Tsunami! Could IT Happen Here?

During a recent trip to Seattle, GillBilly was struck by the many “Tsunami Evacuation Route” signs along the roads of the Washington State coast. Not having seen such attention to the subject of potential tsunami damage in the coastal Southern California or Baja regions, my interest was piqued as to just what these fabled waves are, how they are formed, how we should expect to be warned and what is the proper behavior for those that are threatened. My conclusion is this, take whatever you can that’s most important and hit the road running away from the coast! Living in a marina, I have often thought that you would kick your boat away from the dock and haul bacon for deep water, but the following information I discovered through research has me believing that may be a fool hardy act. If you could reach deeper water quickly enough, one would have to punch through a wave of undetermined height and strength and hope the boat did not break falling off the other side. And, there could be a series of waves of undetermined period, height, and direction making the voyage a daunting and dangerous task. I understand that in a marina the water drains to extreme low tide or perhaps no water at all and then rushes back in with incredible force and fury. That would be something we all would not hope for and quite destructive. As I sit here at the Coral Marina in Ensenada, Mexico writing this article, I realize a wave of perhaps 30 meters (90 feet!) could jump our little jetty enclosure and inundate everything to within hundreds of meters of the coast.

Tsunami is a Japanese word with the English translation, "harbor wave." Represented by two characters, the top character, "tsu," means harbor, while the bottom character, "nami," means "wave." In the past, tsunamis were sometimes referred to as "tidal waves" by the general public, and as "seismic sea waves" by the scientific community. The term "tidal wave" is a misnomer; although a tsunami's impact upon a coastline is dependent upon the tidal level at the time a tsunami strikes, tsunamis are unrelated to the tides.

Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. Waves are formed as the displaced water mass, which acts under the influence of gravity, attempts to regain its equilibrium. When large areas of the sea floor elevate or subside, a tsunami can be created. Large vertical movements of the earth's crust can occur at plate boundaries. Plates interact along these boundaries called faults. Around the margins of the Pacific Ocean, for example, denser oceanic plates slip under continental plates in a process known as subduction. Subduction earthquakes are particularly effective in generating tsunamis.

As a tsunami leaves the deep water of the open ocean and travels into the shallower water near the coast, it transforms. Scientists have discovered that a tsunami travels at a speed that is related to the water depth - hence, as the water depth decreases, the tsunami slows. The tsunami's energy flux, which is dependent on both its wave speed and wave height, remains nearly constant. Consequently, as the tsunami's speed diminishes as it travels into shallower water, its height grows. In the Pacific Ocean, where the typical water depth is about 4000 meters, a tsunami travels at about 600 feet per second, or over 430 miles per hour! Because of this shoaling effect, a tsunami, imperceptible at sea, may grow to be several meters or more in height nearing the shoreline. When it finally reaches the coast, a tsunami may appear as a rapidly rising or falling tide, or a series of breaking waves.

The Tsunami Warning System (TWS) in the Pacific, comprised of 26 participating international member states, has the functions of monitoring seismological and tidal stations throughout the Pacific Basin to evaluate potentially tsunamigenic earthquakes and disseminating tsunami warning information. Tsunami watch, warning, and information bulletins are communicated to appropriate emergency officials and the general public by a variety of communication methods. Local authorities and emergency managers are responsible for formulating and executing evacuation plans for areas under a tsunami warning. The public should stay-tuned to the local media for evacuation orders should a tsunami warning be issued. And, the public should NOT RETURN to low-lying areas until the tsunami threat has passed and the "all clear" is announced by the local authorities.

This planet is covered with sordid men who demand that he who spends time fishing shall show returns in fish.
Leonidas Hubbard, Jr.