Monday, 6 October 2008

What controls the speed of a tsunami wave?

This our latest Earthlearningidea - click here. This activity investigates the relationship between the depth of water in a tank and the velocity of a water wave generated by lifting and then dropping one end of the tank.
Please try this activity with your pupils and let us know their results. What do they think affects the speed at which a tsunami travels? Will the wave travel faster or slower in shallow water than it does in deep water? Write your comments on this blog.

1 comment:

Jan Yo Da said...

The spreading of tsunami wave involves both large and micro scales:(1)the potential energy,given by vertical displacement of extensive water mass,be converted into kinetic energy to drive tsunami wave.(2)Water particles as energy-transfer medium move in circular paths.
The above-mentioned phenomena is incomprehensible to students,but this Earthlearningidea provides a graphic link between the theory of wave motion and potentially lethal natural phenomena to reduce the cognitive load for learning.


(1)Provide animation in form of static key frames, for example, BBC NEWS Special Reports:The tsunami disaster explained(, for attention cueing as a means to enhance learning.Despite well-control experiment, the motion of wave is still too fast to observe.

(2)Provide demonstration to differentiate between 'wave' and 'current'.In my experience, to recognize what difference between wave and current is difficult for the 10th grade student in Taiwan.
For example:
When first wave crest or trough reach the one end of the tank, the leaf just shifts slightly in horizontal position.In profile of view, the leaf vibrates with water vertically.Thus,student can construct prior knowledge for follow-up Earthlearningidea.

(3)Investigating the relationship between the slope of tank and wave height.When a tsunami arrives in shallowing water, the base of the wave is slowed down by friction.The wave crest overtakes the base and may then pile up to form a 'wall of water',which crashes down on the beach.The wall of water is one of the threatening dangers.
Ask students to reason what things might affect the wave height at which a tsunami travels.We can provide some example, such as the wall of water is over 10m height in Sri Lanka, but less than 2m height in Maldives, they are also noted in the disastrous tsunami wave of 26th December 2004 in the Indian Ocean.

Jan Yo Da; National Taiwan Normal University, Department of Earth Sciences.