4. Types of plate boundaries and examples:
·
Divergent: where plates move away from each other - oceanic-oceanic e.g. Mid-Atlantic Ridge,
continental-continental e.g. Great Rift Valley of East Africa
·
Convergent: where plates move towards
each other - oceanic-oceanic e.g.
Mariana Trench, continental-continental e.g. Himalayas, oceanic-continental
e.g. Andes
·
Transform: where plates move past each
other e.g. San
Andreas Fault between the Pacific plate and the North American
Plate.
5. Describe the characteristics of landforms associated with plate
movements.
Oceanic-oceanic plate
divergence: Mid-oceanic ridge and Volcanic islands
•
As the plates move apart due to convection currents inside the Earth. 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.
Continental–continental plate divergence: Rift valleys and block mountains
•
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
Continental–continental
plate divergence
• 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
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 lava which cool and solidify to become 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
Continental-continental
plate convergence: Fold mountains
•
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.
Oceanic-continental plate convergence: oceanic trench and volcano
•
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.
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 - In
1906, an earthquake occurred in San Francisco, southern California between the
Pacific Plate and the North American Plate.
This caused several hundred km 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
6. How is a fold mountain formed?
•
Over millions of years, the folding of rocks creates a landform called fold
mountains.
•
The Himalayas, the Rocky Mountains and the Andes are examples of fold
mountains.
•
Fold mountains are
formed along convergent plate boundaries.
•
The compressional
force causes the layers of rocks to buckle and fold.
•
This process is known
as folding.
•
The upfold is called
the anticline and
•
The downfold is the
syncline.
•
When there is
increasing compressional force on one limb of a fold, the rocks may buckle
until a fracture forms.
The limb may then move forward to ride over the other
limb.
7. Describe the formation of Rift valleys and block mountains.
Rift valleys and block mountains are formed at
divergent plate boundaries.
•
A fault is a fracture in the rocks along which the rocks are displaced.
•
The tensional forces result in parts of the crust being
fractured.
•
This process is called faulting.
• A rift
valley is a valley with steep sides formed along fault lines.
• E.g. East African Rift Valley
•
A block mountain is a block of land with steep sides. It
is formed when sections of the crust extend along fault lines and rock masses
surrounding a central block sink due to tensional forces.
The East African Rift
Valley
Is formed from the Nubian section of the African
Plate and the Somalian section of the African Plate pulling away from one
another.
8.Describe the formation of volcano.
A volcano
is a landform formed by magma ejected from the mantle onto the
earth’s surface. Magma is molten rock found below the earth’s
surface. Magma that is ejected onto the surface is known as lava. The
lava cools and solidifies in layers and form a cone-shaped mountain called a
volcano.
9. Describe and draw the structure of volcanoes.
Structure of volcanoes – crater / caldera, vent,
magma chamber
11.
Explain the shape and size
of volcanoes.
Volcanoes vary
in shapes and sizes due to the characteristics of lava. Low silica lava has low
viscosity (stickiness) while high-silica has high viscosity.
•
Shield volcano is made up of fluid lava with low silica content. It
is more mobile and spreads away from the vent before it solidifies forming
gentle concave slopes. It is associated with quiet eruption e.g. Mauna Loa
(Hawaii), Mount Washington, United States of America
Stratovolcano is a composite cone has a stratified structure. There are periodic violent eruptions with alternate layers of lava and ash accumulated. It is high with steep slopes near the summit and gradient decreases toward the base. Parasitic cones develop due to the development of cracks during violent eruptions. e.g. Mt Fujiyama in Japan, Mt Pinatubo in Philippines, Mount Mayon, Philippines
10. Explain what is a active, dormant or extinct volcano.
Active volcanoes – volcanoes which are currently erupting or are expected to
erupt in the future
Dormant
volcanoes – volcanoes which are currently inactive but
may erupt in near future
Extinct volcanoes – volcanoes without current seismic
activity with no geological evidence of eruptions for the past thousands of
years.
11. Describe the distribution of volcanoes.
Mainly along the Pacific Ring of Fire
which is the boundaries of several converging plates – Pacific Plate, Nazca
Plate, the Philippines Plate and the Eurasian Plate.
Also found where plates are diverging e.g.
Atlantic Ocean and East Africa
12. Explain the cause of earthquake.
Earthquakes occur at the plate boundary because this
is the most active part of the earth’s crust. As plates converge, one plate is
being pushed underneath another, and a zone of subduction is formed. As one
plate moves over the other, the movement is not smooth because the surface of
the crust is not smooth. There is friction and this friction causes the
movement to jerk.
The crust is
also under great stress when the plates move in opposite direction. The stress
in the rocks is so tremendous that it finally causes the rocks to jerk free.
The release of tension in the form of seismic waves made the ground vibrate.
After an earthquake, a series of smaller earthquakes called aftershocks occur
along the fault line. Focus is the place where the earthquake takes place.
Epicentre is the point on the surface above the focus.
13. Explain why some earthquakes more damaging than others.
Some earthquake causes more damage because
the intensity of the earthquake
differs. Places located near to the epicentre
will experience high intensity of the earthquake and thus suffer the greatest
amount of damage.
The damage also depends on the depth of its origin – a
deep-focus
earthquake ( 70-700km below earth surface) has a smaller impact on the land
compared to a shallow-focus earthquake (upper 70km of earth crust) as seismic
waves take a longer time to reach the surface and would have lost most of their
energy by then, A seismograph is used for recording
earthquake. The intensity of earthquake is measured on the Richter scale graded
from 1 to 9. The higher the number on the Richter scale the greater the
intensity of the earthquake. The stronger vibration will lead to the collapse of more buildings and infrastructure which in turn results in more casualties and damage.
Population
density which is the the number of people living in the affected
area is an important factor, Earthquakes in sparsely populated areas are
likely to affect fewer people than in densely populated areas. For example, an earthquake in a city can cause
more casualties and damage than an earthquake in the countryside. The 2001 Kunlun earthquake had a magnitude of
7.8 but 0 casualties due to low population density. Similarly, several earthquakes occur at Solomon islands in 2015 but there are no casualties.
The extent of damage also depends on the amount of development in the areas
where earthquake takes place. An earthquake which struck a desert is less
damaging than in a city.
The
foundations of the buildings and bridges are also important because if the foundation is good,
it will withstand the vibration. Developed areas suffer more damages as water
and gas pipes broke. Urban areas are heavily built up with dense population
densities and heavy traffic movements. As residents in big urban areas usually
live in high rise buildings because land is scarce in the cities, damage to
properties and loss of lives can be phenomenal as the high rise building
collapse when earthquakes occur. As building collapse, other related hazards
usually occur such as fire from damaged power lines. Destruction to highways,
streets, flyover and bridges leads to widespread traffic congestion and
commuters may be killed and hurt. Telephone line and power supply will be
disrupted, and this will affect communication with outside world which in turn
will hamper rescue work.
The strength of the earthquake also depends
on the the geology of the epicentre.
e.g. Mexico,
built on layers of mud and sand, vibrates like jelly in the 1985 earthquake
which killed 7000.
In Christchurch,
many houses and buildings had to be abandoned because of liquefaction where the
ground becomes unstable and saturated soil flows like a liquid after the
earthquake in 2011.
The damage also depends on the level of preparedness and time of occurrence. Preparations such
as having evacuation plans, trained rescue workers and other action plans can
make the damage of an earthquake more manageable if the people are more
prepared. If the earthquake occurs when
most people are sleeping, there is a higher chance that more deaths will occur
as they are trapped in their houses. E.g. more than 2400 people died when an
earthquake occurred after midnight in the Sun Moon Lake Region in Taiwan in 1999.
14. Explain the hazards associated with earthquakes.
•
Disruption of services - An earthquake can disrupt services such as the supply of electricity,
gas and water. The earthquake in Kobe, Japan, in 1995 disrupted electricity,
gas and water supplies to about a million of Kobe city’s 1.4 million residents.
·
Fires are started due to rupture gas
pipes which provide fuel to start fires as well as exposing electrical cables
which ignite flammable items. The earthquake in Kobe, Japan
in 1995 caused extensive fires that raged on an off for 2 days and it spread
quickly due to strong winds. The firemen were unable to control the fires as
there was no water supply due to ruptured water pipes.
·
Landslides caused by earthquakes which
weaken the slopes of hills and mountains due to the shaking of the ground. In
1970, an earthquake off the coast of Peru
triggered a massive landslide on the slopes of Mount
Huascaran and destroyed the town of Ranrahirca killing 18000
people within seconds.
·
Destruction of properties – the
earthquake in Tohoku, Japan in 2011, caused a tsunami
which travelled up to 10km inland, causing extensive structural damage
resulting in hundreds of thousands of people forced from their homes. There was
a severe shortage of housing and long-term consequence on the health of people.
·
Destruction of infrastructure
–earthquakes cause cracks to form in infrastructure such as roads and bridges. Transportation
can be disrupted as it is unsafe to use the damaged roads.
·
Loss of lives and threat of tsunami
·
Aftershocks -there could still be
aftershocks of lower magnitudes as there are adjustments to the repositioning
of the fault. As many buildings are already weakened by the main shock, the
aftershocks will cause more collapse and there will be more casualties. Dead animals and corpse will start to rot and
if not disposed quickly, there might be an outbreak of epidemic such as
Malaria.
15. Explain the cause of
tsunamis.
Tsunamis may be formed by:
·
Movement of the sea floor
during a large earthquake at the subduction zones
·
An explosive underwater
volcanic eruption
·
An underwater landslide;
·
A landslide triggered by
earthquake or volcanic eruption which causes materials to plunge into the
water.
16. Describe the benefits and
risks of living in volcanic areas.
Benefits
of living in volcanic areas
·
Volcanic regions are often rich
in sulphur deposits which can be mined for industrial use. E.g. In East Java,
Indonesia, the sulphur collected is used to make matches and fertilizers, and
refine sugar.
·
Basic lava often produces
fertile soil after weathering which is suitable for cultivation. e.g. fertile
volcanic soils in Java and Deccan Plateau in India
·
Geothermal power may be
utilised for making steam to drive turbines and generate electricity e.g. over
70% of homes in Iceland
are heated by volcanic steam
·
Volcanic areas offer
spectacularly beautiful attractions for tourists. e.g Mt Fuji in Japan. Volcanic
areas can be rich in history e.g. ruins of Pompeii
in Italy
where Mt Vesuvius erupted in 79 CE and buried the town. Every year, almost 3
million people visit the unearthed archaeological site which revealed
buildings, pottery and mosaics left intact.
·
Volcanic ash can be used to
surface roads and manufacture bricks
·
In some parts of the world,
valuable materials such as gold, iron and diamonds have been formed by volcanic
activity, and large mining centres have developed. The old volcanic rocks at
Kimberly in South Africa
are one of the world’s richest sources of diamond.
Risks
of living in volcanic areas
·
Volcanic eruptions claim many
lives and destroy buildings and property. The lava, with high temperatures of
between 500ºC and 1400 ºC burns the area it flows through. Volcanic bombs of
heated rocks destroy property around the volcano e.g. eruption of Kilauea in Hawaii destroyed many
homes and highway.
·
Poisonous gases such as
compounds of sulphur, carbon monoxide and carbon dioxide are produced. Inhaling
the hot ash and gases can result in serious injury or death.
·
Landslide can occur due to
collapse of a volcanic cone. Landslides can obstruct the flow of rivers causing
floods, block roads, and bury villages and farmlands. The eruption of Nevado
del Ruiz in the Andes mountain of South America in 1985 caused lahars which killed more
than 20000 people in the town of Armero.
·
Ash and volcanic dust ejected
by volcanoes may be blown away to pollute the air and disrupt human activities
over a large area from the volcano. It can block sunlight, suffocate crops and
cause severe respiratory problems for people and animals. The eruption of
Eyjafjallajökull in Iceland
in 2010 resulted in the closure of air space over much of Europe
as the volcanic particles pose a serious danger to aircraft engines and
structures. Connecting flights worldwide were cancelled and delays to 1.2
million passengers daily cost the airline industry a total of US$1.8 billion.
·
When snow-capped volcanoes
erupt, a sudden flash flood will also result from the melting of snow and ice.
Mudflow may also be produced.
·
Sulphur dioxide
released from volcanic eruption may react with water vapour and other chemicals
in the atmosphere to form sulphur-based participles which can reflect the sun’
energy back into the atmosphere and temporarily cool the earth. The 1815
eruption of Mount Tambora in Indonesia cause the global
temperatures to drop by as much as 1.7ºC.
17. Discuss the responses of people to earthquakes and tsunamis.
People may respond to natural hazards in several
ways:
Fatalistic approach – people who accept
earthquakes as unavoidable events and may resist evacuation in the face of the
threat of an earthquake. Common for communities in less developed countries
with limited access to other places.
Acceptance approach – people who accept
the risk of living in earth-quake prone areas because the benefits of living in
those areas outweigh the costs of moving away. Common in developed countries.
Adaptation approach – people can
successfully live in earthquake prone areas when they are well prepared with
measures such as earthquake monitoring devices, risk assessments, planning
structures and technology as well as support by well-equipped rescue teams.
Most effective approach to saving lives and property.
18. Assess the effectiveness of strategies in
mitigating the effects of earthquakes and tsunamis
Land use regulation
·
Restrict developments in
certain areas which are at risk of earthquake or liquefaction.
Prohibit
construction of new buildings on low-lying land vulnerable to tsunamis
Success:
·
In California,
USA,
all new buildings are not built across fault lines or areas at risk of
liquefaction.
Development
on low lying areas prohibited except for areas with protective barriers such as
seawalls along the coasts of Japan
and North America where the Pacific Ring of
Fire is located.
Limitations;
·
Some areas may already be
built-up or are privately owned. In some cases, government authorities would
buy land from private owners and compensate those who have to move.
These
strategies are costly and some private owners may be reluctant to move as they
often believe that another hazard would not happen.
Effective Building design
·
Steel and reinforced concrete
·
Buildings constructed with wide
and heavy bases
·
Damping devices as shock
absorbers and counter-weights which move in the opposite direction to the
earthquake.
·
Reduce the collapse of
buildings and minimize the damage caused by an earthquake. e.g. Taipei 101 reinforced
with heavy metal bars
·
Damping devices prevent a
building from swaying too much and collapsing.
Base
isolation bearings absorb the force of the earthquake and reduce the movement
of the building. e.g. lead rubber bearings used at the Sabiha
Gökcen Airport
in Istanbul.
Limitations
·
Higher cost of construction and
maintenance of buildings.
·
Expensive to convert existing
buildings to include earthquake resistance features.
If
conversion is too expensive, buildings have to be demolished and rebuilt e.g. Beijing, China
in 2011.
Infrastructure development
·
Roads, bridges and dams built
to resist the shaking of the ground so that they do not collapse or can be easily
repaired if they collapse.
·
Homes, office buildings and
factories fitted with trip switches that ensure all electrical points are
switched off in the event of an earthquake.
·
Large underground water tanks
provide emergency reservoirs for possible fire fighting after an earthquake.
Success:
·
Although reinforced
infra-structure remains untested until earthquake occurs, past earthquakes in Chile, Japan
and California
showed benefits of reinforced infrastructure such as fewer lives lost, faster
rescue and evacuations, and less money spent on recovery for the affected
areas.
·
In Japan, machines in many factories
automatically shut down when they sense earthquake vibrations which helps to
prevent fire outbreaks.
Underground
water tanks are found in Tokyo, Kyoto
and Kobe in Japan.
Limitation:
Developing infrastructure to resist earthquake is
costly.
Emergency drills
·
People take part in emergency
drills by moving to safe locations, listening to instructions given by trained
personnel and practicing first aid.
·
They may also become members of
local response teams that assist people during a disaster.
Success:
Japan conducts emergency
drills on 1 Sept to commemorate Disaster Prevention Day which prepares the
people mentally on how to create to a disaster. Main roads are blocked and
emergency vehicles have to seek alternative routes to reach affected areas.
· As emergency drills are designed based on the most serious earthquake ever recorded in the area in the past, the emergency frills and evacuation plans might not prepare them adequately to prevent the devastation of the areas such as the 2011 earthquake in Tohoku, Japan.
There might be insufficient time for evacuation as earthquakes are difficult to predict.
Use of technology
Earthquake and tsunami monitoring and warning
systems
·
Installations of earthquake
sensors in earthquake prone zone help monitor the frequency of vibrations and
detect possible developments of an earthquake. E.g. earthquake motion data is
gathered from observation stations installed on bridges and roads in Japan which
enables an earthquake to be predicted.
The
sensors also help to quickly estimate damage to bridges, railways or other
infrastructure.
·
Earthquake sensors are
expensive to obtain, install and use.
·
Warnings may not provide
sufficient time for an evacuation.
·
Noise, lightning or device
failure may interfere with seismograph and result in false warnings given.
19, Evaluate the short term and long term responses to earthquakes.
Short term responses are important
in saving lives however long-term responses need to be put in place to save
more life if an earthquake strikes again.
People
trapped under collapsed buildings must be quickly located and freed. Some survivors are found after being trapped for a couple of
weeks without food. This will help to save life for e.g. after the earthquake
in Tohoku, Japan, in 2011, sniffer dogs and heat sensors were deployed and
successfully rescued man who are trapped. However, rescue workers only have a limited time of 72 hours to find trapped
survivors as they can only survive 3 days without food and water.
E.g.
rescue workers only have 3 days to search through 2 towns after the earthquake
in Tohoku in 2011.
It is also important to provide medical aid, food and clean drinking water provided to survivors to prevent
dehydration and spread of disease. Provision of
immediate aid helps survivors continue with their lives. e.g. after the
earthquake in Afyon in 2002, the Turkish Red Crescent Society responded by
delivering 20000 tents, 50000 blankets and 3000 heaters to the region. However, medical supplies, food and water may not be sufficient and this may
cause social unrest. E.g.
after the earthquake in Haiti
in 2010, looting and fighting broke out as people fought for food and medical
supplies.
Immediately after the earthquake struck, it is also important to manage the status of the affected areas. The affected areas are declared as ‘emergency zone’, a specialized
authority is assigned to provide immediate aid to people and restore emergency
services to affected areas. The basic needs of the affected people such as food, water and shelter
are taken care of. e.g.
the Crisis Management Centre led by the Ministry of interior mobilsed and
coordinated relief effectively within the first few hours of the earthquake in
Afyon, Turkey in 2002. However, some countries are not experience is handling the aftermath of an
earthquake. e.g.
the earthquake in Haiti in 2010 – the emergency relief lacked coordination and
proper supervision, making it difficult to provide aid to affected population.
Tent cities are set up as temporary housing for those who have lost
their homes in the earthquake.Temporary shelters provide a place for survivors to carry on with their
lives.
E.g.
tents accommodated thousands of homeless people after the major earthquake in Afyon, Turkey,
in 2002. They helped to re-establish a sense of community amongst survivors. However, the living conditions in tent cities may be poor and lead to people
dying. E.g.
the outbreak of the water-borne disease, cholera, killed almost 4000 people in
the tent cities of Haiti.
There is a also a need to call for humanitarian help such as aid from foreign and local governments in the form of money, medical
or food aid to an affected area. Affected areas can be rebuilt with the aid provided. e.g. 2 months after the earthquake in Haiti in 2010, governments around
the world donated US$2.5 billion and pledged another US$1.3billion.
Non-governmental
organizations such as International Red Cross and World Vision International
rapidly moved into affected areas and began their work. However, Aid may be delivered later than hoped for may not always be delivered. However, problems such as looting of trucks may also arise while aid is being
delivered. e.g. after the earthquake in Turkey in 2011, trucks delivering
aid were looted before they reached the disaster area.
Long term responses must be put in
place as it helps to save lives from another earthquake which may strike again.
Infrastructure and amenities are rebuilt and improved
upon after a disaster.·Authorities develop stricter building codes to ensure infrastructure is
restored at a higher safety level than before. eg. after the earthquake in Kobe, Japan in 1995, Japan spent billions developing
technology to build more earthquake-resistant buildings.However, reinforced building built to protect against earthquakes, are not
necessarily protected against tsunamis. Additional protection such as
breakwaters needed. e.g.
many of Chile’s
building are earthquake-resistant, the coastal areas suffered massive damage
from a tsunamis when an earthquake struck in 2010.
Compensation is given out through insurance or direct
payments to people who have lost their land and property.Compensation helps people in finding another place to settle down. e.g. the Japanese insurance plans authorized by the government to pay
massive amounts to compensate people who have lost their land and property. However, compensations offered are often insufficient. e.g.
insurance paid in Japan have an upper limit – people who have lost their land
and property may not receive amount enough to cover the cost of the damage.
Steps are taken to ensure that the economy recovers.·The government stimulates the economy by introducing various measures. e.g. direct cash payment were made to individuals to allow them to buy
necessities after the earthquake in Christchurch, New Zealand, in 2011 to
stimulate the local economy as it provided income for local traders. In addition, the New
Zealand government guaranteed bank credit
and insurance payments so that reconstruction could start quickly. However,the recovery of the economy may take a long time as a huge sum of money
is needed to rebuild infrastructure and services.E.g.
China took 3 years to
rebuild the area hit by the earthquake in Sichuan,
China,
in 2008 and provide people with basic living conditions. A huge sum of about
US$123 billion was spent on reconstructing schools, hospitals and homes.
Health
options such as long-term counselling are provided. The loss of loved ones,
homes or jobs after earthquakes cause long-lasting trauma. Problems can be identified and addressed early.
E.g. a year after the earthquake in Christchurch, New Zealand, in 2011, significant
problems of anxiety and depression were identified amongst the affected
population. This resulted in a greater number of health workers being deployed in
the area. However, improving health options, such as restoring the resilience of people
after an earthquake, can be very challenging. e.g. many survivors such as those in Haiti, continue to lack access to
basic necessities after the earthquake in 2010.
Short term
responses are those that occur immediately and last for weeks after the
occurrence of an earthquake. Short-term responses are important as it can help
to save lives. Long-term
responses to earthquakes can stretch over months and years and involve rebuilding
an affected region. However, carrying out such measures and responses can be
costly.
