You might be too young to remember, but a devastating tsunami took place in 2004. It is known as the 2004 Indian Ocean earthquake and tsunami, and as the name suggests, the tsunami was triggered by a massive earthquake. Some of the tsunami waves were 30m high, and over 200,000 people were killed.
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Jetzt kostenlos anmeldenYou might be too young to remember, but a devastating tsunami took place in 2004. It is known as the 2004 Indian Ocean earthquake and tsunami, and as the name suggests, the tsunami was triggered by a massive earthquake. Some of the tsunami waves were 30m high, and over 200,000 people were killed.
But what exactly are tsunamis?
Tsunamis are a series of ocean waves caused by submarine earthquakes or volcanic eruptions. This means that they are secondary hazards. These tsunami waves travel through the ocean and can reach heights of over 30 metres on land.
Earthquakes at convergent plate margins cause most tsunamis. Because of the movement from the earthquake, the seabed is displaced vertically. This, in turn, displaces the water column above. The speed of a tsunami depends on the depth of the ocean. As it approaches shallow water, the tsunami slows down and increases in height, making it very dangerous.
Read our explanation on Earthquakes for more detail (we also mention the 2004 earthquake and tsunami there).
It’s not just earthquakes that cause tsunamis – landslides and volcanic activity are also culprits! Let’s see why.
Large landslides on marine margins can create tsunamis when their mass enters the ocean water or when water displaces behind and in front of an underwater landslide. Earthquakes often initiate landslides.
Here are the different ways volcanic activity can cause tsunamis:
The majority of tsunami sources are in the Pacific Basin where subduction zones exist.
There was a very recent (January 2022) undersea volcanic eruption that caused tsunami waves in Tonga in the South Pacific. There are tons of news articles about it if you’re interested.
Tsunamis causing damage near the source occur, on average, twice per year, whilst tsunamis that are greater and cause damage to distant shores occur approximately twice per decade. Smaller tsunamis occur almost every day with little effect.
The characteristics of tsunami waves differ from wind-generated waves in terms of their period and wavelength.
The period is the time between two consecutive waves. The wavelength is the distance between the two waves.
When a tsunami approaches the shore, its speed decreases (due to shallower water) and its height increases. At the shore, tsunamis can appear as rising and falling tides, breaking waves, or bores.
The impact of tsunamis is influenced by several factors, including the amplitude of the tsunami wave, how far the tsunami wave has travelled, the water column displacement, the duration and number of tsunami waves, the geological structure of the coast, when the tsunami occurs, the amount of development of the coastal area, the distance between the coast and the populated areas, and the quality of tsunami monitoring, forecasting, and warning technology.
The possible damages caused by tsunamis include death and injuries, destruction of and damage to infrastructure, destruction of and damage to boats and marine installations, fires that cause further damage, environmental pollution, and an outbreak of diseases. Small islands hit by tsunamis are often totally destroyed.
The impact of tsunamis can be reduced through effective forecasting and warning. For instance:
We won’t go into too much detail here as we already have a case study explanation on the Tohoku Earthquake and Tsunami. But let’s briefly look at some interesting facts on the 2004 Indian Ocean earthquake and tsunami mentioned at the beginning of this explanation:
The damages that a tsunami can do include death and injuries, destruction of and damage to infrastructure, destruction of and damage to boats and marine installations, fires, environmental pollution, and an outbreak of diseases.
Tsunamis are a series of ocean waves caused by submarine earthquakes or volcanic eruptions. This means that they are secondary hazards. These tsunami waves travel through the ocean and can reach heights of over 30 metres on land.
Tsunamis causing damage near the source occur on average twice per year, while tsunamis that are greater and cause damage to distant shores occur approximately twice per decade. Smaller tsunamis occur almost every day with little effect.
Tsunamis cannot be prevented, but the impact of tsunamis can be reduced through effective forecasting and warning.
What are tsunamis?
Tsunamis are a series of ocean waves caused by submarine earthquakes or volcanic eruptions. This means that they are secondary hazards. These waves can reach heights of over 30 metres on land.
What is the main cause of tsunamis?
Most tsunamis are caused by earthquakes at convergent plate margins. The sea bed is displaced vertically by the movement from the earthquake. This displaces the water in the ocean water column.
How often do tsunamis occur?
Tsunamis causing damage near the source occur, on average, twice per year, while tsunamis that are greater and cause damage to distant shores occur approximately twice per decade.
How can tsunamis be caused by landslides?
Tsunamis can be caused by large landslides on marine margins when their mass enters the water or when water displaces behind and in front of an underwater landslide. The landslides are often initiated by earthquakes.
How do tsunamis differ from wind-generated waves?
Tsunamis differ from wind-generated waves in terms of their period and wavelength. Wind-generated waves tend to have periods of five to 20 seconds and wavelengths of 100 to 200 metres. Meanwhile, tsunamis have periods between ten minutes and two hours and wavelengths greater than 500 kilometres.
What happens to tsunamis as they approach the shore?
As the tsunami approaches the shore, its speed decreases and it consequently increases in height. Tsunamis can form into rising and falling tides, breaking waves, or bores.
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