By: (9b)Maria.A.SWilliam.P.I

Geography

Plate tectonics

Plate tectonics: set of ideas that describes and explains the global distribution of earthquakes, volcanoes, fold mountains and rift valley.

The cause of earth movement is huge convection currents in the earth’s interior, which rise towards the earth’s surface, drag continents apart and cause them to collide

These cause the earth’s surface, drag continents apart and cause them to collide

7 large plates : Pacific, Indo-Australian, Antarctic, North America, South American, African and Eurasian

4 small plates : Caribbean, Iranian, Arabian, Juan de Fuca

Inner core: solid, 5 times more dense than surface rocks

Outer core: semi-molten Mantle: semi-molten and

about 2900 km thick Crust: solid, 2 main types

(depth between 10-70 km);a. Continental : mostly

formed of granite, less dense than oceanic crust

b. Oceanic: plunges beneath the continental one when they come together

Distribution of the world’s volcanoes and earthquakes is very uneven, mostly along plate boundaries which are regions of crustal instability and tectonic activity

There are over 1300 active volcanoes in the world, many of them under the ocean (3/4 active volcanoes & located in the pacific of ring)

Example active volcanoes (pacific ring of fire):

a. Taal volcanoes & Mt. Pinatubo (Philiphines)b. Ulawun (Papua New Guinea)c. Krakatoa, Merapi, Tambora, Kelut (Indonesia)d. Popcatapetl & Colima (Mexico)e. Mt. Fuji (Japan)f. Etc.

A destructive plate boundary is sometimes called a convergent or tensional plate margin. This occurs when oceanic and continental plates move together. The oceanic plate is forced under the lighter continental plate ( A section of the crust that makes up the Earth’s landmasses) . Friction causes melting of the oceanic plate and may trigger earthquakes. Magma rises up through cracks and erupts onto the surface.

E.g:a. Mt St. Helens,USA and Soufriere, Montserrat(Carribean) b.  Nazca plate is forced under the South American Plate.

Destructive plate boundary

A constructive plate boundary, sometimes called a divergent plate margin, occurs when plates move apart. Volcanoes are formed as magma wells up to fill the gap, and eventually new crust is formed.

Example:a. the mid-Atlantic Ridge.b. Eldfell volcano, Heimaey (Iceland)

Constructive plate boundary

Mauna Loa, Kilauea (Hawaii) and Teidi (Tenerife) are located over hot spots.

Hot spots=> isolated plumes of rising magma that have burned through the crust to create active volcanoes.

=> Result of a sudden release of energy in the Earth's crust that creates seismic waves

About 500,000 earthquakes are detected each year by sensitive instruments

Most of them occur in linear chains ( such as along the west coast of South America)

Some earthquakes appear from plate boundaries (mid-west of USA), plate movement.

Earthquake

Some earthquakes are the result of human activity.

Examples:a. Build large dams and deep reservoirs

(increases pressure underground)b. Mining removes underground rocks and

mineralsc. Testing of nuclear weapons underground=> trigger earthquakes (the very long reach of

very large earthquakes)

World’s main fold mountains are related to the main collision zones (destructive plate margins and collision margins)

In contrast, older fold mountains are related to folding between 250 and 450 million years ago, when the location of plate boundaries was different from that of today.

Constructive Margins

caused when two plates move away from each other (diverge). When they move apart from each other a ‘gap’ is created. The gap is filled with hot, molten lava that solidifies when it reaches the surface (meeting either the sea or air). Land is therefore formed. Earthquakes and volcanoes are associated with constructive plate margins.

Destructive Margins

the heavier oceanic crust slides under the lighter, less dense continental crust.This results in both volcanoes and earthquakes, due to land being lost (destroyed).

Collision Plate Margins

occur where two continental crust plates meet. As they are the same density neither is able to slide under the other one. Therefore, fold mountains are created. Earthquakes are common at collision plate boundaries.

ConservativeMargins

They are caused by the friction as the plates rub next to each other.

The plates move at different speeds and in different directions. This is because of the convection currents that operate underneath the earth.

Volcano is opening the earth’s crust trough which hot molten magma (lava), molten rock and ash are erupted onto the land.

They are formed when molten (Molten is melted, liquid), sticky rock called magma (Magma is melted rock inside the Earth), forces its way through a crack in the Earth’s crrust (Crust is the top layer of the Earth).

Volcano

There are 2 type of volcano:Shield volcanoesA shield volcano is a type of volcano usually

built almost entirely of fluid lava flows.Cone-shaped volcanoesA cone-shaped volcanoes is the cone-

shaped hill formed as material from volcanic eruptions piles up around the opening.

Type of volcano

In type of volcano there are divided into:Active volcanoesActive volcano are volcanoes that have erupted in

recent times and could erupt againDormant volcanoesDormant volcanoes are volcanoes that haven’t erupted

for many years or centuries and could errupt againExtinct volcanoesAn extinct volcano is one that are believed will never erupt

again because there is no lava or magma supply to it.

Type of volcano

Vent – a crack on the side of a volcano where magma can escapeCrater – a deep hollow at the top of a volcanoThroat- that allows maga pass through before it reaches to to the surface.

Volcanic StrengthThe strength of a volcano is measured by the volcanic

explosive index. This is based by the amount of material ejected by the volcano.

Predicting VolcanoesThe main methods of predicting volcanoes: Chemical sensors to measure increased sulphur levels Seismometers to record swarms of tiny earthquakes that

accur as the magma rises Laser to detect the physical swelling of the volcno

Volcaoneos

Living with a volcano Some countries, such as Iceland and Philippines, were

created byvolcano activities Volcanic soil are rich, deep and fertile,and allow intensive

agriculture to take place Volcanics areas are important for tourism

Volcanoes

Case StudyMontserrat is a small island in the Caribbean. There is a

volcano on the south of the island called Chances Peak. The volcano had been dormant for over 300 years. In 1995 the volcano began to give warning signs, than the volcano active for 5 years, the most intense eruption is in 1997. Before the eruption the island(11 000 people) had been evacuated, 19 people were killed by the eruption the people choose to stay behind to watch over the crops. Volcanic eruptions and lahars have destroyed large areas of Montserrat. he capital, Plymouth, has been covered in layers of ash and mud. Many homes and buildings have been destroyed, including the only hospital, the airport and many roads.

Volcanoes

Short-term responses and results Evacuation. Abandonment of the capital city. The British government gave money for compensation and

redevelopment. Unemployment rose due to the collapse of the tourist industry.Long-term responses and results An exclusion zone was set up in the volcanic region. A volcanic observatory was built to monitor the volcano. New roads and a new airport were built. Services in the north of the island were expanded. The presence of the volcano resulted in a growth in tourism.

Volcanoes

Earthquakes are a sudden and violent shaking of surface of the earth

Earthquakes

Focus - refers to the place beneath the ground where the earthquake takes placeEpicenter – is the point on the ground surface immediatly above the focusDeep focus earthquake – associated with aubduction zones. 

Fault - a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movementShallow focus earthquake – generally located along constructive boundaries and conservative boundaries

Earthquake damage Strength of earthquake and number of aftershock

– the stronger the earthquake the more damage it canPopulation density – an earthquake that hits high

population density could inflict more damageThe type of building – MEDCs generally have better

quality pf building rather than LEDCsThe time of day – an earthquake during busy time may

cause more death than quite timeThe distance from the centre (epicentre)- the closer

to epicentre the greater damage that is doneThe type of rock and sediment- some material may act

like liquid when shakenSecondary hazards – such as mudslides and tsunami

Earthquake Damage

Several of way dealing with earthquake: Leave the area Do nothing and accept the hazzardThe main ways of dealing with earthquake: Better forecasting and warning Building design and building in good locationSeveral ways predicting and monitoring earthquake: Recording changes in electrical conductivity Nothing strange and unusual animal behaviour Checking history evidence Measuring crustal movement

Dealing with earthquake

Building designBuilding design in the enviorment must

responds quickly to eathwuak force like building a single storey building. A high building responds slowl to earthquake. Places of the building also must be affective, like not building the house beside steep soil because it can cause mudslides

Earthquakes

Case StudyKashmir, Pakistan, 2005 (LEDC)On 8 October 2005, an earthquake measuring

7.6 on the Richter scale hit the Kashmir region of Pakistan. The earthquake was the result of collision between the Indian and Eurasian plates.

Earthquakes

Earthquake

Primary effects

Buildings collapsed.79,000 people were

killed.Landslides, and

large cracks appeared in the ground.

Secondary effects

Broken sewerage pipes contaminated water supplies and spread disease.

People died of cold during the harsh winter.

Effects

Earthquake

Short termThe army and

emergency services arrived to join the rescue effort.

Tents were given out by charities.

Aid workers arrived from abroad to find survivors and treat the injured.

Long termSchools and hospitals

were rebuilt.Building regulations

were improved to reduce damage and the death rate in future earthquakes.

Responses

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