The volcano Mauna Loa is no stranger to outbursts, with Hawaiian authorities warning the volcano is in a ‘state of heightened unrest’.
Mauna Loa is the largest above ground volcano in the world and got that way by regularly oozing lava onto the landscape below.
And right now, the ground is shaking. The Hawaiian Volcano Observatory says during the past 24 hours, they detected 46 small earthquakes 2 to 5 km below Mokuʻāweoweo caldera and 6 to 8 km beneath the upper-elevation northwest flank of Mauna Loa.
Both regions have historically been seismically active during periods of unrest on Mauna Loa.
“Mauna Loa is not erupting and there are no signs of an imminent eruption at this time. Monitoring data show no significant changes within the past 24 hours.”
This heightened level of unrest started back in September. Curtin University volcanologist, Professor Fred Jourdan says a Krakatoa or Hunga Tonga-Hunga Ha’apai type massive eruption is unlikely.
“In Hawaii, the volcanos do not explode nor produce tall ash cloud. Rather, they emit rivers of lava,” says Jourdan.
“These eruptions are not brutally devastating compared to pyroclastic eruptions like Tonga.”
Read more: How the next big volcanic eruption could impact Australia
Why? “Because there is much less gas dissolved in the lava, much less water available to fizz like a soda drink. To get explosive eruptions, you need a subduction zone that will pump water in the mantle. After that, when the magma rises to the surface, the gas will decompress and make the magma fragment in ash.
“Hawaii is above a hot spot, so there’s no water source to feed the magma.“
A paper published in Science yesterday has confirmed that the Hunga Tonga-Hunga Ha’apai volcano was the highest ever recorded volcanic plume and the first to have been observed to break through the atmospheric layer the mesosphere.
| Volcano | Year | Energy (Megatons) | Volume ash (km3) | Plume height (km) | Amount SO2 (Tg) |
| Tonga | 2022 | 61 | 10 | 57 | 0.4 |
| Pinatubo | 1991 | 70 | 10 | 40 | 20 |
| Krakatoa | 1883 | ~200 | 21 | ~ 40 | ? |
| Tambora | 1815 | >1,000 Mt | 175 | ? | ? |
“The Tonga eruption was certainly very big and generated the highest ash cloud ever measured by satellite observations, reaching a height of almost 57 km,” says Jourdan.
“Nevertheless, that does not mean it was the highest ash cloud ever, it means it was the highest that we actually measured. This eruption had a volcanic explosivity index of a small 6, with estimate suggesting an explosive energy equivalent to 61 Megatons (of TNT).”
Compared to the 1883 eruption of Krakatoa, the eruption of Hunga Tonga–Hunga Haʻapai back in January was only one third the size. The 1815 eruption of Mount Tambora was even larger again – potentially producing over 1,000 Megatons of energy.
It’s actually surprisingly hard to measure the height of a volcanic eruption as tall as Hunga Tonga–Hunga Haʻapai. This is because when a plume penetrates the stratosphere (the atmospheric layer before the mesosphere), temperature starts to get weird, and you can no longer use the hot temperature at the top of the plume to measure the height.
The researchers had to use multiple weather satellites instead and apply the parallax effect to these images to be able to pin down where exactly the plume ends.
“It’s an extraordinary result as we have never seen a cloud of any type this tall before,” says lead author of the new paper, University of Oxford atmospheric researcher Dr Simon Proud.
“Furthermore, the ability to estimate the height in the way we did (using the parallax method) is only possible now that we have good satellite coverage. It wouldn’t have been possible a decade or so ago.”
Jourdan says the Tongan volcanic explosion was very similar to an eruption in Mount Pinatubo, both in term of ash cloud size, volume of ash… except for one thing. “The amount of sulphur dioxide (SO2) the ‘chill-house gas’ that can cool down the atmosphere, was much smaller in the case of the Tonga eruption.
“So we can expect less cooling effect from the Tonga eruption compared to the cooling effect that Pinatubo generated (-0.1°C due to eruption globally).
“This is possibly because it was a rather isolated island. Now, compared to the 1883 eruption of Krakatoa, Tonga and Pinatubo are 2 to 3 times smaller eruptions. In any case, the largest eruption in recent history is without contest Tambora in 1815 – a clear winner with an order of magnitude more energy than Tonga.”
Earlier this week there was a ripple of excitement about “earth killer” asteroids being detected in the Solar System. Jourdan compared it to the Tonga volcano for Cosmos. “If you imagine a 115 m wide asteroid crashing on Earth and producing a crater about 900 m in diameter, that’s about the same energy as the Tonga eruption. That’s about the size of the Wolfe Creek crater in Western Australia.”
Yes, the crater which frightened everyone in the famous B-grade thriller.
Originally published by Cosmos as Hawaiian volcano unlikely to explode say experts, but that’s no reason for complacency
Jacinta Bowler
Jacinta Bowler is a science journalist at Cosmos.
They were published in the Best Australian Science Writing 2023.
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