The global record · and the wave-watchers
A wave in the deep ocean, and the world watching for it.
On 26 December 2004 a wave born off Sumatra crossed an entire ocean and took more
than 227,000 lives — many with no warning at all. In the years since, people built a way to see
these waves coming: seismographs that feel the quake, buoys that measure the wave passing overhead
in any weather, and satellites that map the sea surface from orbit. This page holds the real record
— every deadly tsunami NOAA has logged — and shows how the watching works. It is history and
awareness, never a substitute for an official warning.
Behind the map — every source, and how it measures
The red dots + the table
NOAA/NCEI Global Historical Tsunami Database
The authoritative world catalogue of tsunamis — every documented event from roughly 2000 BC to today (~2,700 of them), each tied to the earthquake, landslide or eruption that caused it, the maximum water height reached, and the human toll.
How it is compiled: modern events come from tide-gauge and DART traces plus post-event field surveys — teams measure how high the water climbed from the debris line on trees and buildings and map the sand it left inland; older events are reconstructed from written and eyewitness records and from geology. This map and table read it live.
NOAA NCEI · World Data Service
The blue dots
USGS earthquakes
A live, worldwide catalogue that locates and sizes every significant earthquake within minutes and flags the ones with tsunami potential.
How it measures: hundreds of seismographs record the ground shaking as seismic waves arrive; the differences in their arrival times triangulate the epicentre and depth, and the wave's amplitude gives the magnitude. A quake that thrusts the sea floor upward is the kind that can lift the whole water column and launch a wave.
US Geological Survey · global seismic network
The amber dots
NOAA DART deep-ocean buoys
The network that confirms a tsunami is genuinely out there in the open ocean — the reason a warning can be trusted rather than guessed.
How it measures: a recorder on the sea floor senses the weight of the water above it. When a tsunami — often only centimetres tall in deep water — passes over, the water column's height changes by a hair, and the sensor reads that pressure change to the millimetre. It pings the reading up to a surface buoy, which relays it by satellite to the warning centres in near-real time, in any weather.
NOAA DART · tide-gauge network
The wider ocean watch
Satellite altimetry
Radar satellites that measure the height of the sea surface across the whole planet, day and night. In 2004, Jason-1 and TOPEX/Poseidon crossed the Indian Ocean about two hours after the quake and caught the wave from orbit — the first tsunami ever measured from space. Sentinel-6 and SWOT keep that watch now.
How it measures: the satellite fires a radar pulse straight down and times the echo's return; because its own orbit is known to the centimetre, that round trip gives the sea-surface height just as precisely, everywhere it passes.
NASA · ESA · EUMETSAT
The record — deadliest tsunamis this century (live from NOAA/NCEI)
| Year | Where | Quake | Max wave | Lives lost |
|---|
| Loading the global database… |
Before this century, the record runs back thousands
of years: Lisbon 1755 (~50,000), Krakatau 1883 (~36,000), Messina 1908 (~72,000). Same database, same
ocean, same physics.
From a reading to a warning
The simulation that buys the minutes
The moment a great quake is located, the warning centres run a tsunami through a model of the real
ocean floor — NOAA's forecast system fuses the quake with the first live buoy readings and predicts,
coast by coast, how high the water will come and how many minutes are left. Travel-time maps, drawn
from the same physics, show a wave reaching Hawaii in hours and a near neighbour in minutes. It is
the same discipline as the rest of onway: measure honestly, model carefully, and hand the answer to
the people whose job is to warn.
A tsunami crosses the deep Pacific at roughly the speed of a jet — ~700–800 km/h — yet
only a metre or two high in open water. The warning is a race the science can sometimes win by
hours; near the epicentre, only your own feet can.
NOAA Tsunami Warning Centers →
Tōhoku, Fukushima, and the ocean that carried the trace
What the Pacific remembered
The 2011 Tōhoku quake (M9.1) sent a wave that overtopped the seawalls at the Fukushima Daiichi
plant and caused the nuclear accident that followed. In the years after, scientists tracked the
ocean itself: caesium-134 — a fingerprint isotope that could only have come from Fukushima —
was detected in seawater reaching the North American west coast around 2014–2015, carried across
the Pacific by the currents. The levels were far below any level of concern for people or
wildlife, but they were real and traceable — a quiet demonstration of how completely we can now
measure the sea. The monitoring was done in the open, much of it by volunteers sampling their
own coastlines.
The point is not alarm — the measured levels were a tiny fraction of a health limit —
but proof: the ocean is now watched closely enough that a wave's chemical shadow can be followed
across a planet.
WHOI · Our Radioactive Ocean →
If you ever feel it — do not wait for this page, or any page
Near a coast, a strong or long earthquake is the warning. If the ground shakes hard, or the
sea suddenly draws back or roars, move to high ground or inland at once and stay there — a warning
may arrive after the wave, or not at all. This page is a record and an explainer; the live warning
comes from the official centres below.
The oceans keep their own accounts, and they do not negotiate.
Read the letter — on living within physical limits →