Earthquakes, underwater landslides, volcanic eruptions, meteorite impacts, and even certain weather patterns can all trigger a tsunami. Earthquakes are by far the most common cause, responsible for more than 80% of all historically documented tsunamis. But the full list of triggers is broader than most people realize, and each one generates waves through a different mechanism.
Earthquakes: The Leading Cause
Most tsunamis begin with an earthquake beneath or very near the ocean floor. When a fault ruptures, it can shove the seafloor upward or drop it downward in seconds, displacing an enormous volume of water. That sudden vertical movement is what launches the wave. Tsunamis can technically form on any type of fault, but the largest ones almost always come from reverse (thrust) faults, where one slab of Earth’s crust is pushed up and over another.
Not every undersea earthquake produces a tsunami. The quake generally needs to be magnitude 7.0 or greater, occur less than about 100 kilometers (62 miles) below the surface, and happen under or very close to the ocean. Quakes deeper than that rarely displace the seafloor enough to move the water column. For a tsunami powerful enough to cross an entire ocean basin and still cause damage on a distant shore, the earthquake typically needs to exceed magnitude 8.0. Tsunami warning centers issue alerts at lower thresholds as a precaution: magnitude 7.1 for Pacific and Caribbean coasts, and 6.5 for the U.S. and Canadian Atlantic and Gulf coasts.
Submarine Landslides
Landslides, including underwater slope failures and volcano flank collapses, are the second most common cause of tsunamis. When a massive volume of sediment or rock slides down a continental shelf or volcanic island slope, it shoves the water in front of it and creates a void behind it. Both actions generate waves.
These landslides can be triggered by earthquakes, volcanic activity, or simply the gradual buildup of unstable sediment on a steep underwater slope. Modeling studies show that tsunamigenic landslides can reach speeds up to 60 meters per second (roughly 130 mph) and travel 10 kilometers or more from their source. Landslide tsunamis tend to be extremely dangerous close to shore but lose energy faster over long distances compared to earthquake tsunamis, because the displaced area is usually more localized.
Volcanic Eruptions
Volcanoes can generate tsunamis through several different mechanisms. Pyroclastic flows, the fast-moving avalanches of hot gas and rock that rush down a volcano’s flanks, displace massive amounts of water when they hit the sea. Caldera collapse, where the emptied magma chamber beneath a volcano caves in, can drop or push the seafloor abruptly. Explosive eruptions can blast water outward directly, and the flanks of volcanic islands can fail catastrophically, sending enormous landslides into the ocean.
The 1883 eruption of Krakatoa in Indonesia produced waves with run-up heights of 120 feet, generated primarily by pyroclastic flows entering the water. That event killed over 26,000 people and wiped out coastal villages across the region. In 1980, the eruption of Mount St. Helens caused a partial flank collapse that sent an avalanche into Spirit Lake, producing a localized tsunami 780 feet high. More recently, the 2022 eruption of Hunga Tonga-Hunga Ha’apai demonstrated that atmospheric pressure waves from massive eruptions can also push ocean water and generate tsunami-like surges thousands of miles away.
Meteorite Impacts
An asteroid or meteorite striking the ocean would displace water violently enough to create a tsunami, but this is an extremely rare event. Modeling and experimental studies estimate that a rocky object needs to be at least 10 to 15% of the local water depth in diameter, assuming an average impact speed of about 18 kilometers per second. In a typical ocean basin with water depths of 3.5 to 4 kilometers, that means objects smaller than roughly 500 meters across wouldn’t generate a meaningful tsunami. Bodies that small would lose their energy to the water column without creating waves that propagate outward effectively.
No tsunami from a meteorite impact has occurred in recorded human history, but geological evidence suggests it has happened in the deep past. The asteroid that struck the Yucatán Peninsula 66 million years ago, for instance, generated massive ocean waves that left sediment deposits across the Gulf of Mexico and beyond.
Meteotsunamis: Weather-Driven Waves
Rapid changes in atmospheric pressure can push the ocean surface hard enough to create tsunami-like waves called meteotsunamis. These form when a fast-moving weather disturbance, such as the arrival of a continental cold air mass or a squall line, causes a sudden jump or drop in air pressure over water. If the pressure disturbance moves at roughly the same speed as the shallow-water waves it creates, the energy builds through resonance, producing waves that can reach several feet or more at the coast.
Meteotsunamis are most common in winter and spring when high-latitude cold air masses move over coastal waters. They occur in places like the Mediterranean, the Great Lakes, and along the U.S. East Coast. While rarely as destructive as seismic tsunamis, they can cause dangerous harbor surges and catch coastal communities off guard because there’s no earthquake to serve as a warning.
Glacier Calving
When large chunks of glacier break off and fall into water, the sudden displacement creates localized tsunamis. The severity depends heavily on how the iceberg enters the water. Icebergs that fall from above the waterline (gravity-dominated calving) produce waves roughly ten times larger than icebergs that detach underwater and float upward or simply capsize. In 2014, an iceberg calving event at Eqip Sermia in Greenland generated a wave with an amplitude of 50 meters, destroying nearby infrastructure. Another event near the Helheim outlet glacier in eastern Greenland produced a wave still measurable at 24 centimeters some 25 kilometers away.
These tsunamis are currently a localized hazard, primarily threatening boats, fjord communities, and research stations near active glaciers. As ice sheets continue to lose mass, calving events are expected to become more frequent in places like Greenland and Antarctica.
How Tsunami Waves Travel
Regardless of the trigger, all tsunamis share certain physics once they’re in motion. Their speed depends on ocean depth: in the open ocean, where water may be 4 kilometers deep, tsunamis travel at roughly the speed of a commercial jet, around 700 to 800 kilometers per hour. In shallow coastal waters, they slow dramatically but grow much taller as the energy compresses into a shorter water column. A wave barely noticeable in the deep ocean can become a wall of water at the coast.
Natural Warning Signs
If you’re near the coast, certain signs can indicate a tsunami is approaching. A strong earthquake that lasts 20 seconds or more, or one powerful enough to knock you off your feet, is the most important natural warning for seismically generated tsunamis. A rapid, unusual rise or fall in water level along the shore is another key signal. In many tsunamis, the water recedes dramatically before the first large wave arrives, exposing seafloor that’s normally submerged. A loud, sustained roar from the ocean can also precede the wave.
If you notice any of these signs, move to higher ground immediately, ideally 100 feet above sea level or at least one mile inland. Tsunamis arrive as a series of waves, not just one, and the first wave is often not the largest. The danger can persist for hours after the initial arrival.