tsunamis - a ECT ceanography Natural Disasters What is a...

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Unformatted text preview: : a ECT ceanography Natural; Disasters: What is a Tsunami? A tsunami is an ocean wave that is generated by a sudden displacement of the sea floor. Tsunami is the Japanese word for “harbor wave.” Although they are sometimes mis- labeled “tidal waves", they have nothing to do with tides. The wavelengths (the distance from wave peak to wave peak) of tsunamis typically exceed 200 kilo- meters. The first wave is not necessarily the biggest wave. The first wave can be mild, with the second or third wave causing severe damage. What causes Tsunamis? Tsunamis are usually caused by earthquakes that occur on the sea floor or in the coastal ar- eas. Volcanic eruptions, sub-marine landslides, underwater explosions and human activity may also cause tsunamis. The energy generated Tsunami by the earthquake trans- mits through the water. In deep oceans, the seismic waves are unnoticeable un- til the energy of the wave reaches the shallow waters of coastlines. When it ap- proaches the bays, harbors or coastline, the water is forced into a giant wave and may reach as high as 100 feet or more. Wave ac- tion is the main source of damage and the loss of life caused by tsunamis. Other sources of damage include strong currents and debris acting as projectiles. Where do Tsunamis Happen? Tsunamis and tsun- amigenic earthquakes are particular hazards for the Pacific Ocean islands and locations around the Pacific Rim. Hawaii is especially vulnerable to dangerous tsunamis because of its central location in the path of waves generated at many seismically active points around the Pacific Rim. Tsunamis occur less com- monly along the Caribbean, Atlantic Ocean, and Mediterranean Sea. 3 1998 Project Oceanography Spring Series 14 Tsunami Warning Centers Predicting tsunamis fo- cuses on both identifying earthquakes that are likely to generate tsunamis and on estimating the travel times of tsunamis across the ocean basin. Regional warn- ing systems around the Pa- cific Rim have been very ef- fective at minimizing the loss of life from tsunamis. The success of local warning systems depends heavily on emergency operations plan- ning, as well as on access to timely information about earthquake occurrences and water levels. Other impor- tant factors are the ability of local authorities to assess the danger, the ability to disseminate information very quickly, and the educa- tion of the public to re- spond appropriately in the event of a tsunami emer- gency. Early warning systems in the Pacific Ocean basin make use of information re- layed from the seismic sta— tions to tsunami warning stations via NOAA (National Oceanographic and Atmo- spheric Administration) satellites. Natural Disaster52Tomadoes. Lightning and Tsunamis K 0 T Physics of the Wave Regular wind generated wave Speedzlo-ZOmph Speedz450 -650 mph <——-—— 316.800 feet Speed: 35-220 mph ‘———___ 5,000 to 10.000 feet I 3 1998 Project Oceanography Spring Series 15 Natural- DisasterszTomadoeS. Lightning and Tsun-ms Natural Disasters: IECT ficeanography Act1v1t1es Discussmn Questlons: Speed of Propagation (celery equation) 1. How fast can tsunamis travel? 2. What are typical Materials: o Plastic cake pan V= V'gh tsunami wavelengths o 16 02. water or Rheo- and periods? SCODiC fluid where v is velocity (III/S) 3. What causes tsunamis? o scissors g is the accelerated 4. As wavelength in- - sturdy plastic wrap gravity (10 m/sz) creases, what happens ° tape h is the water depth to wave veIOCilY? (m) 5. Which change will cause Cut a hole in the bottom of the plastic cake pan approx- imately 4”. Tape plastic 1. If the wave depth is 3000m, what is the veloc- ocean waves to be more powerful; doubling their wavelength or their wrap on the outside of the RV? pan covering the hole, mak— 6. ing SurE it is water tight 2. If the water depth is less Fill pan with fluid. Gently deep, only 50m, what is tap the plaSUC wrap 0n the the velocity? How does height? Imagine you live in a coastal community that is susceptible to tsunamis. What should bottom. this compare? 15 this your community do to faster or smaller than a “WWW” the patennal What happens? Why? wave in deep water? damages and loss of life? Discuss the role of beach sand in providing What happens when you 3. If the velocity is 15 m/s 7' change the strength of you what is the depth of the tap? water? protection from waves. Words to Know: Velocity Wave Speed Wavelength © 1998 Project Oceanography Spring Series 16 Natural DisasterszTomadoes. Lightning and Tsunamis Date 1 628 BCE 497 BCE 1293 CE 1 703 CE 1 737 CE 1755 CE 1815 CE 1868 CE 1883 CE 1896 CE 1933 CE 1946 CE 1960 CE 1964 CE 1976 CE 1978 CE 1992 CE 1992 CE 1993 CE Major Historical Tsunamis Location *Santorini Island, Aegean Sea Potidaea, Greece Sanriku Coast, Japan Sanriku Coast, Japan Kamchatka, Russia Lisbon, Portugal *Tamboro, Indonesia Chile and Peru *Krakatoa, Indonesia Sanriku Coast, Japan Sanriku Coast, Japan Hilo, Hawaii Pacific Pacific Philippines Acajutla, Ecuador Nicaragua Indonesia Sea of Japan Death Toll Destroyed Minoan Civilization ? 30,000 approx. 1 00,000 _? approx. 1 0,000 1 2, 000 25,000 36,000 2 7,000 3,000 1 73 200 1 22 3,000 1 00 1 1 6 1 000 1 00 All of these tsunamis were caused by earthquakes except for the three with asterisks (*), which were caused by volcanoes. © 1998 Project Oceanography Spring Series 17 Natural DisasterszTomadoes, Lightning and Tsunamis ...
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