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Tonga’s volcanic eruption may harm environment for years, say scientists

CNA – Tonga’s massive underwater volcanic eruption could deliver long-lasting damage to coral reefs, erode coastlines and disrupt fisheries, said scientists studying satellite images and looking to the past to project the future of the remote region.

Since the eruption, the volcano has been releasing sulphur dioxide and nitrogen oxide – two gases that create acid rain when they interact with water and oxygen in the atmosphere.

With Tonga’s tropical climate, “there is likely to be acid rain around Tonga for a while to come”, said volcanologist Shane Cronin at the University of Auckland.

Acid rain causes widespread crop damage, and could ruin Tongan staples like taro, corn, bananas and garden vegetables. “Depending on how long the eruptions last, food security could be compromised,” Cronin said.

Satellite imagery shows the plume spreading westward, which means Tonga could be spared some of this acid rain though Fiji could then be in its path.

In a bulletin on Monday, the United Nations (UN) humanitarian affairs office said Fiji was monitoring its air quality, and has advised people to cover their household water tanks and stay indoors in the event of rain.

Satellite image shows an undersea volcano eruption at the Pacific nation of Tonga. PHOTO: AP

Tonga’s exclusive economic zone of nearly 700,000 marine square kilometres is 1,000 times larger than its land area. And most Tongans get their food – and livelihood – from
the ocean.

While scientists have yet to investigate on the ground, “the few pictures that are available seem to show a blanket… of ash” on land, said geologist at the University of Otago in New Zealand Marco Brenna. In the ocean, that ash can be harmful to marine life.

Weeks before Saturday’s eruption, Tonga Geological Services had warned that nearby seawater was contaminated with toxic volcanic discharge, and that fishermen should “assume fish in these waters are poisoned or poisonous”.

Inevitably, the eruption has made the situation worse. Murky, ash-filled water near the volcano will deprive fish of food and wipe out spawning beds. Some fish will perish, and survivors will be forced to migrate, scientists said. Further changes in the structure of the sea floor could create new obstacles for fishing vessels.

“It will be a while before the same or new fishing grounds will be restored,” Brenna said.

Falling ash can also smother coral reefs, which in Tonga are the mainstay of a tourism industry that brought in up to USD5 million per year before the coronavirus pandemic.

Even before the eruption, Tonga’s reefs were threatened by disease outbreaks and the effects of climate change including coral bleaching and increasingly strong cyclones.