The Hunga Tonga-Hunga Ha'apai volcano eruption in January 2022 was so powerful it created a "super plasma bubble" in the upper atmosphere over northern Australia, likely disrupting precise GPS for hours.
The bubble, which extended as far south as Townsville, was also the largest so far detected over Australia.
In the journal Space Weather, a team of space scientists led by RMIT University's Brett Carter not only mapped the extent of the bubble over Australia, but also calculated its influence on navigation systems used in mining, agriculture and construction.
And during that time, if you were under the bubble and trying to use precise GPS but didn't already have a lock on satellites, you'd be in for a long wait.
These bubbles can wreak havoc on the radio signals needed to communicate with navigation satellites.
"We calculated it would take around five hours [before you could use the device]," Dr Carter said.
And that's on top of the time it would take to get a lock in the first place.
Churning plasma influences GPS navigation
Using the GPS or Global Positioning System to find the closest cafe or rideshare driver, or simply to figure out your location, is second nature to many of us.
But how well the GPS works depends a lot on a layer of charged particles or plasma in the atmosphere called the ionosphere.
The ionosphere starts around 80 kilometres above our head and stretches more than 800km to the edge of space.
Navigation satellites, such as those in the GPS constellation, transmit radio signals through the ionosphere to receivers below.
But the ionosphere is turbulent. It's churned by strong winds. Waves and bubbles travel through the plasma, changing its density.
When this happens, radio signals from navigation satellites passing through the plasma can get jumbled — or blocked altogether.
Some waves and bubbles are produced by "space weather", such as geomagnetic storms, where massive clumps of plasma are flung from the Sun.
Still others are produced by phenomena below the ionosphere, such as earthquakes, thunderstorms and volcanic eruptions.
The Hunga Tonga-Hunga Ha'apai volcano eruption was no exception. It set off an ionosphere wave that circled the planet four times, affecting GPS in various parts of the world for days.
It also produced a massive bubble that was detected above South-East Asia, and was carried by Earth's magnetic field to the north and south.
Was it all the volcano's doing?
Complicating matters somewhat was the arrival of a geomagnetic storm just before the Hunga Tonga-Hunga Ha'apai eruption, said University of Newcastle space physicist Colin Waters.
Professor Waters had worked with some members of the research team before, but was not involved in the new study.
The geomagnetic storm was considered "moderate" in size, but there's a chance it helped trigger the bubble, Professor Waters said.
Teasing out exactly how much the volcano contributed to the bubble's formation could take some time.
"The generation of plasma bubbles depends on a whole lot of different things," Professor Waters said.
"Here, you've got a moderate geomagnetic storm a couple of hours before the volcano eruption.
"It's quite a complicated event."
When precise GPS matters
Using data from ground-based GPS stations in Australia and the Pacific, Dr Carter and his colleagues could trace the bubble as it extended south, carried along Earth's magnetic field lines, where it hung out above Townsville for a few hours before dissipating.
And it would have affected GPS users, but perhaps not the GPS most people are familiar with.
Common GPS receivers, such as those in our smartphone, are accurate to tens of metres. More advanced devices are accurate to a few centimetres.
This precise GPS can be accomplished in a couple of ways. One relies on a network of ground or reference stations, but the GPS device must be near a station to work.
The other main method is called "precise point positioning", which doesn't need a reference station to calculate your precise position.
"But [this method uses] a complicated algorithm and it does take a fair bit of time, maybe tens of minutes to an hour [to accurately lock onto its location]," Dr Carter said.
Throw a plasma bubble in the mix, and that "fair bit of time" can blow out considerably.
And while precise point positioning is currently limited to, for instance, autonomous vehicles in mining and agriculture, it's set to become ubiquitous as self-driving cars take to the roads.
"The new types of capabilities that will spawn from [precise point positioning] is where the future is," Dr Carter said.
"Not only will it tell you where you are, but it will tell you if your receiver is in your pocket or in your bag."
