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Easc lecture #6 Tsunamis & volcanoes.docx

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Simon Fraser University
Earth Sciences
EASC 104
Brent Ward

Tsunamis What is a tsunami? - A tsunami is not a tidal wave. Tsunamis are a series of waves Wave terminology - Earthquakes are what generate tsunamis Orbital motion versus depth - at half of the wave length there is no movement of water - there is no movement at the wave base - when there is no more wave base, it starts to drag along the bottom of the ocean floor and decreases the velocity of the wave and increases in height Wave’s progression into shallower water - If you are in a tsunami but in deep water, you will not feel or see much Tsunamis and earthquakes - The vertical fault movement of the fault is what triggers a tsunami - In a strike slip fault, we are not likely to trigger a tsunami. Most tsunamis are triggered by a reverse fault because of the hanging wall Tsunami and landslides - If there is sediment build up at a delta, then there is a small landslide off that delta Tsunami and volcanoes - During volcanic eruptions, a slope collapse down into the water which causes a wave and water is displaced which can trigger a tsunami Tsunami- regions at risk - Landslides are something that is difficult to predict Tsunami- reducing the hazard - Installing a detection and a warning signal - Areas that are known for significant risk, walls are built between the city and the ocean—built in Japan, however, the walls did not protect Japan because the waves went right over the wall and the coast dropped, and therefore the wall was shorter than originally expected - Maps are used for planning purposes. Planning where hospitals should be located - Education—how much knowledge people have about tsunamis (eg. knowing that tsunamis come in a series of waves) - Tsunami watch : trying to identify a tsunami - Tsunami warning : You know that the tsunami is coming Volcanoes –Chapter 4 - Volcanoes are symbols of fear and power but provide rich and fertile soil - 7 types of volcanic hazards: o Ash falls/tephras  Particles of ash drift through the wind, stripped leaves and limbs of trees  Thick layers of ash can destroy crops, water made unsuitable for drinking  Roads, houses, communication and water reservoirs can be covered by blankets of ash  Makes driving difficult through the cause of a choking cloud. Also dangerous to aircrafts  causing engines to stop completely by losing power due to the ash o Hot ash flows/pyroclastic flows  Can create Avalanches of hot ash down the slope of a volcano  Ash flows are very dangerous and move very quickly o Volcanic Mudflows/lahars  Floods of water, mud, sand and rocks that rush down river valleys. They move as fast as 50km/hr  Looks like a flow of wet concrete that can even pick up large boulders imbedded in the ground  Anything that is not carried away by the mudflow is buried deep in mud/sand or other debris o Volcanic landslides 
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