Squashed Undersea Volcanoes Cause Rare Tsunami Earthquakes

A new study published in the journal Earth and Planetary Science Letters  reveals that tsunami earthquakes may be caused by extinct undersea volcanoes, a revelation that may lead to improved detection measures.

Tsunami earthquakes happen at relatively shallow depths in the ocean and are small in terms of their magnitude. However, even an earthquake with a relatively low magnitude can generate a massive, devastating tsunami with waves reaching as high as 32 feet (10 meters).

A global network of seismometers enables researchers to detect such minor earthquakes, but the trouble lies in being able to discern between which ones will lead to endangering large tsunamis and which ones won't.

This new study reveals that extinct undersea volcanoes may be to blame, causing a "sticking point" between two sections of Earth's crust called tectonic plates, where one plate slides under another.

The team located two extinct volcanoes off the coast of Poverty Bay and Tolaga Bay that have been squashed and sunk beneath the crust off the coast of New Zealand, a process called subduction - two tsunami earthquakes happened off the coast of New Zealand's north island in 1947.

Data showed that during that time, a build-up of energy caused the two plates to "unstick," and the Pacific plate to move and the volcanoes to become subsumed under New Zealand. This release of energy from both plates was unusually slow and close to the seabed, causing large movements of the sea floor, which led to the formation of very large tsunami waves.

"Thanks to oil exploration data and eyewitness accounts from two tsunami earthquakes that happened in New Zealand more than 70 years ago, we are beginning to understand for first time the factors that cause these events," Dr. Rebecca Bell, from the Department of Earth Science and Engineering at Imperial College London, explained in a statement. "This could ultimately save lives."

All this information can be used to locate similar zones around the world that could be at risk from tsunami earthquakes. The researchers are already working with colleagues in New Zealand to develop a better warning system for residents.