Topic 3 Plate Tectonics Notes PDF

PLATE TECTONICS TOPIC 3 NOTES DE LA SALLE COLLEGE Geography Department Ms.Diane Sammut We will be focusing on... Page The theory of Plate Tectonics 3 Cross-section of the Earth 5 Tectonic plates...

PLATE TECTONICS TOPIC 3 NOTES DE LA SALLE COLLEGE Geography Department Ms.Diane Sammut We will be focusing on... Page The theory of Plate Tectonics 3 Cross-section of the Earth 5 Tectonic plates 8 Plate boundaries 9 Constructive plate boundaries 11 Destructive plate boundaries 13 Collision zones 14 Conservative plate boundries 15 Volcanoes 17 Living in a danger zone 21 Mount St.Helens 23 Supervolcanoes and hotspots 27 Earthquakes 28 Kobe, Japan 32 Tsunami 35 Predict and prepare 36 Glossary 38 2 The theory of Plate Tectonics The theory, or idea, of plate tectonics says that Earth’s outer layer is made up of large, moving pieces called plates. All of Earth’s land and water sit on these plates. The plates are made of solid rock. Under the plates is a weaker layer of partially melted rock. The plates are constantly moving over this weaker layer. Pangaea existed about 240 million years ago. Today, scientists think that several supercontinents like Pangaea have formed and broken up over the By about 200 million years ago this course of the Earth’s lifespan. These include supercontinent began breaking up. Pannotia, which formed about 600 million years Over millions of years, Pangaea separated into ago, and Rodinia, which existed more than a pieces that moved away from one another. These billion years ago. pieces slowly assumed their positions as the continent we recognize today. 3 Wegener based his theory on the following evidences : 4 Cross-section of the Earth Our home planet, the Earth, may look like one life forms. However, the inner part of the Earth huge rock, but it is actually like an onion when cut remained very hot. through its cross-sectional area – it has different layers with different compositions. Billions of The Earth is divided into four main layers, the years ago, Earth was formed from a hot ball of crust, the upper and lower mantle, the outer core nebula gases and as time goes by, the Earth’s and the inner core. surface cooled down and there emerged different LAYER PROPERTIES Inner core Outer core Mantle Crust 5  There are two types of crust, oceanic and continental. Generally oceanic crust is found under the oceans and continental under land. Although plates are usually a combination of oceanic and continental crust, there are some key differences between the two types of crust. the key differences are listed below. OCEANIC CRUST CONTINENTAL CRUST Thinner (this crust is not as deep or thick) Thicker (this crust is deeper and thicker) Denser (therefore comparably heavier) Less Dense (therefore comparably lighter) Sinks (therefore can be destroyed) Doesn’t Sink (therefore can’t be destroyed) Newer Older Common rocks in the crust. Igneous rocks in the first row: granite, gabbro, basalt. Metamorphic rocks in the second row: gneiss, schist, amphibolite. Sedimentary rocks in the third row: sandstone, shale, limestone 6 Seismic waves Since we can't go to the centre of Earth, we have to boundaries between different layers. The waves can rely on observations of the materials of the interior. also bend as they pass from one layer into another. These observations mostly come from seismic Scientists learn about Earth’s layers by studying the waves. paths and speeds of seismic waves traveling through Earthquakes produce three types of seismic waves: Earth. By measuring the time it takes for various primary waves, secondary waves, and surface waves to get from an earthquake to a given waves. seismometer, scientists can understand what the Each type moves through materials differently. In material properties must have been like along the addition, the waves can reflect, or bounce, off path taken by the wave. 7 Tectonic plates Plate tectonics is a scientific theory that explains how major landforms are created as a result of Earth's subterranean movements. The Earth's crust is broken up into pieces called plates. Heat rising and falling inside the mantle creates convection currents generated by radioactive decay in the core. The convection currents move the plates. Where convection currents diverge near the Earth's crust, plates move apart. Where convection currents Plate tectonics cause earthquakes and volcanoes. converge, plates move towards each other. The point where two plates meet is called a plate boundary. Earthquakes and volcanoes are most The movement of the plates, and the activity inside likely to occur either on or near plate boundaries. the Earth, is called plate tectonics. 8 Plate boundaries Scientists now have a fairly good understanding of how the plates move and how such movements relate to earthquake activity. Most movement occurs along narrow zones between plates where the results of plate tectonic forces are most evident. There are four types of plate boundaries: where new crust is generated as the plates pull away from each other. where crust is destroyed as one plate dives under another. where crust is neither produced nor destroyed but changes shape. where crust is neither produced nor destroyed as the plates slide horizontally past each other. 9  PLATE BOUNDARIES MAP 10 Constructive plate boundaries As the plates move apart (very slowly), magma Eventually the new rock builds up to form a rises from the mantle. The magma erupts to the volcano. Constructive boundaries tend to be found surface of the Earth. This is also accompanied by under the sea, ex. the Mid Atlantic Ridge. Here, earthquakes. chains of underwater volcanoes have formed along the plate boundary. One of these volcanoes may When the magma reaches the surface, it cools and become so large that it erupts out of the sea to form solidifies to form a new crust of igneous rock. a volcanic island, ex. Surtsey and the Westman This process is repeated many times, over a long Islands near Iceland. period of time. SURTSEY—ICELAND On November 14,1963 a cook aboard a trawler sailing south of Iceland spotted a column of dark smoke rising from the surface of the sea. Thinking is was a boat on fire and the captain turned his vessel to investigate. They found an island in the process of being born: volcanic eruptions originating from below the sea surface, belching black columns of ash. The new island was later named Surtsey. Eventually, ash had blocked sea water from the crater area. Lava formed a hard cap of solid rocks over the lower slopes which prevented the waves from washing away the island. 11 Living on the Mid-Atlantic ridge Iceland lies on a constructive plate margin. It is Did you know that Iceland is growing in size? part of a submarine mountain chain called the As the two plate move apart new land is formed Mid-Atlantic Ridge, which stretches for every time there is an eruption. thousands of kilometres through the middle of Despite being at risk from occasional earthquake the Atlantic Ocean. Not only is the mid-ocean and volcanic eruptions, the people of Iceland gain a ridge changing the geography of Iceland, it's number of benefits from living on top of this plate also responsible for the volcanic activity boundary. which created the island. THE BENEFITS OF ICELAND’S UNDERGROUND _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ 12 Destructive plate boundary At a destructive boundary the plates are moving The point at which this happens is called towards each other. This usually involves the subduction zone. As the oceanic plate is a continental plate and an oceanic plate. forced below the continental plate it melts to form The oceanic plate is denser than the continental magma and earthquakes are triggered. The magma collects to form a magma chamber. This magma plate so, as they move together, the oceanic plate then rises up through cracks in the continental is forced underneath the continental plate. crust. As pressure builds up, a volcanic eruption may occur. MARIANA TRENCH Mariana Trench is a deep-sea trench in the floor of the western North Pacific Ocean, just east of the Mariana Islands. It is the deepest trench known on Earth. It stretches for more than 2,540km with a width of 69 km. The greatest depths are reached in Challenger Deep, a steep-walled valley on the floor of the main trench. The deepest part of the ocean is called the abyssal zone. Even though it is very cold it has hot water vents from moving plates so it is able to host thousands of species of invertebrates and fish including such oddities as the Angler Fish. 13  PACIFIC RING The “Ring of Fire” is an area of the Pacific Ocean shaped like a horseshoe. It is home to 90% of the world’s OF FIRE earthquakes and 75% of the world’s volcanoes. MAP 14 Collision zone When two plates that carry continental crust The rocks caught within a continental collision are move towards each other, the result is a heated and squeezed until they change from their mountain range. Although one plate does get original rock type. These are called metamorphic stuffed beneath the other, the continental crust is rocks which include slate and marble. These are thick and does not easily subduct like oceanic often seen in old, eroding mountain ranges such as lithosphere. It crumples, bends, breaks and the Appalachians. becomes very thick, creating fold mountains like the Alps and the Himalayas. THE HIMALAYAS The Himalayan mountain range and Tibetan plateau have formed as a result of the collision between the Indian Plate and Eurasian Plate which began 50 million years ago and continues today. The Himalayas are still rising by more than 1 cm per year as India continues to move northwards into Asia, which explains the occurrence of shallow focus earthquakes in the region today. However the forces of weathering and erosion are lowering the Himalayas at about the same rate. The Himalayas and Tibetan plateau trend east-west and extend for 2,900 km, reaching the maximum elevation of 8,848 metres (Mount Everest). 15 Conservative plate boundary At conservative margins mountains are not made, When this stress energy is eventually released it volcanic eruptions do not happen and crust is not sends shock waves through the earth’s crust destroyed. Instead, two plats either slide past forming faults. We know these shock waves as each other in opposite directions, or two plates earthquakes, and a good example of this is the slide past each other at different speeds. As San Andreas fault in California, where the Pacific they move past each other stress energy builds as plate is moving NW at a faster rate than the North the plates snag and grind on one another. American plate. SAN ANDREAS FAULT The San Andreas Fault marks the junction between the North American and Pacific Plates. The fault is 1300 km long and extends to at least 25 km in depth. Although both plates are moving in a north westerly direction, the Pacific Plate is moving faster than the North American Plate. Pressure builds up for years and when it is released the plates slip suddenly and shallow focus earthquakes are generated. San Francisco has historically suffered significant earthquakes, notably in 1906 and 1989. The average rate of movement along the San Andreas Fault is between 30mm and 50mm per year over the last 10 million years. If current rates of movement are maintained Los Angeles will be adjacent to San Francisco in approximately 20 million years. 16  PLATE MARGINS SUMMARY 17 What are volcanoes? Volcanoes are openings (vents) in the ground Volcanoes that have erupted in the past 2,000 where magma (molten rock) from deep inside the years but not recently, are said to be dormant or earth forces its way to the surface. The magma sleeping. These may be dangerous as it is may appear as flows of molten lava, as volcanic difficult to predict when they are going to erupt bombs, as fragment of rock or simply ash and again (ex. Mount Ararat, Turkey) dust. Mountains that are made of these materials Many volcanoes are unlikely ever to erupt again. are called volcanoes. They are said to be extinct because their volcanic Volcanoes may be active, dormant or extinct. activity has finished. Such volcanoes may have erupted over 50 million years ago and have If a volcano has erupted recently and is likely to mostly been worn away by erosion (ex. Mount erupt again, it is described as active. There are Snowdon, Wales). over 700 active volcanoes around the world (ex. Mount Etna, Italy). 18  WHAT COMES OUT OF A VOLCANO? 19 Types of volcanoes Geologists and professional volcanologists usually classify volcanoes into four different types, based on their shape, magnitude, structure, material, and type of eruption. Composite volcanoes are steep-sided volcanoes composed of many layers of volcanic rocks made from thick sticky lava, ash and rock debris (broken pieces) If the magma is thick and sticky (like honey), the gas cannot escape, so it builds up and up until it explodes sending out huge clouds of burning rock and gas(known as pyroclastic flows). EXAMPLES : Shield volcanoes are shaped like a shield with long gentle slopes made by runny lava flows. If the magma is runny, the gas can escape easily and there will not be an explosion. The magma just comes out of the mountain and flows down the sides. EXAMPLES : Cinder cones are the most common type of volcano in the world. circular or oval cones built from erupting lava that breaks into small pieces as it shoots into the air, then fall back to the ground, cool and form cinders around the vent. Most cinder cones are a few hundred feet tall (100 to 150 m), and rarely are larger than 600 to 900 feet (200 to 300 m) in height. EXAMPLES : Lava domes are formed when erupting lava is too thick to flow and makes a steep-sided mound as the lava piles up near the vent. Most domes are small and many do not have a crater. EXAMPLES : 20 21 Living in a danger zone Volcanoes have a wide range of effects on humans. These can be problematic or beneficial. It is usually the destructive nature of volcanoes which is more widely documented. However, many people rely on volcanoes for their everyday survival. Today, many millions of people live close to volcanoes for this very reason. ADVANTAGES DISADVANTAGES 22 Sinabung volcano in Sumatra, Indonesia rumbles away in June 2015, but local farmers appear unconcerned. Many villagers remained in the area an would not only live near the “red zone” (the restricted area within 3km of the summit) but also regularly venture into it and regularly go to farm their land. 23 Mount St. Helens Mount St Helens, Washington State, NW USA is located in the Cascade mountain range and prior to its eruption in 1980 it had been active for over 100 years. The area around the mountains is a National Park which is mainly used for tourism, forestry, salmon farming and some agriculture – therefore the population density of the area is relatively low. The volcano which is a composite cone, sits on a destructive boundary where the Juan de Fuca plate meets the North American plate. Mount St Helens erupted on May 18th 1980 following a period of activity which began in On May 18th, an earthquake measuring 5.1 on the March 1980 with an earthquake measuring 4.0 on richter scale caused a landslide on the northern the richter scale. What followed was 3 months of flank of the volcano, which in turn exposed the seismic activity as magma rose within the cryptodome below, resulting in a sudden release mountain. As the magma rose, a large bulge grew of pressure and a cataclysmic eruption in the form on the north flank of the volcano, this was due to a of a lateral (sideways) blast. The blast zone blockage in the main vent resulting in the growth consisted of 230 square miles with the eruption of a cryptodome (mound of viscous lava) in the leaving a 'lunor' landscape in its wake. side of the volcano. 24 25 CONSEQUENCES OF THE ERUPTION EFFECTS ON THE LANDSCAPE 400 metres was blown off the top of the mountain and a one mile horse shoe-shaped crater was left that was 500m deep. Every plant and animal within 25km north of the volcano was killed – approximately 7000 animals died. Every tree within 30km of the volcano was flattened. Nuée ardente (hot ash and gas) destroyed The water produced from melting ice and forests and logging camps. snow on top of the volcano create lahars (mudflows of ash and water), which choked rivers and killed all fish and water life. Spirit Lake was filled with mud. 12 million salmon died. The eruption also destroyed 250 homes, 47 bridges, 15 miles of railways and 185 miles of highway. 26 EFFECT ON PEOPLE AND THE ECONOMY 63 people were killed, mainly by poisonous gases. Ash clogged up car engines and farm machinery. The cost of ash damaged to farmers crops and machinery totalled £100 million. 15cm of ash fell causing traffic chaos and airline flights to be cancelled. The timber industry in the area was destroyed by the flattening of trees which significantly damaged them. Telephone lines and electricity supplies were knocked out. Tourists no long visited the area causing a reduction in the local economy. RESPONSES TO THE ERUPTION SHORT-TERM AID Rescuing stranded people, providing shelter for those who has lost their homes, giving medical supplies to those who were injured. The aid operation rescued 198 people. Unfortunately, the landscape had changed so much that maps were no longer accurate, this slowed down the rescue efforts. 27 LONG-TERM AID A million tonnes of ash were removed from roads, buildings and airports. Removing the ash cost over $1million in the town of Yakima and it took ten weeks. Millions of trees were replanted because there was a huge loss of timber which would cost $300million. Compensation was given to farmers because what they produced on their farms was destroyed by being covered by ash. This would cost about $70million. New tourist facilities were built because there were less tourists, meetings and conferences in the area after the eruption. It was important to get these people back as they input a lot of money into the economy. River channel was dredged to remove logs and levees were rebuilt to reduce floods which could happen in the future. A new highway was built and major repairs were undertaken because 250km of roads and 25km of railways were damaged, costing $7million. Money was given to rebuild houses after 200 homes were destroyed. Money was given to redevelop the salmon hatcheries after 12 million baby salmon were killed. 28 Super volcanoes and hot spots A super volcano is a volcano on a massive scale. It is different from a volcano because: it erupts at least 1,000 km3 of material (a large volcano erupts around 1 km3) it forms a depression, called a caldera (a volcano forms a cone shape) a super volcano often has a ridge of higher land around it a super volcano erupts less frequently - thin crust A hot spot under the American plate is eruptions are hundreds of thousands of years why Yellowstone National Park has geysers apart and other thermal features. If the hot spot is Most islands are found at tectonic plate under the seafloor (as it is in Hawaii) it produces boundaries either from spreading centres (like undersea volcanoes. Some of these volcanoes Iceland) or from subduction zones (like Japan). build up to the surface of the ocean and become There are few 'hot spots' on Earth and the one islands. Over millions of years the plate may under Hawaii is right in the middle of one of the move across the 'hot spot' and the original largest plates on Earth - the Pacific Plate. volcano become extinct but a new volcano will begin to form in the area of the 'hot spot.' A geologic 'hot spot' is an area in the middle of a plate where molten magma breaks through the YELLOWSTONE Yellowstone is one example of a super volcano. Three huge eruptions have happened in the last 3 million years. the last eruption was 630,000 years ago, and was 1,000 times bigger than the Mount St Helens eruption in 1980. The large volume of material from the last Yellowstone eruption caused the ground to collapse, creating a depression called a caldera. The caldera is 55 km by 80 km wide. The next eruption is predicted to have catastrophic worldwide effects. The super volcano at Yellowstone is formed because of a volcanic hotspot. Every year millions of visitors come to see the related features, such as geysers and hot springs. 29 Earthquakes Earthquakes are caused by the release of built-up stuck. When this happens pressure builds up. pressure inside the Earth's crust. An earthquake's When this pressure is eventually released, an power is measured on the Richter scale using an earthquake tends to occur. instrument called a 'seismometer'. The point inside the crust where the pressure is The effects of an earthquake can be devastating - released is called the focus. The point on the Earth's they can destroy settlements, change landscapes, surface above the focus is called the epicentre. and cause many deaths. Earthquake energy is released in seismic waves. An earthquake is caused by the shaking and These waves spread out from the focus. The waves vibration of the Earth's crust due to movement of are felt most strongly at the epicentre, becoming the Earth's plates (plate tectonics). Earthquakes less strong as they travel further away. The most can happen along any type of plate boundary. severe damage caused by an earthquake will happen close to the epicentre. Earthquakes occur when tension is released from inside the crust. Plates do not always move smoothly alongside each other and sometimes get 30 Richter scale Scientists measure earthquakes using the Richter The Richter scale measures earthquakes in whole scale. This scale, invented in 1934 by California numbers and tenths numbers. Most earthquakes scientist Charles Richter, measures the magnitude register 2.5 or less and are too small to be of an earthquake, and the result is a number from experienced by people. Seismographs register these 0 to 10, as measured on a machine called a quakes, though. seismograph. Scientists estimate that 900,000 of such "small" The scale is not a normal number scale, however; quakes occur every year. Up to 30,000 of quakes rather, it is a logarithmic scale. This means that an measuring 2.5 to 5.4 occur in a year as well, and earthquake that measures 2 on the Richter scale these cause minor damage and are certainly noticed is 10 times as powerful as an earthquake that by people. The higher the number on the Richter measures 1. In addition, each whole number scale, the fewer earthquakes occur every year. increase means 32 times more energy is released. Quakes registering 8.0 or higher occur, on average, only once every 5 to 10 years. 31 Effects of eartquakes Earthquakes can destroy settlements and kill many Effects are often classified as primary and people. Aftershocks can cause even more damage secondary impacts. Primary effects occur as a direct to an area. It is possible to classify the impacts of result of the ground shaking while secondary an earthquake, by taking the following factors into effects occur as a result of the primary effects. account: short-term (immediate) impacts long-term impacts social impacts (the impact on people) economic impacts (the impact on the wealth of an area) environmental impacts (the impact on the landscape) SOCIAL IMPACTS ECONOMIC IMPACTS ENVIRONMENTAL IMPACTS Short-term impacts Long-term impacts 32 Different impacts of eartquakes Magnitude Level of development The higher on the Richter (MEDC or LEDC) Distance from the epicentre scale, the more severe the MEDCs are more likely to earthquake is. have the resources and The effects of an earthquake are more severe at its centre. technology for monitoring, prediction and response. Population may not be well Population density educated about what to do (rural or urban area) in the event of a volcanic The more densely populated eruption or an earthquake. an area, the more likely Construction standards tend there are to be deaths and to be poor in LEDCs. casualties. Homes and other buildings may suffer serious damage Communication Time of day when a disaster occurs. Good infrastructure and Influences whether people are in accessibility helps rescue their homes, at work or travelling. Climate teams reach area of disaster. A severe earthquake at rush hour Influences survival rates in a densely populated urban area and the rate at which could have devastating effects. disease can spread. Match earthquake words with their definition : aftershock number to quantify the size of an earthquake epicentre The size of an earthquake as measured by the energy released. fault The zone of activity that surrounds the Pacific Ocean and the Pacific plate. focus A collapse of a mass of earth from a mountain or a cliff. landslide A smaller earthquake following the main shock of a larger earthquake. An instrument that measures earthquakes. It measures their size and their magnitude duration. Also known as a seismometer. A fracture in a rock formation along which there has been movement of the Ring of fire rocks on either side of the fracture. Richter scale The point on the earth’s surface, directly above the focus of an earthquake. seismograph The place of origin of an earthquake. 33 Kobe, Japan Kobe is located in the south east of Japan, near a destructive plate margin. It is a megacity and has one of the largest container ports in the world. Although further from a plate margin than most of the cities in Japan, Kobe is still found on a fault line. The earthquake that hit Kobe during the winter of 1995 measured a massive 7.2 on the Richter scale. At this plate margin, the Pacific plate is being pushed under the Eurasian plate, stresses build up and when they are released the Earth shakes. This is known as an earthquake happening made earthquake proof during recent years along a subduction zone. The focus was only many of the older buildings simply toppled over 16km below the crust and this happened on or collapsed. A lot of the traditional wooden the 17th Jan 1995 at 5.46am. 10 million people buildings survived the earthquake but burnt live in this area. down in fires caused by broken gas and The effects of this earthquake were catastrophic electricity lines. for a more economically developed country (MEDC). Despite some buildings having been 34 CONSEQUENCES OF THE EARTHQUAKE PRIMARY EFFECTS SECONDARY EFFECTS The collapse of 200,000 buildings and Electricity, water and gas supplies were cut. numerous bridges along the 130km bullet Fires caused by broken gas pipes raged for train route. several days destroyed wooden buildings During the 20 second earthquake, the ground Roads were at gridlock, delaying ambulances and moved up to 50 centimetres horizontally fire engines. and up to 1 metre vertically. 230,000 people were made homeless and had to Collapse of 1km of the Hanshin live in temporary shelters (un-heated gyms or Expressway. open parks) at a time when night-time 120 out of 150 quays destroyed at the port of temperature dropped to –2°C Kobe were destroyed. There was a shortage of supplies (ex. blankets, water, food). Large industries in the area forced to close down (ex. Panasonic, Mitsubishi) Final death toll was at 5500 people. 35 RESPONSES TO THE EARTHQUAKE Water, electricity, gas, telephone services were fully working by July 1995. The railways were back in service by August 1995. A year after the earthquake, 80% of the port was working but the Hanshin Expressway was still closed. By January 1999, 134,000 housing units had to many blocked roads and massive problems been constructed but some people were still of homelessness. having to live in temporary accommodation. Electricity and water supplies were badly New laws were passed to make buildings and damaged over large areas. This meant no power transport structures even more earthquake proof. for heating, lights, cooking, etc. Clean, fresh More instruments were installed in the area to water was in short supply until April 1995. The monitor earthquake movements. government and city authorities were criticised for being slow to rescue people and for Most new buildings and roads have, in the last refusing offers of help from other countries. 20 years, been designed to be earthquake proof, schools and factories have regular Many people had to sleep in cars or tents in earthquake drills, etc. Despite this, many older cold winter conditions. buildings still collapsed or caught fire. This led 36 The wave of destruction A tsunami is a huge wave, usually caused by It is hard to see that a tsunami is approaching. volcanic or earthquake activity under the ocean, The most obvious sign is the coastal water which can eventually crash onto the shoreline. retreats just before the waves reach the shore. The effects on a community can be devastating. This is actually the trough of the wave following behind. When an earthquake, volcano or landslide happens on the ocean floor, water is displaced. The main impact a tsunami has is flooding. The This water forms the start of the tsunami. waters are also able to erode the foundations of coastal structures. When the waves reach shallower water: their height can increase by several metres the shallow water slows the wave the waves get closer together 37 Predict and prepare It's not possible to prevent earthquakes and PREDICTING AN ERUPTION volcanic eruptions. However, careful As a volcano becomes active, it gives off a number management of these hazards can minimise the of warning signs. These warning signs are picked up damage that they cause. Prediction is the most by volcanologists (experts who study volcanoes) important aspect of this, as this gives people time and the volcano is monitored. to evacuate the area and make preparations for the event. Unfortunately volcanic eruptions and earthquakes cannot be prevented. Managing PREPARING FOR AN ERUPTION hazards such as earthquakes and volcanoes can be Everyone who could be affected needs to know the done by prediction and preparation. plan and what they should do if it needs to be put into action. Planning for a volcanic eruption includes: creating an exclusion zone around the volcano being ready and able to evacuate residents having an emergency supply of basic provisions, such as food funds need to be available to deal with the emergency and a good communication system needs to be in place. 38 PREDICTING AN EARTHQUAKE PREPARING FOR AN EARTHQUAKE Earthquakes are not as easy to predict as volcanic Many of the prediction techniques used to monitor eruptions. However, there are still some ways of earthquakes are not 100 per cent reliable. Planning monitoring the chances of an earthquake: and preparing for an earthquake is therefore very important. Laser beams can be used to detect plate movement. People living in earthquake zones need to know A seismometer is used to pick up what they should do in the event of a quake. Training people may involve the vibrations in the Earth's crust. An increase holding earthquake drills and educating people in vibrations may indicate a possible via TV or radio. earthquake. People may put together emergency kits and Radon gas escapes from cracks in the Earth's crust. Levels of radon gas can be monitored - a store them in their homes. An emergency kit may include first-aid items, blankets and tinned sudden increase may suggest an earthquake. food. Earthquake-proof buildings have been constructed in many major cities. Such buildings are designed to absorb the energy of an earthquake and to withstand the movement of the Earth. Roads and bridges can also be designed to withstand the power of earthquakes. 39 Glossary aftershock a smaller earthquake following the main shock of a large earthquake. the gradual movement of the continents across the earth's surface through continental drift geological time. very hot material at the deepest part of the mantle rising, then cooling, convection currents sinking again and then heating, rising and repeating the cycle over and over. crust the outer layer of the earth made up of solid rock layer upon which we live. the hottest part at the centre of the Earth which with its immense heat core energy, the inner core is like the engine room of the planet a sudden violent shaking of the ground, typically causing great destruction, earthquake as a result of movements within the earth's crust or volcanic action. epicentre the point on the earth's surface vertically above the focus of an earthquake. fault a fracture along which the rocks have been displaced. focus the point of origin of an earthquake unerneath the crust. form mainly by the effects of folding on layers within the upper part of the fold mountains Earth's crust. geothermal energy thermal energy generated and stored in the Earth. a place deep within the Earth where hot magma rises to just underneath the hot spot surface, creating a bulge and volcanic activity. a type of rock formed through the cooling and solidification of magma or igenous rock lava. lahars a destructive mudflow on the slopes of a volcano. landslide a collapse of a mass of earth or rock from a mountain or cliff. the resulting rock after solidification and cooling of magma coming out of a lava volcano. molten rock located deep within the mantle of the Earth that comes to the magma surface through the eruption of volcanoes. 40  the layer between the earth’s crust and the outer core made up of semi-molten mantle rock. rock that was once one form of rock but has changed to another under the metamorphic rock influence of heat or pressure. a cloud of gas, ash, and lava fragments ejected from a volcano, typically as part nueé ardente of a pyroclastic flow. plate a massive, irregularly shaped slab of solid rock which floats on the mantle. plate boundary/margin the locations where two tectonic plates meet. the theory that Earth's outer shell is divided into several plates that glide over plate tectonics the mantle. a dense, destructive mass of very hot ash, lava fragments, and gases ejected pyroclastic flow explosively from a volcano and typically flowing at great speed. Richter scale a numerical scale for expressing the magnitude of an earthquake. an instrument that measures and records details of earthquakes, such as force seismometer and duration. seismic waves A wave in the earth produced by an earthquake. a plate boundary where two plates converge, and one plate is forced beneath subduction zone the other. a long, narrow, deep depression in the ocean bed, typically one running parallel trench to a plate boundary and marking a subduction zone. vent the main outlet for the magma to escape. 41