‘Rapid bang’: Kiwis hear eruption

The massive volcanic eruption near Tonga was heard thousands of kilometres away by people across New Zealand, according to GNS Science.

The underwater volcano erupted about 5pm on Saturday. Kiwis started calling GNS Science from across New Zealand with reports of a loud boom about 7pm.

The reports coincided with signals picked up by the Crown science agency’s acoustic monitoring network.

The Hunga-Tonga-HungaHa’apai volcano is more than 2000 kilometres away from New Zealand. GNS Science vulcanologist Geoff Kilgour said it was unusual for a volcanic eruption to be heard from such a large distance.

‘‘People hearing these sorts of sounds from so far away is very rarely recorded, it is only a few times in history,’’ he said.

‘‘For this to happen you need a huge explosion. You can’t have an eruption that builds slowly. It has to be a rapid bang and a huge amount of energy released all at once.’’

The volcanic explosion was ‘‘by far the most violent eruption that we have seen in some time’’, he said.

The last time a volcano had exploded so violently was Pinatubo in the Philippines in 1991, he said.

The volcano could be heard from such a large distance because the explosion was so big, low frequency bass sounds travel a long way and there was little between New Zealand and Tonga to baffle the noise.

‘‘It is just a flat ocean.’’

The sound of the eruption took about two hours to reach New Zealand.

‘‘We saw it on our monitoring network which connected with when people were telling us they were hearing it.’’