A tsunami is a series of waves travelling across the ocean due to a sudden displacement of a large body of water. This displacement can be caused by events such as undersea earthquakes, undersea landslides, land sliding into the ocean, volcanic eruptions or even asteroid impact.
Over 80% of tsunami in the Pacific Ocean are thought to have been caused by undersea earthquakes. Australia is surrounded by 8,000 kilometres of active tectonic plate boundaries and most earthquakes and volcanic eruptions occur where these plates meet. These boundaries are called subduction zones.
Undersea landslides and land sliding into the sea may cause localised tsunami. Undersea landslides occur when a large amount of sediment is dislodged from the seafloor, displacing a water column and potentially generating tsunami. Land sliding into the sea, usually caused by an earthquake, may also cause destructive local tsunami.
Though less common, volcanic eruptions in or near the ocean have potential to cause tsunami. These occur in several ways:
An asteroid impact into the ocean could cause tsunami. Fortunately, this should be rare and there are no documented accounts of an asteroid having generated tsunami.