SEDIMENT
TRANSPORTATION OR
CYCLE OF THE ROCKS
The rock cycle describes the process of the
formation, breakdown and reformation of rocks
Let´s understand some vocabulary
before explaining the topic
Weathering
Weathering is the breakdown of rocks at
the Earth’s surface, by the action of
rainwater, extremes of temperature,
and biological activity. It does not
involve the removal of rock material.
There are three types of weathering,
physical, chemical and biological.
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Erosion & Transport
Erosion is the process by which soil and rock
particles are worn away and moved elsewhere by
wind, water or ice. Weathering involves no moving
agent of transport.
Transport refers to the cycle processes by which the
sediment is moved along – for example, pebbles
rolled along a river-bed or sea shore, sand grains
whipped up by the wind, salts carried in solution
Don´t get confused about these words:
erosion and weathering

Erosion is not the same as weathering. Weathering
is the process where rock is broken down or
dissolved into smaller pieces by physical,
chemical or biological weathering process.

Deposition
• Deposition is the laying down of sediment carried
by wind, water, or ice. Sediment can be transported
as pebbles, sand & mud, or as salts dissolved in
water.
• Salts may later be deposited by organic activity
(e.g. as sea-shells) or by evaporation.

Burial and Compaction
As layers are piled one upon another, the sediments
beneath are buried, sometimes by hundreds of metres of
sediment above. The weight of these layers compacts
(squashes down) the sediment grains.
Minerals deposited from water in the spaces between
the sediment grains gradually cements them together.
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Deformation and Metamorphism
The Earth’s crust is slowly moving. Did you know that the Atlantic Ocean
is getting wider at about the rate your fingernails grow, or that India is
barging its way slowly northward into the continent of Asia?
The huge forces that move continents stretch and squash parts of the
Earth’s crust., generating earthquakes and building mountains. They
cause rocks near the surface to be fractured and faulted.
At greater depth, the heat and pressure involved can cause folding
and/or metamorphism.
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Uplift
Uplift is the key to the rock cycle, as it allows us to see rocks that were
once deeply buried beneath the surface.
If rocks did not get uplifted to form hills and mountains, then the
processes of weathering and erosion would long ago have reduced much
of the world’s land-masses to low-lying, flat plains.
Weathering and erosion, transport and deposition would all effectively
stop.
Mount Everest is made of limestone that must have originally formed on
an ancient sea floor because it contains fossils of marine creatures.
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Melting
Rocks are made up of different minerals that have different melting
points. When hot rocks begin to melt deep down beneath the surface,
some of the minerals start to melt but others stay solid.
The rock of the Earth’s mantle layer only begins to melt in a few zones
where it is disturbed in some way
Rocks melt because of the heat beneath the Earth’s surface, as well as
other factors such as changes in pressure, or the presence of water
within the rock.
Magma reaches the surface because of pressure squeezes the rock like a
sponge, forcing the melted material (magma) to rise toward the surface.
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Crystallization of Magma
•
Magma can have different compositions depending on how it was formed.
Magma also varies in temperature, and in how much dissolved gas it contains. All
of these factors control the viscosity of the magma (whether it is relatively runny
or very thick and sticky).
•
Viscosity, in turn, controls how magma behaves as it rises through the crust,
and erupts at the surface.
•
The rate at which magma cools controls the grain size of the igneous rock
that is formed. More rapid cooling produces finer-grained rocks
THE ROCK CYCLE
When rocks form, they do not stay the same forever. They also do not
stay at one place forever. They move about. The rock cycle is the entire
journey rocks make as they change. These take millions of years.
Let us start the cycle with molten magma in the earth core.
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Molten magma may cool off and crystalize beneath the earth’s crust, forming
intrusive igneous rocks. With time, pressure may cause uplift and rocks end up on the
surface.
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Molten magma may also flow to the surface by volcanic action, causing extrusive
igneous rocks as they harden and crystalize.
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On the surface, they undergo weathering, erosion and transport. Sediments are
therefore carried to low lying places and into rivers and water bodies. The pilling up
of sediments cause compaction and cementation. Sedimentary rocks form.

After a long period of pressure and heat from the overlying weight, the igneous and
sedimentary rocks buried deep inside the crust change to metamorphic rocks, deep
under the earth’s crust.

Some of the metamorphic rocks begin to melt as they get closer to the molten
magma region. Some will also undergo uplift to the surface again, in places where
volcanic activity is not common. If they melt, they get released back to the surface
through volcanic activity, especially in places with high tectonic activity.
LET´S PRACTICE
ANSWER