A tornado tore across the Nullarbor but we’re only just learning about it now

If a tornado tears up the Nullarbor Plain but no-one saw it, did it really happen?

A study in the Journal of Southern Hemisphere Earth Systems Science says the answer is yes after researchers reviewed satellite imagery, snapped in late 2022, of a mysterious clearing in a remote patch of scrub.

The 11-kilometre vegetation-stripped track, ranging between 160 and 250 metres wide, straddles the border of South and Western Australia, about 120km north of Eucla.

It looks like an Australian seagull version of Peru’s Nazca lines.

But study author Matej Lipar, a physical geographer from the Slovenian Academy of Sciences and Arts, says it is the signature of tornado that tore up a shallow layer of silt and clay two years ago as it travelled along the surface.

The “scar” was first noticed earlier this year by a caver looking for openings in the Nullarbor’s karst landscape, a massive area riddled with caves that formed as water dissolved limestone over millions of years.

Word of the track eventually reached Dr Lipar, who went through satellite image archives and discovered the track appeared in November 2022.

He said the cleared track did not appear to be made by people as there would have been larger tracks to transport them to the isolated site.

But what could be seen from satellite images taken of the centre of the scar was a chain of dark rings similar to loops in a piece of string.

Dr Lipar said these were “cycloidal marks”, and the biggest clue to what created the scar.

“We usually see tornadoes as eyewitnesses or concerning how much destruction they left behind,” he said.

“But here it basically just kind of ‘signed’ itself on the surface of the Nullarbor and because there’s not much vegetation, it just remained clearly visible up until today.”

John Allen, a meteorologist at Central Michigan University who was not involved in the study, said it seemed reasonable to conclude a tornado had occurred at the site.

“Cycloidal marks are quite evident, and these are seen in US tornado damage paths,” Dr Allen said.

“The appearance of the path without substantive evidence of flooding as an alternative cause would further lend support to this argument.”

But he is not sold on the study’s suggestions of how big the tornado was or how it formed.

Size and origin of tornado debated

Tornadoes form when weakly rotating air near the Earth’s surface is drawn up quickly into the atmosphere and into a big, fluffy cumulus cloud.

They are different to the smaller and not-so-damaging willy willies or dust devils, and are mostly associated with supercell thunderstorms.

In Australia, supercell tornadoes are most common in northeast Victoria, southeast Queensland and central and eastern New South Wales.

The new study said a significant low-pressure system, conducive to severe weather, formed over the Nullarbor in November 2022.

At the same time, a cold front swept across the area, forming weather conditions like those that saw several tornadoes form in South Australia in 2016.

At the time of the tornado, Dr Lipar was conducting research on the Nullarbor Plain about 100km away, where other storms were brewing.

“It was kind of coincidence that we actually had an images of the weather of the clouds at the same date,” he said.

“We were still experiencing big storms and thunderstorms and flooding basically after that.”

Dr Lipar said looking at the cycloidal marks, it seemed as though the tornado moved eastward, with winds blowing faster than 100 kilometres per hour — possibly more than 200kph.

This would put it at F2 or F3 on the six-category Fujita scale for measuring tornadoes.

But Dr Allen said it was a leap to assign an intensity estimate on the tornado without damage indicators, such as damage to buildings, which are more robust than desert scrub.

He said just using only satellite images from the Nullarbor was not enough to determine the strength of the tornado, and he did not think the storm would have been intense enough to produce a large tornado.

“F2 and F3 tornadoes certainly occur in Australia, but are comparatively rare and are associated with stronger, longer-lived thunderstorms,” he said.

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There’s still plenty researchers don’t know about how often tornadoes form in Australia, which were first recorded by Western science in 1795 in Sydney, but about 30 to 80 are thought to occur annually.

Dr Lipar hopes other researchers will look for scars from previously undetected “missing tornadoes” around Australia.

Dr Allen said there was substantive evidence satellite data could be an effective way to find missing tornadoes.

He said Canadian researchers found missing tornadoes in satellite images and calculated their severity by assessing tree damage.