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Tsunamis

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Geography

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.

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.

What is the main cause of tsunamis?

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).

What are other causes of tsunamis?

Its not just earthquakes that cause tsunamis – landslides and volcanic activity are also culprits! Lets see why.

Tsunamis caused by landslides

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.

Tsunamis caused by volcanic activity

Here are the different ways volcanic activity can cause tsunamis:

  • Underwater volcanic explosions and shock waves can cause tsunamis when the energy travels through the ocean.
  • Pyroclastic flows (mixtures of hot volcanic rock, ash, and gas), lahars, and other parts of volcanoes can cause tsunamis when their mass enters and moves the water.
  • If the roof of an empty magma chamber collapses, water rushes in and displaces the water column of the sea. This then gives rise to a tsunami wave.

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 youre interested.

How often do tsunamis occur?

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.

What are the characteristics of tsunamis?

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.

  • Wind-generated waves tend to have periods of five to 20 seconds and wavelengths of 100 to 200m.
  • Tsunami waves have periods between ten minutes to two hours and wavelengths between 150 to 1000km. Due to their large wavelength, tsunamis lose very little energy as they propagate.

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.

What influences the impact of tsunamis?

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.

What are the possible damages caused by tsunamis?

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.

How do we reduce the impact of tsunamis?

The impact of tsunamis can be reduced through effective forecasting and warning. For instance:

  • The National Tsunami Warning Center in Palmer, Alaska, monitors earthquake activity to provide forecasts on possible tsunamis at the coastlines. Additionally, sea levels are monitored using shallow and deep water instruments to determine whether a tsunami is happening.
  • Tsunami warning systems have been placed in both the Pacific and Indian Oceans. These systems use seismic sensors to detect any underwater earthquakes. They also use a system known as DART (Deep-ocean Assessment and Reporting of Tsunami), which uses seabed sensors and surface buoys to monitor changes in sea level and pressure.

Tsunami case study

We wont go into too much detail here as we already have a case study explanation on the Tohoku Earthquake and Tsunami. But lets briefly look at some interesting facts on the 2004 Indian Ocean earthquake and tsunami mentioned at the beginning of this explanation:

  • The earthquake was an undersea megathrust earthquake measuring 9.1 moment magnitude.
  • The earthquake caused a series of huge tsunami waves that caused massive destruction and loss of life. It is one of the deadliest natural disasters to occur in recent years.
  • Countries affected included Indonesia, Sri Lanka, India, and Thailand.
  • Donations for humanitarian relief amounted to over £10 billion.

Tsunamis 2004 Indian Ocean tsunami affecting Thailand StudySmarterThe 2004 Indian Ocean tsunami, Thailand, David Rydevik, commons.wikimedia.org

Tsunamis - Key takeaways

  • Tsunamis are a series of ocean waves caused by submarine earthquakes or volcanic eruptions.
  • Most tsunamis are caused by earthquakes at convergent plate margins. The seabed is displaced vertically by the movement from the earthquake. This, in turn, displaces the water column above. Landslides and volcanic activity can also cause tsunamis.
  • The characteristics of tsunami waves differ from wind-generated waves in terms of their period and wavelength.
  • The impact of tsunamis can be reduced through effective forecasting and warning.

Tsunamis

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.

Final Tsunamis Quiz

Question

What are tsunamis?

Show answer

Answer

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.

Show question

Question

What is the main cause of tsunamis?

Show answer

Answer

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.

Show question

Question

How often do tsunamis occur? 


Show answer

Answer

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.

Show question

Question

How can tsunamis be caused by landslides?


Show answer

Answer

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.

Show question

Question

How can tsunamis be caused by volcanic activity?


Show answer

Answer

Tsunamis can be caused by underwater volcanic explosions and shock waves as the energy travels through the water. Pyroclastic flows (mixtures of hot volcanic rock, ash, and gas), lahars, and other parts of volcanoes can also cause tsunamis when their mass enters and displaces the water.

Show question

Question

How do tsunamis differ from wind-generated waves?


Show answer

Answer

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. 

Show question

Question

What happens to tsunamis as they approach the shore?


Show answer

Answer

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.

Show question

Question

What influences the impacts of a tsunami?

Show answer

Answer

The impacts of a tsunami are influenced by the amplitude of the tsunami wave, how far the tsunami 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.

Show question

Question

What are the possible damages caused by tsunamis? 


Show answer

Answer

The possible damages caused by tsunamis are death and injuries, destruction of and damage to infrastructure, destruction of and damage to boats and marine installations, fires, environmental pollution, and disease outbreaks.

Show question

Question

What are some methods to reduce the impact of tsunamis?


Show answer

Answer

The impact of tsunamis can be reduced through effective forecasting and warning. For instance, the National Tsunami Warning Center in Palmer, Alaska, monitors earthquake activity to provide forecasts for possible tsunamis at the coastlines. Additionally, sea levels are monitored using shallow and deep water instruments to determine whether a tsunami is occurring.

Show question

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