Tonga Eruption's Massive Tsunami Began as a Single Water Mound [STUDY]

The west coasts of Tongatapu, 'Eua, and Ha'apai were hit by tsunami waves up to 15 meters high caused by the Hunga-Tonga-Hunga-Ha'apai volcano's eruption. According to the researchers, it's possible that the gigantic eruption began as a single water mound about the Statue of Liberty's height before erupting as a series of planet-circling tsunamis.

(Photo : Contains modified Copernicus Sentinel data {{{year}}}/Wikimedia Commons)
Tonga

Water Displacement During the Tonga Volcano Eruption

According to Mohammad Heidarzadeh, a civil engineer from the University of Bath in England, when the Tonga undersea volcano erupted in the South Pacific in January, it displaced a significant amount of water upward. As fluids often do, the water in that enormous mound later flowed downhill to cause the initial wave of tsunamis.

The researchers concluded in the Ocean Engineering report that the explosive eruption created an immense air shock wave that spawned a second set of exceptionally fast-moving tsunamis. They said that this is an uncommon event that might confound early warnings for these oft-destructive waves.

Tsunami Size of Tonga Eruption

Heidarzadeh and his team utilized computer simulations to determine the mound's initial size as well as information from tide gauges and deep-ocean instruments within 1,500 kilometers of the eruption. Many of the eruptions were in or close to New Zealand. Heidarzadeh claims that crucial pieces of information included the times and sizes of the tsunami waves that arrived at certain places.

The nine initial wave alternatives, each with a distinct height and diameter and resembling a baseball pitcher's mound, were examined by the team. According to the researchers, a massive water mound measuring 90 meters high and 12 kilometers in diameter provided the best fit to the real-world data.

There would have been 6.6 cubic kilometers of water in that first wave. The researcher said that this was a really large tsunami.

Another distinctive aspect of the Tongan eruption was the second series of tsunamis, which were brought on by a strong air pressure wave.

The pressure pulse was created by a large amount of seawater entering the hot magma chamber underneath the erupting volcano, which resulted in a steam explosion. Heidarzadeh points out that the pressure wave pushed water in front of it to create tsunamis as it traveled across the ocean's surface at speeds greater than 300 meters per second.

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Gravity Driven Tsunami Wave

These pressure wave-generated tsunamis arrived hours ahead of the gravity-driven waves spreading from the 90-meter-tall water mound over several coastlines, including ones in the Indian Ocean and Mediterranean Sea. At speeds between 100 and 220 meters per second, gravity-driven tsunami waves normally traverse the deepest portions of the ocean, far from continents. When waves slow down, water builds up, and when they hit the shore, where destruction takes place, they are in shallow seas close to the shore.

These earlier-than-anticipated arrival timeframes, along with the fact that the tsunamis caused by the Tongan eruption's pressure waves were around the same size as those caused by gravity, may make it more difficult to issue early warnings for these tsunamis.

According to Hermann Fritz, a tsunami scientist at Georgia Tech in Atlanta, one solution to the problem would be to install instruments that monitor atmospheric pressure alongside the deep-sea equipment currently in place to detect tsunamis.

With that configuration, scientists would be able to determine whether a tsunami going by is connected to a pressure pulse, giving them a hint in real time about how quickly the tsunami wave may be moving.