Geography By: (9b) Maria.A.S William.P.I
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); • Continental : mostly formed of granite, less dense than oceanic crust • 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): • Taal volcanoes & Mt. Pinatubo (Philiphines) • Ulawun (Papua New Guinea) • Krakatoa, Merapi, Tambora, Kelut (Indonesia) • Popcatapetl & Colima (Mexico) • Mt. Fuji (Japan) • Etc.
Destructive plate boundary • 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: • Mt St. Helens,USA and Soufriere, Montserrat(Carribean) • Nazca plate is forced under the South American Plate.
Constructive 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: • the mid-Atlantic Ridge. • Eldfell volcano, Heimaey (Iceland)
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.
Earthquake • => 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.
Some earthquakes are the result of human activity. • Examples: • Build large dams and deep reservoirs (increases pressure underground) • Mining removes underground rocks and minerals • 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.
The plates move at different speeds and in different directions. This is because of the convection currents that operate underneath the earth.
Volcano • 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 (Moltenis melted, liquid), sticky rock called magma (Magmais melted rock inside the Earth), forces its way through a crack in the Earth’s crrust (Crustisthe top layer of the Earth).
Type of volcano There are 2 type of volcano: • Shield volcanoes A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. • Cone-shaped volcanoes A cone-shaped volcanoes is the cone-shaped hill formed as material from volcanic eruptions piles up around theopening.
Type of volcano In type of volcano there are divided into: • Active volcanoes Active volcano are volcanoes that have erupted in recent times and could erupt again • Dormant volcanoes Dormant volcanoes are volcanoes that haven’t erupted for many years or centuries and could errupt again • Extinct volcanoes An extinct volcano is one that are believed will never erupt again because there is no lava or magma supply to it.
Vent – a crack on the side of a volcano where magma can escape Crater – a deep hollow at the top of a volcano Throat- that allows maga pass through before it reaches to to the surface.
Volcaoneos • Volcanic Strength The strength of a volcano is measured by the volcanic explosive index. This is based by the amount of material ejected by the volcano. • Predicting Volcanoes The 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
Volcanoes • 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 Study Montserrat 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.
Earthquakes • Earthquakes are a sudden and violent shaking of surface of the earth
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 movement Shallow focus earthquake – generally located along constructive boundaries and conservative boundaries Focus - refers to the place beneath the ground where the earthquake takes place Epicenter – is the point on the ground surface immediatly above the focus Deep focus earthquake – associated with aubduction zones.
Earthquake Damage Earthquake damage • Strength of earthquake and number of aftershock – the stronger the earthquake the more damage it can • Population density – an earthquake that hits high population density could inflict more damage • The type of building – MEDCs generally have better quality pf building rather than LEDCs • The time of day – an earthquake during busy time may cause more death than quite time • The distance from the centre (epicentre)- the closer to epicentre the greater damage that is done • The type of rock and sediment- some material may act like liquid when shaken • Secondary hazards – such as mudslides and tsunami
Dealing with earthquake • Several of way dealing with earthquake: • Leave the area • Do nothing and accept the hazzard • The main ways of dealing with earthquake: • Better forecasting and warning • Building design and building in good location • Several ways predicting and monitoring earthquake: • Recording changes in electrical conductivity • Nothing strange and unusual animal behaviour • Checking history evidence • Measuring crustal movement
Earthquakes Building design Building 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 Study • Kashmir, 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.
Earthquake Effects • 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.
Earthquake Responses • Short term • The 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 term • Schools and hospitals were rebuilt. • Building regulations were improved to reduce damage and the death rate in future earthquakes.