Transcript Rivers F.E.E.D sample answers for exam

Fluvial Processes, Patterns &
Landforms
5th Year Geography
Ms Cummins
Learning Outcome:
• Understand how fluvial (river) processes transform
the landscape.
• Examine the landforms created during the different
river stages.
• FEEDs for these landforms
• Feature
• Explanation
• Example
• Diagram
Today we will......
• Recall what we already know about fluvial
processes.
• Recap on some important river keyterms.
• Examine what influences the speed/velocity of
a river.
What do I already know about Fluvial
Processes....(Rivers)....????
Rivers transform the landscape
in three main ways
• Erosion; wearing it away.
• Transportation; moving its load
downstream.
• Deposition; dropping its load.
River Key Terms
Tributary, Source, Watershed, Estuary, Mouth, Load,
River Discharge, Confluence, River Basin, Course
- A river transports its _____________ or eroded material.
- The place where a river begins is its _______________.
- The __________, is the route a river takes as it flows from an upland
area down through its valley until it enters the sea
- A stream/river which joins a larger river called a _______________.
- The ____________ is the place where a river enters the sea or lake
- Where a river mouth is tidal is the _________________.
- A ________________ is the entire area which is drained by a river and
its tributaries.
- The high ground that separates two river basins is the
______________.
- ____________________ is the amount or volume of water carried by a
river at a given time.
Rate Of River Erosion
Depends on:
- Size (erodes faster
when in flood)
- Speed/Velocity
(faster rivers
have more
power)
- Hardness of rock
(certain rocks
erode more
easily)
Velocity/Speed of a River
Velocity is influenced by;
Gradient (steeper slope-faster river)
Volume of water carried by river
(greater volume/discharge- greater velocity)
Roughness of the channel (smooth
channel, little friction- greater velocity)
Shape of river channel
Learning Outcome for Today....
•
•
•
•
Examine four processes of erosion.
Identify three types of erosion.
Understand four processes of transportation.
Identify when a river may deposit it’s load.
Video Clip
• http://postprimary.folensonline.ie/resources.a
spx?programme=Horizons_1&chapter_group_
index=10#
• River Usk, Brecon Beacons Mountain Range,
South Wales.
Processes of Fluvial Erosion
Rivers erode through a number of processes:
Hydraulic Action
Abrasion/Corrasion
Solution/Corrosion
Attrition
Processes of Fluvial Erosion
________________________
_________________________
-River load erodes bank and bed.
-The river’s load collides with itself.
-Most effective during times of
flooding.
-When hollows exist in the
riverbed, pebbles are hurled
around.
-These turbulent eddies form
potholes.
-Overtime this reduces the size of
the load.
-It wears down and erodes the load
leaving smoothened stones and
pebbles.
_________________________
_________________________
-Force of the moving water.
-River water dissolves certain types -Erodes river banks, bed and
channel.
of rock, such as chalk and
-Bank Caving; water cuts into river
limestone.
-Dissolved rock is then transported banks, pushes water into cracks,
eventually the bank collapses.
in the river water.
Particularly common on the outside
of a meander bend.
-Cavitation; bubbles of air in the
water collapse, causing shock
waves to spread out through water.
Overtime this weakens river banks,
-Chemical process
Different Types of Erosion in a River Channel
Vertical; the river erodes down into the riverbed.
Lateral; the river erodes the sides of the river
channel, which widens it.
Headward; the erosion backwards (opposite direction
of river flow), of material at the river source.
Headward erosion lengthens a river valley.
River Transportation
1.
2.
3.
4.
Solution
Suspension
Saltation
Traction
River Deposition
Deposition is the dropping of the river’s load.
Rivers deposit their load when the following occurs:





The river loses speed
There is a reduction in waters in the river channel
The river flows into a lake or sea
The slope or gradient of the river is reduced
The river flows over a permeable rock layer, which allows the water to
pass through easily
 The river is carrying a larger load than it can actually transport
Pairwork- Quick Questions
• List the three main ways rivers transform the
landscape.
• What is an estuary?
• Explain the term ‘river discharge’.
• List four factors affecting river velocity.
• What are the four processes of fluvial erosion?
• Explain the term ‘cavitation’.
• What is lateral erosion?
• Give another word for ‘traction’.
• Identify four reasons why a river starts to deposit it’s
load.
River profile
Three stages can be identified:
 Youthful or upper river valley
 Mature or middle river valley
 Old age stage or lower river valley
River
LANDFORMS / FEATURES
F.E.E.D
F: Feature (Name, erosion or deposition, stage it is found)
E: Explain with at least one or two processes explained
E: Three examples, one Irish
D: Clear 1/2/3 diagram/s to show how the feature is
formed.
• V – Shaped Valleys
• Interlocking Spurs
• Waterfalls
•
•
•
•
•
•
•
•
•
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Feature: V-shaped valley (A narrow valley with steep sides and a narrow floor) 2
Explanation:
A V-shaped valley is a landform formed at the youthful stage of the river by processes
of river erosion. 2
V-shaped valleys form in highland areas where streams are flowing down steep
slopes. Such valleys are formed by the river cutting downwards into its bed. This is
known as vertical erosion. 2
The volume and speed of flow of a young river is often low due to the lack of
tributaries feeding the river in its youthful stages. When the rivers velocity increases
vertical erosion will occur, especially in areas of heavy rainfall or melting of winter
snow. 2
Hydraulic action, an erosion process caused by the physical force of flowing water,
loosens and carries away the bedrock and soil of the river channel. 2
Abrasion – erosion caused by the river’s load – will wear down bedrock as the load
hits the sides and bed of the river channel. These 2 processes will deepen the level of
the riverbed and form steeper sides to the channel. 2
The valley sides will also be exposed to weathering and mass movement. Mechanical
and chemical weathering weaken the rock and soil on the valley sides. Rainfall and
snow melt may trigger landslides. 2
The depth of the V is controlled by a combination of several factors: The speed of
vertical erosion, the type of rock and weathering and Mass Movement . 2
Example: River Moy, County Mayo. 2
 Processes of
transportation move
material down river
 Valley with steep sides
and narrow floor remains
 Interlocking spurs may
form
 Areas of high ground that
jut out from each side of
the valley where river
meets resistant hard rock
it is unable to erode
 River flows around the
hard rock while still
eroding downwards
 Creates a series of
interlocking spurs
A typical upper course V-Shaped valley
with interlocking spurs, steep valley
sides and active slope processes.
The diagram below shows the formation
of interlocking spurs.
• V-shaped valleys and
Interlocking spurs
are found in the
upper courses of
many rivers,
including the River
Slaney and River
Liffey.
Waterfalls (a vertical fall of water)
• Formed in the youthful stage of
a river valley. Where the
channel is narrow and deep
• Created where a band of hard
rock lies next to a layer of soft
rock. Differential erosion occurs
whereby soft rock is eroded
and transported downstream
and Leaves hard, more
resistant rock elevated and
standing out.
• As the process continues the
drop over the more resistant
rock becomes steeper. Flow
over the resistant rock forms a
waterfall
 A series of rapids are often formed above the area of resistant rock,
Processes of hydraulic action and abrasion are occurring here.
 A plunge pool forms at the base of the waterfall. The force of the falling
water causes the water to swirl in the pool in a movement called
eddying. It Deepens as a result of hydraulic action and abrasion
 The back wall of the waterfall will be further eroded as a result of the water
spray eroding the soft rock
 Soft rock is eroded and the remaining hard rock is left exposed
 Hard, resistant rock eventually falls into the bottom of the waterfall
Waterfall formation
Look at the diagram, How is a waterfall formed?
Can you put
the labels
below into the
correct place
on he
diagram?
Waterfall
Angel falls is the
highest waterfall in
the world it has a
height of 979
metres. It is located
in Venezuela. It is 15
times higher than
Niagara Falls
Niagara falls is one of the most famous
falls in the world. Situated on the border
of North America and Canada it is the
most powerful waterfall in the world, with
35 million gallons of water rushing over
the edge of the fall every minute.
Victoria Falls on the Zimbabwe/ Zambia
Border is the widest waterfall in the world,
with its mile-long breadth. It is Africa's
biggest tourist attraction.
Homework
• Examine, with the aid of a labelled diagram(s),
the processes that have led to the formation
of one Irish landform of erosion. (30m)
– Use a FEED to answer this question.
• Meanders
• Oxbow lakes
• Flood plains
Meanders
 Meanders are bends or
curves along the course of the
river
 At the mature stage, the
valley is less steep than that
of a youthful river valley
 River flows more slowly
 Many tributaries join
 More discharge
 River erodes laterally
 Volume of water and the
river’s load increases
 Meanders are a result of
erosion and deposition
 Water on the outer bend
of a meander is deep; the
river moves faster and
erosion occurs (hydraulic
action). Bank Caving may
occur
 Water on the inner bend
of a meander is shallow;
the river moves slowly
and deposition takes
place . This area is called
a riffle
 The meander resembles a snake.
 Where erosion has occurred on the outside bend, the
undercut riverbank collapses, this forms a river cliff.
 Where deposition has occurred on the inside bend, this
can build up to form a river beach or point bar.
1
2
Meanders
3
Examples of Meanders
• Mature stage of the
River Shannon, near
Portumna, Co Galway.
• River Moy, Co Mayo.
Ox-Bow Lake
 Ox-bow lakes are horse-shoe shaped lakes
 Formed when a meander is cut-off from the river
 Lateral erosion takes place on the outer bend (hydraulic
action)
 Deposition occurs on the inside bend
 After a long period of time meander neck becomes very
narrow
 Narrow neck is eventually cut through
 River at the cut-off point has very little energy
 Deposits its load leaving a meander loop isolated
 Oxbow lake is eventually formed when deposit seals off
both ends of the cut-off meander loop
 Eventually oxbow lake dries up forming a mortlake
How an Ox-Bow Lake is Made
Examples of Ox-Bow Lakes
• Lower Course of the River Shannon, near
Limerick
• Mortlake- River Liffey, near Ballymore Eustace,
Co. Kildare.
• Levees
• Deltas
Old Age Stage
 River is moving very slowly
 Level low-lying ground
 River has very little energy to erode
 The river deposits its load which has become too
heavy to transport
Video Clip
• http://postprimary.folensonline.ie/resources.a
spx?programme=Horizons_1&chapter_group_
index=10#
• River Usk, Brecon Beacons Mountain Range,
South Wales.
Deltas
 Formed at the mouth of a river where the river enters
an estuary, sea or lake
 River loses speed and its energy to transport recedes
 Deposition of alluvium
 Alluvium build ups and become visible above the water
Types of Deltas
 Lacustine deltas form where rivers
enter lakes
 Marine deltas form where rivers
enter the sea. There are three main
types of marine delta:
 Arcuate delta
 Estuarine delta
 Bird’s foot delta
Lacustrine Deltas
 Form at the mouth of a river as it flows into a lake
 Mainly composed of alluvium
 Bottomset beds are composed of fine deposits – are
carried/transported out furthest
 Foreset beds are composed of coarser deposits – are
deposited close to the river mouth
 Topset beds are composed of differing deposited
material – some fine, some coarser, e.g. silt and sand
 The topset beds divide the river into a number of
distributaries. (finger-like river channels)
Marine Deltas
 Rivers enter the sea;
 Arcuate delta
 Arc/Triangle shape
 Coarse material
deposited
 River Nile, Egypt
 Estuarine delta
 Deposition along the
sides of an estuary
 River Shannon, Co
Clare
 Bird’s foot delta
 Sea waves weak in
comparison to the
river strength
 Deposition of fine
sediment
 Spreads out long
distance
 Mississippi Delta,
USA
ine
Exam Questions
• Explain with the aid of a diagram(s), the
formation of any one Irish landform, resulting
from fluvial action. (30m)
– FEED
Exam Questions
Exam Questions