1) The document discusses tsunamis, massive waves caused by seismic activity under the sea. Tsunamis are often mistakenly called tidal waves but have different causes.
2) Tsunamis are very dangerous due to their immense energy and speed, demolishing coastal communities. The 2004 Indian Ocean tsunami in Aceh was the worst, killing over 300,000 people.
3) Tsunamis are generated when earthquakes or landslides under water displace the sea floor, disrupting the equilibrium of the water above. Large volcanic eruptions and meteor impacts can also cause tsunamis.