Describe The Characteristics And Explain The Causes
Describe the characteristics and explain the causes, of tsunamis. (8 marks)
A Tsunami is a large and potentially destructive sea wave often produced by a submarine earthquake, subsidence or an underwater volcanic eruption. They occur when a large volume of water is displaced in the ocean.
The characteristics of tsunamis differ slightly from normal sea waves. For one, they often have extremely long wave lengths, in deep water an initial wavelength can be up to 100km. Their amplitude contrasts with the length and it is often nearly undetectable, especially in open ocean. When they are first triggered they have been recorded to travel at speeds of up to 600kmph. Once tsunamis reach the shore they first appear as a rapidly receding shore line. When they reach shallow water they slow down, increase rapidly in height and decrease in wave length. Friction and turbulence slow the wave even more. They will continue to travel until all energy has completely dissipated. Often this doesn’t happen until several hundred feet inland, the flow back can also be extremely destructive. Tsunamis also pose one extra threat, they will sometimes last several hours with the first wave being followed by a chain of waves.
The main cause of tsunamis are submarine earthquakes. These are most common at subduction zones. Friction between subducting plates causes a build-up of pressure, eventually this pressure is released causing an earthquake. These submarine earthquakes can displace huge volumes of water. On the 26th December 2004 at the Indian plate/ Burma plate subduction zone, lots of pressure was suddenly released north-west of the coast of Sumatra, resulting in a megathrust earthquake of 9.1 on the Richter scale. A huge volume of water was displaced producing a series of tsunamis which hit 14 countries bordering the Indian Ocean.
The other two causes are less frequent. Subsidence occurs when there is a downwards driving force such as gravity acting upon sea floor material. This
A Tsunami is a large and potentially destructive sea wave often produced by a submarine earthquake, subsidence or an underwater volcanic eruption. They occur when a large volume of water is displaced in the ocean.
The characteristics of tsunamis differ slightly from normal sea waves. For one, they often have extremely long wave lengths, in deep water an initial wavelength can be up to 100km. Their amplitude contrasts with the length and it is often nearly undetectable, especially in open ocean. When they are first triggered they have been recorded to travel at speeds of up to 600kmph. Once tsunamis reach the shore they first appear as a rapidly receding shore line. When they reach shallow water they slow down, increase rapidly in height and decrease in wave length. Friction and turbulence slow the wave even more. They will continue to travel until all energy has completely dissipated. Often this doesn’t happen until several hundred feet inland, the flow back can also be extremely destructive. Tsunamis also pose one extra threat, they will sometimes last several hours with the first wave being followed by a chain of waves.
The main cause of tsunamis are submarine earthquakes. These are most common at subduction zones. Friction between subducting plates causes a build-up of pressure, eventually this pressure is released causing an earthquake. These submarine earthquakes can displace huge volumes of water. On the 26th December 2004 at the Indian plate/ Burma plate subduction zone, lots of pressure was suddenly released north-west of the coast of Sumatra, resulting in a megathrust earthquake of 9.1 on the Richter scale. A huge volume of water was displaced producing a series of tsunamis which hit 14 countries bordering the Indian Ocean.
The other two causes are less frequent. Subsidence occurs when there is a downwards driving force such as gravity acting upon sea floor material. This