A volcanologist who has lived and worked in Vanuatu for a decade and a half told the Daily Post yesterday that the government was getting the best scientific advice available concerning the Ambae volcano. “The decision to evacuate is based on solid science,” said Sylvain Todman.
Mr Todman studied at Universite Pierre et Marie Curie in Paris. He is a geologist/volcanologist.
He started by explaining the large column of steam hanging over the volcano.
“What you’re seeing right now,” he said, “is a lot of what we call hydrothermalism – you don’t have any direct interaction between lava and water.”
Water is “seeping through the ash”, and gathering inside the cinder cone. The big blasts of ash that we’ve seen over the last few weeks are due to occasional bursts of gas and lava into this water.
“When you have a burst of lava and gas getting in contact with the water, and that contact with the water is what we call a phreatomagmatic explosion.” The cool water interacts with the very hot lava, and the effect, say Todman, is like when you throw a couple of drops of water onto a very hot frying pan. The water doesn’t just boil away; it shatters into countless tiny particles.
In this case, though, the lava and stone do the same, creating massive ash clouds. This is the source of the light grey, very fine ash we’ve seen turning the island dark at noon.
The situation, he said, is likely not a transient one. And any announcements and decisions coming from Government are based on good science. “There are areas of concern on both ends of the island as well as on the summit of mount Lombenben.
“The way the juvenile magma is coming up under the Ambae volcano is not the same as with other volcanoes.
“That kind of eruption is really stressful. Not only for the population, it’s stressful for the government as well. They have to monitor it closely. It’s a big and complex volcano.”
Todman told the Daily Post that the Geohazards Unit monitors inflation/deflation (the rising and falling of the mountain as pressure builds and drops). They monitor gas information from satellite, as well as ash volume, composition, auditory and visual input.
The pressure is so intense under the island that the height of mount Lombenben has changed 10-15 centimetres. It was not the case a few months ago.
Gas emissions are one of the main reasons the volcano remains at level 3. “We’ve never seen so much sulphur dioxide from Ambae, historically speaking,” Todman said.
“All the science is showing that it’s still active.”
Based on historical behaviour, a decrease in activity in the next few weeks or months is not a realistic expectation. It’s impossible to predict, though. Volcano science can explain what’s happening, but it can’t see the future.
People need to take on board the information that the government is sharing with them, he insisted. “When you’re doing a volcanic hazard map, what you’re doing is taking into account all the scenarios. Mud flows, ash fall, pyroclastic flows if there’s a large eruption. Lateral eruptions from the mountainside.
“I’m not saying it’s going to get worse, but if you take the situation six months ago, and the situation right now, it’s absolutely different from before. Maybe in six months we’ll meet again and we’ll talk about something else.”
“They have to trust the government. That’s the thing. Believe me, they’re working very hard. Be trustful as the Volcanic Ash Advisory Centre is trustful of the Geohazards Unit. They listen to Esline [Garaebiti, the Director]. They cancelled flights based on her advice.”
According to their website, the Wellington VAAC “is one of nine VAACs that operate under an international system called the International Airways Volcano Watch (IAVW), set up and co-ordinated by the International Civil Aviation Organization (ICAO).”
Of the Geohazards Unit, Todman says, “They’re taking good decisions. They’re making good analysis.” He ought to know. He worked with them for 13 years.
“All my friends from Ambae, they call me, and ask what about this or that. I tell them, ‘If you have a bulletin saying that this is what you have to do—do it.’”