More volcanic upheavals likely to follow, warns Aussie expert

The eruption of the Hunga Tonga-Hunga Ha'apai volcano caused a tsunami to send water flooding into the nation's capital of Nuku'alofa, while large waves and tidal surges rolled across the Pacific region including the east coast of Australia, Japan and Hawaii.

Monash University's Associate Professor of Geochemistry Oliver Nebel told Xinhua news agency on Monday that the disaster was caused by the volcano sitting near the edge of one of the Earth's tectonic plates.

Over time, a plate can "clash" with another, in this case causing an eruption along what is known as the "Ring of Fire" volcanoes, which are already explosive.

"The last eruption of this volcano was about 1,000 years ago, so it was due for a large eruption, and this is likely what happened now," Nebel said.

Nebel said volcanic activity off the Tongan coast had been detected over the Christmas period which was a sign that pressure was building up along the vulnerable plate edges.

He said hot magma was constantly accumulating within volcanoes, and it is expected that they will create lots of ash and can have "a fair bit of a violent eruption".

Volcanoes build up those underground reservoirs and "every now and then this reservoir is emptied, and this causes an eruption".

"Once the magma is evacuated from underneath the volcano, it's likely that eruptions will go on and on. But once you have a violent eruption it's unlikely the next ones will be as disruptive because there's a good chance that a huge amount of the magma has already erupted."

But it is still "not a very predictable" process as to when it would explode, especially given the lack of data currently.

"At the moment, we actually do not have a lot of data. Most of the stations on the volcano would have been destroyed during the day. We have satellite data, but any sort of other measurement needs to be taken on site, which at the moment is not easy, basically impossible to travel there. Without data, it's really difficult to assess what sort of explosivity index can be assigned to the volcano or how much mess was in place."

Nebel said tsunamis were the biggest hazards of such underwater eruptions.

He said the January 15 disaster had been caused by the "displacement of water mass through injection of material from the deep Earth's interior into the ocean and the possible sinking of the volcano due to lava evacuation from underneath".

He also added that during the eruption, "lava burst into tiny particles that formed volcanic ash, and the interaction of lava with cold seawater likely intensified the plumes of ash".

"This ash is also causing a fair bit of air traffic disruption," he said. "The ash is actually tiny particles of rock, it's not like the ash out of a wood fire."

Nebel said the priority for authorities must now be to help those who have been hardest hit by the eruption.

One such priority will be restoring Tonga's undersea communications cable that was severed during the eruption. 

It is believed the repairs could take more time, which means the inhabitants of the island country are essentially cut off from communication with the outside world.