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  3. Q. What is a tsunami?

Q. What is a tsunami?

Tsunami QA

Answers to your Questions:

Q. How do tsunami happens?

A. Tsunamis are caused by sudden movement under the ocean.  These can be from an underwater volcanic eruption, and underwater landslide or an underwater earthquake.  


Q. Why is a tsunami called that?

A. ‘Tsunami’ is the Japanese word for ‘Harbour Wave’ and Japan has had many tsunamis in its history.


Q. How do we know a tsunami is coming?

A. For a local source tsunami, we will know a tsunami is coming due to the natural warning signs eg. A long (over one minute) or strong (hard to stand up in) is only sign of an earthquake.


Q. What does a tsunami look like?

A. It may look like a big surge of water, or in a really big tsunami, which are very rare, like a wall of water.


Q. How fast is a tsunami?

 A. A tsunami travels up to 1000km/hr an hour at deep sea, but slows to 30 km/hr as it hits land.  But with the force of the wave traveling 1000km/hour behind it!  The sea becoming shallower and the force of the water behind is why a tsunami wave gets higher as it approaches land, and in a really big tsunami can become like a wall of water.


Q. How many times does the wave come and go?

A. A tsunami is a series of waves, so you could get several waves coming minutes or hours apart from each other.


Q. Is tsunami underwater or just on the top?

A. In deep water the wave is only a metre or so high, but most of the energy from the wave is underwater, so there can be strong currents.


Q. Can tsunami come from more than one direction?

A. Tsunami travel away from the source of the tsunami in all directions.  However when they hit the East Coast, they are coming from the east – most likely from either the Hikurangi Trench, the Kermadec Trench, or Chile.


Q. How far inland can tsunami go?

A. That depends on how high the tsunami wave is and how high above sea level the land is.  If you are 35 metres (about 70 steps) above sea level or 2 kms (about 20 minutes walking) in land you should be safe, even if it was a very big tsunami.


Q. What three actions do you do in a tsunami?

A. See below: 

  1. Know the natural signs.  The earthquake itself, the sea retreating and the noise.
  2. Head to higher ground or inland by at least 2km
  3. Do NOT go sightseeing at the coast.  Do not return to the coast until the all clear from emergency crews.


Q. What’s the height of the biggest tsunami?

A. The largest recorded tsunami was in 1958 in Alaska.  An earthquake generated an enormous landslide which crashed into the ocean creating a wave that destroyed vegetation over 500 metres above sea level.

In New Zealand, the 1931 Hawke’s Bay earthquake triggered a landslip at Waikare which in turn caused a localised 15.3 metre tsunami.  At Napier there was a tsunami of about 3 metres.  Otherwise the largest recorded tsunami in NZ was in Gisborne in 1947 and it was 10 metres.


Q. Where will the tsunami stop?

A. A tsunami will stop when it runs out of energy.


Q. What happens to the sea animals in a tsunami?

A. Strong swimmers like sea lions, fish and dolphins often respond quickly to a tsunami and swim safely to deeper water.  Birds can be very vulnerable in a tsunami, especially if they are nesting near the coast.   The ecosystem after a tsunami can be altered due to soil being deposited into the sea as the waves recede, and saltwater being deposited onto the land as the waves come inland.  Sometimes this is bad for the animals, but sometimes it is good – dead and decaying material in the sea leads to a growth in plankton, which increases fish species, which in turn increases the dolphin population. Nature has a way of adapting and surviving natural events, but some ecosystems and animals may need extra care from people to help them recover.  


Q. Can boats go up and over a tsunami?

A. When they are in deep water yes – but if they are close to land and it is a large tsunami, they will probably be swept on to land with the force of the water.


Q. Later in life will we be able to stop tsunami?

A. No.  The best thing we can do is to be prepared and well educated on what we can do to look after ourselves and our families.


Q. How do tsunami cause landslides and earthquakes?

A. It’s really the other way round – tsunamis are created by the displacement of large amounts of water due to underwater landslides and earthquakes.  When a tsunami reaches land, the speed and force of the water can dislodge large amounts of soil, therefore creating landslides.