Tsunami

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What are tsunamis?

Tsunamis are waves caused by a sudden movement of the ocean surface. This movement is triggered by large disruptive forces including:

Earthquakes
Volcanic eruptions
Undersea landslides
Land or ice sliding into the ocean
Meteorite impact

(Geoscience Australia)

Tsunamis are different from wind-driven waves you may see at the beach.

Wind-generated waves are movements near the ocean’s surface and are influenced by tides.
- Tides are influenced by the gravity of the Earth, Moon and Sun
Tsunamis move water from the surface to the seafloor. Their speed is controlled by how deep the water is.
- Deeper water results in faster, flatter waves
- Shallower water slows tsunamis and increases their wave height

When tsunamis make landfall, they force water onto the shore. There are usually several waves. They often do not break in the same way as wind-generated waves and instead move inland as a fast-rising surge of water.

Why do tsunamis occur?

Tsunamis occur when other hazards disrupt and displace the ocean’s surface. They are generated when the ocean’s surface rapidly moves up and down.

Earthquakes create sudden upward and downward movement of the seabed, which can cause the ocean above to rise and fall
Landslides and meteorite impacts displace water, generating waves
Volcanoes can disrupt ocean height through landslides, pressure waves, pyroclastic flows (fast-moving volcanic gas and debris) and the collapse of a volcano’s crater

(Geoscience Australia)

Earthquakes are the most common cause of tsunamis, followed by volcanic eruptions. Because of this, almost 80% of the world’s tsunamis occur in the Pacific Ocean around the geologically active area known as ‘the Ring of Fire’ (NOAA).

When and where do tsunamis occur?

Tsunamis are recorded in Australia about once every two years (Bureau of Meteorology). Tsunamis generally pose low risk to Australia’s coastal communities. They often originate offshore and lose energy before reaching the coast. They predominantly affect the marine environment.

Australia’s southern coastline has a low risk of being impacted by a tsunami. Western Australia’s coastline has moderate risk due to its proximity to Indonesia which experiences more frequent earthquakes and volcanic activity.

Examples of tsunamis in Australia:

1977 Cape Leveque Tsunami that reached 6 metres above sea level as it travelled inland.  
1994 Onslow-Exmouth Tsunami that reached 300 metres inland  
The 1960 Earthquake in Chile also had ripple effects felt in Sydney and other harbours across the east coast of Australia.
The 2004 Indian Ocean tsunami caused strong currents and water level changes on the Western Australian coast.

What are the impacts of tsunamis?

Tsunamis are a serious hazard that can cause flooding, strong currents, coastal erosion and risks to life and infrastructure.

The most deadly and destructive tsunami in recorded history was the 2004 Indian Ocean tsunami.

Australia will most likely experience the effects of marine threat tsunami, which include dangerous rips, waves and strong currents. Land threat tsunami are rare but extremely hazardous and can cause inundation in low-lying coastal regions.

Tsunami impacts on maritime communities can include:

Damage to marinas, moorings, navigation aids, ports and offshore infrastructure
Debris can be washed into boats and ships
Coastal erosion and pollution of local waterways

Tsunami impacts on land-based, coastal communities can include:

Flooding and habitat loss
Loss of agricultural land through salt inundation
Structural and critical infrastructure damage
Loss of life and injury
Loss of access to basic services
Fires, transportation accidents, and hazardous material releases

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How do we manage tsunami risk?

While rare in Australia, tsunamis occur throughout our region and it’s important to know what they are and how to stay safe.

We can reduce tsunami risk by:

Using natural features to help reduce the impact of tsunami waves, such as mangroves and coastal dunes
Building or strengthening physical structures to protect people and places from tsunami waves, such as offshore breakwaters and sea walls
Making decisions about where people can live, build and develop so they are safer from tsunami waves

We can also reduce the impact of tsunamis by warning coastal communities early so people can take action, such as leaving the area or moving to higher ground.

To help with this, the Australian Government set up the Joint Australian Tsunami Warning Centre (JATWC) to watch for tsunami risks and issue warnings. JATWC operates 24 hours a day, 7 days a week. It monitors oceanic earthquakes, assesses the likelihood of tsunamis and issues warnings to potentially affected communities.

Tsunami warnings are shared with communities in a variety of ways, including:

On the Bureau of Meteorology’s tsunami warnings page
Via your state’s public hazard alert app
Via a telephone or text message
Through public address systems, community notices, doorknocking and more

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Prepare, plan and stay safe

Governments in tsunami-affected states and territories have resources to help you plan and prepare for tsunamis.

Northern Territory

Queensland

Western Australia

New South Wales

Tasmania

Victoria