Living in an Active Zone Revision
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The document discusses plate tectonics and the movement of tectonic plates. It describes the three main types of plate boundaries - destructive, constructive, and conservative. At destructive boundaries, one plate is subducted under another, leading to features like trenches and volcanoes. At constructive boundaries, plates move apart and new crust is formed via volcanism and rifting. Conservative boundaries involve plates sliding past each other. Overall, the document provides an overview of plate tectonics theory and the associated landforms generated at different plate boundary types.
Living in an Active Zone Revision
- 3. The crust is similar to the shell of a cracked egg, and is made up of large plates of rock. Underneath, the mantle is made up of molten rock. The plates move slowly due to convection currents.
- 4. Plate Names African Plate Indo Australian Plate North American South American Eurasia n Pacific Nazca Antarctic
- 5. • A destructive plate margin is where two plates are moving towards each other. • The point where the two plates meet is called the subduction zone. • One plate is forced beneath another into the mantle. • This can lead to the formation of features like oceanic trenches and volcanic fold mountains. •http://www.absorblearning.com/media/item.action?quick=12s http://www.classzone.com/books/earth_science/terc/content/visualizations/es0804/es0804page01.cfm?chapter_no=visualization
- 6. At a constructive plate boundary, two plates move apart. As the two plates move apart, magma rises up to fill the gap. This causes volcanoes at this type of boundary. However, since the magma can escape easily at the surface the volcano does not erupt with much force. Earthquakes are also found at constructive boundaries. An example of a constructive boundary is the Mid-Atlantic Ridge. Sometimes plates pull apart beneath the sea. Magma wells up and cools to form new crust. This leads to a ridge being developed such in the Atlantic ocean where the Mid-Atlantic ridge is found. Earthquakes can also take place.
- 7. Constructive plate boundaries can also be found on land. The Plates can pull apart to leave a rift valley with steep sides. This has happened in Iceland along the Mid-Atlantic ridge to form the Thingvellir rift valley
- 8. These are low, broad volcanoes and are produced by runny lava that flows over a large area. These volcanoes can be very large and ash can build up around their vents to leave a cinder cone.
- 9. These are steep sided, made by layers of ash and lava, high summit (top) and explosive volcanoes
- 11. Primary Hazards Secondary Hazards These happen because of a change in the environment following an earthquake or eruption These happen as a direct result of the earthquake or volcanic eruption
- 12. • Lava flows are usually slow but can destroy buildings, roads and trees.
- 13. • Pyroclastic flows – A landslide of hot ash, rocks and gases from a violent eruption.
- 14. • Lahars or mudflows are produced when ash or mud mixes with rainwater. These can have very serious consequences.
- 15. • Ash – Powdered rock fragments that are thrown from a volcano during an explosive reaction
- 19. Mt St Helens Consequences of the Eruption N O 10km
- 20. Hot mudflows raise the temperature of the rivers and lakes to 30ºC. Two million birds, animals and fish are killed. 60 people die from the eruption. Mudflows block and divert rivers. The US army takes 18 months to dig out the debris from the River Toutle. Communications routes threatened – railway and road bridges destroyed, Portland harbour blocked Gophers, through their tunnelling, mix the soil with the ash. This increases the fertility of the soil. An increase in tourism Deer mice, chipmunk, vole, gophers, salamander survive the blast. Their population steadily increases due to the absence of predators. A decrease in tourism What benefits might the volcanic activity have brought to Mt St Helens? Damage to crops=$175million The post office and Lone Fir Motel shut down in Cougar. Up to 70mm of ash falls across Washington and East Montana…7000 students have an early Summer vacation due to problems on the roads
- 21. This lava is weathered (broken down) to form a fertile soil Tourists are attracted to areas of volcanic activity Geothermal energy (heat from the earth) can be produced in many volcanic areas Can you think of any other reasons? Why do people live in volcanic areas?
- 23. • Buildings, roads and pipelines can break due to the intense ground shaking.
- 24. • Strong aftershocks can cause more damage and restrict rescue efforts.
- 25. • Marshy soil can lose its strength and become very soft ( like wet concrete) when violently shaken. This causes the foundations of buildings to collapse.
- 26. • A tidal wave that is created when an earthquake occurs.
- 27. • In built up area this is major threat straight after an earthquake. Broken gas pipes can ignite and fires can be quickly spread.
- 28. • Soil, rock and mud can move quickly downhill, blocking road and rail links.
- 29. • The Richter Scale is the best known scale for measuring the magnitude of earthquakes. It is logarithmic. A recording of 7, for example, indicates a disturbance with ground motion 10 times as large as a recording of 6. • A Seismograph which is used to measure the size of an earthquake. The needle moves as the ground shakes and the ink moves across the page to record the size = bigger shake – bigger line!!
- 30. Sometimes snakes and animals behave oddly before volcanic eruptions. There have been observations of this in places like Asia. The ground often changes shape. For example, at Monserrat the lava dome swelled in size in the weeks leading up to 28th July 2008 ( use tilt meters) This is a sure sign that volcanic activity going to happen. As the magma moves up the volcano pressure is put upon the volcano, causing cracks and small earthquakes to occur. May lead to rockfalls If there is a steady increase of sulphur dioxide, this shows there is likely to be an eruption. This shows magma is rising to the surface.
- 31. 1) Development of Observatories, eg Montserrat Volcano Observatory (MVO), collect data on a particular volcano 2) Monitoring Stations placed around volcano, powered by solar panels 3) Seismographs measure even the smallest tremor in the earth’s surface, which trigger warnings for towns and cities 4) Global Positioning Systems (GPS) satellites are used to record even the slightest change in the shape of the volcano 5) Tilt meters are used to measure larger changes in the surface of the ground 6) Radar and Aerial Photographs can be used to record changes in shape 7) Remote sensing satellites can be used to detect changes in heat / temperature of rock surfaces indicating magma rising to the surface.
- 32. THINK Short Term or Long Term
- 33. Responses to the Earthquake The Chinese government responded quickly and provided 50,000 troops to help the relief effort. In the first few days rescuers had to sift through rubble with their hands. Large heavy earth-moving equipment had to be brought in from over seas. Expertise from Japan was needed. Temporary camps were set up. http://news.bbc.co.uk/1/hi/world/7397838.stm All Short Term
- 34. Many residents and rescuers first used their bare hands to clear the debris from collapsed buildings. Local emergency services were quickly on the scene. The army helped to rescue victims. In L'Aquila, 95km (60 miles) north-east of Rome, over 3000 buildings in the medieval city were damaged. A university dormitory, churches and a bell tower are believed to be among the buildings that had collapsed. Local medical facilities were used and a field hospital were set up. http://news.bbc.co.uk/1/hi/world/europe/7984867. All Short Term
- 35. http://news.bbc.co.uk/1/hi/world/7397838.stm Spraying lava with water to cool it and solidify it. Earth barriers have been used to channel the direction of lava flow. Dropping concrete blocks via helicopter to divert the flow. Aerial bombing lava tubes with dynamite to widen them and reduce the flow. All Short Term
- 36. Now Think Long Term !! This is section is about the Three Ps – Plan, Predict and Prepare 1) Planning - a) using strict planning laws to control where areas of new development so that less buildings are in dangerous areas, b) design and create buildings to with stand the effects of earthquakes and minimise damage, c) |Emergency services with specialist teams trained to react to an event; 2) Predict – use technology to predict when hazard may occur ( see slide above) but think Early Warning Systems, Tsunami ocean buoys use to monitor size of waves and predict when wave hits land; 3) Prepare people to react to the effects of an earthquake / volcano – education in schools (earthquake drills) and TV / Radio on what to do – think Tsunami warnings in Japan;