What makes tsunami happen

Volcanic eruptions Tsunami initiated by volcanic eruptions are less common. They occur in several ways: destructive collapse of coastal, island and underwater volcanoes which result in massive landslides pyroclastic flows, which are dense mixtures of hot blocks, pumice, ash and gas, plunging down volcanic slopes into the ocean and pushing water outwards a caldera volcano collapsing after an eruption causing overlying water to drop suddenly.

Share this. Watch the videos. Most tsunamis are caused by earthquakes generated in a subduction zone , an area where an oceanic plate is being forced down into the mantle by plate tectonic forces.

The friction between the subducting plate and the overriding plate is enormous. This friction prevents a slow and steady rate of subduction and instead the two plates become "stuck.

As the stuck plate continues to descend into the mantle, the motion causes a slow distortion of the overriding plate. The result is an accumulation of energy very similar to the energy stored in a compressed spring.

Energy can accumulate in the overriding plate over a long period of time - decades or even centuries. Energy accumulates in the overriding plate until it exceeds the frictional forces between the two stuck plates. When this happens, the overriding plate snaps back into an unrestrained position. This sudden motion is the cause of the tsunami - because it gives an enormous shove to the overlying water.

At the same time, inland areas of the overriding plate are suddenly lowered. The moving wave begins travelling out from where the earthquake has occurred. Some of the water travels out and across the ocean basin, and at the same time, water rushes landward to flood the recently lowered shoreline. Landslides, Volcanic Eruptions, MeteoritesSubmarine landslides, which often occur during a large earthquake, can create a tsunami. During a submarine landslide, the equilibrium sea level is altered by sediment moving along the sea floor.

Gravitational forces then propagate the tsunami given the initial perturbation of the sea level. Similarly, a violent marine volcanic eruption can create an impulsive force that displaces the water column and generates a tsunami. Above water landslides and space borne objects can disturb the water from above the surface. The falling debris displaces the water from its equilibrium position and produces a tsunami.

In any case, the shoaling effect can greatly increase open ocean wave heights upon reaching the coast, with some tsunami reaching an onshore height more than ten metres above sea level.

Such extreme inundation is more likely to occur nearer to the tsunami generation location where oceanic wave heights are larger , and at locations where the coastline shape is particularly favourable to amplification of the tsunami.

Most tsunami do not cause such extreme coastal inundation and the effect of small events may not be noticeable to without careful analysis of tide gauge measurements. Most tsunami are caused by large earthquakes on the sea floor when slabs of rock move past each other suddenly, causing the overlying water to move. The resulting waves move away from the source of the earthquake event. Landslides can happen on the seafloor, just like on land.

Areas of the seafloor that are steep and loaded with sediment, such as the edge of the continental slope, are more prone to undersea landslides. When an undersea landslide occurs perhaps after a nearby earthquake a large mass of sand, mud and gravel can move down the slope. This movement will draw the water down and may cause a tsunami that will travel across the ocean. There is evidence that the Australian coast may have experienced large tsunami during the past few thousand years.

This evidence is revealed through anomalous sedimentary deposits such as those containing shell or coral or other geomorphic features Dominey Howes, ; Goff and Chauge-Goff, More recently, tsunami continue to be recorded in Australia with most presenting little threat to coastal communities. The significant tsunamis recorded in recent times have all been recorded at tide gauges around the country with some causing damage in the marine environment.

The tsunami hazard faced by Australia ranges from relatively low along the southern coasts of Australia to moderate along the west coast of Western Australia. This area is more susceptible because of its proximity to large subduction zones along the south-coast of Indonesia, which is a region of significant earthquake and volcanic activity.

Several significant tsunami have impacted Australia's north west coast region. The largest run-up measured as elevation about sea level was recorded as 7. The largest reported offshore wave height was six metres near Cape Leveque from the August Sunda tsunami.

Dominey-Howes D.