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Vulcanologists are pretty good at predicting a volcano will erupt. They stick monitors all over the mountain and measure seismic activity, magma domes and such. They’re doing that right now on Bali’s Mount Agung.
What they can’t tell is how big the eruption will be. It could be catastrophic, or it might be a bit of coughing and spluttering…. Or anything in-between. That’s not me dissing on vulcanologists, it’s what they admit.
Professor Richard Arculus from Australian National University told ABC news on Monday 27th there was a high chance of the volcano erupting by the end of the week.
“70 to 80 per cent within days, probably 90 per cent within weeks to months, but I’m reserving that 10 per cent in case it doesn’t happen.”
But what if it IS a big one?
OK, let’s look at some previous large eruptions for lessons on how large of an area might be affected, and whether in Kuta you should be worried about being buried in lava.
The size of an eruption is measured by the VEI (volcanic Intensity Index). The index goes to 8.
This infamous eruption is the most-deadly in modern history. The eruption and the 40-metre high tsunami it caused is said to have killed 36,000 people globally. The island on which the volcano stood measured approximately 10kms by 7.5kms. Two-thirds of it disappeared.
Krakatoa’s VEI was 6.
This volcano on Luzon in the Philippines erupted in 1991 also with a VEI of 6.
The devastation was made worse by the fact the eruption coincided with a typhoon; the heavy rain combined with ash caused buildings to collapse, accounting for most of the death toll.
Ash fell on most of the island of Luzon. However, the most severely affected regions were within a 20 kilometre evacuation zone around the mountain.
In the final climatic eruption, pyroclastic surges – masses of super-heated gas – raced down the mountain and reached as far as 16 kilometres away down river valleys. Manila, some 55 kilometres away was shrouded in darkness and had some ash fall (the wind blew most of it in a different direction), but was not affected in a major way.
By the way, the ash cloud from Pinatubo caused the Earth’s temperature to drop by 0.5 degrees.
Mt Agung, Bali
When Mt Agung last erupted in 1963, causing over 1000 deaths, the VEI was 5.
Lava from this event extended for 7 kilometres down the northern slope. Mud, debris and pyroclastic material called lahars flowed down the flanks of the mountain…. But did not extend more than a few kilometres.
This is why there’s a 12 kilometre exclusion zone around the mountain, that’s the limit of the area that may be directly impacted by lava, pyroclastic flows and lahars. Kuta is about 70 kilometres away.
What about the ash cloud?
If Agung does blow its top in a big way there’s almost certain to be a large volcanic ash cloud extending many kilometres into the atmosphere. Planes and ash don’t mix well, not if you want them to keep flying. So it’s likely the airlines won’t want to risk lives, or damage to multi-million-dollar aircraft, and will ground flights.
But a lot of that depends on wind direction. The prevailing winds in Bali at this time of year blow to the south-east – away from the airport which is south-west of Agung. It’s likely flights will be grounded – at least initially – until meteorologists can assess the danger to aircraft.
But is Kuta going to be like Pompeii? No.