Chapter 3

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Environmental Science
Jovan Stefanovic

Chapter 3 Tsunami 31 Introduction to TsunamiTsunami are produced by the sudden displacement of ocean lake or river waterSeveral types of events can trigger a tsunami including a large earthquake landslide or explosive volcanic eruption or an impact in the ocean of an asteroid or comet Most disastrous tsunami are triggered by earthquakes or landslidesWhere tsunami can occur o The Pacific ocean the Indian ocean Atlantic ocean the Caribbean Mediterranean and Black seasEarthquakeTriggered Tsunami An earthquake can cause a tsunami by displacing the seafloor or the floor of a large lake or by triggering a large landslide Displacement of seafloor is probably the most common of these mechanisms and occurs when a block of Earths crust moves rapidly up or down during an earthquake In general it takes an earthquake of magnitude 75 or larger to generate damaging tsunamiA four stage process that culminates with the tsunami rushing ashore commonly far from the source o Displacement of the seafloor during an earthquake sets in motion oscillatory waves that transmit energy outward and upward from the source o In the deep ocean the waves move rapidly and are spaced far apart Their velocity is equal to the square root of the product of the acceleration of gravity and the water depth you would not notice a passing tsunami in the deep ocean o As the tsunami nears land both the water depth and the velocity of the tsunami decrease the decrease in velocity is accompanied by a decrease in the spacing between wave crests and an increase in wave heights o As the first tsunami wave approaches the shore it transforms into a turbulent mass of water that rapidly moves inland During some tsunami the trough of the wave arrives first causing the sea to recede and exposing the seafloorA popular misconception is that tsunami consists of a single immense wave that curls over and crashes on the shore Instead the waves are typically turbulent onrushing surges of debrisladen waterThe runup of the tsunami is the maximum horizontal and vertical distances that the largest wave of a tsunami reaches as it travels inlandA tsunami can also generate other types of waves referred as edge waves that travel along the shore
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