CHAPTER 2 LIVING WITH TECTONIC HAZARDS Risk or Opportunity?

CHAPTER 2

LIVING WITHTECTONIC 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 2 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.

a. What is a natural hazard?

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.

DroughtsEarthquakes

TsunamisWildfiresFloods


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 layer2. 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/structure.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

c. What is a tectonic plate?

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)

c. What is a tectonic plate?

1. Convection currents2. Slab-pull force

d. Why do tectonic plates move?

1. Convection currents•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.


1. Convection currents•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

Pla

tes

mov

ing

tow

ards

ea

ch

othe

rP

lates

moving

towards

each otherPlates

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.


Divergent plate boundaries

1. Oceanic-oceanic plate divergence2. Continental-continental plate divergence


1. Oceanic-oceanic plate divergence


• 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.


• 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.


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


• 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


Convergent plate boundaries

1. Oceanic–oceanic plate convergence2. Continental–oceanic plate convergence3. Continental–continental plate convergence


1. Oceanic–oceanic plate convergence• 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.


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

Philippine plate

1. Oceanic–oceanic plate convergence


1. Oceanic–Oceanic plate convergence


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


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.


E.g. the Himalayas


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.


• 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.

3.Oceanic-continental plate convergence


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


Transform plate 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.


E.g. San Andreas Fault, USA


E.g. North Anatolian Fault, Turkey

How would the plate movement affect the two cities shown in time to come?


CHAPTER 2 LIVING WITH TECTONIC HAZARDS Risk or Opportunity?

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