Explain how tsunamis form and evaluate strategies to predict and mitigate Earth hazards

What this dot point is asking

SCSA wants you to explain tsunami formation and evaluate how hazards are predicted and managed. A strong answer separates the hazard from the risk and weighs how effective each strategy is.

How tsunamis form

A tsunami forms when a large volume of seawater is suddenly displaced. The most common cause is a submarine earthquake at a subduction zone, where the seafloor is thrust upward or dropped, lifting or lowering the water above it. Tsunamis can also be triggered by submarine landslides, volcanic eruptions and, rarely, asteroid impacts.

In the open ocean a tsunami has a very long wavelength but a small height, so ships may not notice it, and it travels fast, comparable to a jet aircraft. As it approaches shallow coastal water it slows, the energy compresses, and the wave height grows dramatically. The water often withdraws from the shore first, a natural warning sign, before the wave surges inland.

Hazard, risk and vulnerability

These terms are distinct and examiners test them.

Risk depends not only on the hazard but on where people live, how buildings are constructed and how prepared communities are. A large earthquake under an unpopulated area carries low risk; a moderate one beneath a dense, unprepared city carries high risk.

Prediction and warning

Some hazards can be forecast better than others.

• Tsunamis: seafloor pressure sensors and seismometers detect the earthquakes and waves that generate them, feeding warning centres such as those in the Pacific and Indian Oceans. Warnings give coastal communities time to evacuate to high ground.
• Volcanoes: monitoring ground deformation, gas emissions and earthquake swarms can signal an impending eruption, allowing evacuation.
• Earthquakes: the exact timing cannot yet be predicted, but seismic hazard maps identify zones of higher long-term risk, and early-warning systems can give seconds of notice once rupture begins.

After the 2004 Indian Ocean tsunami, an Indian Ocean warning system was established, and Australia operates a national tsunami warning capability jointly run by the Bureau of Meteorology and Geoscience Australia.

Mitigation strategies

Mitigation reduces impact through planning and engineering.

• Land-use planning: avoiding building in inundation zones and on unstable slopes.
• Engineering: earthquake-resistant buildings, sea walls and elevated structures.
• Education and drills: teaching people to recognise warning signs and evacuate.
• Emergency planning: evacuation routes, shelters and response coordination.

Evaluating these shows trade-offs: warning systems save lives but need maintenance and public response; engineered defences are costly and can fail against extreme events; education is cheap and effective but relies on people acting.