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PLATE BOUNDARIES
LANDFORMS
PLATE
TECTONICS
VOLCANOES
EARTHQUAKES
PLATE BOUNDARIES
1. CONTRUCTIVE
2. DESTRUCTIVE
3. COLLISION
4. PASSIVE/
CONSERVATIVE/
TRANSFORM
4
3
2
1
LABEL THE DIAGRAM:
( oceanic crust, magma from mantle, ocean, mid-oceanic ridge with volcano)
6
3
4
5
2
1
LABEL THE DIAGRAM:
(oceanic crust, continental crust, subduction zone, earthquake foci, volcano,
ocean)
Collision zones
3
1
2
LABEL THE DIAGRAM
(continental crust, oceanic crust, transform fault)
LANDFORMS AT BOUNDARIES
4
3
1
5
2
Can you describe how each landforms are formed, give examples.
(mid-oceanic ridge, trench, fold mountain, rift valleys, island arcs)
WHAT & WHERE?
CAUSES
FACTORS
EARTHQUAKE
CASE STUDIES
PREDICTION
WHAT & WHERE?
What? A series of shocks & tremors that
result from a sudden release of pressure.
Where occur?
1. At destructive boundaries
2. Volcanic activity
3. Human activity (explosion, nuclear testing,
mining, drilling & construction of dam)
*Create shock waves & pressure change in
underlying rock layers.
CAUSES
• Results from the sudden release of energy deep underground.
• This energy takes the form of a jerk or slippage along a line of
weakness called a fault.
• Shock waves called seismic waves radiate out in all directions from
the point of slippage called the focus
• These waves cause the shaking on the ground surface.
• The greatest effect is felt nearest epicentre (the point on the surface
immediately above the focus of the earthquake.
• Active faults lies at the edge of the plates, that is why the majority
earthquakes occur at plate margins.
HUMAN ACTIVITIES TRIGGER EARTHQUAKE
CONSTRUCTING
A DAM
Constructing a dam can increased earthquake activity:
1. Increase pressure exerted on a fault
2. Water seeping into groundwater zone & lubricating a fault.
E.g. In Zambia, 100 earthquake occurred a year as Lake Kariba
Filled up between 1958 & 1963. the earthquake stopped after
1963.
Underground subsidence following deep mining.
E.g. earthquake in the UK coalfield areas, Stoke-on Trent.
DIGGING UP COAL
FACTORS CONTRIBUTING TO EARTHQUAKE
•
•
•
•
•
EARTHQUAKE MAGNITUDE
ABILITY OF BUILDING
POPULATION DISTRIBUTION
GEOLOGY
A COUNTRY’S WEALTH
EARTHQUAKE MAGNITUDE
• The more powerful the earthquake the
more damage it will cause.
• But it is not always the case, e.g. San
Francisco earthquake 1989 has a Richter
scale 7.1. but only 65 were killed,
whereas a less severe earthquake 6.8 killed
over 25 000 people in Armenia a year
earlier.
Ability of building to withstand
shaking.
• Poor building design in Mexico city in
1985, both low-rise and high-rise building
collapsed. Some buildings toppled over
and others sank into the ground.
POPULATION DISTRIBUTION
• Densely populated area such as Tokyo city
most vulnerable to earthquake.
• In 1923, 143 000 people lost their lives
and 2/3 of the city was flattened.
NATURE OF UNDERLYING
GEOLOGY
• Sands and clays may become liquefied (jellylike) promoting landslips and building collapsed.
• E.g. Mexico city where most of the city lies on
old-lake-bed sediments were attack by
earthquake in 1985.
• In 1989 San Francisco earthquake, most severe
damage to property was in Marina District where
houses constructed on landfill material was
unstable.
WEALTH OF A COUNTRY
• The wealthier a country, the better able it
is to build appropriately and respond
effectively to earthquake hazard.
• In poorer country, there have low building
standards, and there have less money and
emergency resources, to cope up with
aftermath of an earthquake.
PREDICTION
•
•
•
•
PRECURSORS
PLATE TECTONICS THEORY
ELASTIC REBOUND
SEISMIC GAP THEORY
PRECURSORS
Scientists have identified several precursors:
1.
Foreshocks: occur prior to main earthquake,e.g. several
earthquakes occurred in the months before 1989 San Francisco
earthquake.
2.
Geophysical changes: localised uplift and subsidence identified.
E.g. Niigata earthquake in Japan in 1964 accompanied by a
sudden subsidence of coastline by up to 20 cm.
3.
Changes in electrical resistivity: Van method suggests that
electrical curents become disturbed just prior to an earthquake
and causes a change in resistivity. (measured)
1.
Changes in animal behaviour prior to major earthquake, e.g.
Haicheng in 1975, rats panicked, used as earthquake precursor.
PLATE TECTONIC THEORY
The theory is useful in predicting where
earthquake likely to occur.
But scientist do not know when it will occur.
ELASTIC REBOUND
•Stress builds up at a constant rate but only released periodically.
•As the build-up pressure is constant, it is expected the released
of pressure (earthquake) occurs regularly.
•By using historical records and geological evidence (i.e. fault)
scientist able to plot recurrences of earthquakes and use
informaiton to suggest likelihood next earthquake that will occur.
SEISMIC GAP THEORY
• Concept of elastic rebound theory has been developed
into seismic gap theory.
• If earthquakes along a particular fault line are plotted,
gaps appear where no earthquake occurred for some
time.
• Pressure building up in these gaps will be released, thus
these areas might be hit by future earthquake.
CASE STUDY
Draw a concept map for any two case studies:
(effects, causes, contributing factors and lessons learned)
• INDIAN EARTHQUAKE, MAY 1997 (HAZARD, NAGLE,G.,P:17)
• KOBE JAPAN JAN 1995 (HAZARD, NAGLE,G., P:19-23)
VOLCANOES
•
•
•
•
•
•
WHAT
WHERE & HOW
PREDICTION
HAZARD
REDUCING HAZARD
CASE STUDIES
What?
• Volcanoes are openings in the earth’s
crust through which magma, molten rock
and ash can erupt onto the land.
Where & How
1.
2.
3.
4.
At destructive margin
Hot spot
Constructive
Destructive margins
Destructive margin
Ocean/ocean:
• At a destructive margin one plate dives beneath the other.
•
Friction causes it to melt and become molten magma.
•
The magma forces its way up to the surface to form a volcano to the side of the
actial plate margin. (ocean trench)
•
A number of volcanoes may reach the surface to form a string of islands called
an island arc.
•
E.g. Mt. Unzen, Japan(Pacific/Eurasian)
Continent/continent:
Istead of forming volcanic islands, volcanoes occur within
a range of mountain. E.g. Nevado del Ruiz
(Nazca/S. American)
Hot spot
• In places where a plate is particularly thin,
magma may be able to escape to the
surface.
• Such a place called a hot spot.
• A shield volcano will be formed.
Constructive margin
• Where two plates are moving apart, new
magma can reach the surface through the
gap.
• Volcanoes forming along this crack create
a submarine mountain range called an
ocean ridge.
Prediction
• Seismometers record tiny earthquakes that
occur as the magma rises
• Chemical sensors to measure increased sulphur
levels, normally low but will increase before and
during eruption.
• Lasers to detect the physical swelling of the
volcano.
• Ultra sound to monitor low frequency waves in
magma, result fro the surge of gas and molten
rock under surface.
Hazards associated with volcanic
eruptions
•
•
•
•
•
•
•
LAVA FLOWS
ASH
LAHAR/MUDS
PYROCLASTIC FLOWS
GAS EMISSIONS
GLACIAL OUTBURST FLOODS
TSUNAMI
Lava flows
Lava flows extend beyond 10 km from volcanic crater.
Their speed of flow is determined by silica content of lava.
Silica poor lava is very fluid and flows faster and much thicker
A lava flow may destroy farmland, buildings and
lines of communications, but rarely love of live.
ASH
•
Fine-grained ash together with larger pyroclastic (fire
rocks) may be ejected into the air during a violent
eruption.
•
Several hazard:
(i) The sheer weight of deposited ash can cause the
roofs of buildings to collapse
(ii) Air thick with hot ash lead to the asphyxiation of
humans and animals.
(iii) Ash combined with water to form mudflows called
lahars.
(iv) Ash increase supply of condensation nuclei in lower
atmosphere promoting formation of water droplets and
increase rainfall.
GAS EMISSIONS
• The strong smell of sulphur in the air.
• Other gases can be emitted including
carbon dioxide and cyanide.
PYROCLASTIC FLOWS
• The cloud of incandescent gas, ash and
rocks.
• This temperature reach up to 800 C and
speed of 200 km/hr.
• E.g. Mt. Unzen (Japan) in 1991, triggered
by collapse of part of the volcanic summit.
Lahars/mudflows
•
1.
2.
•
•
Two reasons for development:
Rain bringing soot and ash back to ground and washing the
debris downhill.
Heat from a volcano melting snow and ice-the resulting flow of
water picks up sediment.
A lahar can travel at speeds over 30km/hr and may exceed 15 m
in height.
It can destroy houses or whole settlements, ruin communications,
bury crops, animals and people.
GLACIAL OUTBURST FLOODS
• Volcano erupts beneath an ice cap, a vast
amount of ice can be melted, and when
water escapes, large amount of water and
sediment will move down mountainsides
onto plains below.
• E.g. in 1996 an eruption beneath the
Vatnajokull glacier in Iceland melted, led to
water 50 m deep in Grimsvotn volcanic
crater.
TSUNAMI
•
Abnormally high sea waves generated by ground shocks such as earthquakes and
volcanic eruptions.
•
E.g. 1883 Krakatau eruption created waves up to 35 metres high.
•
These immense waves swept along coasts of Java and Sumatra killing over 36 000
people.
•
Tsunami are often responsible for causing more loss of life and damage to property
than more direct effects of volcanic eruptions.
•
This is because they affect low-lying, heavily populated areas and they are
unprepared.
Reducing Hazards
• CONTROLLING FLOWS
• BUILDING DESIGN
• EXPOSURE (HAZARD MAP)
CONTROLLING FLOW
1. Erecting barriers to divert free-flowing
lava away from valuable land or property,
e.g. widely used in Hawaii.
2. A lave flow can be bombed to break it up.
3. Cooling the lava fronts with water to
encourages lithification, e.g. island of
Heimaey (iceland) in 1973.
BUILDING DESIGN
• The danger of building collapse can be
avoided to some extent by encouraging
appropriate building design involving
sloping roofs to discourage the formation
of thick and weighty deposits of ash.
EXPOSURE MAP
• A map indicating areas at greatest risk
from eruption.
• Advances in radar enabled digital
elevation models (DEMs) to be produced.
• These volcanic models can be used likely
paths of lava and pyroclastic flows.
Case studies
MT. ST HELENS, 1980 (HAZARD, NAGLE, G, P:27)
NEVADO DEL RUIZ, COLUBIA 1985 (HAZARD, NAGLE, G. P:31-32)