Tsunami
Ocean-wide waves from undersea events
What is it?
Tsunamis are series of long ocean waves from undersea earthquakes, landslides or volcanic activity. In deep water they are barely noticeable; near shore they slow, stack up and flood inland for many minutes per wave.
How we measure it
Active tsunami events within range from GDACS, with alert level from event magnitude and modelled coastal impact.
GDACS alert levels
- NoneNo eventNo active tsunami threat in range
- GreenInformationEvent logged; minimal coastal threat
- OrangeAdvisoryPossible dangerous currents/waves
- RedWarningDamaging coastal flooding expected
Within safe range
No active events means no current threat — but near the coast, natural warning signs matter more than any feed: strong shaking, sudden sea withdrawal, or a loud ocean roar.
Beyond the range
A tsunami warning means water can arrive within minutes to hours as repeated surges — the first wave is often not the largest, and dangerous waves can continue for many hours. Half a metre of fast-moving water sweeps people away; boats and debris become projectiles.
Precautions
- Strong coastal shaking = your warning: move immediately to high ground or inland.
- Do not wait for official sirens if you feel natural signs.
- Go on foot if roads jam; even 20–30 m elevation dramatically improves safety.
- Stay out of the water and off beaches until officials declare all-clear — hours later.
- Never go to the shore to watch a tsunami.