Transcript 1.3
Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 1.3 © Oxford University Press 2009 What are the major internal forces and processes, and the resulting landforms? Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? How do plate movements shape the land? Internal forces (compressional, tensional and lateral forces) Convection currents Internal processes Folding Faulting Vulcanicity © Oxford University Press 2009 Plate These will be movements the focus of this Unit. Landforms Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is folding? How does compressional force affect rocks? 1-3-1e.mpg NSS eBook: 01_e_movie_02.mpg (Modify CertGeog 1.2_01e.mpg) Howinternal does What compressional force does the force affect experiment rocks? simulate? Compressional force. Rocks are folded up under compressional force. Please click above for footage © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is folding? The process by which rock layers are folded up under compressional force is called folding. Let’s study the structure of a fold. Trough Axial plane Compressional force © Oxford University Press 2009 Syncline (downfold) Anticline (upfold) Crest Limbs Compressional force Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is folding? What will happen when the compressional forces from both sides are equal in strength? The gradient on both sides: the same different The axial plane of fold: tilted vertical © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is folding? What will happen when the compressional forces from both sides are unequal in strength? The gradient on both sides: the same different The axial plane of fold: tilted vertical © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is folding? An example of fold © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is folding? What landform does folding form? What is the of relationship Folding develops parallel ranges mountains. They are between fold mountains and known as _______________. fold mountains plate boundaries? Alps Atlas Mountains All fold mountains are found at ( constructive / destructive ) plate boundaries, where compressional force occurs. © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is faulting? What will happen when forces act on fractured rocks? Please click above for footage © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is faulting? Faulting occurs when rocks at both sides of a crack are displaced horizontally or vertically Horizontal displacement Vertical displacement Fault plane Fault (the crack along which rocks are displaced) Relative movement © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is faulting? Relative movement There are three types of faults. Lateral force Tensional force Compressional force The block is pushed up along the fault plane The block slides down the fault plane Normal fault © Oxford University Press 2009 Reverse fault Two adjacent blocks slide past each other Tear fault Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is faulting? Drag the listed fault types and internal forces into the correct boxes. Let’s revise what we have learned about faults. If the game cannot work properly, click here to download the latest Adobe Flash Player. © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is faulting? An example of fault © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is faulting? What landforms does faulting form? Block mountains (Horsts) Faulting Rift valleys (Grabens) © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is vulcanicity? Why does the soft drink spill out of the can? What internal force does this experiment simulate? Please click above for footage © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is vulcanicity? Vulcanicity Pressure of magma is released. Magma rises through the crust along cracks. Cracks extend downward and reach the magma chamber Cracks develop in the crust Magma flows from the asthenosphere to the magma chamber © Oxford University Press 2009 Magma beneath the crust is under great pressure in the crust Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is vulcanicity? There are two types of vulcanicity. Vulcanicity Intrusive vulcanicity © Oxford University Press 2009 Extrusive vulcanicity Quit Part 1 © Oxford University Press 2009 Opportunities and risks─Is it rational to live in hazard-prone areas? Quit Part 1 © Oxford University Press 2009 Opportunities and risks─Is it rational to live in hazard-prone areas? Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? The Alps Many of the highest mountains in the world are formed by the folding of sedimentary rocks (Credit: Tom Bean/Corbis) © Oxford University Press 2009 Sedimentary rocks are formed by the accumulation of sediment in the sea, therefore fossils of sea creatures are often found in fold mountains Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Block mountains (Horsts) Block mountains or horsts are flat-top mountains formed between two faults. They can be formed by both compressional and tensional forces. Rocks may be eroded away Relative movement © Oxford University Press 2009 Block mountain Example: The Black Forest in Germany Compressional force Central block is uplifted Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Block mountains (Horsts) Block mountains or horsts are flat-top mountains formed between two faults. They can be formed by both compressional and tensional forces. Example: The Black Forest in Germany Relative movement Block mountain Tensional force Side blocks sink © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Rift valleys (Grabens) Rift valleys or grabens are flat-bottom valleys produced between two faults. They can be formed by both compressional and tensional forces. Example: Rhine Rift Valley Relative movement Rocks may be eroded away Rift Valley Compressional force Side blocks are pushed up © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Rift valleys (Grabens) Rift valleys or grabens are flat-bottom valleys produced between two faults. They can be formed by both compressional and tensional forces. Example: East African Rift Relative movement Rift Valley Tensional force Blocks are pulled away from each other. Central block sinks © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is vulcanicity? Intrusive vulcanicity Intrusive vulcanicity refers to the process by which magma enters _________ cracks or __________ chambers in the crust from the asthenosphere. When magma cools and solidifies in the crust, intrusive volcanic features are formed. © Oxford University Press 2009 Please click above for animation Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is vulcanicity? • ________Dome shaped feature • Parallel to the bedding plane Intrusive vulcanicity • ________-like wall feature • Vertical or tilted Dyke Laccolith Sill • ________Dome shaped chamber • Formed deep underground © Oxford University Press 2009 Batholith Bedding plane • ________-like Sheet feature • Parallel to the rock layers Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is vulcanicity? Extrusive vulcanicity Extrusive vulcanicity refers to the process by which the rising magma ejects from the crust through a vent or a fissure. The pressure of the rising magma is ( small / great ). The magma that reaches the earth’s surface is called lava. © Oxford University Press 2009 Why does magma eject from the crust? Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is vulcanicity? Extrusive vulcanicity Extrusive vulcanicity is divided into two types. Vent eruptions: Volcanoes Fissure eruptions: Lava plateaux © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Dykes A dyke in Namibia in southern Africa (Credit: M. Lohmann/Blickwinkel) © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Landforms developed from vent eruptions: Volcanoes Eruption of rock Eruption of rock debris, fragments, debris, fragments, ash, steam and gas ash, steam and gas Crater Layers of volcanic materials Crater Vent Parasitic cone When lava erupts through these cracks, a small cone at the side of the main cone may Magma form. This cone is chamber called a parasitic cone. Volcanic eruption of Mount St Helens, the USA © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Landforms developed from vent eruptions: Volcanoes A volcano will develop other features with time. Volcanic island Secondary cone or conelet Minor eruptions at the vent produce small volcanoes called secondary cones or conelets. When they form in crater lakes, they become volcanic islands. A crater © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Landforms developed from vent eruptions: Volcanoes A volcano will develop other features with time. Violent eruptions may blow off the top of the volcano. Crater A large depression, The lake called a caldera, is former Solidified Caldera formed. cone lava Watch a video clip of Crater Lake, North America Please click to browse online Cooled magma © Oxford University Press 2009 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Landforms developed from fissure eruptions: Lava plateaux A fissure eruption refers to the process by which lava erupts from the crust Watch a video clip of the fissure eruption at through a vent. Kilauea, Hawaii lava wells out through a crack or a fault on a surface. Please click to browse online Lava flows in a sheet form, forming ______ lava ______ flow Sheets of lava pile up, forming a ______ lava _________ plateau © Oxford University Press 2009 Lava flow Example: Deccan Plateau, India Quit