What I have here is a tank to demonstrate a tsunami. Over here we have the deep ocean and the continental shelf coming up to the coastline, and here is the sea level. Normal ocean waves are created by the wind and they happen on the top surface of the water. Tsunamis are quite different to normal ocean waves. They’re caused by a displacement of the water. Tsunami can occur from an earthquake, from a volcanic eruption, from a landslide or even from a meteor crashing into the ocean from outer space. In most cases the tsunami is created by the seafloor displacing the water from underneath. Here we can see how geological forces build up to finally finally caused an earthquake. The water is then displaced and the tsunami radiates in all directions across the ocean. In our case we’ll just displace the water from above. A tsunami in the open ocean would have a wavelength which is thousands of times greater than this. And as the tsunami travels along, the depth of the ocean gets shallower, but the wave builds and the front becomes steeper and crashes on the beach. Compared to the windblown waves that only reach a little way onto the beach, the tsunami wave can run a long way inland. Tsunamis are very dangerous. If you have a distant source if the tsunami happens a long way away, then the travel time before it reaches the coast can be as much as 12 to 15 hours in New Zealand. So you have time for an official warning. But if the tsunami happens very close to the coastline you could just have a few minutes to react. your warning will be the earthquake. If it is so strong you have trouble standing or walking or if it lasts longer than a minute, even if it doesn’t feel that strong. Either of these warnings is a trigger to evacuate. You need to go to high ground, or as far inland as you possibly can. If you are near the coast in New Zealand, you can find out where your local evacuation zones are from your council. Many communities now have designated zones and safe locations. After you have evacuated don’t come back until the official all clear is given. This is very important because the first wave may well not be the last or the biggest. And there may be several hours between each wave.