• Question: How do Tsunami's come?

    Asked by bobbysna to Alan, Caspar, Diana, Murray, Sarah on 21 Mar 2011 in Categories: .
    • Photo: Murray Collins

      Murray Collins answered on 17 Mar 2011:

      Tsunamis are caused by the displacement of large amounts of water in the sea. This might happen if there is a very very large landslide, for example the collapse of a volcanic island in the sea, as long as enough water was displaced. The Tsunami in Japan was caused by an earthquake under the sea, where tectonic plates are rubbing against each other under enormous pressure (at the joins between the different parts of the earth’s surface). Suddenly the force is too much for the plates to stay in the same position, and there is a very large movement between the plates and one gets forced upwards. This is what shakes the ground during an earthquake. In the sea this means the water above is forced upwards. This displaced water then rushes away from that point like a huge ripple in a pond. The wave that this creates in the sea is very very long (instead of normal sea waves which are quite short). This means that when that water reaches the land, it doesn’t just break like a normal short wave. Instead the water piles up and up so that the wave becomes very high, and then floods onto the land. Because the wave is very long the water will keep on coming and can flood the land even several kilometers from the sea.

      By understanding these natural hazards we can create warning systems to let people know tsunamis are coming. However unfortunately the tsunami in Japan arrived at the coast very soon after the earthquake, meaning that there wasn’t enough time to let people know what was happening, which is very sad.

    • Photo: Alan Winfield

      Alan Winfield answered on 20 Mar 2011:

      Hi Bobby. My understanding is that tsunamis are caused by earthquakes or volcanic eruptions on the seabed under the ocean. There are two really nice illustrations on this webpage (about half way down) showing the difference between tidal waves and tsunami waves http://www.weatherwizkids.com/weather-earthquake.htm This shows why tsunamis are so dangerous – as we saw a week ago with such tragic consequences in northern Japan.

      Hope this helps to answer your question:-)

    • Photo: Caspar Addyman

      Caspar Addyman answered on 21 Mar 2011:

      Tsunami are almost always caused by earthquakes but they can sometimes be the result of volcanos. A tsunami is basically a giant ripple caused by the massive release of energy when the earthquake hits. or if a volcano causes a massive landslide. I think that if the earthquake is under the sea (like in japan) the tsunami will be bigger.

      In storms and hurricanes far out at sea you can get very big waves even without an earthquake or a volcano… waves of upto 30 metres high (over three times the height of a house ) are not uncommon.. and there isn’t just one wave there is a whole storms worth.. These can sometimes reach the coast but quite often the fact there are lots of waves causes them to cancel each other out a bit.

      If you search on youtube for giantwaves you will see some very scary pictures of waves bigger than supertankers..

    • Photo: Sarah Thomas

      Sarah Thomas answered on 21 Mar 2011:

      A tsunami is a tidal wave, and they are usually caused by earthquakes, volcanic eruptions or underwater explosions. Tsunami can be generated when the sea floor is abruptly deformed and the overlying water is displaced upwards. The wave formed is then sustained by gravity (it’s not anything to do with the tide). Tsunamis have a small wave height and a very long wavelength, which is why they generally pass unnoticed at sea, forming only a slight swell above the normal sea surface. They grow in height when they reach shallower water.