The devastating impact of seismic sea waves Tsunami The devastating impact of seismic sea waves

Tsunami (harbor wave) earthquake submarine volcanic eruption Caused by processes that abruptly move large volumes of ocean water: earthquake submarine volcanic eruption coastal/submarine landslide or rockfall extraterrestrial impact

How do Earthquakes cause tsunami? http://geology.com/articles/tsunami-geology.shtml

Tsunami causes Unless there is an underwater landslide, strike-slip earthquakes WILL NOT cause tsunami Most tsunami generated by subduction zones

Tsunami wave speed Travel at high speeds : 400 to 500 mph (~200 yards/sec) Alaska to CA 4 to 7 hrs Alaska to Hawaii 4 to 6 hrs Chile to Hawaii 14 to 15 hrs Chile to Japan 22 to 33 hrs

Tsunami nears shore As wave gets into shallow water bottom of wave drags along ocean floor Top of wave still moving fast: can cause cresting of wave, and breaking onto shore

Tsunami run-up Run-up = measurement of height of water onshore observed above a reference sea level Generally don’t get big gigantic wave Water comes as a fast moving rise in tide that rapidly moves inland NOT JUST ONE WAVE…multiple waves coming in about ½ hour or so apart

Damage due to tsunami Waves often full of debris (trees, cars, pieces of wood etc.) As the wave recedes, the debris drags more stuff with it Can recede as much as about ½ mile out to see, leaving shoreline empty with flopping fish, boats, etc. on the bottom

Detecting a tsunami Pressure recorder on bottom of ocean Buoy to communicate readings via satellite Tsunami Warning Centers issue warning

Tsunami Warning Centers Hawaii and Alaska When EQ considered capable of generating tsunami, send warning with estimated arrival time Once tsunami hits somewhere, tsunami watch established to monitor tide gauges and ocean buoys

Tsunami Warning When warning is issued – low lying areas are evacuated U.S. Coast guard issues warnings over marine frequencies Some places have sirens