LIVING WITH TECTONIC HAZARDS

What is a natural hazard?

Internal structure of the Earth

Death Valley, California, USA

Chief Mountain, Montana, USA

Great Rift Valley, Madagascar

San Andreas Fault, California, USA

Cleveland Volcano, Alaska

Chaiten Volcano, Chile

BY THE END OF THE LESSON

Lets be able to

1. Describe the distribution of different types of natural hazards.

2. Compare the different types of natural hazards.

3. Describe the internal structure of the Earth.

QUESTIONS

1. What is a natural hazard?

2. What are the kinds of natural hazards?

NATURAL HAZARD

• A naturally occurring event that threatens human lives and causes damage to property.

• Some examples of natural hazards are earthquakes, volcanic eruptions, floods and tropical cyclones.

QUESTIONS

1. Describe the distribution of different types of natural hazards. [4]

NATURAL HAZARDS

DISTRIBUTION

• Where are tectonic hazards located? [2]

• Where are climate-related hazards located?

[2]

DISTRIBUTION

• Tectonic hazards such as volcanic eruptions are mainly concentrated along the coastlines of the Pacific Ocean,

• with earthquakes lined along the boundaries of tectonic plates.

• Climate-related hazards such as tropical cyclones are found between 8° and 15° north and south of the Equator,

• while droughts and floods are widely distributed between the Arctic Circle and Antarctic Circle.

STRUCTURE OF THE EARTH

STRUCTURE OF THE EARTH

• Crust– Outermost layer of

the Earth

– Consists of solid rocks such as basalt and granite

– Continental crust is less dense than oceanic crust

– Thickness ranges from 5km to 70 km

STRUCTURE OF THE EARTH

• Mantle– Consist of upper

mantle of molten rock called magma and lower mantle of solid rock

– Around 2900km thick

– Temperature between 800°C to 3000°C

STRUCTURE OF THE EARTH

• Core

– Made of mostly iron and nickel

– Molten outer core of around 2100km thick

– Solid inner core of around 1200km thick

– Temperature between 3000°C to 5000°C

LIVING WITH TECTONIC HAZARDS

Why do plates move?

BY THE END OF THE LESSON

Let’s be able to

1. Explain why plates move.

TECTONIC PLATES

• The broken up pieces of the Earth’s crust that move in relation to one another.

• Tectonic plates can be made up of either continental crust, oceanic crust or a combination of both.

WHY DO PLATES MOVE?

• Convection currents

• Slab-pull force

WHY DO PLATES MOVE?

WHY DO PLATES MOVE?

• Convection currents– Magma in the mantle is heated by the core,

causing it to expand, rise and spread out beneath the plates which cause plates to move away from each other.

– As the magma nears the Earth’s surface, it cools, contracts and sinks, bringing plates towards each other.

– The sinking material heats up again as it nears the core and the whole process repeats.

WHY DO PLATES MOVE?

• Slab-pull force– Slab-pull force occurs when a denser oceanic

plate subducts below a less dense continental plate or an oceanic plate.

– As the plate subducts, it pulls the rest of the plate along, contributing to the downward movement of convection currents.

– The magma away from the subduction zone rises thereby contributing to the upward movement of convection currents.

LIVING WITH TECTONIC HAZARDS

Plate movements and resultant landforms

PLATE MOVEMENTS

AND BOUNDARIES

By the end of the lesson, you will be able to,

1. Describe the global distribution of tectonic plates and types of plate boundaries.

2. Describe the different types of plate movement.

3. Explain the formation of landforms as a result of divergent plate movement.

PLATES AND PLATE BOUNDARIES

DISTRIBUTION

• Seven major plates: African Plate, Antarctic Plate, Australian Plate, Eurasian Plate, North American Plate, South American Plate, Pacific Plate.

• Some minor plates: Arabian Plate, Caribbean Plate, Cocos Plate, Nazca Plate, Philippines Plate, Scotia Plate.

• Plates converge, diverge or grind past each other.

PLATE BOUNDARIES

• Divergent

– Plates move away from each other

• Convergent

– Plates move towards each other

• Transform

– Plates move past each other

DIVERGENT PLATE BOUNDARIES

• Areas where two plates diverges or move away from each other due to tensional force, causing magma to move upward to the surface where it cools to form new crust.

SEA FLOOR SPREADING

OCEANIC-OCEANIC PLATE DIVERGENCE

• Fractures and cracks develop along plate boundaries as two oceanic plates move apart.

• Magma rises from the mantle and escapes through the cracks to the surface which cools and solidify to form new sea floor.

• Older crusts are pushed further apart as the new sea floor forms in a process known as sea-floor spreading.

MID-OCEANIC RIDGE

MID-OCEANIC RIDGE

• When two oceanic plates diverges, fractures and cracks are formed at the plate boundary.

• Magma escapes from the mantle through the cracks to the surface and solidifies to form new sea floor.

• As more magma solidifies and piles up, a chain of mountains or undersea ridges is formed on either side of the spreading zone, forming oceanic ridges.

• An example is the Mid-Atlantic Ridge in the middle of the Atlantic Ocean, which was formed when the North American Plate and the Eurasian Plate moved away from each other.

VOLCANIC ISLANDS

• As the magma escapes from various points along the ridge, cools and builds up above sea level, volcanic islands are formed.

• An example is the Azores, a series of nine volcanic islands situated in the North Atlantic Ocean.

Azores Islands, Portugal

CONTINENTAL-CONTINENTAL

PLATE DIVERGENCE

• When two continental plates diverge or move apart, they are stretched, causing fractures to form at the the plate boundary.

RIFT VALLEYS, BLOCK MOUNTAINS

• As two continental plates diverge, rock layers are pulled apart in opposite directions by tensional force.

• As the two platescontinue to pull apart, fractures or fault lines are created at the boundary, creating a central mass of rock.

RIFT VALLEYS, BLOCK MOUNTAINS

• As the land adjacent to the central mass continue to diverge, the central mass sinks, forming a linear depression known as a rift valley.

• The adjacent sections which are left standing are block mountains.

RIFT VALLEYS, BLOCK MOUNTAINS

• As two continental plates diverge, rock layers are pulled apart in opposite directions by tensional force.

• As the two platescontinue to pull apart, fractures or fault lines are created at the boundary, creating a central mass of rock.

RIFT VALLEYS, BLOCK MOUNTAINS

• As the land adjacent to the central mass continue to diverge, they sink, forming a linear depression known as a rift valley.

• The central mass which is left standing is a block mountains.

RIFT VALLEY, BLOCK MOUNTAINS

BY THE END OF THE LESSON

Lets be able to

1. Describe the process of subduction.

2. Explain the formation of landforms as a result of convergence plate movement.

CONVERGENT PLATE BOUNDARIES

• Areas where plates converges or move towards each other due to compressional force, causing land to subduct or fold.

OCEANIC-OCEANIC PLATE

CONVERGENCE

• When two oceanic plates converge, or when an oceanic plate converges with a continental plate, the denser plate subductsunder the less dense plate. The area where this happens is known as the subductionzone.

SUBDUCTION

• Refers to the sideways and downward movement of the edge of a plate of the earth's crust into the mantle beneath another plate.

• When denser plate collides with a less dense plate, the denser plate is subducted (pushed down) into the molten upper mantle, and destroyed.

SUBDUCTION

SUBDUCTION

OCEANIC TRENCH

• As two oceanic plates collide, the denser oceanic plate is forced under/subductedunder the less dense oceanic plate to form a long, deep and narrow depression known as an oceanic trench.

• An example is the Mariana Trench formed by the Pacific Plate subducting under the Philippines Plate.

VOLCANIC ISLAND

• The crust of the subducted oceanic plate melts and forms magma.

• As the magma escapes through the crust, volcanoes and eventually a chain or arc of volcanic islands is formed.

• An example is the Mariana Islands.

CONTINENTAL-CONTINENTAL PLATE

CONVERGENCE

• When two continental plates converge, layers of rock are compressed, leading to folding.

FOLDING

• Folding refers to the geologic process of bending or curving of a stack of originally flat planar surface by compressional processes along plate boundaries.

• Folding generally occurs in areas with sedimentary rocks which are softer and more flexible.

• Folding normally does not lead to earthquakes as stress is released during the process of folding.

FOLD MOUNTAINS

FOLD MOUNTAINS

• Sedimentary rocks, that make up part of the Earth's crust are softer and more flexible.

FOLD MOUNTAINS

• As two plates collide, compressional forces put sedimentary rock layers under great pressure, causing them to bend or fold.

FOLD MOUNTAINS

• As the process continues over time, the folded sedimentary rock layers rise up to great heights, forming fold mountains.

FOLD MOUNTAINS

• The upfold is called the anticline.

• The downfold is called the syncline.

OCEANIC-CONTINENTAL PLATE

CONVERGENCE

• When an oceanic plate converges with a continental plate, the denser plate subductsunder the less dense plate leading to subduction and folding.

SUBDUCTION

SUBDUCTION

OCEANIC TRENCH

• As an oceanic plate collide with an continental plate,

• the denser oceanic plate is forced under/subductedunder the less dense continental plate to form a long, deep and narrow depression known as an oceanic trench.

FOLD MOUNTAINS

• The convergence may cause plate to buckle and fold, forming fold mountains.

• At the subduction zone, the crust is destroyed to form magma.

• The magma may escape through cracks and fractures on the crust, giving rise to volcanoes.

TRANSFORM PLATE MOVEMENT

• Areas where two plates grinds laterally past each other.

• No land is destroyed or formed but sudden release of build-up pressure gives rise to powerful earthquakes.

TRANSFORM PLATE MOVEMENT

Tear Fault /Strike Slip Fault

TRANSFORM PLATE BOUNDARY

• Transform plate movement creates tremendous stress which builds up and when released, results in violent earthquakes.

BY THE END OF THE LESSON

Lets be able to

1. Describe the distribution of volcanoes around the world.

2. Explain how a volcano is formed.

3. Describe the internal structure of a volcano.

4. Compare the difference between a shield volcano and a strato volcano.

VOLCANOES

• A conical mountain or hill, having a crater or vent through which lava, rock fragments, hot vapor, and gas are being or have been erupted from the earth's crust.

DISTRIBUTION

DISTRIBUTION

• Volcanoes are located along convergent and divergent plate boundaries around the world.

• A large number of volcanoes are found around the edges of the Pacific Ring of Fire, which is found along the boundaries of converging plates such as the Pacific Plate and Philippines Plate.

• Volcanoes are also found along diverging plate boundaries such as in the Atlantic Ocean where the African Plate and the South American Plate diverge.

FORMATION

• Cracks and fractures are formed as a result of convergent or divergent plate movements.

• Magma escaped through the cracks and fractures onto the Earth’s surface as lava.

• As the lava cools and solidifies and builds up around the vent, conical mountain or hill is formed which is known as a volcano.

STRUCTURE

SHAPES AND SIZES

• Volcanoes differ in shapes and sizes due to the difference in viscosity, which refers to the stickiness of the lava, which is in turn determined by the amount of silica in the lava.

SHAPES AND SIZES

• Low-silica lava or less viscous lava flows more easily, and allows gases to escape easily.

• High-silica lava or more viscous lava flows less readily, and traps gases more easily.

SHIELD VOLCANOES

• Gently sloping

• Broad submit and base

• Formed by lava low in viscosity (low-silica lava)

• Lava spreads over a large area

• Lava cools and solidifies slowly

• Lava traps less gas

• Less violent eruption

Mauna Loa Volcano, Hawaii

SHIELD VOLCANOES

STRATO VOLCANOES

• Steep slopes at the top• Gentle slopes towards the bottom

– Small and light materials are be deposited further away

• Formed by lava high in viscosity (high-silica lava)

• Lava spreads over a small area and solidifies quickly

• Traps gas• Erupts violently

Mount Mayon, Philippines

Mount Vesuvius, Italy

STRATO VOLCANOES

Mount Vesuvius, Italy

CALDERA

• The summit of a volcano may be blown off during an explosive eruption.

• The sides of the crater collapse inwards due to the loss of structural support.

• As a result, a large depression known as a caldera is formed.

LIVING WITH TECTONIC HAZARDS

Phenomena found at plate boundaries

BY THE END OF THE LESSON

Let’s be able to

1. Describe an earthquake.

2. Describe the focus and epicentre of an earthquake.

3. Describe the factors influencing the impact of earthquakes.

EARTHQUAKES

• A vibration in the Earth’s crust caused by the sudden release of stored energy in the rocks along fault lines.

EARTHQUAKES

• Earthquakes occur when there is plate movement along plate boundaries.

• The plate movements cause the slow build-up of stress on the rocks found on either side of the fault.

• When the rocks can no longer withstand the stress, a slip which can span many metresoccur, causing an earthquake.

FOCUS, EPICENTRE

• The focus of an earthquake refers to the point of origin of the seismic waves released when an earthquake occurs.

• The point on the Earth’s surface directly above the focus is the epicentre.

FACTORS INFLUENCING THE

IMPACT OF EARTHQUAKES.

1. Population density

2. Level of preparedness

3. Distance from the epicentre

4. Time of occurrence

5. Type of soil

POPULATION DENSITY

• Earthquakes are more likely to result in more casualties and damages in areas with high population density due to the presence of more people and properties.

LEVEL OF PREPAREDNESS

• Earthquakes are less likely to result in a lot of damages when there is a high level of preparedness such as the availability of evacuation plans, trained rescue workers and rescue action plans.

DISTANCE FROM THE EPICENTRE

• Earthquakes are more likely to result in more casualties and damages when the area is closer to the epicentre as the strength of seismic waves is strongest at the epicentre.

TIME OF OCCURRENCE

• Earthquakes are more likely to result in more casualties and damages when it happens at night when most people are sleeping, as there is a higher chance of being trapped in houses due to shorter reaction time to evacuate.

TYPE OF SOIL

• Earthquakes are more likely to result in more casualties and damages when it happens in places where sediments are loose and unconsolidated as the seismic waves are amplified in these areas.

BY THE END OF THE LESSON

Let’s be able to

1. Explain how tsunamis are formed by seismic activity.

2. Describe hazards associated with earthquakes.

HAZARDS ASSOCIATED

WITH EARTHQUAKES

• Tsunamis

• Disruption of services

• Fire

• Landslides

• Destruction of properties

• Destruction of infrastructure

• Loss of lives

TSUNAMIS

• Refers to an unusually large sea wave which can be formed by,

– A large offshore earthquake.

– An explosive underwater volcanic eruption.

– An underwater landslide.

– A landslide above sea level which causes materials to plunge into the water.

FORMATION OF TSUNAMIS

• Seismic energy from an offshore earthquake forces out a mass of water, generating large waves.

• The waves may begin at a height of 1 metre with wave lengths of 100km and speeds of around 800km/h.

• On reaching shallow water, greater friction slows the waves down and forces an increase in wave height.

• As the waves reached the shore, the waves could be travelling at 50km/h and reach heights of around 15m, forming a tsunami.

FORMATION OF TSUNAMIS

Japan earthquake, 2011

DISRUPTION OF SERVICES

• Earthquakes can disrupt services such as the supply of electricity, gas and water and potentially affect a large area.

• For example, the earthquake in Kobe, Japan, in 2004 damaged pipes and transmission lines, leading to disrupted electricity and water services for about 1 million people.

FIRE

• Earthquakes may expose electrical cables which may ignite flammable items such as chemicals and leaked gas from ruptured gas pipes.

• For example, the earthquake in Kobe, Japan, in 1995 caused extensive fires as a result of toppled gas cookers and kerosene stoves from households preparing their morning meals.

Japan earthquake, 2011

LANDSLIDES

• Earthquakes may cause landslides, which refer to the rapid downslope movements of soil and rock due to the the weakening of the slopes of hills and mountains, and can bury people and infrastructure in seconds.

• For example, a massive landslide was triggered by an earthquake in Peru in 1970, which lead to a death toll of 18,000.

DESTRUCTION OF PROPERTIES

• Earthquakes may lead to the destruction of properties as homes may be destroyed, causing people to lose their homes overnight.

• For example, the tsunami in 2011 travelled more than 10km inland into Japan, destroying many homes in the process, leading to a severe shortage of homes.

Sichuan earthquake, 2008

DESTRUCTION OF INFRASTRUCTURE

• Earthquakes may cause cracks to form in infrastructure such as roads and bridges hence disrupting transport and rescue services.

• For example, many places became inaccessible after the earthquake in Kobe, Japan, in 1995 due to the destruction of roads.

Haiti earthquake, 2010

LOSS OF LIVES

• Earthquakes and their associated hazards such as landslides and tsunamis often lead to the loss of lives of people living in earthquake zones.

• For example, 28,000 lives are estimated to have been lost in the Tohoku, Japan earthquake in 2011.

BY THE END OF THE LESSON

Let’s be able to

1. Describe the difference between active, dormant and extinct volcanoes.

2. Describe the risks of living near volcanic areas.

3. Describe the benefit of living near volcanic areas

ACTIVE, DORMANT, EXTINCT

• Active volcanoes refer to volcanoes which are currently erupting or are expected to erupt in the near future.

• Dormant volcanoes are currently inactive but may erupt in the near future.

• Extinct volcanoes refer to volcanoes without seismic activity and with no evidence of eruptions for the past thousand of years.

RISKS OF LIVING NEAR

VOLCANIC AREAS

1. Destruction by volcanic materials

2. Landslides

3. Pollution

4. Effects on weather

DESTRUCTION BY

VOLCANIC MATERIALS

• Volcanic eruptions can result in pyroclastic flows which is a fast-moving current of hot gas and rock that can reach speeds of to 700 km/h and 1,000 °C, capable of destroying everything in its path.

• For example, Mount Merapi, Indonesia has been known for violent eruptions that are accompanied by pyroclastic flows.

LANDSLIDES

• Landslides can occur due to the collapse of a volcanic cone during a volcanic eruption and have the potential to obstruct flow of rivers thereby causing floods, block roads or bury entire villages.

• For example, the 1985 eruption of Nevado del Ruiz in the Andes mountains triggered a landslide that killed more than 20,000 people.

POLLUTION

• Volcanic eruptions can release gases such as carbon dioxide, sulphur dioxide and carbon monoxide which is harmful to people when inhaled in large quantity.

EFFECTS ON WEATHER

• Ash particles ejected during volcanic eruptions may reflect the Sun’s energy back into space, leading to global cooling ranging from a few months to years.

• For example, the 1815 eruption of Mount Tanbora in Indonesia reduced global temperatures by 1.7°C.

BENEFITS OF LIVING NEAR

VOLCANIC AREAS

1. Fertile volcanic soil

2. Precious stones and minerals, building materials

3. Tourism

4. Geothermal energy

FERTILE SOIL

• Lava and ash from volcanic eruptions break down to form fertile soils which are favorable to agriculture.

• For example, the volcanic soils of Java and Bali in Indonesia produces very bountiful harvests of crops such as tea and coffee each year.

PRECIOUS STONES AND MINERALS, BUILDING MATERIALS

• Volcanic rocks can be rich in precious stones such as diamonds and materials such as sulphur which can be extracted when the upper layers of volcanic rocks are eroded.

• For example, the old volcanic rocks at Kimberly, South Africa contain one of the world’s richest source of diamonds.

TOURISM

• Volcanic areas are popular tourist attractions as they offer a variety of activities such as hiking, camping or just enjoying the scenery.

• For example, Mount Fuji, Japan is a very popular tourist destination and has been drawing millions of tourists each year.

GEOTHERMAL ENERGY

• Volcanoes are sources of geothermal energy, which refers to energy derived from heat in the earth’s crust.

• For example, most of Iceland’s electricity is generated from geothermal power because of the large number of volcanoes in the country.

BY THE END OF THE LESSON

Let’s be able to

1. Describe the various approaches to responding to earthquakes.

2. Evaluate the effectiveness of preparedness measures in response to earthquakes.

APPROACHES

• Fatalistic approach

– Accepts that earthquakes are unavoidable and

– May resist evacuation when earthquake happens

• Acceptance approach

– Accepts the risks of living earthquakes

• Adaptation approach

– Accepts the risks of living earthquakes and emphasizes well-preparedness to earthquakes.

PREPAREDNESS MEASURES

• Land use regulations

• Building design

• Infrastructure development

• Emergency drills

• Use of technology

QUESTION

• Evaluate the effectiveness of earthquake preparedness measures. [8]

LAND USE REGULATIONS

Land use regulations refers to a set of rules implemented m earthquake zones to restrict development in certain areas. For example, in California, United States of America, all new building developments are not built across fault lines or areas at risk of liquefaction. Although land use regulations have been effective in mitigating the impact of earthquakes, they are very costly to implement. This is because these regulations are often carried out in already built-up areas that require the government to repurpose the land or purchase from private owners first before repurposing. As such, although land use regulations is an effective measure, it is not a measure that can be implemented by earth-quake prone countries with little resources such as Haiti.

BUILDING DESIGN

• Building design refers to constructing buildings with effective design that can reduce the collapse of buildings during earthquakes. For example, the Taipei 101 building, Taiwan, was built with steel and reinforced concrete and sits on a wide and heavy base. This has allowed the skyscraper to withstand earthquakes successfully. However, constructing buildings with such designs are expensive and requires highly skilled labour, hence this strategy is not a available to poor countries that are earthquake prone.

INFRASTRUCTURE DEVELOPMENT

Infrastructure development refers to building infrastructure with advanced engineering to withstand the vibration associated with earthquakes. For example, roads, bridges and dams are built to resist ground shaking in China and Canada so they do not collapse during earthquakes. This has been successful in reducing damages to valuable infrastructure and loss of lives. However, infrastructure development is very costly strategy, be it building new ones or converting existing infrastructure, hence this strategy is not a available to poor countries that are earthquake prone.

EMERGENCY DRILLS

• Emergency drills refers to the frequent practice of steps to take when an earthquake occurs. This creates awareness among the population and prevents widespread panic during an earthquake. For example, Japan conducts emergency drills every year during a Disaster Prevention Day, that involves people all over Japan in an earthquake stimulation exercise. However, emergency drills may lose its effectiveness as people may become complacent overtime, especially when the last earthquake happened a long time ago.

USE OF TECHNOLOGY

BY THE END OF THE LESSON

Let’s be able to

1. Evaluate the effectiveness of short-term and long-term responses to earthquakes.

SHORT-TERM RESPONSES

• Short-term responses are those that occur immediately and last for weeks after the occurrence of an earthquake.

1. Handling the status of the affected area

2. Searching for and rescuing casualties

3. Providing medical aid, food and water

4. Setting up emergency shelters

5. Calling for humanitarian aid

HANDLING THE STATUS

OF THE AFFECTED AREA

SEARCHING FOR AND

RESCUING CAUSALITIES

PROVIDING MEDICAL AID, FOOD AND WATER

SETTING UP EMERGENCY SHELTERS

CALLING FOR

HUMANITARIAN AID

LONG-TERM RESPONSES

• Long-term responses can stretch over months and years and involve rebuilding an affected region.

1. Improving infrastructure

2. Compensating people who lose their land and property

3. Ensuring the affected region recovers economically

4. Improving health options

IMPROVING INFRASTRUCTURE

COMPENSATING PEOPLE WHO LOSE

THEIR LAND AND PROPERTY

ENSURING THE AFFECTED REGION

RECOVERS ECONOMICALLY

IMPROVING HEALTH OPTIONS

QUESTION

• “Long-term responses to earthquakes are more effective than short-term responses.” How far do you agree with this statement?

[8]

END