Tonga reliant on rainfall to harness hazardous volcanic ash, which could be used to rejuvenate Pacific nation

The volcanic ash that coats much of Tonga poses serious health risks if inhaled but once enough rain falls on the Pacific nation, the ash could help rejuvenate the country's soil and is already being collected for building materials.

Efforts to clear a thick blanket of ash continue two weeks after the eruption of the Hunga Tonga-Hunga Ha'apai volcano, which triggered a tsunami and caused widespread destruction across the archipelago. 

Tevita H Hafoka lives in Tonga's capital Nuku'alofa and said it was like the city was in greyscale before the first decent downpour of rain finally came on Friday.

"Everything was covered in ash: it was like a sepia-tone picture," Mr Hafoka said.

"Everything was grey and brown but we're finally seeing some colour.

"We've been getting a lot of rain since [Friday] morning … and the rain has helped immensely in removing the dust and ash off rooftops."

He said trees that were coated in ash were shedding their leaves and new shoots were coming through. 

Ash being used to slow traffic, fertilise soil

Mr Hafoka said Tongans were a resilient and resourceful people and were already working to find uses for the ash, including to slow down cars.

"There was a whole lot of ash and vehicles, particularly heavy-duty vehicles, would drive and kick up all the dust into the air … so people have even resorted to piling [the dust] up and using it as speed bumps to get the cars to slow down," he said.

"People have been packing it up to be used in cement for construction work.

"And I heard on the radio the other day, some people are trying to sell [the ash].

"We're just trying to make do with what we're having to deal with at the moment."

Tonga's Ministry for Land and Natural Resources assistant geologist Pupunu Tukuafu said locals also planned to use the ash to add nutrients to the soil.

"Many people have been collecting the ashes from their rooftops and the roads for fertiliser for gardening," Mr Tukuafu said.

Professor Scott Bryan from Queensland University of Technology's School of Earth and Atmospheric Sciences said the ash would work to bring nutrients to Tonga's main islands, which were essentially uplifted coral reefs.

"The islands themselves are made up of very carbonate-rich rocks," Professor Bryan said.

"In terms of the soils that limestone or carbonate makes, it's pretty poor in nutrients. 

"So in actual fact, the ash being glassy, is going to break down relatively quickly and supply a lot of nutrients to their soils.

"I'm sure in six months to a year, you'd really have to start looking carefully to find remnants of that ash deposit around the place."

While Friday's rainfall was welcomed by locals, more is needed to remove the immediate threat ash poses to people and the natural resources.

New Zealand's Met Service said while it had been mostly dry in Tonga since the eruption, rainfall was expected to increase.

"A few showers are expected over the coming days, but shower activity is expected to increase next week with the odd thunderstorm also a possibility," Met Service Lead Meteorologist Stephen Glassey said.

"Rainfall amounts in the tropics are difficult to predict as it depends on whether a thunderstorm occurs over land or over the ocean."

In the meantime, the ash poses a risk to people, water and food sources and locals have been urged to wear masks to avoid inhaling the ash.

Samples of ash have been sent to New Zealand and are being tested at the University of Auckland, Mr Tukuafu said. 

Professor Bryan said once more was known about the specific compounds of the ash, authorities would be able to assess the risk of diseases such as silicosis, which is caused by breathing in tiny particles of silica, a common mineral found in sand, quartz and other rocks. 

Water, land and livestock at risk

Mr Tukuafu said the ministry was still surveying the damage on the outer islands and testing household water tanks to determine if they were safe to use.

While rain could help to clear trees and rooftops of ash to reinstate local rainwater supplies, the recovery of crops and livestock could take longer, Mr Tukuafu said. 

"Most of the root crops ... [they've] already dried up and this could be a big problem for us in the coming months and maybe in the coming years," he said.

"The root crops, especially yams, kumara … bananas and so forth. 

"Most of the food sources are still covered with ash and some of the cattle are finding it hard to find food sources and with the limited water sources at the moment, it could be a problem finding water for cattle."

He said Tonga's Ministry of Fisheries was encouraging people to fish in deep water to avoid contamination from ash.

Mr Tukuafu said Tonga may be forced to rely on imported food and water sources until local sources are deemed safe.


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