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Year 10 Science Revision Unit: Papatuanuku PAPATUANUKU – EARTH SCIENCE Key words Continental Drift Tectonic plates Subduction Convection currents Earthquakes Focus Epicentre Richter scale Volcanoes Magma Lava Basalt Crust – oceanic, continental Seismometer Viscosity Core Seismograph Andesite Mantle Laurasia, Rhyolite Convergent Boundary – subduction zone – oceanic trench Divergent – sea floor spreading Key definitions to learn: Magma Lava Focus Epicentre Viscosity p-waves s-waves Surface waves subduction Molten material inside the mantle Magma which has been ejected from a volcano The location of the rock movement occurred The point on the Earth’s surface above the focus The thickness/resistance to flow of a liquid Primary waves – compression and rarefaction waves – arrive first (These waves can travel through both solid and liquid) Secondary waves – side to side movement waves – arrive second (These waves cannot travel through liquid) Rolling movement of crustal rock – slowest wave the edge of one plate is forced under another Key Learning Points: The Earth is 4.5 billion years old The earth has defined structure – inner core, outer core, mantle, crust Evidence for Wegener’s continental drift theory: Shapes of adjacent continents/continental shelves fit like a jig saw Matching rock strata on both continents either side of ocean gap Same fossils in same rock layers on adjacent sides of continents Mt ranges/remains of glaciers continuous across neighbouring continents Study of earthquake waves reveals details of this structure The earth’s crust is divided into plates The plates move due to convection currents in the mantle The continents on the Earth have moved from their original positions Earthquakes and volcanoes occur at plate boundaries New Zealand straddles two plate boundaries 1 Year 10 Science Revision Unit: Papatuanuku North Island Volcanic activity caused by plate subduction North Island Volcanoes Andesite in composition Taupo – Rhyolite composition (very viscous and explosive) South Island Alpine fault caused by transform fault Auckland volcanoes caused by hotspot Auckland volcanoes formed from Basalt (least viscous) Youngest Auckland volcano – Rangitoto Earthquakes produce 3 types of waves – primary, secondary and surface waves Earthquake energy measured on the Richter scale (1-10) Convection currents The core is very hot due to heat produced from nuclear reactions. This heat is a source of energy for moving the tectonic plates. As the mantle closest to the core heats, the molten rock expands, becomes less dense and rises. When it reaches the cool crust, the molten rock loses heat energy, contracts, becomes more dense and sinks towards the core where it is heated again. The cycles of hot rock rising and cooler rock sinking are called convection currents. Where they move towards each other the plates converge (destructive plate boundary, where they move away from each other the plates diverge (spreading zone or constructive boundary). New Zealand is geologically active NZ lies on a plate boundary the movements around which cause earthquakes and volcanoes. To the north east of the North Island the oceanic crust of the edge of the Pacific plate is subducting under the continental crust of the Australian plate. This subduction causes the formation of the Hikurangi trench and the friction beneath the North Island melts rock that is forced to the surface in the Taupo volcanic zone as volcanoes. Between the North and South Islands the boundary twists to become a transform fault, the Alpine Fault, where the Australian plate is moving northwards and the Pacific plate is sliding southwards. Off the southwest coast of the South Island, west of Fiordland, the Australian Plate is subducting under the Pacific plate. 2 Year 10 Science Revision Unit: Papatuanuku The Auckland Volcanic Field The Auckland volcanic field covers around 360km2 under the city. It Includes 54 separate volcanoes (5 recently discovered), each of which is considered extinct. However, the field as a whole remains active. The last eruption was Rangitoto, around 600 years ago. Volcanic feature Rangitoto Brown’s Island Meola reef Takapuna boat ramp Lake Pupuke Mt Eden Orakei Basin Savage memorial /Bastion point Domain Cause of the land form that we currently observe Basaltic volcano that erupted through sea water. The summit is a scoria cone flanked by a crater of an earlier eruption. Least modified of Auckland’s volcanoes. Shows all 3 features of Ak volcanoes- it has a scoria cone, a tuff ring and a lava flow Lava, probably from Three Kings, flowed across a large area to form a thick layer of rock that runs through Western Springs into the Waitemata Harbour Large lava flow which breached the Pupuke crater rim and flowed seaward . Cooled around trees so has circular holes in it. Formed by magma rising to hit ground water which rapidly vaporizes causing a large explosion crater filled with water. Auckland’s highest cone formed by several “fire fountains” of molten lava, which, when squirted into the air, cools as red brittle rock. Crater porous and water seeps into ground and emerges at Western Springs Typical explosion crater filled with water to become a caldera. It is surrounded by an asymmetric tuff ring which is unstable White coloured, layered cliffs formed about 25 million years ago by settling of sediment under the sea then was later up lifted. After a large explosive eruption a smaller fire fountain of molten lava to formed a smaller scoria cone in the middle of the crater. Auckland volcanoes are due to a hotspot where magma is close to the surface of the crust which is relatively thin. The magma forces its way to the surface through weaknesses or fissures in the crust. The magma has a low percentage of silica so it is runny (has low viscosity). The lava flows relatively well, so low sided, shield-shaped cones are formed. When the basaltic lava cools on the surface it forms basalt rock that is grey and dense and is in large hexagonal crystals. Basalt turns into scoria if it is thrown into the air. When the basaltic lava is thrown onto the air it reacts with oxygen to form reddish iron oxide compounds. In addition, carbonates decompose to form CO2 gas that makes the cooled rock holey. This is scoria –a holey reddish/brown brittle rock Websites URL for revision: http://www.bbc.co.uk/schools/gcsebitesize/chemistry/changestoearthandatmosphere/ 3 Year 10 Science Revision Unit: Papatuanuku Revision Questions 1. Draw and label a simple diagram of the earth’s structure. 2. Sketch a diagram of a typical andesite volcano eg Taranaki, and label all parts. 3. The Earth is broken up into plates – what are all the types of evidence for this? …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. ……………………………………………………………………………………………………. 4. Radioactive processes generate heat inside the earth which causes convection currents in the mantle. These currents cause the plates to move. There are 3 types of movement of the plates – move apart (divergent) / collide (convergent) / rub against each other (transform) – explain using diagrams what happens when the plates move in these ways. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. 5. Describe New Zealand’s position in relation to the Indo-Australian and Pacific plates. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. 4 Year 10 Science Revision Unit: Papatuanuku 6. Draw a subduction diagram to show how the central North Island volcanoes formed. 7. Explain why NZ has earthquakes and volcanoes but Australia does not. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. 8. What cause earthquakes? …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. 9. Explain the difference between the focus and the epicentre of an earthquake. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. 10. Describe the 3 types of energy waves caused by an earthquake and the speed at which they move. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. 11. Describe how to read a seismograph in order to work out how far away a quake originated and its intensity. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. 12. If you were standing at the epicentre of a magnitude 4 and then a magnitude 7 earthquake, describe what difference you would notice. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. 5 Year 10 Science Revision Unit: Papatuanuku Draw a mindmap for this unit: Add to it, as you develop your learning. Geology Well done you have completed another revision unit. Now reflect on how you can improve further: Which aspects of the unit do I need to revise more carefully? Which aspects of the unit do I need help with? How will I seek this help? 6