Before the recent tsunami in the Indian Ocean in 2004 -

"tsunami that struck Papua New Guinea on July 17, 1998 may have been the most devastating tsunami in this century. The tremendous loss of life is of great concern to all, including the international scientific community. Scientists continue to examine this event, in an attempt to explain the exceptionally high runups with the ultimate hope of mitigating such disasters in the future."
- U.S. Geological Survey

Scientists believe this massive tsunami was triggered, at least in part, by a large underwater landslide.

Aftermath of the Papua New Guinea tsunami, July 17, 1998. "A two-story wooden school building that stood near the church at Sissano Mission was carried 65 m by the wave until caught by a grove of coconut palms. The lower floor of the building collapsed, but the upper floor class rooms were preserved. Schoolwork was still hanging on the wall." Photographer - Hugh Davies, University of PNG; NOAA

Computer-generated simulation of the 1998 Papua New Guinea tsunami. See how the waves generated in this event radiate out from their source. The ripple pattern isn't a perfect ring because of irregularities in the shape of the sea floor. The simulation takes this into account. If the output of the simulation looks like what actually happened, our thinking about how tsunamis are generated may be on the right track. Image and movie courtesy U.S. Geological Survey

What triggers a tsunami? Like the ripples from the impact of a rock thrown into a pond, any event that rapidly displaces large volumes of seawater can trigger the waves of a tsunami. Occasionally a large enough rock, such as an asteroid, might fling itself into the oceans and generate huge ripples in the ocean called tsunami. However, more common triggers are likely to be from more earthly causes.

Common triggers include earthquakes that cause underwater ground rupture, underwater landslides, and the activity of underwater volcanoes. Underwater landslides can be triggered by either earthquakes or gas blowouts near the edges of the continental shelf. The key factor is displacement of water. When lots of rock moves abruptly in the ocean, it displaces water and sets up tsunami waves.

Tsunami are not generally caused by shake-up of water by earthquakes. And no tidal forces are involved so it is bad form to refer to tsunami as tidal waves.

Tsunami risks are high around the Pacific rim because of earthquake and volcanic activity associated with subduction of the Earth's tectonic plates. The Atlantic rim isn't an active tectonic environment so there are fewer earthquakes, volcanoes and tsunami.

Once tsunami are generated, they travel quickly across entire oceans. Detection systems let people know when one is coming their way. With phone communication working at the speed of light, people may have hours to move to higher ground. However, if tsunami are generated just offshore, there's not much time to send out warning. The people of Papua New Guinea were in this situation -- close to the source of the tsunami.

People want to anticipate future events to save lives and minimize loss of property. But before they can pick a solution, they need to find out where these events might happen and how high the water is likely to run up.

Scripps scientist Neal Driscoll is interested in finding out more about the risks of nearshore tsunami. Could unstable ground due to buried deposits of offshore gas trigger such an event in southern California? If so, how can we prepare for this hazard?

At the Ocean Institute
The Ocean Institute's Slopes, Slides & Tsunamis! Station highlights the work of Drs. Neal Driscoll and Jeff Babcock. Using recent technological advances, these researchers are just beginning to understand some of the factors that may contribute to massive underwater landslides. Could a strange ice-gas mixture buried within sea floor sediments play a role?

Students and visitors to the Ocean Institute have the opportunity to investigate sea floor slopes, simulate their own underwater landslides, and generate tsunamis.