TRANSCRIPT
The 2022 eruption of the Hunga Tonga Hunga Ha'apai underwater volcano still weighs on the minds of those living in nearby Tonga.
Mele Manu works as a senior geologist with the Tonga Geological Services.
She says people in low-lying areas have been relocated, and many are still traumatised by the tsunami that followed the eruption.
“It’s been three years now and whenever there's an earthquake or people see some volcanic activities going on, big or small, there'll be a lot of concern, our office will be occupied with people calling in, asking information.”
Associate Professor Rebecca Carey from the University of Tasmania is Chief Scientist for a voyage on the CSIRO research vessel Investigator, which has been studying the area around the volcano, more than three years on.
She’s leading a multi-national scientific team which includes experts from the Pacific and around the world, collaborating with the Tonga Geological Services.
“It was unexpected that this volcano could have such a powerful explosive event, this event is so powerful that we actually don't have numerical models that can explain the power of this event. That fact, essentially, has garnered a lot of international interest because an eruption of this type adjacent to New Zealand or adjacent to any of our other Pacific Island neighbours would be really quite dangerous and have a lot of impact.”The 2022 eruption sparked a tsunami in the Pacific and sent ash and water vapor more than 50 kilometres into the atmosphere.
“We know that probably that volume in the atmosphere is less than 10% of the total volume of that eruption. The rest of the volume is on the sea floor. So this voyage will essentially be able to characterize and quantify the volume on the sea floor.”
The team has mapped the sea floor around and volcano, which was re-shaped by the flow of volcanic sediment.
They’ve found this sediment travelled up to 100 kilometres underwater.
“So that's quite exceptional, given that these flows had to transport material through water, which is much harder than through the atmosphere.”
The sediment is a challenging environment for life to re-establish.
“It’s almost like flour in terms of how fine it is and we’re also seeing in the deep tow camera that this sediment is very mobile on the sea floor and that’s important because it’s demonstrating that even if biological communities do start to recover, that sediment is still moving on the sea floor and potentially inundating those early established communities. And that's essentially like quicksand, I expect, for those communities, and they can't, can't survive in the mud. They have to be on top of it.”
It's unclear how long it will take to compact and make the underwater landscape stable again.
“Over long geological timescales that volcanic mud will compact and that landscape will become more static or more stable but because there's never been an eruption of this type, we've never had a natural laboratory to understand this recovery trajectory. We can't actually answer that question, but it's definitely not three years. It's probably more like 10 to maybe 20 years.” The crew has been conducting a range of tests, gathering scores of samples and deploying a range of equipment including a deep tow camera.
hD student at James Cook University, Lucy Southworth, says they have been able to spot some interesting sea creatures on the sea floor.
“We have seen some areas that will have been hit but in the deeper areas that are quite barren but we’ve seen some areas where there has been some recruitment so for instance there’s these really huge pink hydroids that we've been seeing, and they have almost like a flower shaped area at the top where they've got lots of tentacles that they filter feed with, and they've been up to two meters tall in some instances and we’ve seen lots of shrimp and sea cucumbers in these areas too and they’re probably some of the first species in deeper areas to be recovering.”
er specific focus is on the recovery of coral reefs and fish, following the tsunami.
She says some coral reefs were completely flattened while others were covered in falling ash.
“So although the coral reefs of the inhabited island groups around Tonga have been heavily impacted by the physical tsunami breaking up lots of the corals, we have seen that there are quite a lot of fish still living on the reefs. We just might see a change in the amount of fish and the types of fish that live there which will have a knock on effect for the small scale reef fisheries in Tonga; however people are still able to fish in these areas.”
The 2022 eruption also damaged the undersea cables that link the Tongan islands with the rest of the world.
Mele Manu hopes their work will help guide the location of new cables and other disaster preparedness and resilience measures.
“There are a lot of other submarine volcanoes around here in Tonga, so there's a potential that this event can also happen to those underwater volcanoes.”Associate Professor Carey says the research will be important for many Pacific nations.
“Being able to predict how explosive or how powerfully explosive these volcanoes can be, is important for the Kingdom of Tonga and other countries in order to determine their risk from submarine volcanic eruptions, but also to understand the mitigation measures that they can employ.”
Understanding the risks ... to prepare for the future.
