Tonga Needs Rain and More Brooms After Volcano Eruption Spewed Ash

Protecting agriculture and water and guarding against potential risks to respiratory health are among the key challenges for Tonga as aid arrives in the country of 100,000 people. For residents like Ms. Latailakepa, who manages the Friendly Islands Bookshop in the capital Nuku’alofa, the ash makes daily life difficult.

“At home we’ve had to remove sacks and sacks from the rooftops, and we’ve had to water our gardens and the car and the grass and everything daily, maybe twice or three times a day to clear up the dust,” Ms. Latailakepa said.

Removing the dust from homes, roads and other infrastructure has become an immediate preoccupation for thousands of community-minded Tongans. The Jan. 15 eruption also triggered a tsunami that ravaged parts of the coastline and inundated some smaller islands. The airport runway on Tongatapu, the main island, was cleared of ash by an army of volunteers with brooms, enabling the first relief flights from New Zealand and Australia to land last week.

High-pressure water cleaners are being used in places, but keep breaking down because of overuse, said Ms. Latailakepa. Air-conditioning systems in homes, businesses and cars also face strain because of the ash fall, she said.

Lord Fatafehi Fakafanua, the speaker of Tonga’s parliament, said there aren’t enough brooms to go around—making this simple tool an overlooked item in the international relief effort. Rains can’t come soon enough to the islands, he said.

“They need large sweepers to clean the roofs and the streets. Ash is still the biggest issue right now,” he said. “The concern is over its impact on the short-term, medium-term health of the population and how it affects food and water.”

Scientists in New Zealand are analyzing samples of the ash brought back by one of the first-aid flights. They hope to extract information that will lead to a deeper understanding of the eruption and benefit the recovery effort. For example, knowing the proportion of very fine particles will help to quantify the risks to respiratory health, and understanding the ash’s leaching characteristics will indicate what chemicals come off it when it mixes with water.

Typically, inhaling fine ash can cause short-term effects in healthy people such as a runny nose and uncomfortable breathing, while people with pre-existing respiratory conditions can develop severe symptoms. Long-term exposure to volcanic ash can result in serious lung diseases.

The severity of the eruption’s impact on crops remains unclear. Katie Greenwood, Pacific head of delegation for the International Federation of Red Cross and Red Crescent Societies, said the consequences aren’t as catastrophic as initially feared, and root crops such as cassava, taro and yams may be relatively unscathed.

Still, the aboveground vegetation of root crops is now dying off, and the tubers may be stunted as a result, said Lord Fakafanua, citing discussions with Mordi Tonga Trust, a civil-society group that works on rural development.

Rainfall should mitigate damage to agriculture, though it doesn’t always do so, said Tom Wilson, an expert on volcanic ash and agriculture at the University of Canterbury in Christchurch, New Zealand.

“Any rainfall after an ash fall, from an agricultural point of view, is usually quite good, because it’s washing ash off the plants and hopefully it is starting to integrate into the soil,” he said. However, if the ash is particularly fine it can block the capillary-like flow of water through soil and cause surface flooding.

About three-quarters of Tonga’s exports are agricultural produce such as yams, vanilla beans and watermelons. Tonga is reliant on trade, with countries such as New Zealand, Australia and Japan, and development aid. A substantial amount of its food is imported from New Zealand, while some families supplement that with subsistence farming and fishing.

Mr. Wilson said the near-term crop damage from 2 to 3 centimeters—about an inch—of ash could range from moderate to severe. A potential silver lining is that within a few months there could be a significant boost to soil fertility from elements such as potassium.

“If there’s rainfall which supports it, coupled with mixing this ash into the soil, you could have quite a vibrant agricultural recovery,” he said.

International experience from other eruptions shows that tackling ash in a systematic, coordinated way has benefits. For example, ash in rural areas should be spread through plantations, while ash cleaned up in urban areas should not be dumped in holes or depressions as it could end up polluting ground water, waterways or fisheries. A good approach, Mr. Wilson said, is to cover it with soil so it is stabilized and contained.

If Tonga avoids further significant ash fall, the eruption will be an outlier. The more typical scenario of volcanic activity is a prolonged eruption that deposits ash over weeks, according to joint research from Oxford, Bristol and East Anglia universities and the British Geological Survey.

Single, high-severity eruptions attract the most attention, but are relatively rare, and the median duration of volcanic eruptions is about seven weeks, according to the 2019 study.

Among the more extreme cases, ash fall from the Soufrière Hills volcano on the Caribbean island of Montserrat, which has been erupting since 1995, contributed to severe depopulation of the island. Eruptions at the Tungurahua volcano in Ecuador from 1999 to 2016 prompted mass resettlement, though hundreds of farming families remained on its flanks, adapting by growing hardier crops and farming fewer cows, sheep and guinea pigs—which were less productive or died after eating ash-covered grass.

For Ms. Latailakepa, a return to normal life in Tonga seems a long way off. The ash is a reminder of that. After clearing the outside of the property each day, the effort shifts inside her home.

“It never really clears up,” she said. “We’ve had to mop two or three times and even after mopping the floor it seems like there is this finely sprinkled powder around the floor that makes us almost skate.”

Write to Stephen Wright at stephen.wright@wsj.com