An underwater volcano erupted on Saturday near the remote Pacific nation of Tonga, near the islands of Hunga Tonga, triggering tsunami warnings across the South Pacific and for the West Coast of the United States, and causing strong waves and currents in many coastal areas.

The volcano’s eruption was dramatic, sending plumes of gas and ash thousands of feet into the atmosphere, though early reports of damage were limited.

A four-foot tsunami wave was reported to have hit Tonga’s capital, Nuku’alofa, sending people rushing to higher ground, and witnesses said ash had fallen from the sky. There were no immediate official reports on the extent of injuries or damages, but internet service in the country was disrupted, according to The Associated Press, making it difficult to assess.

Despite Tonga’s geographical isolation, a booming sound after the initial eruption was heard as far away as New Zealand, 1,100 miles southwest of the archipelago’s main island of Tongatapu.

In the United States, officials urged residents of coastal areas in much of the West Coast, Alaska, and Hawaii to stay away from the coastline and move to higher ground.

In Japan, the country’s meteorological agency reported that a four-foot wave had reached the remote southern island of Amami Oshima, according to Reuters, and that smaller surges had hit other areas along Japan’s Pacific Coast.

Across the Pacific warnings were sounded. New Zealand’s National Emergency Management Agency advised people in the coastal areas to expect “strong and unusual currents and unpredictable surges at the shore.” And on their Facebook pages, the meteorological services for Fiji and Samoa also issued alerts, advising people to stay away from low-lying coastal areas.

The volcano, Hunga Tonga-Hunga Ha’apai, which is about 40 miles north of Tongatapu, had been relatively inactive for several years. It began erupting intermittently in December but by Jan. 3 the activity had decreased significantly, according to a report by the Smithsonian Institution’s Global Volcanism Program.

Satellite imagery of the eruption on Saturday, shared on Twitter by New Zealand’s National Institute of Water and Atmospheric Research, showed a “brief spike in air pressure as the atmospheric shock wave pulsed across New Zealand.”

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New Zealand’s Leader Says There Are Signs Of Extensive Damage in Tonga

A day after the volcanic eruption off Tonga’s shores, communications were still out in much of the Pacific island nation, but there were signs of significant damage from the eruption and resulting tsunami, Prime Minister Jacinda Ardern of New Zealand said on Sunday.

Ms. Ardern, whose country has close ties to Tonga, said the tsunami had had “a significant impact on the foreshore on the northern side of Nuku’alofa,” the Tongan capital, “with boats and large boulders washed ashore.”

“Shops along the coast have been damaged and a significant cleanup will be needed,” she said at a news conference.

The tsunami was caused by an eight-minute eruption of the undersea volcano Hunga-Tonga-Hunga-Ha’apai, located about 40 miles north of Tongatapu, Tonga’s main island, on which about 70 percent of the population live.

Contact with Tonga was still extremely limited on Sunday afternoon, and communication with more remote parts of the country had not yet resumed. Ms. Ardern said official damage assessments were not yet available because of the difficulties with communication.

Nuku’alofa was covered in a thick film of volcanic dust, she said, but conditions were otherwise stable and power had been restored to some of the city.

“A clear indication that has come from Tonga is a need for water,” M.s Ardern said. “The ash cloud has, as you can imagine, caused contamination. That’s on top of already a challenging environment, in terms of water supply.”

Countries including Australia and New Zealand have offered the country aid, and a New Zealand Defense Force reconnaissance flight was set to deploy on Monday morning, subject to conditions, including ashfall. A New Zealand Navy vessel will also soon depart for the country, Ms. Ardern said.

In a post on Twitter, the United States secretary of state, Antony J. Blinken, offered his condolences: “Deeply concerned for the people of Tonga as they recover from the aftermath of a volcanic eruption and tsunami. The United States stands prepared to provide support to our Pacific neighbors.”

Tonga, a nation of about 105,000 people, has experienced successive natural disasters in recent years. In 2018, more than 170 homes were destroyed and two people killed by Cyclone Gita, a Category 5 tropical storm. Two years later, in 2020, Cyclone Harold caused an estimated $111 million of damage, including extensive flooding.

The country, which has reported just one case of the coronavirus, has struggled economically during the pandemic. It closed its borders in March 2020, effectively cutting off all tourism to the country, which had previously made up about 12 percent of its GDP.

“We stand ready to support the government and the people of Tonga,” a spokesperson for the United Nations in the Pacific said in a post on Twitter. “Unfortunately this is not over, and more eruptions and consequent tsunamis may follow.”

The History Of The Tonga Islands

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On March 16, 2009, a submarine eruption near Hunga Tonga–Hunga Haʻapai began spewing steam, smoke, pumice, and ash thousands of feet into the sky above the ocean. By March 21, Tonga’s chief geologist, Kelepi Mafi, reported lava and ash issuing from two vents—one on the uninhabited island Hunga Haʻapai and another about 100 m (330 ft) offshore. The eruption had filled the gap between the two separated islands, creating a new land surface that measured hundreds of square meters.^] The eruption devastated Hunga Haʻapai, covering it in black ash and stripping it of vegetation and fauna.

On November and December 2014, volcanic activity at volcanoes and a series of earthquakes occurred north of Tonga for several weeks, indicating renewed volcanic activity in the area.

A new eruption began at Hunga Tonga–Hunga Haʻapai on December 19, 2014. Local fishermen reported a tall white steam plume rising from the ocean over the undersea volcanic mount. Satellite images taken on December 29 showed the eruption continuing, with a smoke and ash plume rising from the site, and discolored seawater (possibly caused by smoke and ash released below the surface, or by disturbance of the seabed). The eruption continued into 2015, with a tall ash cloud rising 3 km (9,800 ft) into the sky on January 6, 2015.

The eruption entered a new stage on January 11, 2015, when the volcano began sending ash plumes as high as 9 km (30,000 ft) into the sky. An Air New Zealand flight on January 12 had to be diverted to Samoa, while a number of other flights between New Zealand and Tonga were canceled. An ash plume reached 4.5 km (15,000 ft) on January 13. Officials identified two vents, one on Hunga Haʻapai and another about 100 m (330 ft) offshore and underwater. Large rocks and wet, dense ash were being ejected up to 400 m (1,300 ft) into the air.  By January 16, a new island had been formed by the explosion. Tongan officials estimated the new island to be 1 km (0.62 mi) wide, 2 km (1.2 mi) long, and 100 m (330 ft) high, although geologists said the new island would probably exist only a few months until ocean waves wore it down. Ash and acid rain were falling in an area about 10km (6.2 mi) from the new island, and Hunga Tonga and Hunga Haʻapai had both been denuded of vegetation.

On 20 December 2021, the volcano erupted again, causing a large plume that was visible from Nukuʻalofa. The Volcanic Ash Advisory Center Wellington issued an advisory to airlines. Explosions could be heard up to 170 kilometers (110 mi) away.^[43] The initial eruption continued until 2 am on 21 December. Activity continued, and on 25 December, satellite imagery showed that the island had increased in size.

Volcanic activity died down on 5 January before restarting on 13 January after the volcano sent an ash cloud 17 km (55,000 ft) into the atmosphere^, The government subsequently issued a tsunami warning. On 15 January, the volcano violently erupted again and was about seven times more powerful than the eruption on 20 December 2021. There were numerous reports of loud booms across Tonga and other countries, such as Fiji and as far away as New Zealand & Australia. A boom was heard in Alaska seven hours after the eruption meaning the sound wave traveled 830 mph. Near the eruption, the explosion damaged property, including shattered windows. A tsunami warning was issued just after 5:30 p.m. by the Tonga Meteorological Services and the tsunami flooded coastal areas in Tonga. A 3.9 ft (1.2 m) tsunami was observed in Nukuʻalofa, Tonga, and a 2.0 ft (0.61 m) one in American Samoa.