Mon. May 23rd, 2022

How do volcanoes affect the weather and what happens to the Hunga Tonga Hunga Ha’apai eruption?

Close to an eruption, there is a huge impact as the volcano releases moisture, ash and gases into the atmosphere.

Within the volcano fan, electric charges can build up to trigger lightning, and aerosols can rain.

Volcanoes can even produce “mud rain” if conditions are right.

When that rain hits the surface, it can do more damage in the form of a lahar, where volcanic ash floats in a deadly mudslide.

Then there is a phenomenon known as “vog”, volcanic fog, when harmful gases linger near the surface.

But it is when the tab gets further up in the atmosphere that it can start to have global effects.

A car is covered in ash in Nuku'alofa, Tonga after the volcanic eruption.
The local effects of the eruption have been devastating, but it does not currently appear that it will have a significant impact on the global climate. (Twitter: Kingdom of Tonga)

Volcanoes can cool the planet

According to Blair Trewin, senior researcher at the Bureau of Meteorology, the biggest global effect of volcanoes is that the major eruptions can temporarily cool the atmosphere by releasing sulfur dioxide.

It blocks the incoming light from the sun and acts as a kind of global shadow.

But to linger and have long-lasting effects, sulfur dioxide must rise above the troposphere.

If it stays in the troposphere where our daily weather takes place, it will quickly rain down to the surface again.

A diagram shows four different layers of grouns: the therosphere at the top, the mesosphere, the strtrosphere and the troposphere.
To stay in the atmosphere, the sulfur dioxide must rise above the troposphere and enter the stratosphere.(Commons: scied.ucar.edu)

The flag from the Tongan volcano is estimated to have reached about 35 kilometers high, far up in the stratosphere.

Emissions from the tropics have a much better chance of spreading over both hemispheres instead of getting stuck in one.

Then two ticks.

But based on initial estimates, it does not appear that the recent Tongan eruption has released enough sulfur dioxide to cause significant cooling.

“The estimates I’ve seen so far suggest somewhere around 0.1-0.2 megatons [million tonnes] of sulfur dioxide has been emitted, “said Dr. Trewin.

The last volcano to have a global cooling effect, Mount Pinatubo in 1991, released significantly more sulfur dioxide.

“Pinatubo Mountain emitted about 15 to 20 megatons, so somewhere in the order of 100 times more than what the Tongan volcano has.”

Sir. Trewin said there could be local cooling around the volcano, where significant ash is generated.

Dr. Trewin does not expect any significant effect on Australian weather from the Tongan volcano.

“Not really, except for attractive sunsets in some places,” he said.

Andrew Tupper of Natural Hazards Consulting and a former head of the Darwin Volcanic Ash Advisory Center also does not predict weather outages in Australia.

According to Dr. Tupperware now raises the volcanic cloud beyond the Indian Ocean after crossing Australia.

Beautiful golden sunset over the sea
The most important weather effect we can expect from the Tongan volcano in Australia is some spectacular sunsets.(Delivered: Trish Moore)

But because it has driven about 35 km up, it does not affect our weather.

“The normal rainfall that we get, even in summer, the maximum altitude of thunderstorms is about 16 or 17 kilometers in the tropics, and usually a little lower at the middle latitudes,” he said.

“So they just do not interact with the volcanic cloud.”

Can there still be more?

The question is whether more sulfur dioxide can be released in subsequent outbreaks.

Heather Handley, volcanologist and adjunct associate professor at Monash University, said it depended on how much of the gas has been lost in the past and how much has been stored.

Her work with samples from the same volcano in 2009 showed that the magma that formed rocks at the surface had traveled fast and retained much of its gas.

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