Tsunamis

A          A tsunami is a series of extremely long oceanic waves that result from the sudden displacement of large quantities of water. The catalyst for a tsunami is often an underwater earthquake or volcanic eruption. Less often, a tsunami is generated by the collapse of great amounts of oceanic sediment or landslides at the coastline. Rarely, a tsunami is created by the impact of a meteor into the sea. The displacement of massive volumes of water, either in the ocean or very close to it, initiates several gargantuan waves that can be quite catastrophic. Major tsunamis qualify as natural disasters, resulting in great destruction of coastal areas throughout the world. Tsunamis are also referred to as seismic sea waves.

B          Tsunamis are unlike the routine waves at the coastline, which regularly roll in as a result of offshore wind. After the triggering event of a tsunami, a sequence of basic, growing waves begin traveling large distances across the ocean. The classic comparison is the proverbial stone thrown into a pool of water. The displacement generates the same effect, yet the ripple of a tsunami is long and large. A seismic impulse that occurs in deep water may create a tsunami that travels up to five hundred miles per hour, at wavelengths of sixty to one hundred and twenty miles. While the tsunami is extremely long as it makes its way to the coast, its amplitudes are only one to two feet. A ship rarely registers a tsunami passing beneath its hull. As the tsunami approaches the shoreline, though, it slows due to friction against the shallow oceanic floor. The wavelength decreases and the energy of the wave must redistribute, causing the tsunami to grow in height. This is where the tsunami is similar to a regular ocean wave. Both reach their greatest height just at the coastline, though only the most massive tsunamis break. Most resemble a large and fast surge, hence the term “tidal wave.”

C         Because of wide-ranging coastal shapes and differing seafloor and shoreline configurations throughout the world, the effects of tsunamis have varied greatly as they have made land. Areas that lie beside deep and open water tend to experience the tsunami in its steepest form, as the space allows the shaping of the wave into a very high crest. Often, the first indication of an impending tsunami is the receding of the water at the shoreline. This is the trough, or bottom, of the first tsunami wave, drastically pulling back the sea and exposing large areas normally submerged in water. Unsuspecting inhabitants may have their curiosity piqued by the bare seafloor and venture into this most dangerous zone. Only a few minutes later, the crest of the first wave will bear down, either breaking or sweeping in a fast tidal current. People and objects are quickly pulled into the wave. The process repeats. Most tsunamis consist of three or four massive waves that occur about fifteen minutes apart, though some can last for hours. The intensity of the impulse event and the topography of the coastline are the biggest factors regarding how large each tsunami will be, and how destructive. A tsunami may reach several hundred meters inland and is capable of crushing homes.

D         Though tidal waves have caused devastation the world over, throughout history, shorelines on the Pacific Ocean have been the most affected by tsunamis. This is due to much volcanic and seismic activity on that ocean’s floor. Elsewhere in the world, ancient civilizations such as the Minoan are believed to have suffered a sharp population decline as the result of a major tsunami. Tsunami destruction has been documented regularly through olden and contemporary times. With intense development and settlement at the world’s coastlines, one tsunami can kill many thousands of people. A tsunami in 1946 destroyed the city of Hilo, Hawaii, and scientists began to take serious steps toward an effective system of seismic wave prediction.

E          Today, international geographic societies work in conjunction with meteorological agencies to forecast possible conditions that could lead to a tsunami. For example, if seismic instruments register a high-magnitude earthquake in the Pacific, meteorologists closely monitor any drastic changes in sea level and movement.  All relevant data to is scrutinized, such as the depth and topography of the ocean floor, in order to estimate the tsunami’s path and magnitude. Time is paramount when tsunami warnings are issued and coastal communities must quickly evacuate.