Tsunami warning today: live alerts, warnings, and coastal threat map

The first tsunami warning center was established in 1949 by NOAA in Honolulu — a direct response to the 1946 Aleutian Island earthquake and tsunami that killed 159 people in Hawaii with no advance notice. The Pacific Tsunami Warning Center (PTWC) grew from that lesson into the anchor of a global network. It monitors seismic stations continuously, and when a significant undersea earthquake is detected, it produces an initial assessment of tsunami potential within minutes.

The warning system runs on two independent data streams. Seismic networks provide the first alert: earthquake location, magnitude, and depth are computed rapidly and fed into models that estimate whether a tsunami-capable event has occurred. But seismic data alone cannot confirm whether a tsunami actually formed. That confirmation comes from DART buoys — Deep-ocean Assessment and Reporting of Tsunamis — pressure sensors anchored to the ocean floor that detect the subtle pressure signature of a passing tsunami wave. When a DART buoy registers an anomalous pressure change, it switches from 15-minute reporting intervals to transmissions every 15 seconds, giving warning centers real-time confirmation that a wave is propagating.

The communication chain from detection to public alert involves multiple layers: warning centers transmit to national emergency agencies, which activate broadcast interruptions, outdoor sirens, and cell tower-based emergency alerts. Japan's Meteorological Agency can issue its first tsunami warning within three minutes of a major earthquake — the fastest national system in the world, built through decades of painful experience.

The Indian Ocean Tsunami Warning and Mitigation System (IOTWMS) is the newest major component of this global infrastructure. Before December 26, 2004, the Indian Ocean had no coordinated warning system at all. The absence cost over 230,000 lives. Today, 26 member states share seismic data, operate DART buoys, and maintain national warning centers capable of issuing alerts within minutes of a triggering earthquake. For seismic event monitoring, see our earthquakes today tracker.

The single most important factor in tsunami survival is the distance between the earthquake source and the coastline — because distance determines how much time exists between the earthquake and wave arrival. This creates a spectrum of warning scenarios with radically different survival challenges.

Local tsunamis — generated by earthquakes within roughly 100 km of the coast — give communities 10 to 30 minutes at best. No warning system can compress seismic analysis, wave modeling, alert issuance, and human response into that window reliably. For local tsunamis, the earthquake itself is the warning. If strong shaking lasts 20 seconds or more, or is violent enough to make standing difficult, coastal residents should move immediately to high ground without waiting for any official alert.

Regional tsunamis (source 100–1,000 km away) allow 1 to 2 hours of warning time — enough for warning centers to confirm a wave, issue alerts, and for organized evacuation to begin in prepared communities. Distant tsunamis from sources over 1,000 km away offer hours of lead time. The 2004 Indian Ocean tsunami, generated off northern Sumatra, took approximately 7 hours to reach the East African coast — ample time to evacuate Somalia and Tanzania had a functioning warning system existed.

One under-appreciated hazard is the all-clear problem. Tsunamis arrive as wave trains — sequences of waves separated by 10 to 45 minutes. The first wave is not always the largest. After the 2011 Tohoku tsunami, residents who returned to the coast after the first wave were struck by subsequent, larger waves. Official all-clear announcements — which require confirmation that wave activity has subsided to safe levels — can take many hours after the last dangerous wave passes. Returning before that announcement has killed people in multiple historical events. For current coastal earthquake data, the global disaster tracker provides the broadest view.

Three terms are frequently confused when coastal flooding is discussed, and the distinctions matter practically for how to respond and how to interpret warnings.

A tsunami is generated by a sudden large-scale displacement of the ocean floor — most commonly from a subduction zone earthquake, but also from submarine landslides, volcanic collapses, or in rare cases, meteorite impacts. The key physics is that the entire water column from sea floor to surface is set in motion. Tsunami waves have wavelengths of 100 km or more, travel at jet-aircraft speeds in deep water, and carry enormous energy that builds as the wave slows and compresses approaching shore. A tsunami can arrive as a rapid flooding surge, a churning bore of water and debris, or a dramatic ocean drawback followed by a wall of water.

A storm surge is driven by an entirely different mechanism: atmospheric pressure and wind from a tropical cyclone or severe storm push surface water toward the coast. Only the upper layer of ocean is involved. Storm surge persists for hours as long as the storm maintains its position and winds, rather than arriving in discrete wave pulses. Surge responds to forecasted storm tracks and is manageable with advance warning — the kind that hurricane tracking provides.

A tidal wave is simply a historically inaccurate term for tsunami. Tides are caused by the gravitational pull of the Moon and Sun and operate on 6- to 12-hour cycles. Tsunamis have nothing to do with tides. The term persists in popular usage but is avoided in scientific and emergency management communications because it implies a predictable, tide-like behavior that tsunamis do not have.

The practical difference for evacuation: a tsunami warning requires immediate movement to high ground and extended shelter there for hours. A storm surge warning requires evacuation before a storm's arrival. Confusing the two can lead to critically wrong responses at exactly the wrong moment.

Horizontal evacuation — moving inland and uphill — is the primary tsunami survival strategy. Most at-risk coastal communities in Japan, Chile, the Pacific Northwest United States, and elsewhere have mapped and signed evacuation routes leading to designated assembly zones at sufficient elevation. The standard guidance is to reach at least 30 meters of elevation or move at least 2 km inland, whichever is achievable faster given the terrain.

When horizontal evacuation is not possible within the available time, vertical evacuation becomes the alternative. Japan has designated hundreds of reinforced structures — purpose-built tsunami towers and selected multi-story buildings — as vertical evacuation refuges, marked with standardized blue signs. The Pacific Northwest United States has pursued a similar program, identifying reinforced concrete structures that can serve as vertical refuges in communities where terrain limits rapid inland movement.

Japan's engineering response to tsunami risk has been the most ambitious globally. After the 1960 Chilean tsunami and the 1993 Okushiri tsunami, Japan constructed extensive seawall systems along vulnerable coastlines — some topping 12 meters in height. When the 2011 Tohoku tsunami arrived with waves measuring 14 to 40 meters at various points along the Sanriku coast, many of these walls were simply overtopped. The walls did slow the flow in some locations, buying additional minutes for evacuation, but the lesson reinforced that engineering barriers are a supplement to evacuation planning, not a substitute.

Evacuation drills are taken seriously in the most prepared countries. Japan conducts national tsunami evacuation drills on March 11 — the anniversary of the 2011 Tohoku disaster — and many coastal communities hold additional local drills. Chile runs regular Pacific coast drills. Communities in these countries show measurably shorter evacuation times in real events compared to communities without drill culture. The active monitoring on this page tracks the earthquake events most likely to trigger coastal evacuations.

The 2004 Indian Ocean tsunami — triggered by a magnitude 9.1 earthquake 160 km west of northern Sumatra on December 26 — remains the deadliest tsunami in recorded history. Waves reached 30 meters in Aceh province, Indonesia. The same waves traveled 1,700 km to kill thousands in Sri Lanka and India, and 7 hours later reached East Africa. Over 230,000 people died across 14 countries. The catastrophe's defining policy legacy was the complete absence of any warning system: Thailand, Sri Lanka, and India received no official alert. The Indian Ocean Tsunami Warning and Mitigation System was operational within two years.

The 2011 Tohoku earthquake and tsunami struck Japan on March 11, generating waves that reached 40 meters in some areas of Miyagi and Iwate prefectures. The Fukushima Daiichi nuclear plant, designed to withstand a 5.7-meter tsunami, was hit by waves of 14 meters. Three reactors melted down. Approximately 18,000 people died, with drowning accounting for over 90% of deaths. The event forced a global recalculation of both tsunami defense standards and nuclear plant siting — and demonstrated that even advanced warning systems and coastal infrastructure cannot fully protect against the largest possible events.

The 1960 Valdivia earthquake in Chile, still the most powerful seismic event ever recorded at magnitude 9.5, generated a trans-Pacific tsunami that killed 61 people in Hilo, Hawaii — 10,000 km from the source — and continued on to kill 138 more in Japan 22 hours after the earthquake. The event directly prompted the formation of the international coordination body that became the Pacific Tsunami Warning System, establishing for the first time that tsunami risk was a shared Pacific responsibility, not just a local hazard.

The 1883 Krakatoa eruption generated a tsunami from a volcanic source rather than a tectonic earthquake, producing waves up to 30 meters that killed over 36,000 people along the Sunda Strait coasts of Java and Sumatra. Krakatoa established volcanic tsunamis as a distinct threat category requiring dedicated modeling. The 1958 Lituya Bay megatsunami in Alaska — triggered by a rockslide into a confined bay — produced a run-up wave of 524 meters, the tallest ever recorded, but its destructive footprint was limited by geography. These two events bracket the extreme range of non-tectonic tsunami generation. For earthquake monitoring that informs current tsunami risk, see our live seismic feed.