Tsunami simulator
Choose a coastal city, set the wave height at the shore, and watch the water climb inland over real elevation data until the ground beats it.
Open the tsunami simulatorWhat this simulator does
Click a coastline. The simulator finds the city at that point, outlines its real administrative boundary and floods it with a wave of the height you set — anywhere from one metre to a deliberately absurd three hundred. The water spreads from the sea over real terrain, fills everything lower than its own level and loses height as it travels, so ridges and embankments stop it while low ground fills.
When it settles you get four numbers: people killed, area flooded, how far inland the water reached, and the deepest water standing over land. Hover anywhere on the flooded area to read the depth at that exact spot and the ground elevation underneath it.
The terrain is real, the physics is simple
Elevation comes from Mapbox Terrain-RGB tiles — a grid ranging from about 7 metres per cell for a small area to 30–80 metres for a whole city. City boundaries and population come from OpenStreetMap.
The water is deliberately crude: it floods any ground lower than its current level and loses one metre of height for every 250 metres it travels inland, standing in for friction against terrain, buildings and vegetation. A hill or a levee wider than one grid cell stops it for real; one narrower than a cell is invisible to the model.
The share of people killed rises with water depth and assumes nobody evacuated. That assumption alone makes the death tolls pessimistic for any coast with a working warning system, and roughly right for one without.
How big do tsunamis actually get?
Most destructive tsunamis arrive as 5 to 15 metres of water at the shore. The 2004 Indian Ocean tsunami reached about 30 metres in parts of Aceh and killed roughly 228,000 people across fourteen countries. The 2011 Tōhoku tsunami topped 40 metres at Miyako and overtopped sea walls that had been built for half that. The tallest wave ever measured was the 1958 Lituya Bay megatsunami in Alaska, where a landslide pushed water 524 metres up the opposite slope — but that was a narrow fjord, not an open coast.
Above roughly 50 metres on the slider you have left the historical record and entered the territory of asteroid impacts and collapsing volcanic flanks.
Scenarios worth trying
- 30 metres at Sendai — close to what arrived in 2011
- 30 metres at Banda Aceh — the 2004 Indian Ocean tsunami
- 15 metres at Lisbon — the wave that followed the 1755 earthquake
- 25 metres at New York — pure hypothetical, and instructive about how flat Manhattan is
Tsunami or sea level rise?
They flood the same streets and they are nothing alike. A tsunami is a pulse: it arrives, it drains, and the damage is violence — buildings knocked off foundations, debris moving at speed. Rising sea level is permanent: the water simply never leaves, and the damage is that a city stops being habitable. If you want the second one, the site has a separate sea level rise map that uses the same terrain data with different rules.
Questions
Are these numbers real?
The terrain, the city boundaries and the population are real data. The water physics is a simplification chosen so it can run in a browser in under a second. Read the results as orders of magnitude.
Why does the water stop before the hills?
Because it loses a metre of height every 250 metres inland. A 10-metre wave has spent itself after about 2.5 km even on perfectly flat ground, which is roughly how real tsunamis behave.
Why can't I put a tsunami on an inland city?
Because water has to come from somewhere. If the point you clicked has no connection to the sea, the simulator says so and offers the nearest coastal city instead.
Does the model include the earthquake that caused the wave?
No — the wave height is yours to set. If you want the shaking as well, run an earthquake separately on the same coast.
Further reading: The deadliest and biggest tsunamis in history
Open the tsunami simulator