Gloria Dickie

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

ACID RAIN

Since the initial eruption, the volcano has been releasing sulfur 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 is a major cause of crop destruction in Tongan, and can lead to widespread damage to crops, including bananas, taro and corn. “Depending on how long the eruptions last, food security could be compromised,” Cronin said.

Satellite imagery has shown the plume expanding westward. Tonga might be spared some acid rain. Fiji may then follow its trail.

According to the U.N. humanitarian affairs bureau, Fiji has been monitoring air quality. They have advised citizens to protect their homes and remain indoors in case it rains.

FISH DIIE-OFFS

Tonga’s exclusive economic zone of nearly 700,000 marine square kilometres (270,271 square miles) 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 Marco Brenna, a geologist at the University of Otago in New Zealand.

The ash may cause damage to sea life in the ocean. 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.”

The situation has only gotten worse with every eruption. Fish will be starved and wiped out by the volcanic ash. Scientists predict that some fish may die and others will migrate. Additional changes to the seafloor could pose new problems for fishermen vessels.

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

SOMOTHERED CORALS

Coral reefs can be harmed by falling ash, as well. Tonga’s tourism sector was worth up to $5million annually before the outbreak of the coronavirus.

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.

Now, “vast areas of the reefs in the immediate impact area at Hunga Tonga are probably buried and smothered by large deposits of volcanic ash,” said Tom Schils, a marine biologist at the University of Guam who has studied volcanic eruptions and corals in the Northern Mariana Islands.

Additionally, such eruptions release iron in the water which may increase the growth of blue green algae and sponges. These can further degrade the reefs.

Brian Zgliczynski (a Scripps Institution of Oceanography coral reef ecologist) said that some reefs might need to be rebuilt. This could prove costly and take many years. “Species more tolerant of poor water quality will arrive first,” while hard corals and fish would take longer to return, he said.

ERODED COASTLINES

Tonga would be less able to handle rising sea levels and storm surges if coral reefs are lost. This is a concern for Tonga, where climate change is driving the sea level to rise by about 6 millimeters (0.2 inches) per year — double the global average.

In a 2015 report https://www.researchgate.net/profile/Leanne-Fernandes/publication/317341776_National_marine_ecosystem_service_valuation_summary_Tonga/links/5bbe5828299bf1010178adac/National-marine-ecosystem-service-valuation-summary-Tonga.pdf, Tonga valued its natural storm buffers including coral reefs as well as coastal seagrasses and mangroves at some $11 million annually.

A Tongan sea-level gauge measured a tsunami of 1.19m (roughly 4ft) during the eruption. It then stopped reporting. It is well-known that tsunamis can cause coastal erosion. Video footage showed the destruction of man-made seawalls before communications systems were lost.

“Coastal defences and reclaimed land could all be strongly impacted by the tsunami waves, leaving the islands more vulnerable,” Cronin said.