How Tsunamis Work

The most common causes of tsunamis are underwater earthquakes. A tsunami is not a single wave, but a series that behave much like the waves rippling out from a stone dropped in a pond. Each wave can last five to 15 minutes, and the danger can last for hours after the initial wave arrives. “Tsunami waves heights cannot be predicted and the first wave may not be the largest,” according to NOAA statement.

Tsunami Infographic from Erica Edwards on Vimeo.

Tsunamis can be generated when chunks of the planet’s crust separate under the seafloor, causing an earthquake. Here’s what happens: One slab of lifting crust essentially rapidly acts as a giant paddle, transferring its energy to the water. Tsunamis can also be caused by volcanic eruptions, underwater detonations and even landslides.

Prediksi Gempa, Akuratkah ?

Gempa susulan yang terus terjadi di Jepang (Google Earth/USGS)

Gempa yang mengguncang Jepang (11/03/11) yang berkekuatan hingga 9 SR dan kemudian diiringi dengan hempasan gelombang tsunami yang meluluhlantakkan sebagian pesisir timur Jepang telah membuat masyarakat dunia kembali berduka. Bencana besar ini telah memakan banyak korban dan  tentunya menimbulkan kerugian yang tidak sedikit jumlahnya.

TSUNAMIS : Killer Waves

Tsunami in Sendai, Japan (12/03/11)

A tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 100 feet (30.5 meters), onto land. These walls of water can cause widespread destruction when they crash ashore.

These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries. When the ocean floor at a plate boundary rises or falls suddenly it displaces the water above it and launches the rolling waves that will become a tsunami.

Most tsunamis, about 80 percent, happen within the Pacific Ocean’s “Ring of Fire,” a geologically active area where tectonic shifts make volcanoes and earthquakes common.

Tsunamis may also be caused by underwater landslides or volcanic eruptions. They may even be launched, as they frequently were in Earth’s ancient past, by the impact of a large meteorite plunging into an ocean.

Epicenter of Japan Earthquake (12/03/11)

Tsunamis race across the sea at up to 500 miles (805 kilometers) an hour—about as fast as a jet airplane. At that pace they can cross the entire expanse of the Pacific Ocean in less than a day. And their long wavelengths mean they lose very little energy along the way.

In deep ocean, tsunami waves may appear only a foot or so high. But as they approach shoreline and enter shallower water they slow down and begin to grow in energy and height. The tops of the waves move faster than their bottoms do, which causes them to rise precipitously.

A tsunami’s trough, the low point beneath the wave’s crest, often reaches shore first. When it does, it produces a vacuum effect that sucks coastal water seaward and exposes harbor and sea floors. This retreating of sea water is an important warning sign of a tsunami, because the wave’s crest and its enormous volume of water typically hit shore five minutes or so later. Recognizing this phenomenon can save lives.

A tsunami is usually composed of a series of waves, called a wave train, so its destructive force may be compounded as successive waves reach shore. People experiencing a tsunami should remember that the danger may not have passed with the first wave and should await official word that it is safe to return to vulnerable locations.

Some tsunamis do not appear on shore as massive breaking waves but instead resemble a quickly surging tide that inundates coastal areas.

The best defense against any tsunami is early warning that allows people to seek higher ground. The Pacific Tsunami Warning System, a coalition of 26 nations headquartered in Hawaii, maintains a web of seismic equipment and water level gauges to identify tsunamis at sea. Similar systems are proposed to protect coastal areas worldwide.

Published By : National Geographic

image by Photograph by Deshakalyan Chowdhury/AFP/Getty Images