Transcript River words - Ysgol Rhyngrwyd KS3 Geography

Process of scenery change
Rivers in particular
1
Processes at work
From the source to mouth of a river
three processes are taking place
River erosion
River Transport River Deposition
2
What is erosion?
Erosion is the way in which rock is worn
away by something else, for example by
wind or water or ice – these 3 are called
agents of erosion – without them no
erosion would take place.
It is not like weathering where the rock
is broken down
– [Can you remember the 3 types of
weathering?]
There are 4 different ways water erodes
the river away
3
River Erosion 1
Attrition is the collision of rock fragments in the
water against one another.
The rock particles are broken into smaller pieces and
become smoother the longer the process continues.
4
The results of attrition
See how these rocks are becoming
smoother at the edges
5
River Erosion 2
Abrasion (or Corrasion,) is the grinding of rock
fragments carried by the river against the bed and
banks of the river.
– Remember – when you scrape your knee if you fall over – this
an abrasion
This action causes the channel to widen and deepen.
This grinding is most powerful in flood time when
large fragments of rock are carried along in the river
bed.
6
River Erosion 3
Corrosion is the process by which river water
reacts chemically with soluble minerals in the
rocks and dissolves them.
– (although this is often called solution – confusing
as solution is also a word used in transportation
– so in general I don’t – but the animation you
will see does!!!)
We often say things like water pipes corrode
– the chemicals in the water seem to eat them
away!
7
River Erosion 4
An additional process is also at work caused
by the force of the water itself known as
Hydraulic action.
In this rocks are dragged away from the bed
and banks by the force of the running water.
It is just like when you turn up a hose and
point it at the ground – the soil and small
stones get washed away
8
Checkout this animation
http://ysgolrhyngrwyd.wikispaces.com/Unit+4+Ch
anging+Earth
It is also on
http://www.bbc.co.uk/schools/gcsebi
tesize/geography/riverswater/riverp
rocessesrev1.shtml
9
River Transport
A river carries or transports eroded
materials such as mud, sand, boulders and
dissolved materials on its journey.
These materials are known as its load.
The load is carried along by four processes.
–
–
–
–
traction
saltation
suspension
solution
10
River Transport 1
Traction is where boulders or stones are rolled
along the stream bed by the force of the
water
11
River Transport 2
Saltation is when small particles such as
tiny pebbles are carried along in the
river.
The small particles bounce along and
leapfrog over each other.
12
River Transport 3
Suspension is when very fine particles
(suspension) such as clay, silt and fine
sand are carried along in the river.
The small particles are held up by the
water as they float because they are
very, very small!
13
An example of suspension
14
River Transport 4
Transportation in solution is when
dissolved materials containing minerals
like calcium and sodium are carried in the
water and are invisible to the naked eye.
No picture here because you cannot see
them!
15
Now go to the animation
http://ysgolrhyngrwyd.wikispaces.com/Unit+4+Ch
anging+Earth
It is also on
http://www.bbc.co.uk/schools/gcsebi
tesize/geography/riverswater/riverp
rocessesrev2.shtml
16
River Deposition
A river drops its load when the speed or volume of the
river decreases.
The load, which it carries, is deposited.
The heavier material is deposited first and the finer
material carried further.
Rivers reduce their speed when they enter flat land,
enters a lake or the sea or reach an arid area.
The volume can be reduced during a dry season or
when the river passes over more porous landscapes
e.g. sand or limestone.
17
Do the River processes test
quiz bite
http://www.bbc.co.uk/apps/ifl/schoo
ls/gcsebitesize/geography/quizengin
e?quiz=riverprocessestest&template
Style=geography
18