Tsunami The devastating impact of seismic sea waves

Tsunami The devastating impact of seismic sea waves

Tsunami (harbor wave) 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, strikeslip 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