Geology Reference
In-Depth Information
The water in tsunami waves doesn't move in the circular, oscillatory motion that regular ocean waves
exhibit, so when they reach the shore the tsunami waves don't build up into rolling breakers but pro-
ceed up onto the shore as illustrated in the second figure in this sidebar. As the water gets shallower
near shore, the wave height increases; a wave that is only a few feet tall in the open sea can build up
to a more than 20-foot-tall wall of water as it moves onto the beach.
The force of all this wave energy pushes a large amount of water up onto shore, well past the normal
sea level. (The height of water above normal sea level is called runup. ) The water can proceed for miles
inland, flowing for 30 minutes or more before gradually running out of energy.
After the Indian Ocean tsunami of 2004, research and public interest in understanding these destructive
waves reached a peak. While the Pacific Ocean had experienced tsunamis in the past, the Indian
Ocean tsunami of 2004 caught the attention of the entire world. The result is that scientists were funded
to further study evidence of past tsunamis in an attempt to develop ways of predicating future tsuna-
mis. The best bet is to prepare thorough advance warnings communicated throughout the international
community, such as the one that constitutes the Tsunami Warning System in the Pacific, centered out
of Hawaii. This system spreads messages and information through the region when geologic events
that may trigger a tsunami occur.
Unfortunately, warning systems are most helpful to regions far away from the origin of the tsunami.
In the 2011 tsunami that struck northern Japan, there was little time to warn people in the regions
where the tsunami struck first (and most catastrophically). Regions across the Pacific Ocean including
Hawaii, California, and South America had plenty of warning and time to prepare but did not experience
the violence and destruction of the early waves that struck the northern islands of Japan.
Not all coastal regions are susceptible to tsunamis — only the ones that are near regions of regular
or intense earthquake activity. A few warning signs can help you recognize whether a tsunami may be
headed your way. If you are near the coast and you feel an earthquake; see the water rapidly move out
away from the shore like an extra-low tide (it often does this before the rush of tsunami water hits the
shore); and hear a loud, train-like noise, the best thing to do is head for higher ground.
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