Download revision-tectonic-landscapes-gcse

TECTONIC LANDSCAPES
When you answer a question that requires a longer answer,
remember the PEEL technique.
P
Make your POINT
E
Give your EVIDENCE
E
EXPLAIN your evidence
L
If possible, LINK to your next
statement or the original point.
Why do earthquakes and
volcanoes both occur where
they do?
3
A theory: Plate tectonics
• The Earth's crust is broken into a
number of large and small plates.
• Plate tectonics is the study of the
structure of the Earth, and how
the Earth's surface changes
according to the movement of
plates.
4
Depending on the direction of the
convection currents, the plates can
move
• Towards each other (convergent)
• Away from each other (divergent)
• Slide past each other (transform)
5
6
The importance of crust
There are two types of crust which have different
characteristics.
Older, lighter, cannot
sink and is permanent.
Younger, heavier,
can sink and is
constantly being
destroyed and
replaced.
7
8
Tectonic plates can include
continental crust or
oceanic crust, and many
plates contain both. For
example, the African Plate
includes the continent of
Africa and parts of the
floor of the Atlantic and
Indian Oceans.
9
10
How to describe the distribution of….
Describe the distribution of volcanoes shown
on Figure 6. Use evidence from Figure 6 in your
answer. (3)
11
Describe the distribution of volcanoes shown
on Figure 6. Use evidence from Figure 6 in your
answer. (3)
E.g. In belts/bands (1) along the coast (1)
Along plate boundaries (1) such as Chaiten
volcano which is located along the plate
boundary of the Nazac and South American
Plates(1)
Some found in centre of ocean (1) such as
Kilauea (1)
12
1- Constructive/divergent margins
As plates move apart, magma comes to the
surface, forming new crust on the ocean floor
at the mid-ocean ridges and forcing plates
apart.
When the magma builds up above the surface
of the ocean, volcanic islands form, e.g.
Iceland
Next slide shows the mid-Atlantic Ridge.
13
Mid-Atlantic
ridge
14
Divergent or constructive boundaries
6-Earthquakes
are caused by
volcanic
eruptions or by
tensional
forces.
5-Submarine
volcanoes appear
along the ridge. Some
may grow to form
islands, e.g. Iceland.
Oceanic crust
3-As the plates move apart,
magma from the mantle rises to
fill the gaps and forms new
oceanic crust.
4-A mid-ocean ridge is
formed by the new crust.
Oceanic crust
1-Convection
currents pull
plates apart.
2-This leads to
gaps being
formed in the
crustal rocks.
15
Describe and explain the characteristic features of a
constructive boundary. (4)
What are the features? Mid-ocean ridges, volcanic
islands and earthquakes are the features of a
constructive boundary.
The question asks for an explanation , i.e. the reasons for
these features.
You may answer this question using the ‘case study’, i.e.
located example, of the Mid-Atlantic constructive
boundary.
The use of a located example may be part of the
question:
With the aid of a located example, describe and explain
……..
16
East African Rift Valley
Constructive boundaries
may also be found in land.
The East African Rift valley
is opening up and new land
is being formed in the
bottom of the valley.
The East African Rift
Zone includes a number
of active as well as
dormant volcanoes (red
triangles on map),
among them: Mount
Kilimanjaro and Mount
Kenya.
The rift is a narrow zone in which the African Plate is in the process of
splitting into two new tectonic plates.
17
Destructive/Convergent
boundaries
A- Oceanic-continental boundaries
B- Continental-continental boundaries
C- Oceanic-oceanic boundaries
18
Ocean-to-continent boundary
7-The collision causes
folding and uplift of
rocks which form fold
mountains.
1-The Nazca
Plate and the
South
American Plate
move towards
each other due
to convection
currents.
6-The Peru-Chile
trench
forms where the
oceanic plate is
being
subducted.
5-The melting plate
creates lighter
magma that rises
towards the surface
to form volcanoes.
Andes fold mountains
Pacific
Ocean
Trench
Volcano
South American
Plate (Continental)
Nazca Plate
(Oceanic)
Mantle
2-The Nazca Plate
(oceanic) is being
subducted below
the South
American Plate
(continental).
Subduction
zone
Earthquakes
3-Friction and pressure
cause earthquakes to
occur along the subduction
zone
4-The heat from
the mantle causes
the oceanic plate
to be destroyed.
b- Continental-to-continental boundary
4- However,
earthquakes
occur due to the
collision of the
plates.
2- This results in
intense folding and
uplift and leads to
the formation of
fold mountains.
3- There is no
subduction. Therefore,
there are no volcanoes.
1- When two
continental plates
meet at a
destructive
boundary, a slow
collision takes place
as both plates have
a low density.
20
Ocean-to-ocean boundaries
4- As the Philippine plate
begins to melt, magma
escapes to the surface to
form volcanoes, a few
kilometres from the
trench.
5- After several eruptions, these
volcanoes break the ocean surface to
form islands
Ryuku Islands (Japan)
Eurasian Plate
Philippine Plate
Subduction zone
1- Due to convection
currents in the mantle,
the two oceanic plates
collide.
6- When several
volcanic islands form
together they are
called an island arc.
21
3- As it is subducted, friction and
pressure cause earthquakes
along the subduction zone.
2-The Philippine Plate is
subducted beneath the
Eurasian Plate.
Conservative [transform] boundaries
Plates just slide past each other with crust neither created nor
destroyed.
Friction builds up and energy is released when the plates ‘jerk’,
causing earthquakes.
The San Andreas Fault in
California marks the
junction of the North
American and Pacific plates.
Both plates are moving
north-west but at different
speeds. Instead of slipping
smoothly past each other,
they tend to ‘stick’. The
pressure builds up until
suddenly the plates move
forward and an earthquake
occurs.
There is no volcanic action
because the crust is not being
destroyed.
22
Why do some volcanoes not occur
on plate boundaries?... Hot spots
23
TECTONIC HAZARDS
Volcanoes at HOTSPOTS
In this lesson you will discover :
(I) The reason why some volcanoes do not
occur on plate boundaries.
(II) What happens to volcanoes located
over a hotspot as they are carried away by
the tectonic plate.
25
Study the distribution of volcanoes shown on figure 6.
Where is Kilauea located?
Kilauea is located in the
middle of the Pacific Ocean
far from plate boundaries.
26
Extinct volcanoes
Underwater
volcano
27
A few key words to help you
Stationary: which doesn’t move.
VIDEO
Motion=movement
Intrusion: Magma slowly
pushes up from deep within
the earth into any cracks or
spaces it can find.
Solid part of the mantle
Mantle Plume: A column
of hot rock rising inside
the mantle
Semi-molten part of the mantle (magma)
An extinct volcano is not expected to erupt again.
As the plate moves over the stationary hotspot, new volcanoes
are formed.
29
RECAP: Understanding hotspots
Some volcanoes do not occur on plate
boundaries. These volcanoes are formed over
hotspots.
These are fixed points in the mantle that
generate intense heat. Small, long lasting,
exceptionally hot areas of magma exist under
the Earth's surface which in turn sustains longlasting volcanic activity.
30
At areas where the pressure is greater in the
mantle, magma erupts through the crust as
when the plume reaches the crust it causes the
crust to dome (and crack).
Volcanoes are created if the magma rises above
the ocean surface.
As the crustal plate moves over the stationary
hotspot, new volcanoes are formed.
Hotspots are associated with chains of islands
such as Hawaii.
31
How are earthquakes measured?
Two main methods are used to measure
earthquakes.
The Mercalli scale gives an indication of the
intensity of an earthquake
while the Richter scale refers to its magnitude.
32
Comparing the scales
33
Question
Outline the differences between the Mercalli
and the Richter scales. (4)
The Mercalli scale measures the intensity of an
earthquake whereas the Richter scale measure
its magnitude.
The Mercalli scales is based on observations by
people while the Richter scale is based on
accurate measurements by a seismograph.
34
What is the focus and epicentre of an earthquake?
• The focus of an earthquake is its central pointthe point deep below the surface where the
earthquake starts. Seismic waves are released
and then spread in all directions.
• The point on the surface directly above the
focus is called the epicentre. It is the place on
the surface that is nearest to the focus and
therefore where the greatest effects will be
felt.
35
36
Epicentre
Seismic waves are
released and then
spread in all
directions
The focus is the
point deep below
where the
earthquake starts
37
Why do people continue to live
in areas of tectonic activity?
Social reasons
Economic reasons
Environmental reasons
38
Case study-example
The causes and effects of a volcanic eruption:
Montserrat, 1997
See knowledge organiser
39
Prediction and prevention of the
effects of volcanic eruptions and
earthquakes
40
Prediction and prevention of the effects of volcanic
eruptions
Most volcanic eruptions are preceded by clear
warning of activity from the volcanoes. After
the first seismic activity was detected in 1992
in Montserrat measures were taken to
predict if and when the volcano was going to
erupt:
41
Can volcanic eruptions be
predicted?
42
4 methods to monitor volcanoes
1-.Sulphur dioxide is produced by magma in
large quantities and so its emmissions are
monitored as they are a good indicator that
magma is near the surface. e.g. The area
surrounding Mount Pinatubo was evacuated
because of gas monitoring.
2- Mesuring ground deformation by using GPS .
Pressure form rising magma changes the shape
of the volcano.
43
3- As the magma collects in the magma
chamber, its movement creates small
earthquakes and tremors. Seismometers close
to the volcano record ground movements. E.g.
In Montserrat, 14 seismometers used
4- Tiltmeters measure tiny changes in the slope
angle of the ground e.g. Five electronic
tiltmeters record ground movement in
Montserrat.
44
Montserrat hazard map
• Three Zones have been defined:
• Exclusion Zone: No admittance except for scientific
monitoring and National Security Matters.
• Central Zone: Residential area only, all residents on
heightened state of alert. All residents to have rapid
means of exit 24 hours per day. Hard hat area, all
residents to have hard hats and dust masks.
• Northern Zone: Area with significantly lower risk,
suitable for residential and commercial occupation.
45
How to lessen the impact (effect) of
earthquakes?
1- Education:
(i) Emergency drills such as in Japan (1 September
/Disaster Prevention Day)
(ii) In the USA, the Federal Emergency Management
Agency gives information on how to prepare for an
earthquake 6 ways learn 4
2- Building design
46
47
Case study: the San Francisco International
Airportprhttp://
Science.howstuffworks.com/transport/enginesequipment/bearing4.htmecautions can
people take to protect themselves from
earthquakes? (4)
3-What can be done to limit the effects of:
(i) Volcanic eruptions (6)
(ii) Earthquakes (6)
Include names examples in your answers.
48
What can be done to limit the effects of volcanic eruptions (6)
1- Hazard map: Three Zones have been defined in Montserrat
after the first eruption in 1995 including an exclusion zone
in the south with no admittance except for scientific
monitoring and National Security Matters.
2- Three ways to divert or stop lava flows:
(i) Divert lava flows by detonating explosives, for instance
in 1996, the Italian army used explosives to block a lava
flow from Mount Etna threatening villages below.
(ii) Construction of earth walls can deflect lava. Used
successfully in July 2001 eruption of Mount Etna to protect
tourist facilities.
(iii) Spraying large volumes of water can cool an advancing
flow. Two small lava flows from Mount Etna were cooled by
using this method.
49