Earthquakes can cause a tsunami that wreaks devastation to coastal regions, but how do they affect a ship? To find out, let’s look at what a tsunami is and how they travel across oceans.
What is a tsunami?
A tsunami is created by activity such as earthquakes or major landslides displacing a large volume of water very quickly. This sudden movement of such a large amount of water creates a series of powerful waves. While the waves might not cause much damage locally, the energy they carry can have far-reaching consequences.
When travelling in the open ocean, the tsunami waves are virtually harmless, and can be difficult to detect. The deep, wide open water allows the waves to spread out, and they may only raise the surface of the ocean by 30 centimetres (1 foot). However, in the ocean the waves can travel at great speeds, up to 800 kilometres (500 miles) per hour. At this speed, they can cross the entire ocean in 12 hours, demonstrating the enormous power behind them.
How does a tsunami affect a cruise ship?
For a ship, being at sea when a tsunami is predicted is the best choice. When a warning is issued, it is common for port facilities to close down and for every ship to depart as soon as possible.
As the tsunami reaches coastal areas, it’s potential for damage increases. The shallower water causes the waves to slow down, and gather closer together. This can raise the level of the ocean many metres, and sweep much further inland than may be expected. In the past, the waves have been known to pick up cars, boats or even boulders and carry them up to 300 metres inland.
For a ship that is caught in port when a tsunami hits, the results can be devastating. The rapid rise in water level can cause mooring lines to break, leaving the ship free to move around the harbour. Strong currents as the water flows in and out of the harbour can smash a ship against the dock or other vessels. Unless there are special circumstances, it is unlikely a harbour authority would allow a ship to remain in port if a tsunami warning has been issued.
As well as the immediate danger to the ship, the surrounding port facilities may be damaged. This can include gangways, buildings or the dock itself. Following the 2011 earthquake in Japan, the port we were due to visit in Hawaii was closed for several hours while an extensive assessment was carried out. Only when the harbour master was satisfied it was safe were ships allowed to return to harbour.
How do cruise ships stay safe?
Thankfully, any event that may cause a tsunami will be closely monitored. In the Pacific region, 26 nations have come together to form the Tsunami Warning System. They work together to monitor seismological and tidal stations across the region, and generate warnings when appropriate. They’re able to make predictions of when and where a tsunami may arrive, however like any forecast or prediction they may not be 100% accurate.
A network of buoys across the Pacific Ocean give updates on the position of the waves. This information allows better predictions regarding when, where and how big the tsunami may be. Each country is responsible for distributing the updates appropriately, and for ships we can receive each update through the same channels as weather forecasts or navigation warnings.
There will always be times when a prediction isn’t as accurate as we’d like, or when we’re caught by surprise by an event close by. But generally the communication regarding earthquakes and their potential to generate a tsunami is accurate and in plenty of time to allow ships in the affected area to respond.
If there is one place to be when a tsunami hits, it’s on a cruise ship in the middle of the ocean!
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