Many people in Tonga evaded the powerful waves set off by an undersea volcanic eruption, in some cases by sprinting inland or clambering up trees. But another problem settled over the island nation in a monochromatic blanket: an ash cloud unleashed by the blast.

The challenges are both immediate and long-term. First, in the four days after the towering eruption, ash prevented relief flights from landing at the country’s main airport, with the initial plane arriving today. Efforts by the Tongan armed forces to clear the main runway by hand took longer than expected, in part because the ash was still falling.

Ash has also contaminated some of the wells and rainwater tanks where people get their drinking water. While the New Zealand military aircraft that was the first to touch down today bore supplies of water, experts said that keeping the country’s water supply safe from ash-related hazards was likely to be an abiding project. They also said that the ash could harm agriculture and livestock but that the effects were hard to predict.

Then there is the air. Scientists who study airborne pollution were watching closely to see what types of particles fell to the ground or remained suspended in the air. Compared with power plant emissions, they said, the airborne health risks of a volcanic eruption can be harder to assess in real time because each volcano has a unique profile.

“You see visible smoke coming, and of course we call it volcanic smog,” said Rajasekhar Balasubramanian, an expert on air quality at the National University of Singapore.

“But the overall atmospheric and health impact of the volcanic eruption will depend on the magnitude of the plume, the behavior of the plume, the altitude which the plume reaches and the concentration of gases, particles and ash,” he said.

Today was a breakthrough moment for Tonga. The New Zealand air force cargo plane, packed with relief supplies like generators, communications gear and shelter kits, touched down late in the afternoon. An Australian military plane landed a few hours later.

The official death toll stood at three as of this evening. Yet with an undersea cable knocked out for weeks by the disaster — making satellite phones the only reliable means of communicating with the outside world — the full extent of the devastation was still not fully clear.

Photographs trickling in today showed boulders the size of car tires sprinkled among palm trees in a coastal area, its once vibrant greens dusted by grayish ash. In one of them, rubble was strewn around two seaside benches in a spot where families might have once stopped for lunch.

On Tongatapu, the main island, many residents were reporting that volcanic ash was still a problem.

“There is just dust everywhere,” Kofeola Marian Kupu, 40, a journalist for a radio station in the capital, Nuku’alofa, said in an interview by satellite phone today. “From rooftop to road to offices, there’s just gray dust.”

On her way to work, she said, only a handful of homes and businesses seemed to be cleaned up. People were covering their faces with masks. Car windows were smeared with a layer of gray.

Perhaps most importantly, she said, there was volcanic debris in the water supply.

“Normally in our homes we have tanks to collect rainwater for drinking, but it’s all covered with ash,” she said. “What we really need is water.”

Falling ash and saltwater from the tsunami that accompanied the eruption Saturday have polluted drinking water sources for tens of thousands of people across Tonga, which has a population of about 100,000, the International Federation of Red Cross and Red Crescent Societies said this week.

​​Sainiana Rokovucago, the group’s program director for the Pacific, said in an interview today that the government was busy distributing freshwater that had been stockpiled in tanks well before the eruption. She said she was not sure whether the effort had reached all of the affected households; the Tongan islands are spread over 270,000 square miles.

But this much was clear, she said: Compared with three recent volcanic eruptions in neighboring Vanuatu, where the drinking water mostly comes from streams, Tonga’s eruption posed a greater threat because of the use of wells and rainwater tanks.

For most residents of Tonga, “You’re so used to having water from your own tank,” she said. “But after this disaster, you can’t. It’s a mental transformation.”

Two New Zealand navy vessels were set to arrive Friday with relief supplies and up to 250,000 liters of fresh water, as well as a desalination plant. New Zealand’s defense minister, Peeni Henare, said today that a third navy ship would follow.

But Rokovucago, who is based in Fiji, said that cleaning up the country’s drinking water supply could be a long-term effort that requires desalination projects and distribution of water purification tablets.

Carol Stewart, a deputy director at the International Volcanic Health Hazard Network, said today that initial reports that about 1 to 2 centimeters, or less than 1 inch, of ash had fallen on Tonga appeared to be accurate, based on early photographs.

Scientists are now trying to obtain and study samples of the ash fall to better understand its potential health impacts, said Stewart, who teaches at Massey University’s School of Health Sciences in Wellington, the New Zealand capital. One thing they will test for is the presence of acids and salts that can pose hazards to grazing livestock.

“It has rained on Tongatapu, so that is helpful for washing the ash,” she said in an email.

Because ash is acidic, it can cause crop failure. That is a risk in a place like Tonga, where the economy is closely tied to agriculture, even if the ash itself will eventually make the soil more fertile.

Jonathan Veitch, a United Nations disaster coordinator in Fiji, said today that Tonga’s agricultural land was not as inundated with ash as previously assumed. Still, he said, the longer-term impact of ash on Tongan agriculture was unknown.

“We don’t yet know whether the ash will kill the crops or not,” he added. “We have no idea.”

It was also unclear what risks the ash might pose to those who breathe it in. Unlike smoke from wildfires, it is coarser-grained and tends to settle more quickly. Stewart said that particles bigger than 0.1 millimeter are not breathing hazards because they are too large to remain airborne.

Sean Casey, the World Health Organization’s COVID-19 incident manager for the Pacific, said in an interview today that there was still some ash on the ground being picked up and blown about in the wind but that no new ash was raining down. He also said that there had been no increase in hospital admissions linked to ash-related breathing problems.

Still, scientists say that the undersea volcano that erupted off Tonga was unusually powerful — and that its potential effects should not be underestimated. That is partly because small particles can be inhaled if an ash deposit is stirred up by wind, vehicles or other sources.

Sulfur dioxide, a byproduct of combustion commonly released during volcanic eruptions, poses a particular threat to the lungs.

Some of the effects of ash clouds may be felt immediately, especially for people with underlying conditions like asthma or bronchitis, said Balasubramanian, the air quality expert. He said that residents should avoid ash by staying indoors, closing their windows, using air purifiers and wearing N95 masks.

But following such guidelines may be a challenge for people in Tonga, a remote country where the per capita income in 2019 was less than $5,000. Rokovucago said that aid workers were so far only distributing surgical masks, not the more effective N95s.

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This article originally appeared in The New York Times.

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