Geography 2152F/G Lecture 3: HAZARD-L3
29 Sep 2020
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Tsunamis: japanese for harbour wave , produce by sudden displacement of water. Caused: displacement of seafloor, landslide that enters water. *earthquake must be at least m7. 5 to trigger tsunami. Stage 1: displacement of seafloor sets waves in motion that transmit energy up/outward: when waves reach surface of water, spread outward. Stage 2: waves move more rapidly across open ocean (can reach 500km/h: space of wave crest large (100km, height (amplitude) of wave small (less 1m) Passengers on ships rarely notice tsunamis passing beneath. Stage 3: as approach land, water depth increase. Stage 4: as impacts land, waves reach heights of dozens metres. Increase in wave amplitude: wave speed can be up to 50km/h making them impossible to outrun, water first recedes from shore and exposes seafloor. Consist series of large waves reaching shore that can last for several hours. Run-up: max vertical distance that largest wave of tsunami reaches as it travels inland.
