals, and abrasion.
Weathering & Natural Erosion
plant growth trees (and other plant) roots enter cracks in rock and
force it apart as the roots grow and expand
The rate of weathering increases as more and more of the rock’s surface area is exposed.
water – most important cause of chemical weathering, because water dissolves rock.
oxygen – the process when iron combines with oxygen when water is present is called oxidation (rust)
Good to Know
The causes of chemical
weathering include the
actions of water,
oxygen, carbon dioxide.
Weathering & Natural Erosion
carbon dioxide – in the atmosphere, CO2 combines with rainwater. In soil, it becomes carbonic acid that easily weathers marble and limestone.
Good to Know
The causes of chemical
weathering include the
actions of water, oxygen,
carbon dioxide.
This creates holes or soft
spots in rock, which
helps with breaking
down the rock.
Weathering & Natural Erosion
living organisms – lichens grow on rocks and seeds sprout in cracks to produce weak acids.
Good to Know
The causes of chemical
weathering include the
actions of water, oxygen,
carbon dioxide.
This creates holes or soft
spots in rock, which helps
with breaking down the rock.
Weathering & Natural Erosion
acid rain – chemicals (sulfur, carbon, and nitrogen compounds) from air pollution mix with water vapor forming acids that fall with raindrops.
Weathering & Natural Erosion
Good to Know
The causes of chemical
weathering include the
actions of water, oxygen,
carbon dioxide.
This creates holes or soft
spots in rock, which helps
with breaking down the
rock.
Rates of Weathering climate - the average weather
conditions, including temperature, precipitation, and wind, most often occur in a particular region.
Good to Know
Some kinds of rocks weather
more rapidly than others
The most important factors that
determine the rate at which
weathering occurs are the
type of rocks and the climate.
Rates of Weathering permeable – material is full of tiny, connected air spaces that allow water to seep through it. Good to Know
Some kinds of rocks weather more rapidly than
others
The most important factors that determine the
rate at which weathering occurs are
the type of rocks and the climate.
Rocks that dissolve in water will
weather faster than rocks that
do not dissolve in water.
Chemical weathering happens
faster at high temperatures.
Both chemical and mechanical
weathering happen faster in wet
climates.
The End Products Of Weathering
Weathering breaks down rocks into particles of many sizes (clay, silt, sand, pebbles, cobbles, boulders)
Soil is a mixture of rock and organic material. Soils are the result of weathering and biological activity over long
periods of time. A mature soil profile shows three distinct horizons. The A-horizon
(topsoil) is dark and rich in humus. The B-horizon (subsoil) is lighter in color, has more clay, and less
humus. The C-horizon is made of slightly weathered bedrock (rock fragments).
Beneath the three horizons is the unweathered bedrock. Soils may be residual (form from underlying bedrock) or transported
(form from sediments that have been carried from some other place).
Different Climates, Particle Sizes, Composition & Exposure Affects the Weathering Process At high latitudes and high altitudes, where it is cold and humid, frost action is the major form of weathering.
In warm and humid climates chemical weathering is most important. In arid (dry) climates, very little weathering takes place. Local climatic conditions (winds, nearness to cities, etc.) can affect the
of weathering. Small rock particles will weather faster than a single large sample of
the same mass because more surface area exposed by the small particles.
Rocks containing more resistant minerals will weather at a slower rate. Rocks that are not exposed to the atmosphere and hydrosphere will
weather at the slowest rate.
It's a Hard Rock Life