Volcanoes, earthquakes and floods
The structure of the Earth
The Earth comprises of a crust – a hard outer layer like the skin of an apple, a mantle – a
layer of very hot and dense rock that flows and moves and a core – the hot centre of Earth
that is believed to be made entirely from metal.
A hard layer called the crust covers the Earth. This layer is the outermost layer of rock that
covers the Earth and is like the skin of an apple. The crust is thinner in some places than in
others. Mountains are areas where the crust is thick. This crust is not one large solid piece;
it consists of many smaller pieces that are called ‘tectonic plates’ which are thousands of
kilometres in size. These tectonic plates float on the underlying layer of magma and exert
pressure as they move.
The mantle comprises of layers of hot slow-moving magma, which causes the tectonic
plates to move. This movement causes earthquakes and volcanic eruptions.
http://science.howstuffworks.com/nature/29595-100-greatest-discoveries-platetectonics-video.htm
http://science.howstuffworks.com/nature/29595-100-greatest-discoveries-platetectonics-video.htm
How the crust moves
The crust is not one large solid piece of rock. It consists of many smaller pieces that are
called ‘tectonic plates’ which are thousands of kilometres in size. These tectonic plates float
on the underlying layer of magma and exert pressure as they move. The edges of the
tectonic plates are called ‘plate boundaries’. The tectonic plates move on the layer of hot
slow-moving magma that lies underneath the crust. When the plates move, they push and
pull against each other causing pressure or sudden shifts.
There are seven large plates and many smaller plates that move very slowly each year. The
The core is the hottest layer of the Earth, comprising of an outer and inner core. Scientists plates that lie beneath the continents are called continental plates and the plates that lie
believe that the outer core is made up of nickel and iron, whilst the inner core is largely beneath the oceans are called oceanic plates.
iron. The outer core is more liquid than that of the inner core. The temperatures within the
core range from 5000 – 7000 degrees Celsius. The pressure for the rest of the Earth causes
the inner core to be mostly solid, even though the temperature of the core is hot enough
to melt the iron.
Activity 1
a) Name the three main layers of the Earth.
(1)
b) Describe a tectonic plate.
(2)
c) How does magma contribute to earthquakes?
(1)
d) Describe the structure of
the core.
(5)
The internal structure of the Earth
Total:
(9)
http://www.nhm.ac.uk/nature-online/Earth/plate-tectonics/index.html
http://science.nationalgeographic.com/science/Earth/the-dynamic-Earth/platetectonics-article/
Oceanic plates
The Tectonic plates
The edges of the tectonic plates are called ‘plate boundaries’. New crust is formed and old
crust is returned to the core at these boundaries. The process of the Earth’s crust being
formed and returned to the core can take about 100 million years.
These plates meet in different ways:
Convergent boundaries:
These occur when two tectonic plates push against each other and one plate is forced
upwards. This movement causes the formation of mountains or volcanoes. The other plate
sinks back into the core and melts. Earthquakes can occur along this type of boundary.
Transform boundaries:
This type of boundary is where two plates meet and move against each other horizontally,
in different directions. As they move, neither plate is displaced up or down. This movement
causes a build up of energy, which may be released in a sudden movement which can
cause an earthquake.
Activity 2
Divergent boundaries:
These occur when the tectonic plates pull away from each other. The crust breaks apart.
The space that remains is called a rift. Magma seeps up to fill the rift and so new crust is
made.
a) Define a plate boundary.
(1)
b) How do the tectonic plates move?
(1)
c) Name and describe three areas where tectonic plates meet.
(6)
d) List the names of three tectonic plates.
(3)
e) Describe the difference between continental and oceanic tectonic
plates. (2)
f ) Explain why the Great Rift Valley in Africa is a good example of
divergent convergence.(3)
Total: 16
Volcanoes
Locations around the world
A volcano allows molten rock form the mantle to flow out on to the Earth’s surface through
the Earths crust, in the form of lava. Currently, there are approximately 1500 active volcanoes
around the world. A small portion of these volcanoes are located beneath the oceans.
http://science.howstuffworks.com/nature/231-how-volcanoes-work-video.htm
http://www.nhm.ac.uk/nature-online/Earth/volcanoes-earthquakes/volcano/volcanotypes/index.htm
A volcano erupting beneath the ocean
Diagram of the African plate, showing the
East African Rift zone.
http://video.nationalgeographic.com/
video/news/west-mata-submarinevolcano-vin?source=searchvideo
info file:
Lakes of the Great Rift Valley as seen from
space.
There are
1500
active
volcanoes
world
wide
Volcanoes are often found near the
edges of the tectonic plates that cover
the surface of the Earth. The image
below illustrates the occurrence of
volcanoes around the world and the
position of the tectonic plates.
A volcanic eruption
Volcanoes can erupt
through the same fault or
vent over a long period of
time. A crater forms at the
top of the volcano. After
each eruption, lava coats the
edge of the crater and builds
a cone as the lava cools.
Diagram of a volcano
The Ring of Fire is a ring of volcanoes that is found in Pacific Ocean. There are
approximately 450 volcanoes in this area. There are frequent earthquakes and volcanic
eruptions in this area.
A famous volcanic eruption was that of Mount St Helens in the United States of America. The
eruption occurred on 18 May 1980. The eruption destroyed approximately 250 homes and
killed 57 people. The eruption removed almost 400m of the volcano leaving a horseshoe
shaped crater in the volcano.
http://www.discovery.com/video-topics/other/other-topics-volcano-videos.htm
Why volcanoes occur
The pressure caused by the movement of magma beneath the Earth’s crust can force
magma up through faults in the Earth’s surface. This movement of magma causes a volcano.
When the magma reaches the Earth’s surface, it is called lava. As the lava pours onto the
surface, the lava emits poisonous gases. The heat of the lava causes clouds of steam in the
atmosphere. The force of the pressure of a volcano can cause rocks, ash and volcanic dust
to be blasted into the air. http://video.nationalgeographic.com/video/volcano-lava
From top left clockwise, Mount St Helens before, during
and after eruption.
Activity 3
a) Where do volcanoes occur? (3)
b) Describe a volcano.
(3)
c) Explain the difference between magma and lava.
(1)
d) Why do volcanoes occur?
(2)
e) Describe the Ring of Fire.(2)
e) Briefly describe the eruption of Mount St Helens.
(4)
world’s earthquakes and 81% of the world’s largest earthquakes occur along the Ring of Fire.
The December 2004 earthquake just off the coast of Sumatra which caused a devastating
tsunami, was in the Alpide belt. This belt has 17% of the world’s largest earthquakes.
Total: 15
Earthquakes
Earthquakes occur when part of the Earth’s crust moves. The area where the crust moves is
called the ‘fault’ or ‘fault plane’. Large earthquakes occur when the movement is about one
to two metres. A small earthquake occurs when the crust moves in millimetres.
The Earth’s outer surface is broken up into what geologists call ‘plates’. Earthquakes occur
when the plates move under, over or slide past each other. Most earthquakes occur on the
edges of these plates that make up the Earth’s crust. The location below the Earth’s surface
where the earthquake starts is called the ‘hypo centre’, and the location directly above it on
the surface of the Earth is called the ‘epicentre’.
Instruments called seismographs record earthquakes. The recording they make is called
a seismogram. The seismograph has a base that sets firmly in the ground and a heavy
weight that hangs free. When an earthquake causes the ground to shake, the base of the
seismograph shakes too, but the hanging weight does not. Instead the spring or string that
it is hanging from, absorbs the movement. The difference in position between the shaking
part of the seismograph and the motionless part is what is recorded.
An earthquake is a sudden, rapid shaking of the Earth caused
by the release of energy stored in rocks. This energy can be built
up and stored for many years and then released in seconds or http://science.howstuffworks.com/nature/236-how-earthquakes-work-video.htm
minutes. Many earthquakes are so small that humans cannot
feel them. Some have caused great destruction and killed many http://video.nationalgeographic.com/video/101-videos/earthquake-101?source=relatedvideo
of people.
http://www.nhm.ac.uk/nature-online/earth/volcanoes-earthquakes/earthquakes/index.html
Sometimes an earthquake has ‘foreshocks’. These are smaller
earthquakes that happen in the same place as the larger earthquake that follows. The
A seismograph
largest, main earthquake is called the ‘mainshock’. Mainshocks always have aftershocks
The size of an earthquake depends on the size of the fault and
that follow. These are smaller earthquakes that occur afterwards in the same place as the
the amount of slip on the fault. A seismogram recording made
mainshock.
on seismographs will determine how large the earthquake
was.
There are two major regions of earthquake activity on the planet. One region is called the
circum-Pacific belt and is also known as the Pacific Ring of Fire, which encircles the Pacific
A short wavy/undulating line that doesn’t move very much
Ocean. The other region is called the Alpide belt, which extends from Java to Sumatra
means the earthquake was a small earthquake. A long wavy
through the Himalayas, the Mediterranean, and out into the Atlantic.
line that moves a lot means a large earthquake. The length
of the wave depends on the size of the fault, and the size
The Ring of Fire is a zone where earthquakes happen frequently. As much as 90% of the
of the wave depends on the amount of slip. A Richter scale
measures the enormity of an earthquake based on
the semiography fluctuations.
An example of a seismogram
info file:
Earthquakes measuring six and above are considered
major quakes. Earthquakes measuring seven and above cause
great damage and kill many people.
No one
can predict
when an
earthquake
will occur.
Other famous earthquakes:
22 May 1960, Chile: quake measuring 9.5
on the Richter scale – struck Santiago and
Concepción, triggering tidal waves and
volcanic eruptions.
5000 killed, 2000 000 homeless.
Earthquake Rocks China!
An earthquake of 7.8 magnitude hit
China’s Sichuan province on Monday, May
12, 2008.
Within one week of the massive quake, at
least 32,000 people were reported dead
and more than 200,000 injured. Hundreds
of aftershocks rippled through the region
after the quake, causing landslides and
other damage.
Unlike hurricanes, no one can predict
when an earthquake will hit. There is no
warning and no evacuation time. The U.S.
Geological Survey (US
GS) says
that at
least one
earthquake
happens
somewhere
on the
globe every
day, usually
small and
in remote
regions where few people live. But when
big earthquakes hit in heavily populated
areas, it can easily become a catastrophe.
China Mourns Quake Dead
MONDAY, MAY 19, 2008 Aljazeer
With the toll from the quake standing at more than 32,000, China’s leaders have declared
three days of national mourning for the dead.
Many more are still listed as missing and officials say the final toll could rise above 50,000.
As the mourning period began on Monday, state media reported that more than 200
recovery workers had been buried by landslides over the past two days
in the disaster zone.
The official Xinhua news agency gave no details of where the incidents
happened, but the report highlights the continued danger faced by
relief teams racing against time to find survivors.
On Sunday, at least three people were killed in a 6.0-magnitude
aftershock.
The aftershocks and heavy rain have put recovery crews on heightened
alert, fearful further strong tremors could bring down already weakened
buildings.
But while recovery efforts are switching to focus on clearing up the
tonnes of debris, a few survivors are still being pulled out alive from
collapsed buildings.
The authorities, meanwhile, are also battling to prevent the outbreak of disease, with the
risks heightened by the rotting carcasses of 12.5 million livestock and poultry.
“Combating epidemics is the most urgent and the biggest task facing us right now,” Wei
Chaoan, the vice-minister of agriculture, said on Saturday.
The World Health Organisation said that the lack of safe drinking water or proper waste
disposal along with cramped conditions in temporary shelters was “conducive” to outbreaks.
“Preventing communicable disease outbreaks is the key public health issue now facing the
People’s Republic of China,” the UN body said in a statement.
info file:
28 March 1964, Alaska: quake followed
by tsunami – claimed 125 lives, caused
millions in property loss. Measuring 9.2 on
the Richter scale, it was felt over a large area
of Alaska and in parts of Yukon Territory and
British Columbia.
Activity 4
Read the articles that follow and answer the questions in your class workbooks.
http://www.dallasnews.com/sharedcontent/dws
Aftershocks
and disease
kill many
survivors
after an
earthquake
a) In which country and on which continent is Sichuan located? (2)
b) The world map below shows the earthquakes that took place within a week dated
26 May 2008. Indicate the location of Sichuan on the map. (1)
Floods
A flood causes a great amount of damage. Heavy rain causes rivers and dams to flood,
damaging homes and other buildings, removes bridges and roads, devastates food crops
and kills livestock. Floods can be devastating to the local population that live in areas of
the flood.
Unusually heavy rains generally cause floods when the natural watercourses fail to contain
the amount of water accumulated. Floods are also caused by other natural phenomena
such as tropical cyclones and tsunamis.
http://www.nhm.ac.uk/nature-online/earth/volcanoes-earthquakes/floods/
http://video.nationalgeographic.com/video/101-videos/floods
Tropical cyclones
Tropical cyclones are also known as ‘typhoons’ and ‘hurricanes’. A cyclone is a storm system
characterised by a low-pressure centre and powerful thunderstorms that produce strong
winds and flooding rain. A tropical cyclone feeds on heat released when moist air rises,
resulting in condensation of water vapour contained in the moist air.
info file:
Fortunately,
cyclones
can be
predicted in
advance.
c) What was the size of this earthquake? (1)
d) There were many aftershocks reported after the earthquake. What further damage
did these aftershocks cause? (1)
e) Can earthquakes be predicted? (1)
f ) Why is it more catastrophic when an earthquake hits a densely populated area,
than when an earthquake hits a less populated area? (2)
g) Provide the abbreviation for the World Health Organisation.
(1)
h) What role did the WHO play in the aftermath of the Earthquake in Sichuan? (1)
A cross section of a cyclone
Cyclones circulate counter clockwise in the Northern Hemisphere and clockwise in the
Southern Hemisphere.
Cyclones, hurricanes and typhoons can be predicted several days in advance. These
disasters are usually more destructive than floods.
Possible damage by cyclones:
High winds cause major damage to infrastructure and housing.
They are generally followed by heavy rains and floods and by tidal waves in flat coastal
areas.
Storm surges develop over large bodies of warm water, and lose their strength if they move
over land. This is the reason coastal regions can receive significant damage from a tropical
cyclone, while inland regions are relatively safe from receiving strong winds.
Storm surges can produce massive coastal flooding (up to 40 kilometres from the coastline)
and heavy rainfall can produce inland flooding
Accurate landfall predictions of a cyclone can give only a few hours’ notice to threatened
populations. People generally opt to wait until the very last minute before abandoning
their home and possessions. Deaths from drowning in the high tides and sudden flooding
and material losses are therefore often very high.
info file:
The World
Meteorological
Organiation
uses lists
to name
hurricanes.
Information adapted from:
http://www.ifrc.org/what/disasters/about/types/hydrometeorologic/
hurricanes.asp
How are hurricanes/cyclones named?
Hurricane classification
Hurricanes are classified into five categories based on their current maximum wind
speed. This rating scale is called the Saffir-Simpson Hurricane Scale, named after Herb
Saffir and Robert Simpson, who developed it.
Category 1 -- Winds 119 – 153 km/h Minimal damage
Category 2 -- Winds 154 – 177 km/h Moderate damage
Category 3 -- Winds 178 – 209 km/h Extensive damage
Category 4 -- Winds 210 – 249 km/h Extreme damage
Category 5 -- Winds over 249 km/h Catastrophic damage (these are very rare)
There are very few Category 5 storms; most storms that achieve Category 5 status only
hit Category 5 status for a very short time, then the winds subside to a less powerful
level. Some of the strongest recent hurricanes (Atlantic Ocean tropical cyclones) that hit
Category 5 status include:
Hurricane Felix (September 2007) -- Caribbean
Hurricane Dean (August 2007) -- Gulf of Mexico, Yucatan Peninsula, Mexico, Caribbean
Hurricane Wilma (October 2005) -- Gulf of Mexico, Yucatan Peninsula, Mexico, Cuba, and
Southern Florida
Hurricane Rita (September 2005) -- hit Texas, Louisiana
Hurricane Katrina (August 2005) -- hit southern Louisiana, Mississippi and Alabama
Hurricane Isabel (September 2003) -- hit North Carolina, Maryland, Delaware, Virginia,
and Washington, D.C.
Hurricane Mitch (October 1998) -- hit Honduras, Nicaragua, El Salvador, and Guatemala
Hurricane Andrew (August 1992)-- hit south-eastern Florida and south-eastern Louisiana
All hurricanes are given names to help us identify storms and track
them as they move across the ocean. There can be more than one
hurricane at a time and without naming them, we could get confused Cyclone Nargis
about which storm we’re talking about.
On 2 May 2008 tropical
cyclone Nargis hit the
An Australian meteorologist began giving women’s names to tropical storms before the coast of Myanmar and
end of the 19th century. In 1953, the US National Weather Service, began using female devastated large parts of
names for storms. By 1979, both women and men’s names were used.
the low-lying Irrawaddy
One name for each letter of the alphabet is selected, except for Q, U and Z.
delta. Winds exceeding 190
kilometres per hour ripped
These are the hurricane names used in 2007:
through the Myanmar’s
Andrea, Barry, Chantal, Dean, Erin, Felix, Gabrielle, Humberto, Ingrid, Jerry, Karen, Lorenzo, biggest city Yangon for
Melissa, Noel, Olga, Pablo, Rebekah, Sebastien, Tanya, Van, Wendy
more than ten hours. Homes
were flattened, structures
The World Meteorological Organization uses six lists in rotation to name hurricanes. The damaged, trees uprooted
same lists are reused every six years. The only time a new name is added is if a hurricane is and power lines collapsed.
very deadly or costly. Then the name is retired and a new name is chosen.
In rural parts of the country
up to 95 per cent of homes
Some of the retired names are:
were demolished.
Katrina, Andrew, Rita and Wilma
Activity 5
Tsunamis
Look at the pictures below. These pictures tell the devastating story of cyclone Nargis
that hit Myanmar on 2 May 2008. List the ways in which the people of Myanmar were
affected by the cyclone.
(9)
Japan’s most powerful earthquake since records began has struck the northeast coast,
triggering a massive tsunami. The quake was the fifth largest in the world since 1900.
http://science.howstuffworks.com/nature/230-how-tsunamis-work-video.htm
http://www.nhm.ac.uk/nature-online/Earth/volcanoes-earthquakes/tsunami/how-tospot-a-tsunami/index.html
On March 11 2011, measuring at 8.9 by the US Geological Survey, the tsunami struck at
05:46 GMT at a depth of about 24km.
A 10m-wave struck Sendai, burying farmland and sweeping cars across the airport’s
runway. Fires broke out in the centre of the city. Cars, ships and buildings were swept away
by a wall of water after the 8.9 magnitude tremor, which struck about 400km (250 miles)
northeast of Tokyo. Japan’s NHK television showed a massive surge of debris-filled water
reaching far inland, consuming houses, cars and ships. Motorists could be seen trying to
speed away from the wall of water.
The tsunami rolled across the Pacific Ocean at 800km/h before hitting Hawaii and the US
West Coast, but there were no reports of major damage from those regions.
Thousands of people evacuated coastal areas in the states of California, Oregon and
Washington. The biggest waves of more than 2m were recorded near California’s Crescent
City.
A tsunami warning extended across the Pacific to North and South America, where many
other coastal regions were evacuated, but the alert was later lifted in most parts, including
the Philippines, Australia and China.
Activity 6
Answer the following questions:
1) True or False
a) The Earthquake caused the most damage in Japan.
b) A tsunami was triggered by the Earthquake.
c) The epicentre of the Earthquake took place at sea.
d) The Earthquake occurred on the Pacific tectonic plate.
(4)
2) Why was the chance of surviving the Japanese tsunami wave highly
unlikely? (2)
3) Look at the picture a) How do you know that this tsunami wave was powerful and
forceful?(2)
b) What type of debris can be seen in the tsunami wave?
(2)
Total: 10
Reducing the impact
Preparing and responding to floods
The wave from a tsunami crashes over a street in Miyako City, Iwate
The damaging effects of a flood are worsened by the destruction of the natural environment.
The terrifying wall of water that smashed into northeast Japan was unstoppable. It Dunes, wetlands and barrier islands can protect the land against the effects of a coastal
wasn’t the Earthquake but the following tsunami that caused most devastation in Japan. storm. Forests and floodplains natural absorb floodwaters. Deforestation, alien vegetation,
land degradation and the diversion of rivers are factors that can contribute the damaging
The tsunami was triggered by an 8.9-magnitude earthquake. This earthquake effect of floods.
took place around 400 kilometres from Tokyo, off the coastal city of Sendai.
info file:
Tsunami’s are
triggered
by an
earthquake
The tremor itself was a result of the Pacific tectonic plate submerging
beneath the North American and Eurasian tectonic plate. The
tectonic plate, could not withstand the pressure of submerging.
When it cracked, the upper part of the Pacific plate rebounded,
causing the sea level to rise by up to 4 meters along a 100 to 150
kilometre fracture zone. This resulted in a wave that travelled at
high speed through the ocean towards the shore.
http://w w w.n hm . ac. uk/nat ure - online/Ear t h/volc anoesearthquakes/tsunami/how-an-earthquake-causes-a-tsunami/index.html
The tsunami reached a wave height of approximately 10 meters. It is not only the height of
the wave that is so dangerous, it is the wavelength of 200 meters that unfolds the deadly
impact as a huge volume of water filled with debris, cars, ships and even parts of houses
crashes onto shore. The chances of surviving this are highly unlikely.
Deforestation
Land degredation
Activity 7
In a paragraph, explain what can be done to resolve each of the factors that contribution
to the damaging effects of a flood. (4)