Indonesia has experienced more tsunamis with significant wave heights than any other country over the past century. A global review covering 1900 to 2020 found that more tsunamis with water heights above one meter struck Indonesia than anywhere else on Earth. Japan, however, faces what researchers describe as the world’s highest overall tsunami hazard and risk when population exposure and coastal density are factored in. The distinction between raw tsunami count and total risk matters, and it shapes how scientists, governments, and coastal residents think about preparedness in very different ways.
Indonesia’s Unmatched Tsunami Count
Indonesia sits at the convergence of three major tectonic plates, and that geography produces tsunamis from an unusually wide range of sources. Subduction-zone earthquakes are the most familiar trigger, but Indonesia also generates deadly tsunamis from crustal faults, submarine landslides, and volcanic eruptions. That diversity of sources is a big part of why its tsunami count is so high. A 2022 global review confirmed that during 1900 to 2020, more tsunamis exceeding one meter in water height occurred in Indonesia than in any other country.1Pure and Applied Geophysics. Tsunami Occurrence 1900–2020: A Global Review, with Examples from Indonesia
The country’s eastern waters illustrate the complexity well. The Banda and Seram Seas sit at the triple junction of the Eurasian, Indo-Australian, and Pacific Plates, with a megathrust that bends roughly 180 degrees along the Banda Arc. That arc alone contains at least nine distinct segments capable of generating major tsunamis.2Geoscience Letters. Tectonic and tsunami characteristics of Banda and Seram Seas: identifying tsunami-prone villages And this is just one corner of an archipelago stretching more than 5,000 kilometers. The western coast faces the Sunda megathrust; the northern edge interacts with the Philippine Sea Plate. Virtually every part of Indonesia’s coastline has some tsunami exposure.
What makes Indonesia’s situation especially dangerous is the combination of frequent tsunami generation with densely populated and extensive coastal zones. Many communities live right at the water’s edge, on low-lying ground, with limited evacuation routes. Landslide and volcanic tsunami sources, along with coastal features like narrow bays, have historically produced extreme local wave heights and high death tolls even from events that would barely register on a Pacific-wide scale.1Pure and Applied Geophysics. Tsunami Occurrence 1900–2020: A Global Review, with Examples from Indonesia The 2018 Sulawesi tsunami, triggered by an earthquake combined with submarine landslides, and the 2018 Sunda Strait tsunami, caused by volcanic flank collapse at Anak Krakatau, both demonstrated how quickly a locally generated wave can devastate a coast with almost no warning time.
Japan’s Unique Position in Tsunami Risk
If you shift from counting events to measuring total hazard and risk, Japan rises to the top. Researchers have described Japan as facing the world’s highest tsunami hazard and risk, driven by its tectonic environment, high population density, and extreme concentration of infrastructure along the coast.3International Journal of Disaster Risk Reduction. Tsunami inundation hazard across Japan Japan’s Pacific coast runs along one of the most active subduction zones on the planet, where the Pacific Plate dives beneath the North American and Philippine Sea Plates. The 2011 Tohoku earthquake and tsunami, which killed nearly 20,000 people, demonstrated the extreme upper end of what this margin can produce.
A 40-year survey of Pacific tsunamis from 1971 to 2011 found that Japan generated more confirmed tsunami events than any other Pacific region during that period, followed by New Caledonia, New Guinea, the Solomon Islands and Vanuatu, and the Kamchatka-Kuril Islands region.4Springer / Pure and Applied Geophysics. Tsunami Risk Management in Pacific Island Countries and Territories (PICTs): Some Issues, Challenges and Ways Forward That same survey counted 305 tsunamis affecting the Pacific in those four decades, with earthquakes responsible for more than 92 percent of them.
Japan has responded to its extreme exposure with one of the most sophisticated tsunami preparedness systems in the world. Seawalls, offshore breakwaters, dedicated evacuation towers, and a dense network of monitoring stations all reflect centuries of hard experience. The country invests in both deep-ocean buoys (DART systems) and experimental GPS-based detection, and it operates cabled seafloor observatories for real-time monitoring.5PubMed Central. Evolution of tsunami warning systems and products Despite all this, the 2011 event proved that even the best-prepared nation can be overwhelmed when a tsunami exceeds the design assumptions built into its defenses.
Why Subduction Zones Matter So Much
The reason Indonesia, Japan, Chile, and a handful of other countries dominate the tsunami record comes down to subduction, the process where one tectonic plate slides beneath another. When a locked subduction fault ruptures in a large earthquake, the overriding plate snaps upward, displacing a massive column of water and launching a tsunami. But the geometry of the fault matters as much as the size of the earthquake. Megasplay faults, which are long thrust faults branching upward from the main subduction boundary and breaking through to the seafloor, can dramatically increase the vertical displacement of the ocean floor during a quake. Research on the Nankai Trough off Japan showed that a megasplay fault has progressively steepened over time, substantially increasing its potential for vertical seafloor uplift and making that margin especially prone to generating large tsunamis.6PubMed. Three-dimensional splay fault geometry and implications for tsunami generation
This splay-fault mechanism is not unique to Japan. Modeling of the Cascadia subduction zone off the Pacific Northwest of North America shows that splay fault structure influences how coseismic seafloor displacements occur, which in turn shapes the tsunami that follows a megathrust rupture.7AGU Advances. Structural Controls on Splay Fault Rupture Dynamics During Cascadia Megathrust Earthquakes The takeaway for the general reader is that not all subduction zones produce equally dangerous tsunamis. The specific architecture of the faults beneath the seafloor determines how efficiently earthquake energy translates into wave energy, and countries sitting above steeply angled, splay-faulted subduction zones face disproportionate hazard.
Chile and the Eastern Pacific
Chile holds the record for the largest earthquake ever instrumentally recorded, the 1960 magnitude 9.5 event, which sent a devastating tsunami across the entire Pacific Ocean. The Chilean coastline runs parallel to the Peru-Chile Trench, one of the world’s longest continuous subduction zones, and the geological record shows that great tsunamis have struck this coast repeatedly over centuries. Sediment cores from the Tirúa River estuary, located in the overlapping rupture zones of both the 1960 and 2010 earthquakes, preserve sand layers from at least four large tsunamis over the past 450 years, including the well-documented 2010 and 1960 events and two older ones likely dating to roughly 1751 and 1575.8GeoScienceWorld (Geology). Five centuries of tsunamis and land-level changes in the overlapping rupture area of the 1960 and 2010 Chilean earthquakes
Chile’s tsunami history is somewhat different from Indonesia’s. Chile’s events tend to be generated overwhelmingly by subduction-zone earthquakes rather than from a mix of volcanoes, landslides, and different fault types. The tsunamis can be enormous, but they come from a narrower range of sources. Chile also sends transoceanic tsunamis more readily than Indonesia because the open Pacific provides an unobstructed path for wave propagation. The 1960 tsunami killed people in Hawaii, Japan, and the Philippines hours after the earthquake struck Chile.
The Mediterranean Tsunami Hazard
Most people associate tsunamis with the Pacific and Indian Oceans, but the Mediterranean has a long and documented history of destructive waves. A unified catalogue of Mediterranean tsunamis lists 290 events going back to roughly 6150 B.C.9Annals of Geophysics. The Euro-Mediterranean Tsunami Catalogue Among the most famous is the AD 365 event triggered by a massive earthquake near Crete, which sent a tsunami across much of the eastern Mediterranean. The historian Ammianus Marcellinus described the sea pulling back and then returning to kill thousands by drowning, with ships left perched on rooftops.10PubMed Central. Mediterranean megaturbidite triggered by the AD 365 Crete earthquake and tsunami
The Eastern Hellenic Arc and Trench system, running from Crete toward Rhodes, has been particularly active. Analysis of tsunami records from this zone, from antiquity through the modern era, identified 18 reported tsunamis, of which eight are well-documented and nine remain uncertain. The estimated average recurrence interval for strong tsunamis in this area is about 142 years.11Natural Hazards and Earth System Sciences. Tsunami hazards in the Eastern Mediterranean: strong earthquakes and tsunamis in the East Hellenic Arc and Trench system That may sound infrequent compared to the Pacific, but it means the Mediterranean is overdue for its next significant event by some estimates, and coastal development along southern European and North African shores has exploded since the last one.
Italy, Greece, and Turkey are the Mediterranean countries with the most documented tsunami exposure, though Algeria, Egypt, and other North African nations have also been affected. The risk is lower in absolute terms than in Indonesia or Japan, but it catches many people off guard because the Mediterranean is not typically thought of as a tsunami zone.
Tsunamis That Do Not Start with Earthquakes
Earthquakes account for the vast majority of tsunamis globally, more than 92 percent of Pacific events in recent decades.4Springer / Pure and Applied Geophysics. Tsunami Risk Management in Pacific Island Countries and Territories (PICTs): Some Issues, Challenges and Ways Forward But the remaining fraction includes some of the most destructive and least predictable events.
Submarine landslides can displace water almost as efficiently as fault rupture. During the 1964 Great Alaska earthquake, submarine landslides in Port Valdez generated a local tsunami that destroyed much of the old town of Valdez and killed 32 people at that location alone. High-resolution seismic imaging of the fjord floor has since revealed six older landslide deposits beneath the 1964 layer, each between roughly 7 and 23 meters thick, indicating that this kind of failure has happened repeatedly over thousands of years.12Journal of Geophysical Research: Solid Earth. Submarine Landslide Kinematics Derived From High‐Resolution Imaging in Port Valdez, Alaska
Volcanic eruptions can generate tsunamis through pyroclastic flows entering the sea, flank collapses, or caldera implosions. Indonesia is particularly vulnerable to these because of its dense chain of active volcanic islands. The 2022 Hunga Tonga-Hunga Ha’apai eruption in Tonga demonstrated that a volcanic explosion can even generate pressure waves in the atmosphere that trigger tsunami-like waves thousands of kilometers away, a mechanism that blurred the traditional boundary between seismic and atmospheric sources.
Meteotsunamis, waves in the tsunami frequency range generated by rapidly moving atmospheric pressure disturbances, add another layer of complexity. These are not caused by earthquakes or underwater events at all. A meteotsunami that struck southwestern Kyushu in February 2009 reached an estimated maximum amplitude of about 290 centimeters, exceeding a well-known 1979 event at Nagasaki. The atmospheric disturbance that produced it originated from a gravity wave over southeastern China and was propagated by the jet stream toward Japan.13Natural Hazards and Earth System Sciences. Atmospheric pressure-wave bands around a cold front resulted in a meteotsunami in the East China Sea in February 2009 Research on meteotsunamis has grown significantly in recent decades as scientists recognize that these events are more common than previously thought, affecting coastlines in the Mediterranean, the Great Lakes, and many other bodies of water that would never experience a seismic tsunami.14Reviews of Geophysics. Meteorological Tsunamis: From Local Hazard to Global Relevance
Coastal Shape and Reef Effects
The country where a tsunami originates is not always the country that suffers the worst impact. Coastal geography plays a huge role in how waves behave when they reach shore. Narrow bays that taper inland can funnel and amplify wave heights far beyond what open coastline experiences. Modeling of the 2009 tsunami that struck American Samoa showed that embayments narrowing landward, combined with incised deep channels, caused significant increases in wave heights, inundation distances, and water velocities compared to straight coastlines.15Earth-Science Reviews. Effects of fringing reefs on tsunami inundation: American Samoa
Coral reefs present a more complicated picture than most people expect. Narrow reefs, less than about 200 meters wide, can actually make things worse by shoaling the wave and increasing onshore heights. Only as reef width increases does bottom friction begin to dominate, reducing wave heights and limiting how far inland the water travels. The roughness of the reef surface also matters: smooth, degraded reefs allow faster water velocities onshore than healthy, rough reefs do. For small island nations in the Pacific and Indian Oceans, where fringing reefs are the primary coastal defense, the condition of those reefs is directly tied to tsunami vulnerability.
How Sea-Level Rise Changes the Equation
Tsunamis do not operate in a vacuum. They interact with tides, storm surge, and the baseline sea level at the moment they arrive. As global sea levels rise, the starting water level from which a tsunami builds is higher, which means even a moderate tsunami can push farther inland and flood areas previously considered safe. Modeling for Macau, a densely populated coastal city in the South China Sea, found that a modest half-meter rise in sea level, projected to occur by roughly 2060, would increase the frequency of tsunami-induced flooding by a factor of about 1.2 to 2.4. A one-meter rise, projected by around 2100, could increase flooding frequency by a factor of roughly 1.5 to 4.7.16PubMed Central. A modest 0.5-m rise in sea level will double the tsunami hazard in Macau
Indonesia faces a compounded version of this problem. Research coupling sea-level rise scenarios with tsunami modeling for Banda Aceh found that the impact of tsunamis triggered by magnitude 8.2 to 8.6 earthquakes could roughly double when combined with projected sea-level rise.17International Journal of Disaster Risk Reduction. Coupling sea-level rise with tsunamis: Projected adverse impact of future tsunamis on Banda Aceh city, Indonesia Parts of Indonesia also experience local land subsidence from groundwater extraction, which effectively raises relative sea level faster than the global average. This means that even before the next major earthquake, the baseline vulnerability of many Indonesian coastal communities is already growing.
Similar concerns apply to the U.S. West Coast. Modeling of tsunami scenarios for Southern California found that sea-level rise produces increases in maximum credible tsunami elevations of more than a foot in some locations, an amount comparable to the influence of tides on tsunami behavior.18Earth’s Future. Climate‐Driven Sea Level Rise Exacerbates Alaskan and Cascadian Tsunami Hazards in Southern California: Implications to Design Parameters This finding matters for building codes and infrastructure planning in areas that might otherwise consider themselves at the margins of tsunami risk.
The Problem with Tsunami Databases
Any answer to “which country has the most tsunamis” comes with a significant caveat: tsunami databases are incomplete. A critical review of these databases noted that they contain summary information about individual events but will always be incomplete because of fragmentary data about past events and the difficulty of updating information for events already included.19Elsevier (Geoforum). Tsunami databases: The problems of acceptance and absence Countries with long written histories and scientific institutions, such as Japan, tend to have much more complete records than countries where oral traditions were the primary means of transmitting disaster knowledge.
Efforts to compile historical tsunami records in places like the South China Sea have run into problems with translation errors between languages, calendar discrepancies, and changed place names.20Copernicus Publications (Natural Hazards and Earth System Sciences). Written records of historical tsunamis in the northeastern South China Sea – challenges associated with developing a new integrated database One region’s “205 reported events” might distill down to just 58 actual tsunami events after careful cross-checking. This means that raw event counts favor well-documented coastlines. Indonesia’s first-place ranking in the modern era is robust because the 1900-to-2020 period falls within the era of instrumental recording. But the further back you look, the murkier the picture becomes, and some regions that appear quiet in the historical record could simply have poor documentation.
What Paleotsunami Evidence Reveals
Geologists increasingly turn to paleotsunami deposits, layers of sand, marine shells, and other debris left by ancient waves, to reconstruct tsunami histories that predate written records. Kamchatka, on Russia’s far eastern coast, is a striking example. The historical record of earthquakes and tsunamis there is very short, but the coastline preserves tsunami sand layers interbedded with volcanic ash from dateable eruptions. This combination of tsunami deposits and marker tephra offers what researchers describe as an unprecedented opportunity to study tsunami frequency over thousands of years.21Copernicus Publications (Natural Hazards and Earth System Sciences). Historical and paleo-tsunami deposits on Kamchatka, Russia: long-term chronologies and long-distance correlations
Paleotsunami work has reshaped hazard assessments in several regions. The Cascadia subduction zone was not considered a major tsunami threat until geological evidence in the late 1980s and 1990s revealed that it produces great earthquakes and transoceanic tsunamis at intervals of roughly 200 to 600 years. Similarly, paleotsunami studies along the coasts of New Zealand, Papua New Guinea, and various Pacific islands have identified events that never appeared in any written catalogue. As this evidence accumulates, the global picture of tsunami frequency shifts. Countries that appear safe in the historical record may simply be between events, and the geological clock is indifferent to how recently anyone started paying attention.
Warning Systems and the Preparedness Gap
Nine countries currently operate deep-ocean tsunami detection buoys (DART systems) and share data globally in real time: Australia, Chile, Colombia, Ecuador, India, Japan, Russia, Thailand, and the United States.5PubMed Central. Evolution of tsunami warning systems and products Additional nations invest in cabled seafloor observatories or GPS-based systems, though not all of these share data internationally. Modern warning systems integrate seismic sensor networks, wave detection buoys, and satellite monitoring to provide rapid alerts, but challenges remain in building accurate propagation models and integrating real-time data to minimize false alarms.22Water. Tsunami Early Warning Systems: Enhancing Coastal Resilience Through Integrated Risk Management
The preparedness gap between countries is enormous. Japan can issue a tsunami warning within three minutes of detecting a large offshore earthquake. Many small island nations in the Pacific have no local warning infrastructure at all and depend entirely on international alert centers that may be thousands of kilometers away. For locally generated tsunamis, which can arrive at shore in under 15 minutes, this distance is a fatal disadvantage. Indonesia has invested heavily in warning infrastructure since the 2004 Indian Ocean disaster, but maintaining sensor networks across such a vast archipelago remains a persistent challenge, and many coastal communities still depend on natural warning signs (ground shaking, receding water) rather than technological alerts. The country with the most tsunamis is also the country where closing the gap between detection and evacuation may matter more than anywhere else on Earth.