Scientists are on their way to the site of a large undersea volcano that has been erupting for days near Tonga, sending columns of smoke and ash thousands of feet into the sky above the Pacific Ocean.
The spectacular plumes are erupting from the ocean about six or seven miles (10 - 12 km) off the coast of the main island of Tongatapu, near the low-lying twin volcanic islands of Hunga Tonga and Hunga Ha'apai.
The eruption can be seen clearly from the capital, Nuku'alofa, although residents only reported seeing columns of smoke rising from the sea on Wednesday, two days after it is believed to have begun.
Locals described it as a cloud of ash visible above the waterfront. Nuku'alofa resident Mary Fonua said the eruption appeared to have increased in size during Wednesday.
"The plume is bigger than it was this morning when you could have mistaken it for a cloud," Ms Fonua said, "but it's far enough away not to be threatening."
Authorities in Tonga said there was no immediate danger to people living on the island. Tonga's chief geologist, Kelepi Mafi, said: "It's a very significant eruption, on quite a large scale." However, he added, "This is not unusual for this area and we expect this to happen here at any time."
Tonga's police deputy commander Taniela Faletau said coastal villages close to the broiling ocean site were not yet at risk and that no warnings had been issued. On Thursday, trade winds were blowing gas and steam away from the island, although large amounts of pumice thrown up by the volcano would probably soon line beaches on the southern coast of nearby Fiji said Mr Mafi
However if the volcano continued to grow, it had the potential to be devastating, one expert told The Times. Professor Simon Turner, a geochemist at Macquarie University in Sydney, said: 'Underwater volcanos can be violent, and have a strong climatic effect..This one isn't getting into the stratosphere yet but as it continues to grow that is a possibility.
"Pinatubo's big eruption in the 1990s reduced northern hemisphere temperatures by 0.2 C - the same as El Nino. I would be surprised if this even got close to that but it's hard to completely predict the natural world.
"Two years ago we were mapping around Tufoa (a Tongan island) where a volcano erupted about 1000 years ago. We found ash several metres thick several kilometres away; it shows what devastation these volcanoes can cause."
Without comprehensive data from Tonga or from the eruption site, it was still too early to say whether this volcano would be short-lived or continue to grow, he said. It was not yet known how close to the surface the eruption is.
During the past three weeks sharp tremors have been felt in Nuku'alofa about twice a week. On Friday, an earthquake measuring 4.4 on the Richter scale struck about 20 miles (35 km) from the capital at a depth of nearly 150 km and Tonga officials said the tremors could be related to the erution. However Professor Turner said the events were probably not linked.
"If this eruption was caused by the earthquake, it would mean magma coming 110 km to the surface in a few days," he said. "I think that would be fairly unlikely."
An eruption in 2002 in the same area off the western end of Tongatapu, near two small volcanic islands, resulted in an islet appearing for several weeks afterwards and leaving a thick layer of pumice covering the sea for miles. Geologists believe this eruption is already bigger than that one.
Submarine volcanoes are underwater fissures in the earth's surface from which magma can erupt and are usually caused by shifting of tectonic plates. Most are located in the depths of oceans, but some do exist in shallow water, and it is these which throw material into the air during an eruption.
Tonga, a 170-island archipelago about halfway between Australia and Tahiti, is part of the Pacific "ring of fire" — an arc of earthquake and volcanic zones where continental plates in the earth's crust collide.