CHAPTER 2 LIVING WITH TECTONIC HAZARDS Risk or Opportunity? CHECK-IN: Mount Merapi • The biggest eruption of Mount Merapi in Java, Indonesia occurred on 5 November 2010. • More than 350 people were killed and over 300,000 people were forced to leave their homes. • However, despite several warnings leading up to the eruption, some stayed behind to care for their cattle. • On Java itself, there are 30 volcanoes. Despite this, people have settled down and established croplands in areas prone to natural hazards such as earthquakes and floods. • What do you think draws people to these places? CHECK-IN: Mount Vesuvius • Mount Vesuvius, in Italy, is one of the world’s most dangerous volcanoes. • Mount Vesuvius has had 30 major eruptions ever since it wiped out the city of Pompeii in CE 79. • Despite a 27 per cent prediction of Mount Vesuvius erupting in the next 100 years, about 600,000 people continue to live near the volcano, within the ‘danger zone’. • Why do you think this is so? CHAPTER 2 LIVING WITH TECTONIC HAZARDS In this Chapter, you will explore three key questions: 1.Why are some areas more prone to tectonic hazards? 2.What landforms and associated tectonic phenomena are found at plate boundaries? 3.How do people prepare for and respond to earthquakes? CHAPTER 2 LIVING WITH TECTONIC HAZARDS KQ1: Why are some area more prone to tectonic hazards? a. b. c. d. e. What is a natural hazard? What is the internal structure of the Earth? What is a tectonic plate? Why do tectonic plates move? What are the different types of plate boundaries? a. What is a natural hazard? • A natural hazard is a natural event that threatens human lives and causes damage to property. • Read the article in the next slide. – Is this incident a natural hazard? Why? a. What is a natural hazard? NEA confirms it was raining hailstones in Singapore From Channel NewsAsia, 27 March 2008 SINGAPORE: The sudden downpour on Thursday afternoon brought more than just heavy rain. Hailstones were raining down in some parts of Singapore, according to callers to Channel NewsAsia’s hotline. The National Environment Agency later confirmed that hailstones were reported in central Singapore between 3.15 pm and 3.45 pm. Callers said the hailstones were the size of 5 cent coins. They were seen mainly in Bishan, Toa Payoh and Ang Mo Kio. a. What is a natural hazard? What about the picture on the right? Does it show the impacts of a natural hazard? If so, why? And what hazard could have caused this? a. What is a natural hazard? Distribution of natural hazards Figure 2.7 a. What is a natural hazard? Observing patterns and relationships From Figure 2.7 1.Describe the distribution of earthquakes and volcanoes. 2.Compare the areas prone to volcanic activity, earthquakes and storms. How similar or different are their distribution? a. What is a natural hazard? Types of natural hazards: • Tectonic hazards • Climate-related hazards Impacts of natural hazards: • Large scale • Small scale a. What is a natural hazard? Classify the following types of hazards into tectonic hazards and climate-related hazards. Droughts Earthquakes Tsunamis Floods Volcanic eruptions Storms a. What is a natural hazard? Examples of Natural Hazards • Tectonic hazards • Earthquakes • Volcanic eruptions • Tsunamis • Climaterelated hazards • Droughts • Floods • Storms a. What is a natural hazard? • Tectonic hazards are caused by movements in the Earth’s crust. • Examples: – Earthquakes – Volcanic eruptions – Tsunamis a. What is a natural hazard? Name some areas that are more prone to tectonic hazards. a. What is a natural hazard? Do you know the latest… tectonic hazard that just happened? Visit: http://earthobservatory.nasa.gov/NaturalHazards/ a. What is a natural hazard? Why are some areas more prone to tectonic hazards? a. What is a natural hazard? How likely do you think the major destructions caused by volcanic eruptions of Mount Merapi and Mount Vesuvius will be repeated? CHAPTER 2 LIVING WITH TECTONIC HAZARDS KQ1: Why are some area more prone to tectonic hazards? a. b. c. d. e. What is a natural hazard? What is the internal structure of the Earth? What is a tectonic plate? Why do tectonic plates move? What are the different types of plate boundaries? b. What is the internal structure of the Earth? b. What is the internal structure of the Earth? b. What is the internal structure of the Earth? Think, Pair, Share… How is a Ferrero Rocher® chocolate similar to the internal structure of the earth? b. What is the internal structure of the Earth? Core •Composed mostly of iron and nickel •Divided into inner core + outer core 1. Inner core – about 1,200 km thick – solid layer 2. Outer core – about 2,100 km thick – liquid layer •Temperature between 3,000⁰C and 5,000⁰C b. What is the internal structure of the Earth? Mantle •Mostly solid rock (flows under high temperature and pressure) •2,900 km thick •Divided into uppermost mantle + asthenosphere 1. Uppermost mantle – a layer of solid rock 2. Asthenosphere – below uppermost mantle – rocks close to melting point, easily deformed •Temperature between 800⁰C and 3,000⁰C b. What is the internal structure of the Earth? Crust •Outermost layer on which we live •Oceanic crust is found beneath oceans •Continental crust is found beneath the continents •Thickness ranges from a few km to more than 70 km b. What is the internal structure of the Earth? Lithosphere = Crust + Uppermost mantle • Makes up the Earth’s rigid outer shell • When the rocks in the lithosphere melt, hot molten rock called magma is formed. b. What is the internal structure of the Earth? Recap through the video at: http://www.learner.org/interactives/dynamicearth/stru cture.html CHAPTER 2 LIVING WITH TECTONIC HAZARDS KQ1: Why are some area more prone to tectonic hazards? a. b. c. d. e. What is a natural hazard? What is the internal structure of the Earth? What is a tectonic plate? Why do tectonic plates move? What are the different types of plate boundaries? c. What is a tectonic plate? • A tectonic plate is made up of the lithosphere (i.e. crust + uppermost mantle). • The earth’s crust is broken into several pieces of tectonic plates. • These plates move in relation to one another. • Tectonic plates can be made up of: – oceanic crust – continental crust or – a combination of both c. What is a tectonic plate? Point out the differences between the oceanic crust and continental crust. c. What is a tectonic plate? Oceanic crust vs Continental crust Oceanic Crust • Located beneath deep ocean • Very thin — between 5 and 8 km • Denser (e.g. basalt) Continental Crust • Located beneath land masses and under shallow seas • Very thick — between 30 and 60 km • Less dense (e.g. granite) CHAPTER 2 LIVING WITH TECTONIC HAZARDS KQ1: Why are some area more prone to tectonic hazards? a. b. c. d. e. What is a natural hazard? What is the internal structure of the Earth? What is a tectonic plate? Why do tectonic plates move? What are the different types of plate boundaries? d. Why do tectonic plates move? 1. Convection currents 2. Slab-pull force d. Why do tectonic plates move? 1. Convection currents • Convection currents are movements of heat within the mantle. • Material in the mantle is heated by the core. • This causes convection currents in the molten mantle material. • Mantle expands, rises and spreads out beneath the plates. • Plates are dragged along and move away from each other. d. Why do tectonic plates move? 1. Convection currents •Subsequently, the hot molten mantle cools slightly and sinks, pulling the plates along •Hence plates move towards each other. •The sinking mantle material heats up again as it nears the core and the whole process repeats. d. Why do tectonic plates move? Plates moving away from each other Ocean floor Plates Mantle Figure 2.8a) Core Tectonic plates float on molten mantle, driven by heat energy/convection currents d. Why do tectonic plates move? 2. Slab-pull force •This occurs when an oceanic plate (denser) subducts (see E in Figure 2.8b) under a less dense plate and pulls the rest of the plate along •The subducting plate drives the downward-moving portion of convection currents (see F in Figure 2.8b) •While mantle material away from the subduction zone (see G in Figure 2.8b) drives the rising portion of convection currents d. Why do tectonic plates move? Plates moving away from each other Ocean floor E F G Mantle Core Figure 2.8b) Plates d. Why do tectonic plates move? Imagine this… On average, tectonic plates move a few centimetres a year. This is about the rate your nail grows. How long will your nails be if… you don’t cut it for a year? d. Why do tectonic plates move? Changing positions of the Earth’s continents • Plate movements have altered the distribution of the Earth’s land masses over several hundred million years. CHAPTER 2 LIVING WITH TECTONIC HAZARDS KQ1: Why are some area more prone to tectonic hazards? a. b. c. d. e. What is a natural hazard? What is the internal structure of the Earth? What is a tectonic plate? Why do tectonic plates move? What are the different types of plate boundaries? e. What are the different types of plate boundaries? Figure 2.12 e. What are the different types of plate boundaries? Observing plate movements From Figure 2.12 1. In which direction is the Indian Plate moving? 2. In which direction is the Nazca Plate moving? Which plate would it converge with? 3. What type of plate movement occurs between the Juan De Fuca Plate and Pacific Plate? e. What are the different types of plate boundaries? • Divergent: where plates move away from each other • Convergent: where plates move towards each other • Transform: where plates move past each other Within plates, there is also evidence of plate movement in different directions and fractures. These are known as developing plate boundaries. e. What are the different types of plate boundaries? Divergent Plate Boundaries 1. Oceanic-oceanic plate divergence 2. Continental-continental plate divergence e. What are the different types of plate boundaries? 1. Oceanic-oceanic plate divergence e. What are the different types of plate boundaries? 1. Oceanic-oceanic plate divergence e. What are the different types of plate boundaries? • Magma rises from the mantle to fill the gap between the plates as they diverge. • New sea floor is formed when the magma cools and solidifies. This process is called sea-floor spreading. • Magma rises at the zone of divergence/spreading zone to form a ridge of new ocean floor called mid-oceanic ridge. e. What are the different types of plate boundaries? • The newly formed (youngest) rocks are closest to the middle of the ridge/plate boundaries. • At various points along the ridge, magma builds up above the ocean to form volcanic islands. • E.g. the Mid-Atlantic Ridge is found in the middle of the Atlantic Ocean cutting across Iceland, a volcanic island. e. What are the different types of plate boundaries? E.g. Mid-Atlantic Ridge and Iceland NORTH AMERICAN PLATE EURASIAN PLATE Mid-Atlantic Ridge Atlantic Ocean IT Link •Formation of Iceland: http://www.youtube.com/w atch?v=_rG6q2Npw8Y&fe ature=related e. What are the different types of plate boundaries? 2. Continental–continental plate divergence •Can result in the breakup of continents •E.g. Great Rift Valley (East Africa) – a lowland with steep sides and flat valley floor – formed by Somalian boundary of the African Plate moving away from the Nubia plate boundary of the African Plate (Figure 2.15) – 6,000 kilometres long – between 30 to 100 kilometres wide – Evidence of tectonic activity: active volcanoes and earthquake fractures found e. What are the different types of plate boundaries? E.g. East African Rift Valley 1. Draw arrows to indicate the direction of plate movement on Figure 2.15. 2. Account for the shape of the lakes around the rift valley. Figure 2.15 e. What are the different types of plate boundaries? • Can result in the formation of linear sea • E.g. Red Sea and Gulf of Aden near the Great Rift Valley – Elongated/linear shape – 1,900 km long – 300 km at its widest stretch – Average depth of 500 m – Evidence of tectonic activity — formation of new volcanic island in Red Sea e. What are the different types of plate boundaries? E.g. East African Rift Valley Figure 2.15 e. What are the different types of plate boundaries? Formation of the Red Sea e. What are the different types of plate boundaries? Convergent Plate Boundaries 1. 2. 3. Oceanic–oceanic plate convergence Continental–oceanic plate convergence Continental–continental plate convergence e. What are the different types of plate boundaries? 1. Oceanic–Oceanic Plate Convergence • When two oceanic plates converge, one subducts under the other. • A subduction zone forms, creating a deep oceanic trench. • The subduction of the oceanic plate causes the solid mantle material to melt and magma is formed. • The magma rises through the mantle and ocean floor to emerge as volcanoes. • Eventually a chain or arc of islands called island arc is formed. e. What are the different types of plate boundaries? 1. Oceanic–Oceanic Plate Convergence • Earthquakes may also occur. • E.g. the Pacific Plate converging with the slower-moving Philippine plate (Figure 2.17) Oceanic crust e. What are the different types of plate boundaries? 1. Oceanic–Oceanic Plate Convergence Mariana Islands Mariana Trench Pacific Plate Oceanic crust Philippine Plate Oceanic crust Uppermost mantle Asthenosphere e. What are the different types of plate boundaries? What do you observe about the shape and distribution of these islands? Correlate these features with plate boundaries. e. What are the different types of plate boundaries? Locate the Indonesia Archipelago and Japan. Explain the shape and distribution of these islands. e. What are the different types of plate boundaries? 2. Continental-continental plate convergence • Plates made largely of continental crust may collide with other plates made largely of continental crust. • However, both plates have similar densities and hence, resist subduction. • Instead, the plates break, slide along fractures in the crust and fold, forming fold mountains. • E.g. the Himalayas - convergence of the Indian Plate and the Eurasian Plate (Figure 2.18). e. What are the different types of plate boundaries? E.g. the Himalayas Figure 2.18 e. What are the different types of plate boundaries? Himalayas EURASIAN PLATE Tibetan Plateau INDIAN PLATE Figure 2.16 Based on evidence shown in the animation clip in the IT Link on the previous slide and Figure 2.16, explain why marine fossils have been found at the peak of Himalayas. e. What are the different types of plate boundaries? E.g. the Alps, Europe What are the plates that converge to form the Alps? e. What are the different types of plate boundaries? 3.Oceanic-continental plate convergence • When an oceanic plate meets a continental plate, the denser oceanic plate subducts under the less dense continental plate. • A subduction zone forms, creating a deep oceanic trench along the plate boundary. • The subduction of the continental plate causes the soild mantle material to melt and magma is formed. e. What are the different types of plate boundaries? 3.Oceanic-continental plate convergence • The magma rises through the mantle and crust to emerge as volcanoes on land. • The edge of thick continental plate buckles to form fold mountains. • Earthquakes may also occur. • E.g. the Australian Plate subducting under a section of the Eurasian Plate near Sumatra formed the Sunda Trench. e. What are the different types of plate boundaries? 3.Oceanic-continental plate convergence Barisan Mountains EURASIAN PLATE AUSTRALIAN PLATE Oceanic crust Uppermost mantle Asthenosphere Continental crust e. What are the different types of plate boundaries? 3.Oceanic-continental plate convergence e. What are the different types of plate boundaries? Transform Plate Boundaries • Plates slide past each other. • As they do so, tremendous stress builds up. • This stress is eventually released, often as a violent earthquake. • E.g. San Andreas Fault, USA & North Anatolian Fault, Turkey e. What are the different types of plate boundaries? Transform Plate Boundaries e. What are the different types of plate boundaries? E.g. San Andreas Fault, USA • In 1906, an earthquake occurred in San Francisco, southern California between the Pacific Plate and the North American Plate. – This caused several hundred kilometres of North American Plate to move an average of 2.5 m, – and at one point almost 7 m all in less than 1 minute. e. What are the different types of plate boundaries? E.g. San Andreas Fault, USA e. What are the different types of plate boundaries? E.g. North Anatolian Fault, Turkey How would the plate movement affect the two cities shown in time to come? CHAPTER 2 LIVING WITH TECTONIC HAZARDS KQ1: Why are some area more prone to tectonic hazards? a. b. c. d. e. What is a natural hazard? What is the internal structure of the Earth? What is a tectonic plate? Why do tectonic plates move? What are the different types of plate boundaries? CHAPTER 2 LIVING WITH TECTONIC HAZARDS Complete Check Point Question 6 which summarises all types of plate boundaries and their associated landforms.