The Physical World
Revision Notes
The Physical World
• This unit is all about Rivers,
Coasts and Glaciers and how
these physical entities change
the land on which we live over
thousands of years.
• In particular, you will need to
know in detail how various
land forms are created, and
the processes that help to
create the landforms.
• A Landform is a particular
shape of the land resulting
from thousands of years of
change.
• A process is a continuing force
that can change the natural
world.
Rivers – How they change from
source to mouth
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Rivers change immensely on their
journey from Source areas (where they
start) to their finishing point at their
mouths.
Velocity increases as more water is
added to rivers via tributary rivers. This
means that less of the water is in contact
with the bed of the river and the mouth
so there is less energy used to overcome
friction. Hence rivers flow progressively
faster on their journey downstream.
Width and depth increases as more water
is added from tributaries.
Gradient (the slope of the land)
decreases as rivers flow because the
river meanders across the land rather
than erode into it and follow a straight
path as it does in the source. This means
it covers a decrease in height over a
longer distance the further downstream
you get.
Stone size decreases downstream and
the stones get rounder and smoother as
rivers erode the rocks progressively as
the stones are transported downstream.
Rivers – How they change from
source to mouth
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Watershed
Interlocking
spur
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A diagram of the drainage
basin
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The diagram on the right shows the
major changes downstream.
In the source area the drainage
basin (an area of land drained by a
river and its tributaries) contains V
shaped valleys and waterfalls, and
the dominant processes are
erosional. Erosion tends to be
vertical (straight down into the
land).
In the middle section of the
drainage basin the river starts to
erode laterally. This section
contains meanders and Ox bow
lakes, and the river creates a flood
plain often with Levees. Here,
Material is deposited and erosion
can also occur.
In the lower drainage basin
deposition dominates as a river
enters a sea or lake, the valley is at
its widest and deltas and estuaries
are major landforms and habitats.
Landforms in upper River Valleys Waterfalls
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Waterfalls are created by erosion
processes.
They occur where a band of hard rock
(e.g. granite) overlies a softer rock
(e.g. sandstone).
Erosion processes such as Hydraulic
Action (the force of the water) and
Abrasion (where the river rubs stones
that are being transported against the
bed of a river thereby breaking it
down) dominate.
The softer rock is eroded quicker than
the harder rock.
This creates a plunge pool where
water is swilled around.
Over time, the softer rock is eroded
further creating an over hang of hard
rock.
Eventually, this hard rock collapses
because it is unsupported and the
waterfall moves back upstream.
This creates Gorges, steep sided deep
river valleys.
Landforms in upper River Valleys –
V-shaped valleys
• Vertical erosion processes
wear away the rock in upper
valleys.
• As the river erodes down
over it leaves behind valley
sides that are shaped like a
letter V
• The result is that the river
valley contains interlocking
spurs, slivers of land that
interlock. Interlocking spurs
are areas of more resistant
rock left behind because the
river erodes softer rock
quicker. The river moves
between the interlocking
spurs.
Landforms in the middle valley – Meanders and
Ox-bow lakes
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Meanders occur in the middle valley and are the result of erosion AND
deposition processes on a river.
In this section of the valley the river erodes laterally and migrates across the
valley floor over time, widening the valley. Within the river itself, the fastest
current is found on the outside of a bend and the slowest current on the inside
of the bend. This is because the depth of the water on the outside of the bend
is deeper, so there is less friction and hence higher velocities.
Over time, this means that erosion occurs on the outside of meanders bends
and deposition occurs on the inside.
In the diagrams, erosion of the outside of the meander means that the neck of
land becomes narrower and narrower over time.
On the inside of the bend the slow flow encourages the deposition of beaches.
After a long time the neck of land gets totally cut through by erosion processes
such as hydraulic action and abrasion.
This cuts off the meander bend which is totally isolated by deposition leaving
an Ox bow lake
Landforms in the middle valley –
Floodplains and Levees
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Rivers flood on a regular basis.
When rivers flood in the middle
valley the cover an area of land
known as the flood plain.
When they flood velocity is
slowed and deposition of any
rocks being transported is
encouraged.
This deposition leaves a layer
of sediment across the whole
floodplain.
After several floods there are
several layers of sediment
(rocks) deep on the flood plain.
In addition, the largest rocks
and most deposition occurs
next to the river channel. This
leaves a ridge of higher material
next to the river channel on
both banks of the river known
as a levee.
Landforms in the lower valley –
Estuaries and Deltas
• Deposition dominates in the lower
valley as river velocity falls as it enters
a sea or lake.
• This results in deposition of fine
sediments such as silt and clay.
• This sediment can build up over time
forming estuaries and deltas.
• Deltas have distributaries where the
river channel splits up into smaller
rivers on its journey to the sea.
• Birds foot deltas are comprised of fine
sediments like silt and a good example
is the Mississippi delta seen on the top
photograph.
• Arcuate deltas are composed of coarser
sands and gravels and can be seen on
the river Nile on the bottom photograph.
What are
Glaciers?
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Glaciers are large sheets of ice that
sit on the surface of the land.
How do glaciers form?
Glaciers form in regions where
there is enough snow fall. Over
several years when enough snow
accumulates the snow is
compacted into ice. This happens
because the weight of the snow on
the top layers forces the air out of
the snow in the bottom\layers
closest to the rock surface.
Why do glaciers form?
Glaciers form where ever
temperature is low enough to allow
permanent ice and snow cover that
doesn’t all melt over summer. High
latitudes (e.g The polar regions) and
areas of high altitude (e.g.
Mountains) are the best places to
find glaciers. North facing slopes,
that receive less sunlight due to the
angle that the sun hits the Earth,
also get glaciers.
How do Glaciers Move?
There are 4 factors responsible for glacier movement;
• Weight (Mass) – Glaciers can be huge, kilometres long
and hundreds of meters deep. They therefore weigh a
lot.
• Slope – Glaciers that occur in mountainous areas are
found on steep slopes, this allows quicker movement.
• Gravity -this is the force responsible for pulling these
huge slabs of ice down the mountainside.
• Water at the base helps to allow some glaciers to move
How do glaciers erode?
• Plucking
• First, ice has the property of
being able to freeze to rock.
The glacier uses this to adhere
to part of the ground. Then, as
the glacier forces the ice
frozen to the ground to
continue moving down slope,
the rock may be pulled out of
the ground and moved down
slope as well.
How do Glaciers erode?
• Abrasion
• Second, once glaciers have
rock and sediment at their
bases they can push this
sediment against the ground
and use it like sandpaper. This
abrasion of rock against rock
can scour the landscape and
leave large gouges, small
striations, or even a finely
polished surface.
How Corries Form
• Corries form in hollows
where snow can
accumulate. The snow
compacts into ice. This
moves down hill, plucking
and abrading the hollow.
This creates a steep back
wall and a hollow known
as a corrie or cirque.
When the ice melts a
corrie lake forms.
How Corries form
Landforms Created by Glaciers.
U – Shaped Valleys.
These are steep sided, wide
valleys in the shape of the letter
U.
They are formed by a valley
glacier that moves down the
valley because of gravity.
As the glacier moves down the
valley it plucks the rock from
beneath and those rocks then
rub against the bed of the
valley, eroding it further.
This deepens and widens the
valley.
Glacial Landforms
• Truncated Spurs.
• These are interlocking spurs
without the land that interlocks!
• As a river erodes the upper valley
it cuts down into the rock and
meanders in and out of the
surrounding rock.
• When glaciers form as the
temperature decreases they move
down the valley.
• As the glacier moves it plucks the
rock from the floor and it abrades
the valley sides and floor.
• At the front edge of the glacier
material is bulldozed forward.
• The end result is that the
interlocking spurs are eroded,
creating truncated (cut off) spurs.
Glacial Landforms
Ribbon Lakes.
These are Long and thin lakes that
form after the glacier has
melted. During glaciation the
glacier erodes some parts of
the valley floor more than
others. When the glacier melts
water fills the depressions
(holes) where the valley floor
was eroded most.
Hanging Valleys
These are the valleys of tributary
(smaller) glaciers that are left high
above the floor of the main glacier.
You often get waterfalls here.
The Changes Glaciers make to River Valleys
River Valleys
Have interlocking
spurs
The river has less
erosion power than a
glacier
Are V shaped
During Glaciation
Ice occupies the
valley floor
Interlocking spurs are
eroded
Plucking and
Abrasion occurs
After Glaciation
Ribbon lakes,
truncated spurs,
Hanging valleys and
shaped valleys are
left.
Additional Diagrams
The coastal system
• Coasts are dynamic
environments that have
inputs of sediment and
losses of sediment.
• The major processes
are;
• Erosion- Hydraulic
action, corrosion,
abrasion, attrition.
• Weathering – Chemical,
biological and physical.
Coastal Landforms - Erosion
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Cliffs retreat inland as a result
of erosion processes.
Waves pound the base of cliffs,
hydraulic action (the sheer
force of the water) and abrasion
(rocks hurled against the base
of the cliff) erode a wave cut
notch.
Eventually, the material on the
cliff face, weakened by
weathering, collapses because
it is unsupported.
This material is washed away
by the sea and the cliff retreats
in land.
This may leave a very flat
smooth area of rock in front of
the cliff known as a wave cut
platform.
Coastal Landforms - Erosion
Stacks
• Stacks, stumps and caves
are formed on cliffs.
• Waves attack vertical lines
of weakness in the rock
known as Faults.
• Processes such as hydraulic
action and abrasion widen
the cracks into caves.
• Over time, the cave will be
eroded into an arch,
accessible to the sea on
both sides. Finally, the
erosion continues and the
arch collapses leaving
behind a stack (a vertical
column of rock)
Coastal Landforms - Erosion
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Softer rock
Harder Rock
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Coves and bays form where
rock runs in bands horizontal
to the direction of wave attack.
There is a band of resistant
rock closest to the sea and a
band of less resistant rock
inland.
The waves seek out faults in the
hard rock and erode through to
the soft rock.
Wave processes erode the
softer rock faster and this
leaves a circular cove with a
narrow entrance where the sea
enters.
A good example of this is
Lulworth cove. Which can be
seen opposite.
Lulworth Cove
Coastal landforms - Deposition
• Beaches are formed by wave
processes.
• Gently sloping beaches are
formed by strong destructive
waves that backwash more
material away from the beach
that they swash up the beach.
• Steeply sloping beaches occur
by constructive waves that
swash more material up the
beach than they backwash
away, building up a steep
beach gradient.
Coastal Landforms -Deposition
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Spits are created by the
process of Long shore drift.
Material is carried along the
shore in a zigzag fashion by
waves as they swash material
up the beach at an angle and
backwash material down the
beach at a right angle.
Wherever there is a break in the
coastline (e.g. across a river or
a change in coastline direction)
then material is deposited
closest to the shore.
Eventually this material builds
up out into sea to form a spit.
As seen in the picture opposite
of Spurn Head
Spits often have salt marshes
build up behind them.