What is a tsunami?
A tsunami is a series of ocean waves, often called a wave train. These waves are produced by the vertical displacement of a large volume of water.
Tsunamis are a type of wave known as "long waves," and their speed is related to the ocean depth. In deep water, they can travel quickly at around 200 metres per second. While they move fast in the open ocean, they may have an amplitude (height) of only a metre or so. This makes them barely noticeable in open water.
However, as they reach shallow water, their speed reduces and the wave height increases. This is the reason tsunamis can be so destructive when they reach the coast.
In extreme cases, they can attain a height of 10 to 30 metres or more. This happens particularly where the waves become confined and amplified by the local coastal topography.
Lituya Bay in Alaska is known for being prone to large tsunamis due to the shape of the bay and the region's vulnerability to earthquakes. The run-up from a 1958 tsunami in Lituya Bay was around 520 metres; this is considered the largest tsunami in modern times.
What causes tsunamis?
Several different processes can cause this displacement of water including:
- Undersea earthquakes
- Submarine landslides
- Terrestrial landslides
- Volcanic eruptions
- Asteroid and comet impacts
- Man-made explosions
- Ice calving (the release of ice chunks from glaciers into the ocean)
Additionally, a form of tsunami known as a "meteotsunami" can result from a sudden change in air pressure, which is often caused by storm events.
Impact of Tsunamis
Tsunamis can cause huge loss of life due to drowning. They also cause crush or impact injuries arising from the debris carried by the water.
Even after the tsunami has abated, public health issues often arise. A lack of sanitation and contaminated food and water supplies means that disease-related deaths and illness are common in the aftermath.
Impacts from a tsunami can be widespread, affecting large swathes of coastline and stretching inland for hundreds of metres. The destruction of infrastructure poses a significant hazard. This includes the destruction of primary care services, such as hospitals and fire stations. When combined with the submersion, destruction, or blocking of transport networks, this damage can severely hamper disaster relief efforts.
Over 227,000 lives were lost in the Sumatra Boxing Day Tsunami of 2004. This tragedy galvanised global efforts to understand tsunami risk and to establish warning and detection networks to mitigate the impact of future events.
How is NOC's work transforming tsunami preparedness?
The NOC's efforts in sensor deployment, combined with geological studies, seismic studies, and fibre-sensing technologies, are transforming how we observe and understand tsunamis. Ultimately, this work helps us prepare for these events and protect vulnerable coastal communities worldwide.
How does NOC share tsunami knowledge?
NOC scientists and engineers have delivered training in the UK and overseas regarding the installation and maintenance of tsunami monitoring tide gauges. We also provide training on how to use that data for tsunami monitoring and detection. NOC scientists also provide advice to UK policymakers on tsunami risk.
NOC commemorates World Tsunami Awareness Day annually on 5th November. We use this day for activities that promote tsunami awareness and resilience among the general public.
Publications
Deep-sea observations and modeling of the 2004 Sumatra tsunami in Drake Passage
Rabinovich, Alexander B.; Woodworth, Philip L. 
ORCID: https://orcid.org/0000-0002-6681-239X; Titov, Vasily V..
2011
Deep-sea observations and modeling of the 2004 Sumatra tsunami in Drake Passage.
Geophysical Research Letters, 36, L16604.
5, pp.
10.1029/2011GL048305
2011
Article
Large, deepwater slope failures: Implications for landslide-generated tsunamis
Interested in learning more?
Explore our resources on volcanoes and discover how volcanic activity influences tsunamis, climate, and Earth systems.