What are Tsunamis?

Tsunamis are ocean waves triggered by large earthquakes that occur near or under the ocean, volcanic eruptions, submarine landslides, and by onshore landslides in which large volumes of debris fall into the water. Scientists do not use the term "tidal wave" because these waves are not caused by tides. Tsunami waves are unlike typical ocean waves generated by wind and storms, and most tsunamis do not "break" like the curling, wind-generated waves popular with surfers. Tsunamis typically consists of multiple waves that rush ashore like a fast-rising tide with powerful currents. Tsunami waves can travel much farther inland than normal waves. When tsunamis approach shore, they behave like a very fast moving tide that extends far inland. If a tsunami-causing disturbance occurs close to the coastline, a resulting tsunami can reach coastal communities within minutes. A rule of thumb is that if you see the tsunami, it is too late to outrun it. Even small tsunamis (for example, 6 feet in height) are associated with extremely strong currents, capable of knocking someone off their feet. Because of complex interactions with the coast, tsunami waves can persist for many hours.

As with many natural phenomena, tsunamis can range in size from micro-tsunamis detectable only by sensitive instruments on the ocean floor to mega-tsunamis that can affect the coastlines of entire oceans, as with the Indian Ocean tsunami of 2004. If you hear a tsunami warning or if you feel strong shaking at the coast or very unusual wave activity (e.g., the sea withdrawing far from shore), it is important to move to high ground and stay away from the coast until wave activity has subsided (usually several hours to days).

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What is it about an earthquake that causes a tsunami?

Although earthquake magnitude is one factor that affects tsunami generation, there are other important factors to consider. The earthquake must be a shallow marine event that displaces the seafloor. Thrust earthquakes (as opposed to strike slip) are far more likely to generate tsunamis, but small tsunamis have occurred in a

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What is the difference between a tsunami and a tidal wave?

Although both are sea waves, a tsunami and a tidal wave are two different and unrelated phenomena. A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon, and Earth. ("Tidal wave" was used in earlier times to describe what we now call a tsunami.) A tsunamis is an ocean wave

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Is there a system to warn populations of an imminent occurrence of a tsunami?

NOAA maintains the U.S. Tsunami Warning Centers, which work in conjunction with USGS seismic networks to help determine when and where to issue tsunami warnings. If an earthquake meets certain criteria for potentially generating a tsunami, the pop-up window and the event page for that

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Could a large tsunami happen in the United States?

Large tsunamis have occurred in the United States and will undoubtedly occur again.

Significant earthquakes around the Pacific rim have generated tsunamis that struck Hawaii, Alaska, and the U.S. west coast. One of the largest and most devastating tsunamis that Hawaii has experienced was in 1946 from an earthquake

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Date published: February 1, 2016

50-Year-Old Mystery Solved: Seafloor Mapping Reveals Cause of 1964 Tsunami that Destroyed Alaskan Village

Minutes after the 1964 magnitude-9.2 Great Alaska Earthquake began shaking, a series of tsunami waves swept through the village of Chenega in Prince William Sound, destroying all but two of the buildings and killing 23 of the 75 inhabitants. 

Date published: September 18, 2015

Are American Cities Prepared For Massive Tsunamis?

Are American Cities Prepared For Massive Tsunamis?

Date published: September 17, 2015

California Prepares for Someday's Bigger Tsunami

California Prepares for Someday's Bigger Tsunami

Date published: August 20, 2015

Disaster Scenario: SoCal Tsunami Could Hit Quickly

Disaster Scenario: SoCal Tsunami Could Hit Quickly

Date published: September 5, 2013

California Tsunami Would Have Costly Aftermath

The fearsome aftermath of a tsunami striking California might cost at least $3.4 billion to repair, but neither of the state's nuclear power plants would be damaged, suggests a new analysis that could help officials and the public prepare for a tsunami and reduce risks before any such disasters happen.

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Animation of Tsunami Scenario in the Pacific Northwest
February 1, 2017

Animation of what a potential tsunami would look like generated from a large and hypothetical magnitude 9 subduction earthquake in the U.S. Pacific Northwest. The height of the tsunami waves is exaggerated compared to the land surface. Credit: Eric Geist, USGS

Southeast Asia - Tsunami brought in distructive waves and destruction.
November 28, 2016

Southeast Asia in May 2013. Tsunami brought in dangerous waves and destruction. 

Image: Exposed Tsunami Sand Layers
August 8, 2012

An outcrop composed of six tsunami deposits on the inland side of the lowland backing Stardust Bay over 0.5 miles from the sea. Brown soils developed into the top of each sand sheet and black tephra (air fall volcanic ash) layers between two of the sand deposits aided correlation of the six sand sheets across the study area.

Location: Stardust Bay, Sedanka Island, Alaska

video thumbnail: Indonesian Capacity Building in Seismology and Tsunami Detection
September 10, 2009

The December 2004 Indian Ocean Tsunami was one of the deadliest natural disasters of modern history, killing over 225,000 people. As a result of this catastrophe, the U.S. Geological Survey has partnered with the international community to create an Indian Ocean Tsunami Warning System (IOTWS). An important aspect of this work is the training of employees of the Indonesian Meteorological, Climate, and Geophysical Agency (BMKG). This movie presents an overview of the training courses held in Indonesia and what has been accomplished since 2004.

Image: Tsunami Carried Boat

The tsunami generated by the M 8.8 earthquake carried many boats onto land - in some cases hundreds of meters inland. The tsunami wave height at this location in Concepcion Harbor (Talcahuano), Chile was about 4-5 meters (12-15 feet).

Nehalem town with tsunami evacuation sign

Tsunami evacuation sign in the town of Nehalem. OR.

Wrecked buildings and washed-up boat far from water after the 2011 earthquake and tsunami in Japan in 2011.

Extensive damage to buildings and roads, and large boats washed far ashore, provide valuable information to tsunami researchers. Here, in Natori, Japan, south of Sendai, the height of damage indicates that the water flow from the tsunami wave was about 10 meters (33 feet).