Transcript Key terms - Geog On | Geography at Langley School

Key terms
CHECKLISTS
Let’s see what
we have
managed to
cover this half
term.
Learning objectives
To understand landforms of fluvial erosion and
deposition.
Potholes
Rapids
Waterfalls
Gorges
Meanders
Oxbow lakes
Braiding
Floodplains
Levees
Deltas
Upper course
landforms
Lower course
landforms
Overview
Landforms Overview
• Rivers are constantly shaping the
landscape as they carry water and
sediment along their courses
• Where a river has excess energy it will
erode its channel creating waterfalls and
gorges.
• When energy levels fall deposition will
occur forming extensive floodplains
• Erosion and deposition can combine to form
meanders
Can you match up the landforms
and the pictures?
1. Potholes
• Potholes are circular depressions in
the river bed
• Process
– Rock fragments are drilled into
holes/cavities by the turbulent whisking
action of a river
– Erosional process = corrasion
– Rock will overtime become smooth =
Abrasion
Kukdi River, Nighoj,
India
Pothole and the
rock fragment that
formed it
ACTIVITY - Draw two diagrams to show the
processes that cause a pothole to form
Over time, they may widen and join with other
potholes to form larger potholes, and the
whole river bed is deepened.
2. Rapids
• A river flows over a variety of different
rock
• Tougher rock = eroded less easily
• Weaker rock = eroded quicker
• This results in irregular steps in the long
profile of a river
• Cause turbulent flow in a stretch of river
• This is known as a rapid.
Rapids form stretches of white water as the river
plunges over jagged rocks and mini waterfalls to form
dangerous whirlpools and fast-flowing tubes of water
How do you
think
waterfalls
are formed?
Who can name and describe the
formation of these landforms?
Learning objectives
To understand landforms of fluvial erosion and
deposition.
Potholes
Rapids
Waterfalls
Gorges
Meanders
Oxbow lakes
Braiding
Floodplains
Levees
Deltas
Upper course
landforms
Lower course
landforms
3. Waterfalls
Watch this!
• http://www.youtube.com/watch?v=jqCR-9nBgWQ
• http://www.youtube.com/watch?v=YP1J1csZaCM&feature=re
lated
EXAMPLE
High Force waterfall on the River Tees
• Water plunges 20 metres over the edge of a tough
outcrop of dark igneous rock called dolerite
• Beneath the dolerite are mainly sedimentary rocks
like limestone and shale
• Sedimentary rocks erode quicker causing the
formation of a plunge pool
• This undercuts the waterfall at its base causing the
overhanging dolerite to collapse
• This cycle repeats
• Formation of a 1.5km gorge.
http://maps.google.co.uk/maps?hl=en&q=river%20tees%20map&bav=on.2,or.r_gc.r_pw.r_qf.&bpcl=37189454&biw=1024&bi
h=648&wrapid=tlif135218804049521&ie=UTF-8&sa=N&tab=il
Waterfall Formation
Waterfall Formation
ACTIVITY 2
Create a story board to the formation of HIGH
FORCE waterfall in the upper course of the River
Tees.
1. Use the 6 statements to help you do this.
2. Label your diagrams with these key words
The formation of a waterfall – Example___________________________
1
3
5
2
4
6
• The water starts to undercut soft rock
underneath the hard rock, creating the beginnings
of a plunge pool
• Water flows over a gap in hard rock
• Falling rock and the force of water also help to
create a plunge pool through erosional processes
like hydraulic action and corrasion
• As the waterfall retreats it leaves a steep-sided
gorge. Over thousands of years the waterfall can
move several miles
• The waterfall retreats over time, with the process
starting again
• The overhanging hard rock eventually falls into the
water as the base of the waterfall has been
undercut
1. Water flows over a gap in hard rock
2. The water starts to undercut soft rock
underneath the hard rock, creating the beginnings
of a plunge pool
3. The overhanging hard rock eventually falls into
the water as the base of the waterfall has been
undercut
4. Falling rock and the force of water also help to
create a plunge pool through erosional processes
like hydraulic action and corrasion
5. The waterfall retreats over time, with the
process starting again
6. As the waterfall retreats it leaves a steep-sided
gorge. Over thousands of years the waterfall can
move several miles
Learning objectives
To understand landforms of fluvial erosion and
deposition.
Potholes
Rapids
Waterfalls
Gorges
Meanders
Oxbow lakes
Braiding
Floodplains
Levees
Deltas
Upper course
landforms
Lower course
landforms
The Middle Course of the
River
Learning objectives
To understand landforms of fluvial erosion and
deposition.
Potholes
Rapids
Waterfalls
Gorges
Meanders
Oxbow lakes
Braiding
Floodplains
Levees
Deltas
Upper course
landforms
Lower course
landforms
The Middle Course
• More tributaries join the River Severn.
• These increase the volume of water in
the River. Increasing the River’s
Discharge.
Middle
course
Upper
Course
LANDFORM of the Middle/Lower Courses
Flood Plains
• During wet weather rivers increase in
size.
• Sometimes rivers cannot hold all of the
water flowing into them.
• The banks burst and the river floods on
a flood plain.
• Therefore a flood plain is the area of
broad flat land either side of the
river.
The floodplain creates U shaped
valleys in the middle course.
FLOODPLAIN
5. Meanders
Meanders are
sweeping bends
in the river’s
course
MEANDERS ARE
FORMED DUE
TO EROSION
AND
DEPOSITION!!
What is a
meander?
Watch this!!!
Processes that cause a meander to form….
and a
Riffles
created
• Pool
When
riverare
emerges
due to the ‘corkscrew’
from
the upper
(helicoidal) like flow.
course, it begins to
Pools
and or
riffles
often occur
‘swing’
meander
in
inorder
meandering
channels
during
to use
up surplus
low flow conditions
energy
– shallow,
fastwater
flowing
•Riffles
This is
because
moves inwater
a helicoidal
flow!
Pools –SWIRLS!
deep, slow flowing
water
Processes AND features of a meander
Water flows
faster on the
outside bend,
due to
centrifugal
force. This fast
flowing water is
called the
THALWEG.
This causes
LATERAL
EROSION
through
ABRASION.
This creates a
RIVER CLIFF.
A
B
Draw a plan
view of a
meander
Water flows much slower on the inside
bend as the river lacks energy to carry
its load. This causes DEPOSITION.
This creates a slip off slope.
Can you label the
correct processes and
landforms of a meander?
What is a
cross
section?
Cross Section From A to B
Aoutside
Information on the
outside of the meander…
Outside- UNDERCUT
The
volume and
velocity of
the river
are higher The water has
more energy
to transport
its load
Fastest flowing
water is called the
THALWEG
Binside
Material is
carried in
SUSPENSION
The force of the
water ERODES and
UNDERCUTS the
river bank by
ABRASION
This feature is
called a River Cliff
Cross Section From A to B
On the inside of a meander….
A - outside
B - inside
The river is
shallow and
slow flowing
Material is
therefore
The river lacks
the energy to
carry its load
deposited
This feature is called a
POINT BAR
Processes creating meanders…
LATERAL EROSION
On the outside of a
bend
DEPOSITION
On the inside of a
bend
6. Oxbow Lakes
Lateral
erosion on
outer bend
Continued
erosion results
in the narrowing
of the neck of
the meander
The two outer bends meet
.The river takes the
shortest route. Deposition
occurs in slack water.
The river cuts the
most efficient
course. It cuts off
the former bend,
leaving an oxbow lake
PREP
• Create a A3 summary sheet of
landforms of rivers as they move
downstream
• UPPER, MIDDLE AND LOWER
COURSE
• Use as many key words around the
diagrams as possible!
6. Formation of a Oxbow Lake
Cross Section of a meander From A to B
The Lower Course landforms
Learning objectives
To understand landforms of fluvial erosion and
deposition.
Potholes
Rapids
Waterfalls
Gorges
Meanders
Oxbow lakes
Braiding
Floodplains
Levees
Deltas
Upper course
landforms
Lower course
landforms
7. Floodplains
= an extensive flat area of land on either
side of the river which periodically
becomes flooded.
• Mostly in lowland areas, where they can
be several kilometres wide
• Often used for farming as the silt that
is deposited there is very fertile
Formation of floodplains
– Every time the river floods it deposits a fresh
layer of silt on top of the existing floodplain
– The width of the floodplain depends upon the
amount of meandering of the river
– If lateral erosion is high at the apex of each
bend the river will meander across the
floodplain and cut into the bluff (valley edge)
– This widens the valley and extends the
floodplain.
ACTIVITY
Copy diagram 1.52 page 38 in your books
underneath your notes.
8.
Levees
8. Levees
= when the river’s banks become raised.
Formation of Levees
• During high flow conditions – due to high rain fall or
snow melt rivers are unable to contain the increased
volume of water flowing into it.
• Water flows over banks
• Coarse, larger and heavier sediment is deposited on
top of the banks. WHY?
– as the velocity of the river is slower here.
• Coarse sediment traps smaller sediment
• Banks become raised.
ACTIVITY
Draw three labelled diagrams is illustrate the
formation of natural levees.
9. Braiding
What is
it?
9. Braiding
= when a river becomes sub-divided into
many separate channels.
Why?
• River is overloaded with sediment that it is
unable to carry
• Sediment is dumped
• Forms islands in the middle of the river
• Smaller channels are made around the
island – steepening the gradient and
increasing efficiency.
Braiding is common in rivers where the load is large
e.g. at the snouts of a glacier
OR fluctuating discharge e.g. semi arid areas
10. Deltas
• They occur at the mouth of a river
• A river rapidly loses energy when entering the
sea or a lake
• Sand, silt and clay are deposited in a fan shape
• Overtime there is a build up of material –
creates new land called a delta.
• Deposition rate exceeds the rate of removal by
the sea. This can happen when;
1. When the sediment load is large
2. Weak currents or a small tidal range
• Often delta is split into separate channels =
distributaries
• Two main types of delta;
1. Arcuate
delta =gently
curved
E.g. River Nile
2. Birds foot = deposition along the edges of several
distributaries
E.g. Mississippi
Learning objectives
To understand landforms of fluvial erosion and
deposition.
Potholes
Rapids
Waterfalls
Gorges
Meanders
Oxbow lakes
Braiding
Floodplains
Levees
Deltas
Upper course
landforms
Lower course
landforms