Chapter 1 gateway 1

CHAPTER 1
LIVING WITH
TECTONIC HAZARDS
Risk or Opportunity?

• The biggest eruption of Mount
Merapi in Java, Indonesia
occurred on 5 November
2010.
• More than 350 people were
killed and over 300,000
people were forced to leave
their homes.
• However, despite several
warnings leading up to the
eruption, some stayed behind
to care for their cattle.
• On Java itself, there are 30
volcanoes. Despite this,
people have settled down and
established croplands in areas
prone to natural hazards such
as earthquakes and floods.
• What do you think draws
people to these places?
CHECK-IN: Mount Merapi

CHECK-IN: Mount Vesuvius
• Mount Vesuvius, in
Italy, is one of the
world’s most
dangerous volcanoes.
• Mount Vesuvius has
had 30 major
eruptions ever since it
wiped out the city of
Pompeii in CE 79.
• Despite a 27 per cent
prediction of Mount
Vesuvius erupting in
the next 100 years,
about 600,000 people
continue to live near
the volcano, within
the ‘danger zone’.
• Why do you think this
is so?

In this Chapter, you will explore three
key questions:
1.Why are some areas more prone to
tectonic hazards?
2.What landforms and associated tectonic
phenomena are found at plate boundaries?
3.How do people prepare for and respond to
earthquakes?
CHAPTER 1 LIVING WITH
TECTONIC HAZARDS

CHAPTER 1 LIVING WITH
TECTONIC HAZARDS
Gateway 1: Why are some area more prone to
tectonic hazards?
a. What is a natural hazard?
b. What is the internal structure of the Earth?
c. What is a tectonic plate?
d. Why do tectonic plates move?
e. What are the different types of plate boundaries?

• A natural hazard is a natural event that threatens
human lives and causes damage to property.

Distribution of natural hazards

Types of natural hazards:
• Tectonic hazards
• Climate-related hazards
Impacts of natural hazards:
• Large scale
• Small scale

Classify the following types of hazards into
tectonic hazards and climate-related hazards.
Droughts
Earthquakes
Tsunamis
Wildfires
Floods

Examples of natural hazards
• Tectonic
hazards
• Earthquakes
• Volcanic eruptions
• Tsunamis
• Climate-
related
hazards
• Droughts
• Floods
• Storms

• Tectonic hazards are caused by movements in the
Earth’s crust.
• Examples:
– Earthquakes
– Volcanic eruptions
– Tsunamis

Name some areas that are more prone to tectonic hazards.

Do you know the latest…
tectonic hazard
that just happened?
Visit: http://earthobservatory.nasa.gov/NaturalHazards/

b. What is the internal structure of the earth?

Think, Pair, Share…
How is
a Ferrero Rocher®
chocolate
similar to
the internal structure of
the earth?

Core
• Composed mostly of iron and nickel
• Divided into inner core + outer core
1. Inner core
– about 1,200 km thick
– solid layer
2. Outer core
– about 2,100 km thick
– liquid layer
• Temperature between 3,000⁰C and 5,000⁰C

Mantle
• Mostly solid rock (flows under high temperature and
pressure)
• 2,900 km thick
• Divided into upper mantle + lower mantle
Upper mantle
– a layer of solid rock + asthenosphere
– below uppermost mantle
– rocks close to melting point, easily deformed
• Temperature between 800⁰C and 3,000⁰C

Crust
• Outermost layer on which we live
• Oceanic crust is found beneath oceans
• Continental crust is found beneath the continents
• Thickness ranges from a few km to more than 70 km

• Makes up the Earth’s rigid outer shell
• When the rocks in the lithosphere melt,
hot molten rock called magma is formed.
Lithosphere
= Crust + Uppermost mantle

Recap through the video at:
http://www.learner.org/interactives/dynamicearth/str
ucture.html
b. What is the internal structure of the Earth?

• A tectonic plate is made up of the lithosphere
(i.e. crust + uppermost mantle).
• The earth’s crust is broken into several pieces
of tectonic plates.
• These plates move in relation to one another.
• Tectonic plates can be made up of:
– oceanic crust
– continental crust or
– a combination of both

Oceanic crust vs Continental crust
Oceanic Crust
• Located beneath deep
ocean
• Very thin — between 5
and 8 km
• Denser (e.g. basalt)
Continental Crust
• Located beneath land
masses and under
shallow seas
• Very thick — between 30
and 60 km
• Less dense (e.g. granite)

1. Convection currents
2. Slab-pull force

•Convection currents are movements of heat within the
mantle.
•Material in the mantle is heated by the core.
•This causes convection currents in the molten mantle
material.
•Mantle expands, rises and spreads out beneath the
plates.
•Plates are dragged along and move away from each
other.

•Subsequently, the hot molten mantle cools slightly
and sinks, pulling the plates along
•Hence plates move towards each other.
•The sinking mantle material heats up again as it
nears the core and the whole process repeats.

Tectonic plates float on molten mantle, driven by heat
energy/convection currents
Plates moving away from each other
Platesmoving
towardseachother
Plates
moving
towards
eachother
Plates
Ocean floor

2. Slab-pull force
• This occurs when an oceanic plate (denser) subducts
under a less dense plate and pulls the rest of the
plate along.
• The subducting plate drives the downward-moving
portion of convection currents.
• While mantle material away from the subduction
zone drives the rising portion of convection currents.

Imagine this…
On average, tectonic plates move a few
centimetres a year.
This is about the rate your nail grows.
How long will your nails be if…
you don’t cut it for a year?

Changing positions of the earth’s
continents
• Plate movements have altered the
distribution of the earth’s land masses
over several hundred million years.

e. What are the different types of plate
boundaries?

• Divergent: where plates move away from each
other
• Convergent: where plates move towards each
other
• Transform: where plates move past each other
Within plates, there is also evidence of plate
movement in different directions and fractures.
These are known as developing plate
boundaries.
boundaries?

Divergent plate boundaries
1. Oceanic-oceanic plate divergence
2. Continental-continental plate divergence
boundaries?

1. Oceanic-oceanic plate divergence
boundaries?

• Magma rises from the mantle to fill the gap
between the plates as they diverge.
• New sea floor is formed when the magma cools
and solidifies. This process is called sea-floor
spreading.
• Magma rises at the zone of
divergence/spreading zone to form a ridge of
new ocean floor called mid-oceanic ridge.
boundaries?

• The newly formed (youngest) rocks are closest to
the middle of the ridge/plate boundaries.
• At various points along the ridge, magma builds up
above the ocean to form volcanic islands.
• E.g. the Mid-Atlantic Ridge is found in the middle of
the Atlantic Ocean cutting across Iceland, a volcanic
island.
boundaries?

2. Continental–continental plate divergence
• Can result in the breakup of continents
• E.g. Great Rift Valley (East Africa)
– a lowland with steep sides and flat valley floor
– formed by Somalian boundary of the African Plate moving
away from the Nubia plate boundary of the African Plate
– 6,000 kilometres long
– between 30 to 100 kilometres wide
– Evidence of tectonic activity: active volcanoes and earthquake
fractures found
boundaries?

• Can result in the formation of linear sea
• E.g. Red Sea and Gulf of Aden near the Great
Rift Valley
– Elongated/linear shape
– 1,900 km long
– 300 km at its widest stretch
– Average depth of 500 m
– Evidence of tectonic activity — formation of new
volcanic island in Red Sea
boundaries?

Convergent plate boundaries
1. Oceanic–oceanic plate convergence
2. Continental–oceanic plate convergence
3. Continental–continental plate convergence
boundaries?

• When two oceanic plates converge, one subducts
under the other.
• A subduction zone forms, creating a deep oceanic
trench.
• The subduction of the oceanic plate causes the solid
mantle material to melt and magma is formed.
• The magma rises through the mantle and ocean floor
to emerge as volcanoes.
• Eventually a chain or arc of islands called island arc is
formed.
boundaries?

• Earthquakes may also occur.
• E.g. the Pacific Plate converging with the slower-moving
Philippine plate
boundaries?

1. Oceanic–Oceanic plate convergence
boundaries?

Locate the Indonesia Archipelago and Japan. Explain the
shape and distribution of these islands.
boundaries?

2. Continental-continental plate convergence
• Plates made largely of continental crust may collide
with other plates made largely of continental crust.
• However, both plates have similar densities and
hence, resist subduction.
• Instead, the plates break, slide along fractures in the
crust and fold, forming fold mountains.
• E.g. the Himalayas - convergence of the Indian Plate
and the Eurasian Plate.
boundaries?

E.g. the Himalayas
boundaries?
Continental crust
Continental crust
Himalayas
Tibetan
Plateau
Uppermost mantle
Asthenosphere
EURASIAN
PLATE
INDIAN
PLATE

3.Oceanic-continental plate convergence
• When an oceanic plate meets a continental plate, the
denser oceanic plate subducts under the less dense
continental plate.
• A subduction zone forms, creating a deep oceanic
trench along the plate boundary.
• The subduction of the continental plate causes the
soild mantle material to melt and magma is formed.
boundaries?

• The magma rises through the mantle and crust to
emerge as volcanoes on land.
• The edge of thick continental plate buckles to form
fold mountains.
• Earthquakes may also occur.
• E.g. the Australian Plate subducting under a section
of the Eurasian Plate near Sumatra formed the Sunda
Trench.
boundaries?

boundaries?

Transform plate boundaries
• Plates slide past each other.
• As they do so, tremendous stress builds up.
• This stress is eventually released, often as a violent
earthquake.
• E.g. San Andreas Fault, United States of America &
North Anatolian Fault, Turkey
boundaries?

Transform plate boundaries
boundaries?

E.g. San Andreas Fault, United States of America
• In 1906, an earthquake occurred in San
Francisco, southern California between the
Pacific Plate and the North American Plate.
– This caused several hundred kilometres of
North American Plate to move an average of
2.5 m,
– and at one point almost 7 m all in less than 1
minute.
boundaries?

E.g. San Andreas Fault, USA
boundaries?

E.g. North Anatolian Fault, Turkey
How would the plate movement affect the two
cities shown in time to come?
boundaries?

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