Geography

By: (9b)Maria.A.SWilliam.P.IGeographyPlate tectonicsPlate 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 earths interior, which rise towards the earths surface, drag continents apart and cause them to collideThese cause the earths surface, drag continents apart and cause them to collide7 large plates : Pacific, Indo-Australian, Antarctic, North America, South American, African and Eurasian4 small plates : Caribbean, Iranian, Arabian, Juan de Fuca

Inner core: solid, 5 times more dense than surface rocksOuter core: semi-moltenMantle: semi-molten and about 2900 km thickCrust: solid, 2 main types (depth between 10-70 km);Continental : mostly formed of granite, less dense than oceanic crustOceanic: plunges beneath the continental one when they come together

Distribution of the worlds volcanoes and earthquakes is very uneven, mostly along plate boundaries which are regions of crustal instability and tectonic activityThere 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):Taal volcanoes & Mt. Pinatubo (Philiphines)Ulawun (Papua New Guinea)Krakatoa, Merapi, Tambora, Kelut (Indonesia)Popcatapetl & Colima (Mexico)Mt. Fuji (Japan)Etc.

A destructive plate boundary is sometimes called aconvergentortensional plate margin. This occurs when oceanic and continental plates move together. The oceanic plate is forced under the lightercontinental plate ( A section of the crust that makes up the Earths landmasses) . Friction causes melting of the oceanic plate and may trigger earthquakes. Magma rises up through cracks and erupts onto the surface. E.g:Mt St. Helens,USA and Soufriere, Montserrat(Carribean) Nazca plate is forced under the South American Plate.

Destructive plate boundary

A constructive plate boundary, sometimes called adivergent 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:the mid-Atlantic Ridge.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 instrumentsMost 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:Build large dams and deep reservoirs (increases pressure underground)Mining removes underground rocks and mineralsTesting of nuclear weapons underground=> trigger earthquakes (the very long reach of very large earthquakes)

Worlds 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 Marginscaused 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 Marginsthe 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 Marginsoccur 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.ConservativeMarginsThey 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 earths 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 Earths crrust (Crust is the top layer of the Earth).

VolcanoThere are 2 type of volcano:Shield volcanoesAshield volcanois a type ofvolcanousually built almost entirely offluidlava flows.Cone-shaped volcanoesAcone-shaped volcanoesis the cone-shapedhillformed as material fromvolcanic eruptions piles up around the opening.Type of volcanoIn 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 havent 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 volcanoIt normally takes 10,000 years without any eruptions or seismic activity to be declare extinct.19

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 levelsSeismometers to record swarms of tiny earthquakes that accur as the magma risesLaser to detect the physical swelling of the volcno

VolcaoneosLiving with a volcanoSome countries, such as Iceland and Philippines, were created byvolcano activitiesVolcanic soil are rich, deep and fertile,and allow intensive agriculture to take placeVolcanics areas are important for tourismVolcanoesCase 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 andlaharshave 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.VolcanoesShort-term responses and resultsEvacuation.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 resultsAn 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.

VolcanoesEarthquakes are a sudden and violent shaking of surface of the earthEarthquakes

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 planarfractureor discontinuity in a volume ofrock, across which there has been significant displacement along the fractures as a result of earthmovementShallow focus earthquake generally located along constructive boundaries and conservative boundariesConservative plate boundaries are faults that occur when two plates slide against one anotherconstructive plate boundaries two plates move away from each other causing new oceanic crust to be formed.

26Earthquake 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 DamageSeveral of way dealing with earthquake:Leave the areaDo nothing and accept the hazzardThe main ways of dealing with earthquake:Better forecasting and warningBuilding design and building in good locationSeveral ways predicting and monitoring earthquake:Recording changes in electrical conductivityNothing strange and unusual animal behaviourChecking history evidenceMeasuring crustal movementDealing with earthquakeBuilding 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 mudslidesEarthquakesCase 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.

EarthquakesEarthquakePrimary effectsBuildings collapsed.79,000 people were killed.Landslides, and large cracks appeared in the ground.

Secondary effectsBroken sewerage pipes contaminated water supplies and spread disease.People died of cold during the harsh winter.

EffectsEarthquakeShort 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.

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