Around 80 percent of tsunamis happen within the Pacific Ocean's "Ring of Fire", which means New Zealand sits right in the firing line.
A tsunami is basically a series of ocean waves caused by an underwater earthquake, landslide or volcanic eruption.
We've seen the damage they can cause on land, but there's also a lot going on beneath the water we don't see.
A tsunami has three stages:
Once triggered, waves can spread in any direction and, incredibly, can travel up to 950 kilometres per hour.
The first wave is usually not the strongest, and it's not always a wave: a dangerous tsunami may also manifest itself as changing water currents.
Civil Defence says if you're near the coast, watch out for:
If any of these happen, immediately head to high ground or as far inland as you can.
If you find yourself in the water don't try and swim ashore. Instead, try to reach a floating object and allow the current to carry you.