08 - LAST TIME... What is a wave? Waves are energy moving...

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Unformatted text preview: LAST TIME... What is a wave? Waves are energy moving through a medium, not the medium moving itself (duck bobbing on sea surface). Anatomy of a wave...(crest, trough, height, wavelength, period, crest, frequency) Ocean waver disturbing and restoring forces (free vs forced wave) Wind waves grow from capillary waves influenced by wind strength, duration, and fetch travel in "trains" change to shallow water waves as they approach the shore (d < wavelength) influenced by interference, refraction, diffraction, reflection Why are there such BIG waves at this one spot?? Mavericks: Big waves in CA Other types of ocean waves (in addition to wind waves)... waves)... internal waves storm surges seiches tsunamis tides wind waves Internal ocean waves Internal waves are waves that travel within the interior Internal waves can form between masses of water with of a fluid. different densities, especially at the base of the pycnocline. The waves propagate at the interface or boundary between two layers with sharp density differences, such as temperature. They occur wherever strong tides or currents and stratification occur in the neighborhood of irregular topography. They can propagate for several hundred kilometers. can contribute significantly to oceanic mixing when they break, influencing how nutrients are distributed and how energy is transported throughout the ocean Image shows movement of internal waves through the Strait of movement Messina (between Italy and the island of Sicily). The colors indicate indicate differences in water density through a cross section of ocean. The The arrows indicate the speed of the waves in meters per second. 1 Storm Surges A storm surge is an abrupt bulge of water driven on shore by a tropical cyclone or a frontal storm. Storm Surges Form beneath Strong Cyclonic Storms Storm surges are short-lived. shortStorm surges consist of only a crest, so they cannot be assigned a period or wavelength, and cannot be called a wave. Storm surges are sometimes called storm tides. tides. A storm surge. The low pressure and high winds generated within a hurricane can produce a storm surge up to 9 meters (30 feet) high. Storm surge in a closed basin can lead to a "seiche" Water rocking back and forth at a specific resonant frequency in a confined area is a seiche. seiche. Seiches are also called standing waves. The node is the position in a standing wave where water moves sideways, but does not rise or fall. Seiche sloshing standing wave A seiche is a long wave in a lake or ocean basin that sloshes back and forth from one end of the basin to another. The rocking frequency depends on the length of the basin. At the node, water moves sideways and does not rise or fall. A graph of a seiche in Lake Erie. Strong westerly winds in November 2003 caused a seiche with more than 4 meters (13 feet) of difference in water level from Toledo on the western end of the lake to Buffalo on the eastern end. TSUNAMIS What? Why? When? Where? From a Japanese word meaning harbor ("tsu") and wave ("nami") Tsunami are caused by water displacement Tsunami are long-wavelength, shallow-water, longshallowprogressive waves caused by the rapid displacement of ocean water. What can generate tsunami? Fault motion Landslides Icebergs falling from glaciers Volcanic eruptions Asteroid impacts Other direct displacements of the water surface http://www.tsunami.noaa.gov/tsunami_story.html Tsunami is a set of ocean waves caused by any large, abrupt disturbance of the sea-surface. 2 Tsunami are always shallow-water waves shallowSeismic waves can reach tremendous size, causing destruction and loss of life. The great Indian Ocean tsunami of 26 December 2004 began when a rupture along a plate junction lifted the sea surface above. The wave moved outward at speeds of 212 meters per second (472 miles per hour). At this speed, it took only about 15 minutes to reach the nearest Sumatran coast and 28 minutes to travel to the city of Banda Ache. Fig. 10-28, p. 286 Was the 2nd largest earthquake on record! 9.2 on Richter scale The regional Indonesian capital of Banda Aceh before the 26 Dec 04 tsunami. ...and after Tsunami move at high speed How can the speed of a tsunami be calculated? Remember, because tsunami have extremely long wavelengths, they always behave as shallow water waves. The speed of a tsunami can be calculated using the same formula used for other shallow-water waves: shallow__ C = -- gd g = 9.8 meters per second (the acceleration due to gravity) d = depth (a typical Pacific abyssal depth is 4,600 meters) 1960 tsunami that originated in western Chile and sent destructive waves to Japan 2.5 hours after the earthquake 3 Tsunami have a long & destructive history Warning systems Film Questions... Is a tsunami usually just one wave, or several Are earthquakes the only force that can generate What kind of tectonic plate boundary generated the 2004 tsunami? How are tsunami different from wind waves? Where in the US is there a risk of tsunami? What steps are being taken to better understand tsunami and prevent disasters on the scale of the 2004 event? tsunami? waves? 5 ...
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This note was uploaded on 04/29/2008 for the course EAS 104 taught by Professor Brown during the Spring '08 term at Purdue University-West Lafayette.

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