You are watching: Which of the following describes what happens to tsunami waves as they move towards the shore?
Tsunamis come at a shore as a collection of succeeding crests (high water levels) and also troughs (low water levels) - usually developing 10 to 45 minutes apart. Together they enter the shallow waters of coastlines, bays, or harbors, their speed decreases to around 50-60 km/h. For example, in 15 m the water the speed of a tsunami will certainly be only 45 km/h. Yet 100 or much more kilometers away, an additional tsunami wave travels in deep water towards the exact same shore in ~ a much better speed, and also still behind it there is an additional wave, travel at even greater speed. As the tsunami waves come to be compressed close to the coast, the wavelength is shortened and also the wave energy is directed upward - hence increasing your heights considerably. Just just like ordinary surf, the energy of the tsunami waves must be had in a smaller volume of water, so the waves prosper in height. Even though the wavelength shortens near the coast, a tsunami will generally have a wavelength in excess of ten kilometers once it come ashore. Relying on the water depth and the coastal configuration, the waves may undergo considerable refraction - another procedure that might converge their power to details areas ~ above the shore and thus increase the heights also more. Also if a tsunami tide may have been 1 meter of less in the deep ocean, it may flourish into a vast 30-35 meter wave once it sweeps over the shore. Thus, tsunami waves may smash into the shore favor a wall of water or relocate in together a quick moving overwhelming or birds - carrying everything on your path. One of two people way, the waves come to be a far-ranging threat to life and property. If the tsunami tide arrive in ~ high tide, or if there room concurrent storm tide in the area, the effects will it is in cumulative and also the inundation and destruction also greater. The historic record reflects that there have actually been many tsunamis that have struck the shores with disastrous force, periodically reaching heights of an ext than 30-50 meters. Because that example, the 1946 tsunami generated by one earthquake off Unimak island in Alaska"s Aleutian Islands, reached heights of much more than 35 meters, which ruined a reinforced concrete lighthouse and killed its occupants. Finally, the maximum elevation a tsunami get on coast is dubbed the runup. It is the vertical distance in between the maximum elevation reached through the water ~ above shore and the average sea level surface. Any type of tsunami runup end a meter is dangerous. The flooding through individual tide will typically last native ten minutes to a half-hour, for this reason the danger duration can last because that hours. Tsunami runup at the suggest of affect will rely on exactly how the energy is focused, the travel path of the tsunami waves, the seaside configuration, and the offshore topography. Impacts on IslandsSmall islands with steep slopes generally experience little runup - tide heights there are just slightly higher than top top the open up ocean. This is the factor that islands with steep-sided fringing or obstacle reefs are only at moderate risk from tsunamis. However, this is no the case for islands such together the Hawaiian or the Marquesas. Both of these island chains do not have extensive barrier reefs and also have vast bays exposed to the open ocean. Because that example, Hilo Bay in ~ the island that Hawaii and Tahauku Bay in ~ Hiva Oa in the Marquesas are particularly vulnerable. The 1946 Aleutian tsunami brought about runup, which gone beyond 8 m in ~ Hilo and also 10 m at Tahauku; 59 human being were killed in Hilo and two in Tahauku. Similarly, any gap in a reef place the surrounding shoreline in ~ risk.
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The neighborhood tsunami from the Suva earthquake that 1953 did small damage due to the fact that of Fiji"s comprehensive offshore reefs. However, 2 villages on the island of Viti Levu, located on the contrary gaps in the reef, were broadly damaged and five world were drowned.