Many disaster movies have portrayed giant earthquakes and the tsunami’s that follows as changing the world as we know it. Through the eyes of Hollywood directors we have been able to watch as a single monster wave washes away entire countries. At some point, many people have probably wonder just how realistic this could be.
A tsunami is a series of waves that are generated in an ocean or other body of water. They can happen as a result of earthquakes, landslides, volcanic eruptions or meteoric impact. The size of the tsunami is directly related to the size of the under water occurance.
Earthquakes occur when there is a shift in the tectonic plates. Tectonic plates are huge slabs of rock 50-650 feet (15-200 kilometers) thick that carry the earth’s continents and seas on underground access of m uch hotter and semi-solid material. Cracks in these plates are called fault lines. When these plates collide they cause the earth to shake.
Undersea earthquakes are the same as any other except they take place under water. They normally occur at the boundaries between the earths tectonic plates. In these cases where the plates collide they can elevate, lower or raise major sections of the ocean floor. This causes the water above them to be moved up or down. The waves of the tsunami are formed as this displaced water tries to find a stable position.
There are four stages to the formation of a tsunami as a result of an earthquake:
Stage 1- Initiation
-The earthquake occurs, displacing the water.
Stage 2- Split
-Within several minutes of the earthquake, the tsunami is formed and then splits.
– Following this split, one travels to the deep ocean. This is known as a distant tsunami. The other travels toward the coast. This one is known as a local tsunami.
– The height of these two waves are approximately one-half of the original wave.
– The distant wave travels faster than the local wave.
Stage 3- Amplification
– As the local tsunami travels inland the height of the wave increases and the length decreases.
Stage 4- Runup
– Runup is the measurement of the height of the water onshore that is observed above a reference at sea level.
– The wave normally doesn’t come in like a giant breaking wave but like a very strong, very fast tide.
Sometimes inaccurately called tidal waves, tsunami have little to do with tides and have few similarities to regular waves. Normal waves are caused by offshore winds and are much smaller in comparison.
Approximately 80% of tsunamis caused by earthquakes occur in the Pacific Ocean. However, they can happen wherever there is a large body of water including inland lakes. Regardless of their location they can cause a great amount of destruction when they hit the coastline.
In the open ocean, these monster waves can be more than 62 miles (100 km) across but are only about one mile (1.6 km) high. They can travelas fast as 435 mph (700 kmh) as they make their journey inland.
As the waves get closer to the shore they slow in speed and grow in height, potentially up to and possibley over 65 ft (20 m). Just minutes before they hit the shore, the water near the shore may recede, showing the ocean floor that is normally covered.
The first wave may not be the lasrgest. This first wave may be followed by others every 10-60 minutes. Unlike normal waves, they do not curl and break. Moving much faster than anyone can run, the danger can last for several hours after the first wave.
Tsunamis that form as a result of earthquakes can be devastating. They can cause flooding for hundreds of meters inland. They move with such force they can crush buildings and homes. They may not actually be exactly as portrayed in movies, but they are devastating none the less.
